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Charge carrier and phonon transport in nanostructured thermoelectrics
NASA Astrophysics Data System (ADS)
There is currently no quantum mechanical transport model for charge (or phonon) transport in multiphase nano-crystalline structures. Due to absence of periodicity, one cannot apply any of the elegant theorems, such as Bloch's theorem, which are implicit in the basic theory of crystalline solids. Atomistic models such as Kubo and NEGF may assume an accurate knowledge of the interatomic potentials; however, calculations for real 3D random multi-phase systems require so large computational times that makes them practically impossible. In a multi-phase nano-crystalline material, grains and interfacial microstructures may have three distinct types as depicted in figure. In such a material, the physical processes in each individual grain no longer follow the well described classical continuum linear transport theory. Therefore, a proper model for coupled transport of charge carriers and phonons that takes into account the effect of their non-equilibrium energy distribution is highly desirable. Two new theories and associated codes based on Coherent Potential Approximation (CPA) one for electron transport and one for phonon transport are developed. The codes calculate the charge and phonon transport parameters in nanocomposite structures. These can be nano-crystalline (symmetric case) or the material with embedded nano-particles (dispersion case). CPA specifically considers multi-scattering effect that cannot be explained with other semi-classical methods such as Partial Wave or Fermi's golden rule. To our knowledge this is the first CPA code developed to study both charge and phonon transport in nanocomposite structures. The codes can be extend to different types of nano-crystalline materials taking into account the average grain size, as well as the grain size distribution, and volume fraction of the different constituents in the materials. This is a strong tool that can describe more complex systems such as nano-crystals with randomly oriented grains with predictive power for the properties of electrical and thermal properties of disordered nano-crystalline electronic materials.
Norouzzadeh, Payam
Charge-carrier transport properties of ultrathin Pb films
NASA Astrophysics Data System (ADS)
The charge-carrier transport properties of ultrathin metallic films are analysed with ab initio methods using the density functional theory (DFT) on free-standing single crystalline slabs in the thickness range between 1 and 8 monolayers and compared with experiments for Pb films on Si(111). A strong interplay between bandstructure, quantised in the direction normal to the ultrathin film, charge-carrier scattering mechanisms and magnetoconduction was found. Based on the bandstructure obtained from the DFT, we used standard Boltzmann transport theory in two dimensions to obtain results for the electronic transport properties of 2 to 8 monolayers thick Pb(111) slabs with and without magnetic field. Comparison of calculations and experiment for the thickness dependence of the dc conductivity shows that the dominant scattering mechanism of electrons is diffuse elastic interface scattering for which the assumption of identical scattering times for all subbands and directions, used in this paper, is a good approximation. Within this model we can explain the thickness dependences of the electric conductivity and of the Hall coefficient as well as the anomalous behaviour of the first Pb layer.
Vilfan, I.; Pfn�r, H.
Communications: A nonperturbative quantum master equation approach to charge carrier transport in organic molecular crystals.
We present a nonperturbative quantum master equation to investigate charge carrier transport in organic molecular crystals based on the Liouville space hierarchical equations of motion method, which extends the previous stochastic Liouville equation and generalized master equation methods to a full quantum treatment of the electron-phonon coupling. Diffusive motion of charge carriers in a one-dimensional model in the presence of nonlocal electron-phonon coupling was studied, and two different charge carrier diffusion mechanisms are observed for large and small average intermolecular couplings. The new method can also find applications in calculating spectra and energy transfer in various types of quantum aggregates where the perturbative treatments fail. PMID:20192281
Wang, Dong; Chen, Liping; Zheng, Renhui; Wang, Linjun; Shi, Qiang
Hydrodynamical Modeling of Charge Carrier Transport in Semiconductors
Enhanced functional integration in modern electron devices requires an accurate modeling of energy transport in semiconductors in order to describe high-field phenomena such as hot electron propagation, impact ionization and heat generation in the bulk material. The standard drift-diffusion models cannot cope with high- field phenomena because they do not comprise energy as a dynamical variable. Furthermore for many applications
Hydrodynamical Modeling of Charge Carrier Transport in Semiconductors
Enhanced functional integration in modern electron devices requires an accurate modeling of energy transport in semiconductors in order to describe high-field phenomena such as hot electron propagation, impact ionization and heat generation in the bulk material. The standard drift-diffusion models cannot cope with high-field phenomena because they do not comprise energy as a dynamical variable. Furthermore for many applications in
Angelo Marcello Anile; Vittorio Romano
Thermal generation and mobility of charge carriers in collective proton transport in hydrogen-bonded chains
The transport of protons in hydrogen-bonded systems is a long standing problem which has not yet obtained a satisfactorily theoretical description. Although this problem was examined first for ice, it is relevant in many systems and in particular in biology for the transport along proteins or for proton conductance across membranes, an essential process in cell life. The broad relevance makes the study of proton conduction very appealing. Since the original work of Bernal and Fowler on ice, the idea that the transport occurs through chains of hydrogen bonds has been well accepted. Such proton wires'' were invoked by Nagle and Morowitz for proton transport across membranes proteins and more recently across lipid bilayers. In this report, we assume the existence of such an hydrogen-bonded chain and discuss its consequences on the dynamics of the charge carriers. We show that this assumption leads naturally to the idea of soliton transport and we put a special emphasis on the role of the coupling between the protons and heavy ions motions. The model is presented. We show how the coupling affects strongly the dynamics of the charge carriers and we discuss the role it plays in the thermal generation of carriers. The work presented has been performed in 1986 and 87 with St. Pnevmatikos and N. Flyzanis and was then completed in collaboration with D. Hochstrasser and H. Buettner. Therefore the results presented in this part are not new but we think that they are appropriate in the context of this multidisciplinary workshop because they provide a rather complete example of the soliton picture for proton conduction. This paper discusses the thermal generation of the charge carriers when the coupling between the protons and heavy ions dynamics is taken into account. The results presented in this part are very recent and will deserve further analysis but they already show that the coupling can assist for the formation of the charge carriers.
Peyrard, M.; Boesch, R.; Kourakis, I. (Dijon Univ., 21 (France). Faculte des Sciences)
Charge-carrier transport mechanism in copper indium di-selenide thin films
NASA Astrophysics Data System (ADS)
Thin films of copper indium di-selenide have been grown onto glass substrates by a stacked elemental layer (SEL) deposition technique in vacuum. The elemental composition of the films was ascertained by proton-induced x-ray emission (PIXE) spectroscopy. The electrical dc conductivity and the Hall coefficient of the films have been measured in the temperature range of -130 to +127 �C. The mode of transport of the charge carriers has been analysed. It is found that a multiple scattering effect is operative in the transport process.
Firoz Hasan, S. M.; Subhan, M. A.; Mannan, Kh M.
Improvement of the charge-carrier transport property of polycrystalline CdTe for digital fluoroscopy
NASA Astrophysics Data System (ADS)
Minimizing the radiation impact to the patient is currently an important issue in medical imaging. Particularly, in case of X-ray fluoroscopy, the patient is exposed to high X-ray dose because a large number of images is required in fluoroscopic procedures. In this regard, a direct-conversion X-ray sensor offers the advantages of high quantum efficiency, X-ray sensitivity, and high spatial resolution. In particular, an X-ray sensor in fluoroscopy operates at high frame rate, in the range from 30 to 60 image frames per second. Therefore, charge-carrier transport properties and signal lag are important factors for the development of X-ray sensors in fluoroscopy. In this study, in order to improve the characteristics of polycrystalline cadmium telluride (CdTe), CdTe films were prepared by thermal evaporation and RF sputtering. The deposition was conducted to form a CdTeO3 layer on top of a CdTe film. The role of CdTeO3 is not only to improve the charge-carrier transport by increasing the life-time but also to reduce the leakage current of CdTe films by acting as a passivation layer. In this paper, to establish the effect of a thin oxide layer on top of a CdTe film, the morphological and electrical properties including charge-carrier transport and signal lag were investigated by means of X-ray diffraction, X-ray photoemission spectroscopy, and resistivity measurements.
Oh, K. M.; Heo, Y. J.; Kim, D. K.; Kim, J. S.; Shin, J. W.; Lee, G. H.; Nam, S. H.
Application of admittance spectroscopy to evaluate carrier mobility in organic charge transport materials
NASA Astrophysics Data System (ADS)
We examine the feasibility of admittance spectroscopy (AS) and susceptance analysis in the determination of the charge-carrier mobility in an organic material. The complex admittance of the material is analyzed as a function of frequency in AS. We found that the susceptance, which is the imaginary part of the complex admittance, is related to the carrier transport properties of the materials. A plot of the computer-simulated negative differential susceptance versus frequency yields a maximum at a frequency ?r-1. The position of the maximum ?r-1 is related to the average carrier transit time ?dc by ?dc=0.56?r. Thus, knowledge of ?r can be used to determine the carrier mobility in the material. Devices with the structure ITO/4,4',4'' -tris[N, -(3-methylphenyl)-N-phenylamino] triphenylamine/Ag have been designed to investigate the validity of the susceptance analysis in the hole mobility determination. The hole mobilities were measured both as functions of the electric field and the temperature. The hole mobility data extracted by susceptance analysis were in excellent agreement with those independently obtained from time-of-flight (TOF) measurements. Using the temperature dependence results, we further analyzed the mobility data by the Gaussian disorder model (GDM). The GDM disorder parameters are also in good agreement with those determined from TOF.
Tsang, S. W.; So, S. K.; Xu, J. B.
Distribution of charge carrier transport properties in organic semiconductors with Gaussian disorder
NASA Astrophysics Data System (ADS)
The charge carrier drift mobility in disordered semiconductors is commonly graphically extracted from time-of-flight (TOF) photocurrent transients yielding a single transit time. However, the term transit time is ambiguously defined and fails to deliver a mobility in terms of a statistical average. Here, we introduce an advanced computational procedure to evaluate TOF transients, which allows to extract the whole distribution of transit times and mobilities from the photocurrent transient, instead of a single value. This method, extending the work of Scott et al. (Phys. Rev. B 46, 8603 (1992)), is applicable to disordered systems with a Gaussian density of states and its accuracy is validated using one-dimensional Monte Carlo simulations. We demonstrate the superiority of this new approach by comparing it to the common geometrical analysis of hole TOF transients measured on poly(3-hexyl thiophene-2,5-diyl). The extracted distributions provide access to a very detailed and accurate analysis of the charge carrier transport. For instance, not only the mobility given by the mean transit time but also the mean mobility can be calculated. Whereas the latter determines the macroscopic photocurrent, the former is relevant for an accurate determination of the energetic disorder parameter ? within the Gaussian disorder model. ? derived by using the common geometrical method is, as we show, underestimated instead.
Lorrmann, Jens; Ruf, Manuel; Vocke, David; Dyakonov, Vladimir; Deibel, Carsten
Relationship between defect density and charge carrier transport in amorphous and microcrystalline silicon
The influence of dangling-bond defects and the position of the Fermi level on the charge carrier transport properties in undoped and phosphorous doped thin-film silicon with structure compositions all the way from highly crystalline to amorphous is investigated. The dangling-bond density is varied reproducibly over several orders of magnitude by electron bombardment and subsequent annealing. The defects are investigated by electron-spin-resonance and photoconductivity spectroscopies. Comparing intrinsic amorphous and microcrystalline silicon, it is found that the relationship between defect density and photoconductivity is different in both undoped materials, while a similar strong influence of the position of the Fermi level on photoconductivity via the charge carrier lifetime is found in the doped materials. The latter allows a quantitative determination of the value of the transport gap energy in microcrystalline silicon. The photoconductivity in intrinsic microcrystalline silicon is, on one hand, considerably less affected by the bombardment but, on the other hand, does not generally recover with annealing of the defects and is independent from the spin density which itself can be annealed back to the as-deposited level. For amorphous silicon and material prepared close to the crystalline growth regime, the results for nonequilibrium transport fit perfectly to a recombination model based on direct capture into neutral dangling bonds over a wide range of defect densities. For the heterogeneous microcrystalline silicon, this model fails completely. The application of photoconductivity spectroscopy in the constant photocurrent mode (CPM) is explored for the entire structure composition range over a wide variation in defect densities. For amorphous silicon previously reported linear correlation between the spin density and the subgap absorption is confirmed for defect densities below 10{sup 18} cm{sup -3}. Beyond this defect level, a sublinear relation is found i.e., not all spin-detected defects are also visible in the CPM spectra. Finally, the evaluation of CPM spectra in defect-rich microcrystalline silicon shows complete absence of any correlation between spin-detected defects and subband gap absorption determined from CPM: a result which casts considerable doubt on the usefulness of this technique for the determination of defect densities in microcrystalline silicon. The result can be related to the inhomogeneous structure of microcrystalline silicon with its consequences on transport and recombination processes.
Astakhov, Oleksandr; Carius, Reinhard; Finger, Friedhelm; Petrusenko, Yuri; Borysenko, Valery; Barankov, Dmytro [Forschungszentrum Juelich, Institute of Energy Research-Photovoltaic, 52425 Juelich, Germany and National Science Center-Kharkov Institute of Physics and Technology, Cyclotron Science and Research Establishment, 61108 Kharkov (Ukraine); Forschungszentrum Juelich, Institute of Energy Research-Photovoltaic, 52425 Juelich (Germany); National Science Center-Kharkov Institute of Physics and Technology, Cyclotron Science and Research Establishment, 61108 Kharkov (Ukraine)
Electric field dependence of charge carrier hopping transport within the random energy landscape in an organic field effect transistor
NASA Astrophysics Data System (ADS)
We extended our analytical effective medium theory [Phys. Rev. BPRBMDO0163-182910.1103/PhysRevB.81.045202 81, 045202 (2010)] to describe the temperature-dependent hopping charge carrier mobility at arbitrary electric fields in the large carrier density regime. Special emphasis was made to analyze the influence of the lateral electric field on the Meyer-Neldel (MN) phenomenon observed when studying the charge mobilities in thin-film organic field-effect transistors (OFET). Our calculations are based on the average hopping transition time approach, generalized for large carrier concentration limit finite fields, and taking into account also spatial energy correlations. The calculated electric field dependences of the hopping mobility at large carrier concentrations are in good agreement with previous computer simulations data. The shift of the MN temperature in an OFET upon applied electric field is shown to be a consequence of the spatial energy correlation in the organic semiconductor film. Our calculations show that the phenomenological Gill equation is clearly inappropriate for describing conventional charge carrier transport at low carrier concentrations. On the other hand a Gill-type behavior has been observed in a temperature range relevant for measurements of the charge carrier mobility in OFET structures. Since the present model is not limited to zero-field mobility, it allows a more accurate evaluation of important material parameters from experimental data measured at a given electric field. In particular, we showed that both the MN and Gill temperature can be used for estimating the width of the density of states distribution.
Fishchuk, I. I.; Kadashchuk, A.; Ullah, Mujeeb; Sitter, H.; Pivrikas, A.; Genoe, J.; B�ssler, H.
Effect of lateral transport of photoinduced charge carriers in a heterostructure with a two-dimensional electron gas
It is shown that the nonequilibrium charge carriers produced by a local optical disturbance of the heterostructure with a\\u000a two-dimensional electron gas are transported in the plane of the structure over an extremely large distance from the excitation\\u000a location, which greatly exceeds the diffusion length in the bulk. The effect is attributable to the fact that the photogenerated\\u000a electrons and
V. A. Sablikov; O. A. Ryabushkin; S. V. Polyakov
Charge transport, carrier balance, and blue electrophosphorescence in diphenyl[4-(triphenylsilyl)phenyl]phosphine oxide devices
NASA Astrophysics Data System (ADS)
Diphenyl[4-(triphenylsilyl)phenyl]phosphine oxide (EMPA1) displays a wide highest occupied molecular orbital-lowest unoccupied molecular orbital gap (4.1 eV), singlet (4.3 eV) and triplet (3.4 eV), and an electron-dominated charge transport that follows a trap-free space charge limited model with an average electron mobility of 5.7�10-6 cm2 V-1 s-1 and a hole mobility of 1.1�10-6 cm2 V-1 s-1. At high driving voltages (>6 V), ambipolar charge transport is observed, resulting in a balanced charge density in the active layer. Highly efficient blue phosphorescent organic light-emitting diodes were realized, showing a high external quantum efficiency (21%) and a luminance efficiency of 45 cd/A using a bis[2-(4',6'-difluorophenyl)-pyridinato-N,C2']iridium(III) picolinate dopant.
Mamada, Masashi; Ergun, Selin; P�rez-Bol�var, C�sar; Anzenbacher, Pavel
Charge carrier photogeneration and transport properties of a novel low-bandgap conjugated polymer for organic photovoltaics
NASA Astrophysics Data System (ADS)
The overall power conversion efficiency of organic solar cells depends on many factors, some of which such as photon absorption, charge carrier photogeneration, separation and transport are intrinsic properties of the active material. The use of low-bandgap conjugated polymers in polymer/fullerene bulk heterojunctions improves the spectral overlap between the polymer absorption and the solar irradiance spectrum, and is therefore a promising route toward increased light harvesting and higher power conversion efficiency of polymer photovoltaics. We present our studies on the optical and charge transport properties of a novel low-bandgap conjugated polymer, poly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b']dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)], PCPDTBT, with an optical energy gap of E g=1.46 eV. The combination of steady-state and transient photoconductivity with photoinduced absorption measurements has allowed us to investigate the charge carrier photogeneration and charge transport mechanisms in pristine PCPDTBT and PCPDTBT:PCBM interpenetrating networks, and to compare them to the P3HT and P3HT:PCBM model systems. The picture of the photophysics of PCPDTBT:PCBM emerging from these studies is very similar to that of P3HT:PCBM blends. We discuss the potential of PCPDTBT as a new material for high efficiency polymer solar cells.
Soci, Cesare; Hwang, In-Wook; Yang, Cuiying; Moses, Daniel; Zhu, Zhengguo; Waller, David; Gaudiana, Russel; Brabec, Christoph J.; Heeger, Alan J.
Charge transport and carrier dynamics in liquids probed by THz time-domain spectroscopy.
We examine the transport properties and the dynamics of free electrons in n-hexane by means of femtosecond spectroscopy using an ultraviolet pump pulse to create the electrons and a THz electromagnetic pulse as a probe. The complex dielectric response of the photogenerated electrons is determined over a broad range of frequencies, from which we infer the electron scattering time and density through the Drude model. The time evolution of the carrier density reveals nongeminate electron-ion recombination within hundreds of picoseconds at high ion concentration. PMID:11177826
Knoesel, E; Bonn, M; Shan, J; Heinz, T F
Electric field dependence of charge-carrier hopping transport at large carrier concentrations in disordered organic solids: Meyer-Neldel and Gill energies
NASA Astrophysics Data System (ADS)
Effective medium approach has been extended to describe the temperature dependent hopping charge-carrier mobility at arbitrary electric fields in the large carrier density transport regime. We take into account the spatial energy correlations in organic materials with Gaussian disorder. The theory is applied to describe recent experimental measurements of the electron transport properties in a C60-based OFET for different lateral electric fields FDS. Since this model is not limited to zero-field mobility, it allows a more accurate evaluation of important material parameters from experimental data measured at a given electric field. The shift of the Meyer-Neldel energy EMN upon applied lateral electric field FDS and the Gill energy EG upon the gate voltage VG in an OFET is shown to be a consequence of the spatial energy correlation effects in the organic semiconductor film. We showed that both the Meyer-Neldel and Gill energies can be used for estimating the width of the Gaussian density-of-states distribution.
Fishchuk, I. I.; Kadashchuk, A.; Ullah, Mujeeb; Sitter, H.; Sariciftci, N. S.; B�ssler, H.
Electroluminescence from both a light-emitting layer and hole transport layer: spectral evidence for charge carrier tunneling injection
NASA Astrophysics Data System (ADS)
We investigate the electroluminescence spectra of a series of double- and triple-layered devices based on a rare-earth complex PTT, tris-(1-phenyl-3-methyl-4-isobutyryl-5-pyrozolone)-bis(triphenyl phosphine oxide) terbium. In triple-layer devices, besides green electroluminescence from the light-emitting layer PTT, blue emission from the hole transport layer TPD ( N, N'-bis (3-methylphenyl)- N, N'-diphenyl-benzidine) occurs at high electric field strength (EFS) and its peak intensity increases with EFS. This indicates a charge carrier tunneling injection mechanism. At high EFS, the Fowler-Nordheim (FN) plot is close to linear, supporting the tunneling mechanism. The large barriers at the cathode and anode interfaces are responsible for this FN behavior. In double-layer devices where the 8-hydroxyquinoline-aluminum layer is absent, TPD emission dominates the electroluminescence, proving that PTT possesses high electron mobility.
Gao, Xi-Cun; Cao, Hong; Huang, Chun-Hui; Li, Biao-Guo; Ibrahim, K.; Liu, Feng-Qin; Umitani, Shigeo
Direct Imaging of Minority Charge Carrier Transport in Triple Junction Solar Cell Layers.
National Technical Information Service (NTIS)
An optical, contact-free method for measuring minority carrier diffusion lengths is developed and demonstrated for a range of semiconductor materials used in high efficiency triple junction solar cells. This method uses a Scanning Electron Microscope (SEM...
T. J. Mills
Effects of contact resistance on the evaluation of charge carrier mobilities and transport parameters in amorphous zinc tin oxide thin-film transistors
NASA Astrophysics Data System (ADS)
Accurate determination of the charge transport characteristics of amorphous metal-oxide transistors requires the mitigation of the effects of contact resistance. The use of additional electrodes as voltage probes can overcome contact resistance-related limitations and yields accurate charge carrier mobility values, trap depths and temperature and carrier density dependencies of mobility as well as trap depths. We show that large differences in measured charge carrier mobility values are obtained when such contact resistances are not factored out. Upon exclusion of the contact resistance, the true temperature dependence of charge carrier mobility appears in the form of two clearly distinct mobility regimes. Analyzing these revealed mobility regions leads to a more accurate determination of the underlying transport physics, which shows that contact resistance-related artefacts yield incorrect trends of trap depth with gate voltage, potentially leading to a misconstruction of the charge transport picture. Furthermore, a comparison of low- and high-mobility samples indicates that the observed effects are more general.
Schulz, Leander; Yun, Eui-Jung; Dodabalapur, Ananth
Charge carriers and excitons transport in an organic solar cell-theory and simulation
NASA Astrophysics Data System (ADS)
An organic solar cell model is developed that consists of both excitonic and classical bipolar aspects of solar cells. In order to achieve this goal, the photon recycling term is imported into the equations to connect the Shockley-Queisser theory and the classical diode theory. This model for excitonic and classical bipolar solar cells can describe the combined transport and interaction of electrons, holes and excitons. For high mobilities this model reproduces the Shockley Queisser efficiency limit. We show how varying the respective mobilities of the different species changes the operation mode of the solar cell path between excitonic and bipolar. Then, the effect of conduction band offset on transport will be described in this paper. Finally, validity of reciprocity theorem between quantum efficiency and electroluminescence in this model will be discussed.
Shahini, Ali.; Abbasian, Karim.
Charge-Carrier-Scattering Spectroscopy With BEEM
NASA Technical Reports Server (NTRS)
Ballistic-electron-emission microscopy (BEEM) constitutes basis of new spectroscopy of scattering of electrons and holes. Pointed tip electrode scans near surface of metal about 100 angstrom thick on semiconductor. Principle similar to scanning tunneling microscope, except metal acts as third electrode. Used to investigate transport phenomena, scattering phenomena, and creation of hot charge carriers in Au/Si and Au/GaAs metal/semiconductor microstructures.
Hecht, Michael H.; Bell, Lloyd D.; Kaiser, William J.
Photoinduced reversible switching of charge carrier mobility in conjugated polymers
Photoinduced reversible switching of charge carrier mobility in conjugated polymers was studied by theoretical and experimental methods. The quantum chemical calculations showed that the presence of dipolar species in the vicinity of a polymer chain modifies the on-chain site energies and consequently increases the width of the distribution of hopping transport states. The influence of photoswitchable charge carrier traps on
M. Weiter; J. Navr�til; M. Vala; P. Toman
Charge photo-carrier transport from silicon nanocrystals embedded in SiO2-based multilayer structures
NASA Astrophysics Data System (ADS)
Experimental investigation of photoconductivity in Si-rich silicon oxide (SRSO)/SiO2 multilayer (ML) structures prepared by magnetron reactive sputtering is reported. Photocurrent (PC) measurements show that the PC threshold increases with decreasing the thickness of SRSO layer. Photo-conduction processes in our samples are shown to be dominated by carrier transport through quantum-confined silicon nanocrystals embedded in the SiO2 host. In addition, the observed bias-dependence of photocurrent intensity is consistent with a model in which carrier transport occurs by both tunneling and hopping through defect states in the silicon oxide matrix. A photocurrent density Jph of 1-2 mA cm-2 is extracted from our results. Although this photocurrent density along the ML absorber film is relatively low, the results presented in this work are believed to be a valuable contribution toward the implementation of all-Si tandem solar cells.
Dridi Rezgui, B.; Gourbilleau, F.; Maestre, D.; Palais, O.; Sibai, A.; Lemiti, M.; Br�mond, G.
High-rate charge-carrier transport in porphyrin covalent organic frameworks: switching from hole to electron to ambipolar conduction.
Well conducted: a two-dimensional porphyrin covalent organic framework is described. Owing to the eclipsed stacking alignment, the framework is conductive and allows high-rate carrier transport through the porphyrin columns. The central metal in the porphyrin rings changes the conducting nature of the material from hole to electron, and to ambipolar conduction. It also drives the high on-off ratio photoconductivity of the framework. PMID:22290932
Feng, Xiao; Liu, Lili; Honsho, Yoshihito; Saeki, Akinori; Seki, Shu; Irle, Stephan; Dong, Yuping; Nagai, Atsushi; Jiang, Donglin
Low temperature charge carrier hopping transport mechanism in vanadium oxide thin films grown using pulsed dc sputtering
NASA Astrophysics Data System (ADS)
Low temperature charge transport in vanadium oxide (VOx) thin films processed using pulsed dc sputtering is investigated to understand the correlation between the processing conditions and electrical properties. It is identified that the temperature dependent resistivity ?(T) of the VOx thin films is dominated by a Efros-Shklovskii variable range hopping mechanism [Efros and Shklovskii, J. Phys. C 8, L49 (1975)]. A detailed analysis in terms of charge hopping parameters in the low temperature regime is used to correlate film properties with the pulsed dc sputtering conditions.
Bharadwaja, S. S. N.; Venkatasubramanian, C.; Fieldhouse, N.; Ashok, S.; Horn, M. W.; Jackson, T. N.
Analysis of photoexcited charge carrier density profiles in Si wafers by using an infrared camera
We demonstrate the mapping of lateral photoexcited charge carrier density profiles in a Si wafer that is illuminated in a spot by strongly absorbed light, using an infrared camera. The radial decay measured for the charge carrier density yields information on the effective carrier lifetime. The lifetime is extracted from the infrared camera image by modeling the transport. The carrier
Rolf Brendel; Michael Bail; Benno Bodmann; J�rg Kentsch; Max Schulz
Dynamics of spin charge carriers in polyaniline
NASA Astrophysics Data System (ADS)
The review summarizes the results of the study of emeraldine forms of polyaniline by multifrequency (9.7-140 GHz, 3-cm and 2-mm) wavebands Electron Paramagnetic Resonance (EPR) spectroscopy combined with the spin label and probe, steady-state saturation of spin-packets, and saturation transfer methods. Spin excitations formed in emeraldine form of polyaniline govern structure, magnetic resonance, and electronic properties of the polymer. Conductivity in neutral or weakly doped samples is defined mainly by interchain charge tunneling in the frames of the Kivelson theory. As the doping level increases, this process is replaced by a charge thermal activation transport by molecular-lattice polarons. In heavily doped polyaniline, the dominating is the Mott charge hopping between well-conducting crystalline ravels embedded into amorphous polymer matrix. The main properties of polyaniline are described in the first part. The theoretical background of the magnetic, relaxation, and dynamics study of nonlinear spin carriers transferring a charge in polyaniline is briefly explicated in the second part. An original data obtained in the EPR study of the nature, relaxation, and dynamics of polarons as well as the mechanism of their transfer in polyaniline chemically modified by sulfuric, hydrochloric, camphorsulfonic, 2-acrylamido-2-methyl-1-propanesulfonic, and para-toluenesulfonic acids up to different doping levels are analyzed in the third part. Some examples of utilization of polyaniline in molecular electronics and spintronics are described.
Krinichnyi, V. I.
Clustered impurities and carrier transport in supported graphene
NASA Astrophysics Data System (ADS)
We investigate the effects of charged impurity distributions and carrier-carrier interactions on electronic transport in graphene on SiO2 by employing a self-consistent coupled simulation of carrier transport and electrodynamics. We show that impurity clusters of characteristic width 40-50 nm generate electron-hole puddles of experimentally observed sizes. The residual conductivity and the linear-region slope of the conductivity versus carrier density dependence are determined by the impurity distribution, and the measured slope can be used to estimate the impurity density in experiment. Furthermore, we show that the high-density sublinearity in the conductivity stems from carrier-carrier interactions.
Sule, N.; Hagness, S. C.; Knezevic, I.
Electrical Transport in a Disordered Medium: NMR Measurement of Diffusivity and Electrical Mobility of Ionic Charge Carriers
NASA Astrophysics Data System (ADS)
Electrical transport in porous media plays an important role in many fields of pure and applied science. The basic microscopic processes of the charge transport have attracted considerable theoretical interest for a long time. However, on a microscopic level there was up to now no experimental access to this problem. In the present paper we demonstrate, by using a suited porous system, that two combined NMR methods can offer such a first experimental access. We apply common PFG NMR methods and the special electrophoretic NMR (ENMR) technique for the measurement of self-diffusion coefficient D +and electric mobility u +of a cation ((C 4H 9) +4) in a disordered gel-like medium (Sephadex LH-20) filled with electrolyte solution. We find a, qualitatively expected, observation time-dependence of D +, but for the first time such a time-dependence is also observed for u +, which means the detection of the phenomenon of "anomalous field assisted diffusion" or "anomalous mobility." For the measurement of the short-time behavior of the mobility a new pulse sequence is presented. The time-dependent mobilities were measured at three different external electrical fields E.From the long-time behavior of D +, u +, and DH 2Othree independent values for the tortuosity Tof the porous system could be derived. We find equality of the tortuosities T(D +) and T(u +), which represents a first experimental proof of the validity of the Einstein relation (D +� u +) in a disordered medium. Finally, we discuss advantages of the possible use of "anomalous field assisted diffusion" over the commonly used "anomalous diffusion" in morphology studies by dynamic imaging in porous media.
Heil, Stefan R.; Holz, Manfred
Charge carrier diffusion profiles in wide band gap semiconductors
Although n-type doping by phosphorous meanwhile opens the route to ambipolar electronics on the basis of diamond, the majority of devices so far realized rely on hole transport only. Unipolar charge carrier diffusion is therefore a widely spread and important phenomenon for diamond electronics. Even without equilibrium between electrons and holes inside the semiconductor, the holes alone will establish a
J�rgen Ristein
Structure and charge transport properties in MEH-PPV
The charge carrier transport in MEH-PPV is investigated with respect to different molecular weight distributions and with different tetrahedral defect densities. The defect density influences the charge transport behaviors significantly. With smaller defect density, MEH-PPV exhibits better charge transport which further depends upon the morphology. Position disorder parameter which is due to the morphology difference dominates the charge transport properties
Anto Regis Inigo; Hsiang-Chih Chiu; Wunshain Fann; Ying-Sheng Huang; C. H. Hsu; Kang-Yung Peng; Show-An Chen
An acoustic charge transport signal processing module featuring a low-temperature co-fireable ceramic chip carrier
Acoustic charge technology (ACT) has been integrated with digital control circuitry to achieve complex signal processing chips. The basic ACT device with the added digital circuitry calls for several different types of signals for operation including RF, DC, and digital control signals. Proper signal management is critical for minimizing direct-feed-through electromagnetic and common ground coupling. A low-temperature multilayer cofired technology
Timothy W. Brooks
Diffusive charge transport in graphene
NASA Astrophysics Data System (ADS)
The physical mechanisms limiting the mobility of graphene on SiO 2 are studied and printed graphene devices on a flexible substrate are realized. Intentional addition of charged scattering impurities is used to study the effects of charged impurities. Atomic-scale defects are created by noble-gas ions irradiation to study the effect of unitary scatterers. The results show that charged impurities and atomic-scale defects both lead to conductivity linear in density in graphene, with a scattering magnitude that agrees quantitatively with theoretical estimates. While charged impurities cause intravalley scattering and induce a small change in the minimum conductivity, defects in graphene scatter electrons between the valleys and suppress the minimum conductivity below the metallic limit. Temperature-dependent measurements show that longitudinal acoustic phonons in graphene produce a small resistivity which is linear in temperature and independent of carrier density; at higher temperatures, polar optical phonons of the SiO2 substrate give rise to an activated, carrier density-dependent resistivity. Graphene is also made into high mobility transparent and flexible field effect device via the transfer-printing method. Together the results paint a complete picture of charge carrier transport in graphene on SiO2 in the diffusive regime, and show the promise of graphene as a novel electronic material that have potential applications not only on conventional inorganic substrates, but also on flexible substrates.
Chen, Jianhao
Evaluation of Intrinsic Charge Carrier Transport at Insulator-Semiconductor Interfaces Probed by a Non-Contact Microwave-Based Technique
NASA Astrophysics Data System (ADS)
We have successfully designed the geometry of the microwave cavity and the thin metal electrode, achieving resonance of the microwave cavity with the metal-insulator-semiconductor (MIS) device structure. This very simple MIS device operates in the cavity, where charge carriers are injected quantitatively by an applied bias at the insulator-semiconductor interface. The local motion of the charge carriers was clearly probed through the applied external microwave field, also giving the quantitative responses to the injected charge carrier density and charge/discharge characteristics. By means of the present measurement system named field-induced time-resolved microwave conductivity (FI-TRMC), the pentacene thin film in the MIS device allowed the evaluation of the hole and electron mobility at the insulator-semiconductor interface of 6.3 and 0.34 cm2 V-1 s-1, respectively. This is the first report on the direct, intrinsic, non-contact measurement of charge carrier mobility at interfaces that has been fully experimentally verified.
Honsho, Yoshihito; Miyakai, Tomoyo; Sakurai, Tsuneaki; Saeki, Akinori; Seki, Shu
Evaluation of intrinsic charge carrier transport at insulator-semiconductor interfaces probed by a non-contact microwave-based technique.
We have successfully designed the geometry of the microwave cavity and the thin metal electrode, achieving resonance of the microwave cavity with the metal-insulator-semiconductor (MIS) device structure. This very simple MIS device operates in the cavity, where charge carriers are injected quantitatively by an applied bias at the insulator-semiconductor interface. The local motion of the charge carriers was clearly probed through the applied external microwave field, also giving the quantitative responses to the injected charge carrier density and charge/discharge characteristics. By means of the present measurement system named field-induced time-resolved microwave conductivity (FI-TRMC), the pentacene thin film in the MIS device allowed the evaluation of the hole and electron mobility at the insulator-semiconductor interface of 6.3 and 0.34?cm� V?� s?�, respectively. This is the first report on the direct, intrinsic, non-contact measurement of charge carrier mobility at interfaces that has been fully experimentally verified. PMID:24212382
Honsho, Yoshihito; Miyakai, Tomoyo; Sakurai, Tsuneaki; Saeki, Akinori; Seki, Shu
Evaluation of Intrinsic Charge Carrier Transport at Insulator-Semiconductor Interfaces Probed by a Non-Contact Microwave-Based Technique
We have successfully designed the geometry of the microwave cavity and the thin metal electrode, achieving resonance of the microwave cavity with the metal-insulator-semiconductor (MIS) device structure. This very simple MIS device operates in the cavity, where charge carriers are injected quantitatively by an applied bias at the insulator-semiconductor interface. The local motion of the charge carriers was clearly probed through the applied external microwave field, also giving the quantitative responses to the injected charge carrier density and charge/discharge characteristics. By means of the present measurement system named field-induced time-resolved microwave conductivity (FI-TRMC), the pentacene thin film in the MIS device allowed the evaluation of the hole and electron mobility at the insulator-semiconductor interface of 6.3 and 0.34?cm2 V?1 s?1, respectively. This is the first report on the direct, intrinsic, non-contact measurement of charge carrier mobility at interfaces that has been fully experimentally verified.
Honsho, Yoshihito; Miyakai, Tomoyo; Sakurai, Tsuneaki; Saeki, Akinori; Seki, Shu
Columnar mesophases of hexabenzocoronene derivatives. II. Charge carrier mobility.
Combining atomistic molecular dynamic simulations, Marcus-Hush theory description of charge transport rates, and master equation description of charge dynamics, we correlate the temperature-driven change of the mesophase structure with the change of charge carrier mobilities in columnar phases of hexabenzocoronene derivatives. The time dependence of fluctuations in transfer integrals shows that static disorder is predominant in determining charge transport characteristics. Both site energies and transfer integrals are distributed because of disorder in the molecular arrangement. It is shown that the contributions to the site energies from polarization and electrostatic effects are of opposite sign for positive charges. We look at three mesophases of hexabenzocoronene: herringbone, discotic, and columnar disordered. All results are compared to time resolved microwave conductivity data and show excellent agreement with no fitting parameters. PMID:19044876
Kirkpatrick, James; Marcon, Valentina; Kremer, Kurt; Nelson, Jenny; Andrienko, Denis
Electroluminescence from both a light-emitting layer and hole transport layer: spectral evidence for charge carrier tunneling injection
We investigate the electroluminescence spectra of a series of double- and triple-layered devices based on a rare-earth complex PTT, tris-(1-phenyl-3-methyl-4-isobutyryl-5-pyrozolone)-bis(triphenyl phosphine oxide) terbium. In triple-layer devices, besides green electroluminescence from the light-emitting layer PTT, blue emission from the hole transport layer TPD (N,N?-bis (3-methylphenyl)-N,N?-diphenyl-benzidine) occurs at high electric field strength (EFS) and its peak intensity increases with EFS. This indicates
Xi-Cun Gao; Hong Cao; Chun-Hui Huang; Biao-Guo Li; K. Ibrahim; Feng-Qin Liu; Shigeo Umitani
Electrochemical reactions and charge transport in undiluted room-temperature melts of oligo(ethylene glycol)-based electron carriers
We report how the covalent attachment of short oligo (ethyleneglycol) chains to cobalt tris(bipyridine) complexes (I), tetrathiafulvalene (II), tetraphenylporphyrin (III), and ferrocenecarboxylate (IV) transforms these normally crystalline materials into room-temperature melts which freely dissolve electrolytes like LiClO{sub 4} to yield ionically conductive and is a novel electroactive molten salt. This paper describes a microelectrode-based voltammetric study of diffusion and electron transport phenomena in compounds I-IV in undiluted forms. 15 refs., 1 fig.
Velazquez, C.S.; Hutchison, J.E.; Murray, R.W. [Univ. of North Carolina, Chapel Hill, NC (United States)
Charge carrier kinetics in MnOx, Mn2O3 and Mn3O4 films for water oxidation
NASA Astrophysics Data System (ADS)
Manganese oxide films on conductive substrates were prepared by electrochemical deposition. Charge carrier kinetics in these films was studied by contactless transient photoconductivity measurements. These measurements revealed the generation of mobile charge carriers with a nonneglectable lifetime. The transport from charge carriers generated in the oxides to the substrate was observed.
Ram�rez, A.; Friedrich, D.; Kunst, M.; Fiechter, S.
Ballistic-Charge-Carrier Spectroscopy Of CoSi(2)/Si Interfaces
NASA Technical Reports Server (NTRS)
Report discusses experiments in which ballistic-electron-emission microscopy (BEEM) and related ballistic-hole and charge-carrier-scattering spectroscopies used to investigate transport of electric-charge carriers (electrons and holes) in epitaxial CoSi2/Si system.
Hecht, Michael H.; Kaiser, William J.; Fathauer, Robert W.; Bell, Lloyd D.; Lee, Edwin Y.
Charge-carrier relaxation dynamics in highly ordered poly( p -phenylene vinylene): Effects of carrier bimolecular recombination and trapping
NASA Astrophysics Data System (ADS)
We have studied the charge-carrier relaxation dynamics in highly ordered poly( p -phenylene vinylene) over a broad time range using fast (t>100ps) transient photoconductivity measurements. The carrier density was also monitored (t>100fs) by means of photoinduced absorption probed at the infrared active vibrational modes. We find that promptly upon charge-carrier photogeneration, the initial polaron dynamics is governed by bimolecular recombination, while later in the subnanosecond time regime carrier trapping gives rise to an exponential decay of the photocurrent. The more sensitive transient photocurrent measurements indicate that in the low excitation regime, when the density of photocarriers is comparable to that of the trapping states (�1016cm-3) , carrier hopping between traps along with transport via extended states determines the carrier relaxation, a mechanism that is manifested by a long-lived photocurrent �tail.� This photocurrent tail is reduced by lowering the temperature and/or by increasing the excitation density. Based on these data, we develop a comprehensive kinetic model that takes into account the bipolar charge transport, the free-carrier bimolecular recombination, the carrier trapping, and the carrier recombination involving free and trapped carriers.
Soci, Cesare; Moses, Daniel; Xu, Qing-Hua; Heeger, Alan J.
Auto Carrier Transporter Loading and Unloading Improvement.
National Technical Information Service (NTIS)
Thousands of vehicles (cars, trucks and vans) are transported every day from one location to another. These vehicles are moved around the country on Auto Carrier Transports (ACTs). Delivering these vehicles involves large quantities of time, money and ene...
B. M. Miller
The impact of hot charge carrier mobility on photocurrent losses in polymer-based solar cells.
A typical signature of charge extraction in disordered organic systems is dispersive transport, which implies a distribution of charge carrier mobilities that negatively impact on device performance. Dispersive transport has been commonly understood to originate from a time-dependent mobility of hot charge carriers that reduces as excess energy is lost during relaxation in the density of states. In contrast, we show via photon energy, electric field and film thickness independence of carrier mobilities that the dispersive photocurrent in organic solar cells originates not from the loss of excess energy during hot carrier thermalization, but rather from the loss of carrier density to trap states during transport. Our results emphasize that further efforts should be directed to minimizing the density of trap states, rather than controlling energetic relaxation of hot carriers within the density of states. PMID:25047086
Philippa, Bronson; Stolterfoht, Martin; Burn, Paul L; Ju�ka, Gytis; Meredith, Paul; White, Ronald D; Pivrikas, Almantas
The impact of hot charge carrier mobility on photocurrent losses in polymer-based solar cells
A typical signature of charge extraction in disordered organic systems is dispersive transport, which implies a distribution of charge carrier mobilities that negatively impact on device performance. Dispersive transport has been commonly understood to originate from a time-dependent mobility of hot charge carriers that reduces as excess energy is lost during relaxation in the density of states. In contrast, we show via photon energy, electric field and film thickness independence of carrier mobilities that the dispersive photocurrent in organic solar cells originates not from the loss of excess energy during hot carrier thermalization, but rather from the loss of carrier density to trap states during transport. Our results emphasize that further efforts should be directed to minimizing the density of trap states, rather than controlling energetic relaxation of hot carriers within the density of states.
Philippa, Bronson; Stolterfoht, Martin; Burn, Paul L.; Juska, Gytis; Meredith, Paul; White, Ronald D.; Pivrikas, Almantas
Free charge carriers in mesoporous silicon
NASA Astrophysics Data System (ADS)
Free charge carriers in mesoporous Si (meso-PS) consisting of Si nanocrystals of small dimensions of about 6-10 nm are investigated by the infrared-absorption technique. Adsorption of acceptor molecules or filling the pores with dielectric liquids are found to increase the concentration of free holes (p) in meso-PS up to the half of the doping level of the heavily boron-doped p+-Si substrate (p~5�1018 cm-3) from which the meso-PS was made. Considering the value of p and the dc electrical conductivity ?, the hole mobility is determined as about 5�10-4 and 5�10-3 cm2 V-1 s-1 for as-prepared meso-PS and meso-PS filled with a polar dielectric liquid, respectively. The activation energy is larger for ? than for p giving evidence for thermal activation of the hole mobility. A model of the dielectric confinement for charge carriers and hydrogenic impurities is applied to explain the dependence of ? and p on the dielectric constant of the ambience of the Si nanocrystals.
Timoshenko, V. Yu.; Dittrich, Th.; Lysenko, V.; Lisachenko, M. G.; Koch, F.
Carrier transport and collection in fully depleted semiconductors by a combined action of the space charge field and the field due to electrode voltages
A semiconductor charge transport device and method for making same, characterized by providing a thin semiconductor wafer having rectifying junctions on its opposing major surfaces and including a small capacitance ohmic contact, in combination with bias voltage means and associated circuit means for applying a predetermined voltage to effectively deplete the wafer in regions thereof between the rectifying junctions and the ohmic contact. A charge transport device of the invention is usable as a drift chamber, a low capacitance detector, or a charge coupled device each constructed according to the methods of the invention for making such devices. Detectors constructed according to the principles of the invention are characterized by having significantly higher particle position indicating resolution than is attainable with prior art detectors, while at the same time requiring substantially fewer readout channels to realize such high resolution.
Rehak, Pavel (Patchogue, NY); Gatti, Emilio (Lesmo, IT)
Scattering mechanisms of charge carriers in transparent conducting oxide films
Scattering mechanisms of charge carriers in Transparent Conducting Oxide (TCO) films have been analyzed theoretically. For the degenerate polycrystalline TCO films with relatively large crystallite sizes and high carrier concentrations (higher than 5 � 1018 cm-3), the depletion layers between crystallites are very thin compared to the crystallite sizes, and the grain boundary scattering on electrical carriers makes a small
D. H. Zhang; H. L. Ma
Scattering mechanisms of charge carriers in transparent conducting oxide films
Scattering mechanisms of charge carriers in Transparent Conducting Oxide (TCO) films have been analyzed theoretically. For the degenerate polycrystalline TCO films with relatively large crystallite sizes and high carrier concentrations (higher than 5�1018 cm-3), the depletion layers between crystallites are very thin compared to the crystallite sizes, and the grain boundary scattering on electrical carriers makes a small contribution to
D. H. Zhang; H. L. Ma
Charge-carrier photogeneration in doped metal-free phthalocyanine
NASA Astrophysics Data System (ADS)
Photoconductivity and electric-field-induced fluorescence quenching measurements on X-metal-free phthalocyanine photovoItaic cells show that doping with metal�phthalocyanines can both increase charge-carrier photogeneralion and decrease cell resistance. Charge-carrier photogeneration appears to be extrinsic, involving field-assisted exciplex dissociation.
Menzel, E. Roland; Loutfy, Rafik O.
Charge transport in photorefractive polymers
NASA Astrophysics Data System (ADS)
This dissertation describes the experimental investigation of photoconductivity and charge carrier mobility in photorefractive polymers. The photorefractive polymer composite containing an electro-optic polymer, bisphenol A 4,4'-nitrostilbene (bisA-NAS), and 30% weight of a hole transport agent, benzaldehyde- diphenyl hydrazone (DEH) was used extensively for these studies. The results show how to improve the response times in photorefractive polymers. We measured the photoconductivity and photorefractive response in the photorefractive composite as a function of applied electric field, temperature, light intensity and wavelength. The results show that photoconductivity is strongly dependent on temperature and applied electric field. The intensity-dependent photoconductivity measurements indicate a transition from unfilled to filled trapping states, giving an estimate of the shallow trap density. Two-beam coupling experiments (2BC), which measure the steady state photorefractive grating strength, and degenerate four-wave mixing experiments, which determine the transient photorefractive properties, were performed to characterize the photorefractive properties of the polymer composite. We measured the hole mobilities in the photorefractive polymer composite bisA-NAS:DEH as a function of temperature and applied electric field, using a conventional time-of-flight (TOF) technique. The results are described by the Gaussian disorder model (GDM) based on hopping through a manifold of states with superimposed energetic and positional disorder. The results reveal that the hole mobility is very low and is strongly dependent on temperature and applied electric field. Using several model systems, we investigated the effect of the polar additives on the carrier mobility in photorefractive polymers. Two different electro-optic chromophores having large dipole moments of order 7 Debye, two polymer binders with repeat unit dipole moments of 0.1 and 1 Debye, and several hole and electron transport agents covering a range of dipole moments from 0.8 to 4 Debye were used for this study. The results revealed that the strong dipolar chromophores required in photorefractive polymers significantly decrease the carrier mobility but low dipolar transport agents improve the carrier mobility and hence the speed of response.
Goonesekera, Arosha Wimala
The solute carrier 6 family of transporters.
The solute carrier 6 (SLC6) family of the human genome comprises transporters for neurotransmitters, amino acids, osmolytes and energy metabolites. Members of this family play critical roles in neurotransmission, cellular and whole body homeostasis. Malfunction or altered expression of these transporters is associated with a variety of diseases. Pharmacological inhibition of the neurotransmitter transporters in this family is an important strategy in the management of neurological and psychiatric disorders. This review provides an overview of the biochemical and pharmacological properties of the SLC6 family transporters. PMID:22519513
Br�er, Stefan; Gether, Ulrik
47 CFR 36.381 - Carrier access charge billing and collecting expense.
Code of Federal Regulations, 2010 CFR
...2009-10-01 false Carrier access charge billing and collecting expense...CARRIER SERVICES JURISDICTIONAL SEPARATIONS PROCEDURES; STANDARD PROCEDURES...36.381 Carrier access charge billing and collecting expense...billing and collecting of access charges to interexchange...
47 CFR 36.381 - Carrier access charge billing and collecting expense.
Code of Federal Regulations, 2010 CFR
...2010-10-01 false Carrier access charge billing and collecting expense...CARRIER SERVICES JURISDICTIONAL SEPARATIONS PROCEDURES; STANDARD PROCEDURES...36.381 Carrier access charge billing and collecting expense...billing and collecting of access charges to interexchange...
47 CFR 36.381 - Carrier access charge billing and collecting expense.
Code of Federal Regulations, 2013 CFR
...2013-10-01 false Carrier access charge billing and collecting expense...CARRIER SERVICES JURISDICTIONAL SEPARATIONS PROCEDURES; STANDARD PROCEDURES...36.381 Carrier access charge billing and collecting expense...billing and collecting of access charges to interexchange...
Temperature delocalization of charge carriers in semiconductor lasers
The temperature dependences of emission characteristics are investigated for laser diodes based on asymmetric separate-confinement heterostructures with a broadened waveguide. It is established that an increase in the charge-carrier concentration in the waveguide layer is the basic mechanism of saturation in the light-current characteristic with increasing temperature in the CW mode. It is experimentally shown that the temperature delocalization of charge carriers leads to increasing internal optical losses and decreasing external differential quantum efficiency. It is shown that the degree of delocalization of charge carriers depends on the charge-carrier temperature distribution, the threshold concentration, and the quantum-well depth. The effect of thickness and energy depth of the quantum well on the temperature sensitivity of the threshold current and output optical power is considered.
Slipchenko, S. O., E-mail: firstname.lastname@example.com; Shashkin, I. S.; Vavilova, L. S.; Vinokurov, D. A.; Lyutetskiy, A. V.; Pikhtin, N. A.; Podoskin, A. A.; Stankevich, A. L.; Fetisova, N. V.; Tarasov, I. S. [Russian Academy of Sciences, Ioffe Physicotechnical Institute (Russian Federation)
Low-field carrier transport properties in biased bilayer graphene
NASA Astrophysics Data System (ADS)
Based on a semiclassical Boltzmann transport equation in random phase approximation, we develop a theoretical model to understand low-field carrier transport in biased bilayer graphene, which takes into account the charged impurity scattering, acoustic phonon scattering, and surface polar phonon scattering as three main scattering mechanisms. The surface polar optical phonon scattering of carriers in supported bilayer graphene is thoroughly studied using the Rode iteration method. By considering the metal-BLG contact resistance as the only one free fitting parameter, we find that the carrier density dependence of the calculated total conductivity agrees well with that observed in experiment under different temperatures. The conductivity results also suggest that in high carrier density range, the metal-BLG contact resistance can be a significant factor in determining the BLG conductivity at low temperature, and both acoustic phonon scattering and surface polar phonon scattering play important roles at higher temperature, especially for BLG samples with a low doping concentration, which can compete with charged impurity scattering.
Hu, Bo
Signals Induced by Charge Carrier Trapping
NASA Astrophysics Data System (ADS)
Cryogenic germanium detectors used in dark matter searches operate at ranges of low temperature < 100 mathrm {mK} and electric field � 1 mathrm {V/cm} such that charge trapping in the bulk of the detector plays a significant role in the net charge collected following a particle interaction. It is shown that in EDELWEISS FID800 detectors, these trapped charges induce residual charge signals that perturb the measurement of the total charge, significantly degrading the energy resolution at high energy. It is also shown that, by reading out the signal on all the electrodes, it is possible to clearly identify these effects and correct the total charge measurement accordingly, resulting in a � 30 % improvement of the resolution at high energy. This effect is demonstrated with data. A simple analytical model based on Shockley-Ramo's theorem is presented, whereby this effect is due to the position dependence of signals induced by trapped charges.
Arnaud, Q.
The solute carrier 6 family of transporters
The solute carrier 6 (SLC6) family of the human genome comprises transporters for neurotransmitters, amino acids, osmolytes and energy metabolites. Members of this family play critical roles in neurotransmission, cellular and whole body homeostasis. Malfunction or altered expression of these transporters is associated with a variety of diseases. Pharmacological inhibition of the neurotransmitter transporters in this family is an important strategy in the management of neurological and psychiatric disorders. This review provides an overview of the biochemical and pharmacological properties of the SLC6 family transporters. LINKED ARTICLES BJP published a themed section on Transporters in 2011. To view articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.2011.164.issue-7/issuetoc
Broer, Stefan; Gether, Ulrik
Polymer optical sensor based on photochromic switching of charge carrier mobility
NASA Astrophysics Data System (ADS)
Polymer photoelectronic device based on interaction between ?-conjugated polymer matrices and photochromic molecules was fabricated. The theoretical and experimental studies proved that the photochromic reaction in studied devices should eventuate in changes of optical and electrical properties of polymers such as luminescence and conductivity. The quantum chemical calculations showed that the presence of dipolar species in the vicinity of a polymer chain modifies the on-chain site energies and consequently increases the width of the distribution of hopping transport states. Optical switching was studied using standard absorption and photoluminescence spectroscopy. A strong photoluminescence quenching after the photochromic conversion caused by radiative energy transfer was observed. The influence of photoswitchable charge carrier traps on charge transport was evaluated by current-voltage measurement and by Impedance spectroscopy method. It was shown that deep traps may significantly affect energy of the transport level, and thus control the transport of charge carriers. Based on these findings, polymer optical sensor was proposed.
Weiter, Martin; Vala, Martin; Zmeskal, Oldrich; Navratil, Jiri; Toman, Petr; Nespurek, Stanislav
Charge transport in disordered organic field-effect transistors
In this thesis we study charge transport in organic semiconductors. We do this by focusing on the physical characterization of disordered organic field-effect transistors. It will be made clear that the disorder in the polymer films is crucial for the interpretation of the data. The field-effect transistor geometry allows variation of the charge carrier density in the semiconductor, without the
E. J. Meijer
Anisotropic dynamics of charge carriers in graphene
NASA Astrophysics Data System (ADS)
Computer simulation by numerically solving the time-dependent Schr�dinger equation was used to investigate the spreading of electronic wave packets on the graphene surface injected from a local probe. The simulations show a highly anisotropic in-plane dynamics following a 60? angular periodicity even near the Fermi energy. The wave packet first tunnels onto the small graphene clusters below the tip and the electronic states of these clusters govern the further spreading of the electron on the graphene surface. It was found that in the vicinity of the injection point the molecular physical behavior dominates, but at larger distances the wave propagation is governed by solid-state physical rules. The calculations show complex charge-spreading phenomena at graphene grain boundaries. Our results reveal a new picture of charge propagation in graphene, which has important consequences for nanoelectronic applications.
M�rk, G�za I.; Vancs�, P�ter; Hwang, Chanyong; Lambin, Philippe; Bir�, L�szl� P.
Resolving the ultrafast dynamics of charge carriers in nanocomposites
NASA Astrophysics Data System (ADS)
Here, we describe an optical method to determine the dynamics of optically excited carriers in nanostructured composite samples. By combining pump-probe time-resolved reflectivity with scattering measurements, we extract the characteristic times for charge carrier evolution. We use the 3D Maxwell-Garnett formulae, modified to include the Drude optical response, to model the results. The method, applied to hydrogenated amorphous silicon containing crystalline silicon nanoparticles, showed that the recombination times in the nanocrystals and in the matrix were ~4.9 ps and ~22 ps, respectively. The charge transfer time between the crystals and the matrix was ~4 ps.
Barreto, J.; Roger, T.; Kaplan, A.
Lifetime of charge carriers in multiwalled nanotubes.
The nature of low-energy excitations in multiwalled nanotubes (MWNTs) is investigated by means of two-color time-resolved photoemission. A careful analysis of the ballistic transport, secondary excitations, and band structure effects was employed in order to extract single electron lifetimes from the observed relaxation trend. It is demonstrated that in the vicinity of the Fermi level the energy dependence of e-e scattering times is inversely proportional to approximately the square of the excitation energy. This result provides strong evidence that electron transport in MWNTs exhibits a Fermi-liquid behavior, indicating that long-range e-e interaction along the tube vanishes due to screening. PMID:15783675
Zamkov, M; Woody, N; Shan, B; Chang, Z; Richard, P
Lifetime of Charge Carriers in Multiwalled Nanotubes
The nature of low-energy excitations in multiwalled nanotubes (MWNTs) is investigated by means of two-color time-resolved photoemission. A careful analysis of the ballistic transport, secondary excitations, and band structure effects was employed in order to extract single electron lifetimes from the observed relaxation trend. It is demonstrated that in the vicinity of the Fermi level the energy dependence of e-e
M. Zamkov; N. Woody; B. Shan; Z. Chang; P. Richard
ERIC Educational Resources Information Center
In Antelope Valley, California, a regional transportation consortium, cooperatively run by six adjacent school districts, is operating an electric-powered school bus as a pilot project. Although the prototype bus cost nearly six times more than a traditional school bus, lower operating and maintenance expenses and safety factors appeal to many�
Vail, Kathleen R.
Modeling charge transport in organic photovoltaic materials.
The performance of an organic photovoltaic cell depends critically on the mobility of charge carriers within the constituent molecular semiconductor materials. However, a complex combination of phenomena that span a range of length and time scales control charge transport in disordered organic semiconductors. As a result, it is difficult to rationalize charge transport properties in terms of material parameters. Until now, efforts to improve charge mobilities in molecular semiconductors have proceeded largely by trial and error rather than through systematic design. However, recent developments have enabled the first predictive simulation studies of charge transport in disordered organic semiconductors. This Account describes a set of computational methods, specifically molecular modeling methods, to simulate molecular packing, quantum chemical calculations of charge transfer rates, and Monte Carlo simulations of charge transport. Using case studies, we show how this combination of methods can reproduce experimental mobilities with few or no fitting parameters. Although currently applied to material systems of high symmetry or well-defined structure, further developments of this approach could address more complex systems such anisotropic or multicomponent solids and conjugated polymers. Even with an approximate treatment of packing disorder, these computational methods simulate experimental mobilities within an order of magnitude at high electric fields. We can both reproduce the relative values of electron and hole mobility in a conjugated small molecule and rationalize those values based on the symmetry of frontier orbitals. Using fully atomistic molecular dynamics simulations of molecular packing, we can quantitatively replicate vertical charge transport along stacks of discotic liquid crystals which vary only in the structure of their side chains. We can reproduce the trends in mobility with molecular weight for self-organizing polymers using a cheap, coarse-grained structural simulation method. Finally, we quantitatively reproduce the field-effect mobility in disordered C60 films. On the basis of these results, we conclude that all of the necessary building blocks are in place for the predictive simulation of charge transport in macromolecular electronic materials and that such methods can be used as a tool toward the future rational design of functional organic electronic materials. PMID:19848409
Nelson, Jenny; Kwiatkowski, Joe J; Kirkpatrick, James; Frost, Jarvist M
High-Field Carrier Transport in Inhomogeneous Semiconductors
NASA Astrophysics Data System (ADS)
The carrier transport in inhomogeneous solids is reevaluated in respect to the differences between a built-in field within a space charge region and an external field, and related to differences in carrier redistribution and carrier heating, resulting in a different field-dependence of the mobility. With the assistance of electrostatic and electrochemical potential distributions the regions of substantial carrier heating can be identified as regions in which the current is carried by diffusion only (DO), or by drift only (DRO) in forward (or low reverse), and in high reverse bias respectively, and are distinguished from the region of a major electrostatic potential drop (Boltzmann region) in which the net current is small compared to drift and diffusion. In junction devices major carrier heating does only occur in DO- and DRO regions, and only for minority carriers.Translated AbstractLadungstransport in Inhomogenen Halbleitern bei hohen Feldst�rkenUnter Ber�cksichtigung des Unterschieds zwischen einem internen Feld in einem Raumladungsgebiet und einem externen Feld wird der Ladungstr�gertransport im inhomogenen Festk�rper unter Beachtung der M�glichkeiten der Ladungstr�gerumverteilung oder -erw�rmung, die zu einer unterschiedlichen Feldst�rkenabh�gigkeit der Beweglichkeit f�hren, behandelt. Mit Hilfe von elektrostatischen und elektrochemischen Potentialverteilungen k�nnen die Gebiete intensiver Ladungstr�gererw�rmung als solche identifiziert werden, in denen der Strom nur aus entweder einer Diffusionskomponente (DO) bei treibender oder auch kleiner Gegenspannung oder einer Driftkomponente (DRO) bei hoher Gegenspannung besteht, und die verschieden von Gebieten mit einem wesentlichen elektrostatischen Potentialabfall (Boltzmannbereich) sind, in welchem der Nettostrom klein, ist im Vergleich zu Drift und Diffusion. In �bergangsbereichen tritt wesentliche Ladungstr�gererw�rmung nur in DO- und DRO-Gebieten und nur an Minorit�tsladungstr�gern auf.
B�er, K. W.
Cyclodextrin carriers of positively charged porphyrin sensitizers.
The cationic sensitizer 5,10,15,20-tetrakis(N-methylpyridinium-4-yl)porphyrin (TMPyP) forms supramolecular complexes with native, per-methylated, sulfonated and dimethyl-sulfonated cyclodextrins (CDs). Binding interactions were proved by NMR, mass spectra, capillary zone electrophoresis, UV-Vis and fluorescence spectroscopy. The 2D-NMR experiments on native CDs indicate that the interaction of TMPyP with the external CD surface is the dominant binding mode. The high binding affinity of TMPyP towards sulfonated CDs is due to electrostatic interactions. Binding is accompanied by an increase of the TMPyP basicity. Whereas betaCD does not affect the lifetime of the TMPyP triplet states, binding with sulfonated CDs causes the protonation of the TMPyP triplet states even in neutral solution. The diprotonated anionic sensitizer 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin (TPPSH(2)(2+)) forms host-guest complexes with native betaCD and gammaCD, similarly as in its non-protonated state. The positive charge of pyrrole nitrogen atoms does not significantly influence the mode of the interaction. In contrast to TMPyP, the lifetimes of the triplet states of bound TPPSH(2)(2+) to native CDs increase. PMID:19707685
Mosinger, Jir�; Slavet�nsk�, Lenka; Lang, Kamil; Coufal, Pavel; Kub�t, Pavel
Spatial Imaging of Charge Transport in Germanium at Low Temperature
NASA Astrophysics Data System (ADS)
The purpose of this experiment is to observe the oblique propagation of electrons through germanium by exciting a point source of charge carriers with a focused laser pulse on one face of a germanium crystal. After the electrons are drifted through the crystal by a uniform electric field, the pattern of charge density arriving on the opposite face is mapped and used to reconstruct the trajectories of the electrons. These measurements will verify in detail the Monte Carlo analysis utilized in the Cryogenic Dark Matter Search to model the transport of charge carriers in high-purity germanium detectors, including both oblique electron propagation and inter-valley scattering.
Moffatt, R. A.; Cabrera, B.; Kadribasic, F.; Redl, P.; Shank, B.; Young, B. A.; Brandt, D.; Brink, P.; Cherry, M.; Tomada, A.
Combined Charge Carrier Transport and Photoelectrochemical Characterization of BiVO4 Single Crystals: Intrinsic Behavior of a Complex Metal Oxide
ABSTRACT: Bismuth vanadate (BiVO4) is a promising photoelectrode material for the oxidation of water, but fundamental studies of this material are lacking. To address this, we report electrical and photoelectrochemical (PEC) properties of BiVO4 single crystals (undoped, 0.6% Mo and 0.3% W:BiVO4) grown using the floating zone technique. We demonstrate that a small polaron hopping conduction mechanism dominates from 250-400 K, transitioning to a variable range hopping mechanism at lower temperatures. An anisotropy ratio of ~3 was observed along the c-axis, attributed to the layered structure of BiVO4. Measurements of the AC field Hall effect yielded an electron mobility of ~0.2 cm2 V-1 s-1 for Mo and W:BiVO4 at 300 K. By application of the G�rtner model, a hole diffusion length of ~140 nm was estimated. As a result of low carrier mobility, attempts to measure the DC Hall effect were unsuccessful. Analyses of the Raman spectra showed that Mo and W substituted for V and acted as donor impurities. Mott-Schottky analysis of electrodes with the (001) face exposed yielded a flat band potential of 0.03-0.08 V vs. RHE, while incident photon conversion efficiency tests showed that the dark coloration of the doped single crystals did not result in additional photocurrent. Comparison of these intrinsic properties to other metal oxides for PEC applications gives valuable insight into this material as a photoanode.
Rettie, Alexander J.; Lee, Heung Chan; Marshall, Luke G.; Lin, Jung-Fu; Capen, Cigdem; Lindemuth, Jeffrey; McCloy, John S.; Zhou, Jianshi; Bard, Allen J.; Mullins, C. Buddie
High charge-carrier mobility enables exploitation of carrier multiplication in quantum-dot films
Carrier multiplication, the generation of multiple electron�hole pairs by a single photon, is of great interest for solar cells as it may enhance their photocurrent. This process has been shown to occur efficiently in colloidal quantum dots, however, harvesting of the generated multiple charges has proved difficult. Here we show that by tuning the charge-carrier mobility in quantum-dot films, carrier multiplication can be optimized and may show an efficiency as high as in colloidal dispersion. Our results are explained quantitatively by the competition between dissociation of multiple electron�hole pairs and Auger recombination. Above a mobility of ~1?cm2?V?1?s?1, all charges escape Auger recombination and are quantitatively converted to free charges, offering the prospect of cheap quantum-dot solar cells with efficiencies in excess of the Shockley�Queisser limit. In addition, we show that the threshold energy for carrier multiplication is reduced to twice the band gap of the quantum dots.
Sandeep, C. S. Suchand; Cate, Sybren ten; Schins, Juleon M.; Savenije, Tom J.; Liu, Yao; Law, Matt; Kinge, Sachin; Houtepen, Arjan J.; Siebbeles, Laurens D. A.
Electronic polarization effects on charge carriers in anthracene: A valence bond study
NASA Astrophysics Data System (ADS)
A semiempirical quantum-chemical model based on a fragment orbital formalism is presented to assess molecular parameters relevant to charge transport in organic crystals. The mixed valence bond/Hartree-Fock approach provides an efficient integrated framework to evaluate the electronic polarization effects induced by localized charge carriers and the associated impact on the matrix elements mediating electron migration in the hopping regime. This formalism, applied here to anthracene clusters of increasing sizes and dimensionalities, yields the electrostatic and polarization contributions to the total interaction energy of the neutral and charged aggregates and leads to a reduction in the effective bandwidth by �10%-20% as a result of the polarization cloud.
Castet, Fr�d�ric; Aurel, Philippe; Fritsch, Alain; Ducasse, Laurent; Liotard, Daniel; Linares, Mathieu; Cornil, J�r�me; Beljonne, David
Balanced ambipolar charge carrier mobility in mixed layers for application in hybrid white organic light-emitting diodes
We investigate the electron and hole mobility in mixed layers of N,N'-di(naphthalen-1-yl)-N,N'-diphenyl-benzidine and bis(2-methyl-8-quinolinato)-4-phenylphenolate aluminum with different mix ratios, using both space-charge limited currents of single-carrier devices with electrically doped charge transport layers and time-of-flight measurements. Both experimental methods yield consistent results. The 1:1 blend shows balanced ambipolar charge carrier transport, which is advantageous for the application as exciton blocking
Gregor Schwartz; Tung-Huei Ke; Chung-Chih Wu; Karsten Walzer; Karl Leo
Photogeneration of charge carriers in anisotropic multilayer structures of phthalocyaninato-polysiloxane
NASA Astrophysics Data System (ADS)
The photoinduced generation and the transport of charge carriers have been investigated in sandwich structures of Langmuir-Blogdett films of phthalocyaninato-polysiloxane between aluminum and gold electrodes. The diodelike current-voltage characteristics as well as the photovoltaic properties are directly related to the asymmetric electrode configuration. Under short-circuit conditions the photoactive region is located close to the aluminum electrode. By applying an external bias, the photoactive region is enlarged throughout the whole film thickness, and collection efficiencies of up to 0.3% are observed. Recombination effects have been studied by investigating the intensity dependence of the photocurrent. Nearly square root behavior under short circuit conditions is due to efficient charge carrier recombination whereas a linear intensity dependence is observed under reverse bias, indicating charge carrier diffusion to the electrodes. The transition between these two regimes is analyzed with respect to the charge carrier mobility yielding a value as small as 10-11 cm2/V s. The anisotrope molecular orientation in the film causes a photoconductivity clearly depending on the polarization of the incident light. The formation of a microcavity in these structures strongly influences the spectral properties and it allows, in agreement with theoretical calculations, to obtain an improved efficiency in a selected region of low film absorption. Atmospheric oxygen doping results in clear increase in the dark current, but the charge generation process remains nearly unaffected.
Gattinger, P.; Rengel, H.; Neher, D.
Bipolar charge-carrier injection in semiconductor/insulator/conductor heterostructures: Self-consistent consideration
NASA Astrophysics Data System (ADS)
A self-consistent model of bipolar charge-carrier injection and transport processes in a semiconductor/insulator/conductor system is developed, which incorporates space-charge effects in the description of the injection process. The amount of charge carriers injected is strongly determined by the energy barrier emerging at the contact, but at the same time the electrostatic potential generated by the injected charge carriers modifies the height of this injection barrier itself. In our model, self-consistency is obtained by assuming continuity of the electric displacement and of the electrochemical potential all over the system. The constituents of the system are properly taken into account by means of their respective density of state distributions. The consequences resulting from our model are discussed on the basis of an indium tin oxide/organic semiconductor/conductor structure. The distributions of the charge carriers and the electric field through the electrodes and the organic layer are calculated. The recombination- and current-voltage characteristics are analyzed for different heights of injection barriers and varying values of the recombination rate and compared with the measured current-voltage dependences for an indium tin oxide/poly(phenylene vinylene)/Ca structure. The voltage dependences of the recombination efficiency for the different values of injection barriers and recombination rate reveal optimum conditions for the device performance.
Yampolskii, S. V.; Genenko, Yu. A.; Melzer, C.; Stegmaier, K.; von Seggern, H.
Identification of the Charge Carriers in Cerium Phosphate Ceramics
The total conductivity of Sr-doped cerium orthophosphate changes by nearly two orders of magnitude depending on the oxygen and hydrogen content of the atmosphere. The defect model for the system suggests that this is because the identity of the dominant charge carrier can change from electron holes to protons when the sample is in equilibrium with air vs. humidified hydrogen. In this work are presented some preliminary measurements that can help to clarify this exchange between carriers. The conduction behavior of a 2percent Sr-doped CePO4 sample under symmetric atmospheric conditions is investigated using several techniques, including AC impedance, H/D isotope effects, and chronoamperometry.
Ray, Hannah L.; Jonghe, Lutgard C. De
Charge Transport in Synthetic Metals
The phenomenology of charge transport in synthetic metals is reviewed. It is argued that the conventional quasiparticle picture and Boltzmann transport theory do not apply to these materials. The central ideas of Fermi liquid theory are reviewed, and the significant corrections produced by quasiparticle scattering from ferromagnetic spin fluctuations in liquid {sup 3}He are described. It is shown that Sr{sub 2}RuO{sub 4} does not display the symptoms of a nearly-ferromagnetic Fermi liquid, so the source of its odd angular momentum pairing remains to be understood. The solution of an assisted-tunneling model of charge transport in quasi-one dimensional materials is described. This model has a quantum critical point and gives a resistivity that is linear in temperature or frequency, whichever is greater.
Emery, V. J.; Kivelson, S. A.; Muthukumar, V. N.
Field effect transistor based on protons as charge carriers
We demonstrated a field effect transistor based on the modulation of the proton flow in confined water-containing nanochannels. The device resembles an MOSFET transistor with the difference that the charge carriers here are ions (i.e. protons) instead of electrons. The effective cross-section of the conductive channels in the transistor is defined by the intensity of the electrical double layer and
J. Matovic; N. Adamovic; Z. Jak�i?; U. Schmid
Photogeneration of charge carriers in anisotropic multilayer structures of phthalocyaninato-polysiloxane
The photoinduced generation and the transport of charge carriers have been investigated in sandwich structures of Langmuir-Blogdett films of phthalocyaninato-polysiloxane between aluminum and gold electrodes. The diodelike current-voltage characteristics as well as the photovoltaic properties are directly related to the asymmetric electrode configuration. Under short-circuit conditions the photoactive region is located close to the aluminum electrode. By applying an external
P. Gattinger; H. Rengel; D. Neher
Highly mobile oxygen hole-type charge carriers in fused silica
NASA Technical Reports Server (NTRS)
Some peculiar positive charge carriers are thermally generated in fused silica above 500 C. These charge carriers appear to be positive holes, chemically O-states, probably arising from dissociation of peroxy defects. The charge carriers give rise to a pronounced positive surface charge which disappears upon cooling but can be quenched by rapid quenching from about 800 C. Reheating to 200 C remobilizes these charge carriers and causes them to anneal below 400 C. The generation of positive holes charge carriers may be important to understand failure mechanisms of SiO2 insulators.
Freund, Friedemann; Masuda, Michael M.; Freund, Minoru M.
Carrier transport in molecularly doped organic materials
NASA Astrophysics Data System (ADS)
This contribution examines in details the effects of dopants on the hole transporting properties of N,N'- diphenyl-N,N'-bis (1-naphthyl) (1,1'-biphenyl)- 4,4'diamine (NPB). Dopants for NPB are copper phthalocyanine (CuPc), 4-(dicyanomethylene)-2-methyl-6-(pdimethylaminostyryle)-4H-pyran (DCM1), 4-dicyanomethylene-2-methyl- 6-[2-(2,3,6,7-tetra-hydro-1H,5H-benzo[ij] quinolizin-8-yl)vinyl]-4H-pyran (DCM2), 2-(4-biphenyl0-5-(4- tertbutylphenyl)-1,3,4-oxadiazole (tBu-PBD) and 2,9-dimethyl-4, 7-diphenyl-1,10-phenanthroline (BCP). The effects of these dopants on the hole transport of NPB will be presented. Generally, the dopant molecules behave like hole traps or scatterers. Their detailed behaviors are determined by their highest occupied molecular orbitals relative to that of NPB. Traps are found to induce significant reduction in hole mobility. However, hole scatterers only alter the mobility slightly. Two different underlying charge transport mechanisms are proposed and then it is further examined by temperature dependent measurements.
So, S. K.; Tsung, K. K.
Charge-carrier relaxation dynamics in highly ordered poly( p -phenylene vinylene): Effects of carrier bimolecular recombination and trapping
We have studied the charge-carrier relaxation dynamics in highly ordered poly( p -phenylene vinylene) over a broad time range using fast (t>100ps) transient photoconductivity measurements. The carrier density was also monitored (t>100fs) by means of photoinduced absorption probed at the infrared active vibrational modes. We find that promptly upon charge-carrier photogeneration, the initial polaron dynamics is governed by bimolecular recombination,
Cesare Soci; Daniel Moses; Qing-Hua Xu; Alan J. Heeger
Fractal like charge transport in polyaniline nanostructures
NASA Astrophysics Data System (ADS)
The structural and electrical properties of camphorsulfonic acid (CSA) doped nanotubes, and hydrochloric acid (HCl) doped nanofibers and nanoparticles of polyaniline have been studied as a function of doping level. The crystallinity increases with doping for all the nanostructures. Electrical transport measurements in the temperature range of 5-300 K show an increase in conductivity with doping for the nanostructures. All the nanostructures exhibit metal to insulator (MIT) transition below 40 K. The metallic behavior is ascribed to the electron-electron interaction effects. In the insulating regime of the nanotubes conduction follows the Mott quasi-1D variable range hopping model, whereas the conduction in the nanofibers and nanoparticles occur by variable range hopping of charge carriers among superlocalized states without and with Coulomb interaction, respectively. The smaller dopant size in case of HCl makes the polymer fractal resulting in superlocalization of electronic wave-functions. The confined morphology of the nanoparticles results in effective Coulomb interaction dominating the intersite hopping.
Nath, Chandrani; Kumar, A.
Imbalance of the charge on a carrier moving through a gaseous medium
The paper is focused on the charge exchange processes occurring between small metal charge carrier and the gaseous medium through which the carriers travels; these processes lead to a charge imbalance. In most of the experiments, a small lead pellet was propelled at different speeds through air under the ballistic conditions. The charge carried by the pellet was tracked along
Zdenek Kucerovsky; William D. Greason
Hot Carrier Transport and Photocurrent Response in Graphene
Strong electron-electron interactions in graphene are expected to result in multiple-excitation generation by the absorption of a single photon. We show that the impact of carrier multiplication on photocurrent response is enhanced by very inefficient electron cooling, resulting in an abundance of hot carriers. The hot-carrier-mediated energy transport dominates the photoresponse and manifests itself in quantum efficiencies that can exceed
Justin C. W. Song; Mark S. Rudner; Charles M. Marcus; Leonid S. Levitov
Diffusive charge transport in graphene on SiO 2
NASA Astrophysics Data System (ADS)
We review our recent work on the physical mechanisms limiting the mobility of graphene on SiO 2. We have used intentional addition of charged scattering impurities and systematic variation of the dielectric environment to differentiate the effects of charged impurities and short-range scatterers. The results show that charged impurities indeed lead to a conductivity linear in density ( ?(n)?n) in graphene, with a scattering magnitude that agrees quantitatively with theoretical estimates; increased dielectric screening reduces the scattering from charged impurities, but increases the scattering from short-range scatterers. We evaluate the effects of the corrugations (ripples) of graphene on SiO 2 on transport by measuring the height-height correlation function. The results show that the corrugations cannot mimic long-range (charged impurity) scattering effects, and have too small an amplitude-to-wavelength ratio to significantly affect the observed mobility via short-range scattering. Temperature-dependent measurements show that longitudinal acoustic phonons in graphene produce a resistivity that is linear in temperature and independent of carrier density; at higher temperatures, polar optical phonons of the SiO 2 substrate give rise to an activated, carrier density-dependent resistivity. Together the results paint a complete picture of charge carrier transport in graphene on SiO 2 in the diffusive regime.
Chen, J.-H.; Jang, C.; Ishigami, M.; Xiao, S.; Cullen, W. G.; Williams, E. D.; Fuhrer, M. S.
Combinatorial Auctions for Transportation Service Procurement: The Carrier Perspective
The procurement of transportation services is an important task for shippers because of the need to control costs at the same time as providing high service levels. When shippers with goods and\\/or materials to transport seek transportation services from outside companies they typically put out a request for quotes from a set of carriers. They then assign contracts based on
A C Regan; Jiongjiong Song
Scaling Properties of Charge Transport in Polycrystalline Graphene
Polycrystalline graphene is a patchwork of coalescing graphene grains of varying lattice orientations and size, resulting from the chemical vapor deposition (CVD) growth at random nucleation sites on metallic substrates. The morphology of grain boundaries has become an important topic given its fundamental role in limiting the mobility of charge carriers in polycrystalline graphene, as compared to mechanically exfoliated samples. Here we report new insights to the current understanding of charge transport in polycrystalline geometries. We created realistic models of large CVD-grown graphene samples and then computed the corresponding charge carrier mobilities as a function of the average grain size and the coalescence quality between the grains. Our results reveal a remarkably simple scaling law for the mean free path and conductivity, correlated to atomic-scale charge density fluctuations along grain boundaries.
Vertical charge transport in junction charge-coupled devices
NASA Astrophysics Data System (ADS)
Vertical charge transport in junction charge coupled devices (JCCD's) and its application in logic circuits were analyzed. Charge can be vertically injected into the JCCD transport channel through the steering gates by applying a vertical NPN transistor (injector), which can be made without any additional fabrication processing steps. The substrate PNP transistor, formed by the steering gate, the transport channel, and the substrate, can be used for the detection of surplus charge. The substrate PNP transistor was applied in a very simple, amplifying JCCD output structure, having a gain more than 100 while harmonic distortion is less than - 50 dB. Circuits based on vertical charge injection and vertical charge overflow of surplus charge were realized. And-or-invert circuits were operated at more than 50 MHz. A Full Adder was operated at 5 MHz. Performance can be improved by a fast charge-normalizing stage and a thinner epilayer.
Vanderklauw, Cornelis Leonardus Maria
Optical detection of charge carriers in multilayer organic light-emitting diodes: Experiment and theory
NASA Astrophysics Data System (ADS)
We have investigated a multilayer organic light-emitting diode with 1,3,5-tris (N,N-bis-(4-methoxyphenyl)aminophenyl)-benzene acting as the hole transporting layer (HTL) and tris (8-hydroxy-quinolinolato) aluminum (Alq3) as the electron transporting layer. Positive charge carriers in the HTL were detected optically as a function of the applied bias. It was found that a hole injecting layer, consisting of 3,4 polyethylene-dioxy-thiophene doped with polystyrenesulfonate, forms an ohmic contact to the HTL by inducing a thin layer of holes in the interfacial region. An analytical model is developed to describe the observed carrier concentrations as well as the current-brightness-voltage characteristics quantitatively.
Book, K.; Nikitenko, V. R.; B�ssler, H.; Elschner, A.
Solid-State Dynamics and Carrier Transport in Supervelocity Semiconductors.
National Technical Information Service (NTIS)
We investigated a number of critical theoretical issues in two important research areas; namely, (1) spin polarized carrier transport and relaxation in low dimensional structures and (2) coupled quantum-based systems. In particular, we concentrated our ef...
K. W. Kim M. A. Littlejohn
Charge transport in nanoscale junctions.
Understanding the fundamentals of nanoscale charge transfer is pivotal for designing future nano-electronic devices. Such devices could be based on individual or groups of molecular bridges, nanotubes, nanoparticles, biomolecules and other 'active' components, mimicking wire, diode and transistor functions. These have operated in various environments including vacuum, air and condensed matter, in two- or three-electrode configurations, at ultra-low and room temperatures. Interest in charge transport in ultra-small device components has a long history and can be dated back to Aviram and Ratner's letter in 1974 (Chem. Phys. Lett. 29 277-83). So why is there a necessity for a special issue on this subject? The area has reached some degree of maturity, and even subtle geometric effects in the nanojunction and noise features can now be resolved and rationalized based on existing theoretical concepts. One purpose of this special issue is thus to showcase various aspects of nanoscale and single-molecule charge transport from experimental and theoretical perspectives. The main principles have 'crystallized' in our minds, but there is still a long way to go before true single-molecule electronics can be implemented. Major obstacles include the stability of electronic nanojunctions, reliable operation at room temperature, speed of operation and, last but not least, integration into large networks. A gradual transition from traditional silicon-based electronics to devices involving a single (or a few) molecule(s) therefore appears to be more viable from technologic and economic perspectives than a 'quantum leap'. As research in this area progresses, new applications emerge, e.g. with a view to characterizing interfacial charge transfer at the single-molecule level in general. For example, electrochemical experiments with individual enzyme molecules demonstrate that catalytic processes can be studied with nanometre resolution, offering a route towards optimizing biosensors at the molecular level. Nanoscale charge transport experiments in ionic liquids extend the field to high temperatures and to systems with intriguing interfacial potential distributions. Other directions may include dye-sensitized solar cells, new sensor applications and diagnostic tools for the study of surface-bound single molecules. Another motivation for this special issue is thus to highlight activities across different research communities with nanoscale charge transport as a common denominator. This special issue gathers 27 articles by scientists from the United States, Germany, the UK, Denmark, Russia, France, Israel, Canada, Australia, Sweden, Switzerland, the Netherlands, Belgium and Singapore; it gives us a flavour of the current state-of-the-art of this diverse research area. While based on contributions from many renowned groups and institutions, it obviously cannot claim to represent all groups active in this very broad area. Moreover, a number of world-leading groups were unable to take part in this project within the allocated time limit. Nevertheless, we regard the current selection of papers to be representative enough for the reader to draw their own conclusions about the current status of the field. Each paper is original and has its own merit, as all papers in Journal of Physics: Condensed Matter special issues are subjected to the same scrutiny as regular contributions. The Guest Editors have deliberately not defined the specific subjects covered in this issue. These came out logically from the development of this area, for example: 'Traditional' solid state nanojunctions based on adsorbed layers, oxide films or nanowires sandwiched between two electrodes: effects of molecular structure (aromaticity, anchoring groups), symmetry, orientation, dynamics (noise patterns) and current-induced heating. Various 'physical effects': inelastic tunnelling and Coulomb blockade, polaron effects, switching modes, and negative differential resistance; the role of many particle excitations, new surface states in semiconductor electrodes, various mechanisms for
Albrecht, Tim; Kornyshev, Alexei; Bj�rnholm, Thomas
Charge transport in single crystal organic semiconductors
NASA Astrophysics Data System (ADS)
Organic electronics have engendered substantial interest in printable, flexible and large-area applications thanks to their low fabrication cost per unit area, chemical versatility and solution processability. Nevertheless, fundamental understanding of device physics and charge transport in organic semiconductors lag somewhat behind, partially due to ubiquitous defects and impurities in technologically useful organic thin films, formed either by vacuum deposition or solution process. In this context, single-crystalline organic semiconductors, or organic single crystals, have therefore provided the ideal system for transport studies. Organic single crystals are characterized by their high chemical purity and outstanding structural perfection, leading to significantly improved electrical properties compared with their thin-film counterparts. Importantly, the surfaces of the crystals are molecularly flat, an ideal condition for building field-effect transistors (FETs). Progress in organic single crystal FETs (SC-FETs) is tremendous during the past decade. Large mobilities ~ 1 - 10 cm2V-1s-1 have been achieved in several crystals, allowing a wide range of electrical, optical, mechanical, structural, and theoretical studies. Several challenges still remain, however, which are the motivation of this thesis. The first challenge is to delineate the crystal structure/electrical property relationship for development of high-performance organic semiconductors. This thesis demonstrates a full spectrum of studies spanning from chemical synthesis, single crystal structure determination, quantum-chemical calculation, SC-OFET fabrication, electrical measurement, photoelectron spectroscopy characterization and extensive device optimization in a series of new rubrene derivatives, motivated by the fact that rubrene is a benchmark semiconductor with record hole mobility ~ 20 cm2V-1s-1. With successful preservation of beneficial pi-stacking structures, these rubrene derivatives form high-quality single crystals and exhibit large ambipolar mobilities. Nevertheless, a gap remains between the theory-predicted properties and this preliminary result, which itself is another fundamental challenge. This is further addressed by appropriate device optimization, and in particular, contact engineering approach to improve the charge injection efficiencies. The outcome is not only the achievement of new record ambipolar mobilities in one of the derivatives, namely, 4.8 cm2V-1s-1 for holes and 4.2 cm2V-1s-1 for electrons, but also provides a comprehensive and rational pathway towards the realization of high-performance organic semiconductors. Efforts to achieve high mobility in other organic single crystals are also presented. The second challenge is tuning the transition of electronic ground states, i.e., semiconducting, metallic and superconducting, in organic single crystals. Despite an active research area since four decades ago, we aim to employ the electrostatic approach instead of chemical doping for reversible and systematic control of charge densities within the same crystal. The key material in this study is the high-capacitance electrolyte, such as ionic liquids (ILs), whose specific capacitance reaches ~ ?F/cm2, thus allowing accumulation of charge carrier above 1013 cm-2 when novel transport phenomena, such as insulator-metal transition and superconductivity, are likely to occur. This thesis addresses the electrical characterization, device physics and transport physics in electrolyte-gated single crystals, in the device architecture known as the electrical double layer transistor (EDLT). A detailed characterization scheme is first demonstrated for accurate determination of several key parameters, e.g., carrier mobility and charge density, in organic EDLTs. Further studies, combining both experiments and theories, are devoted to understanding the unusual charge density dependent channel conductivity and gate-to-channel capacitance behaviors. In addition, Hall effect and temperature-dependent measurements are employed for more in-depth unders
Xie, Wei
Measuring charge carrier diffusion in coupled colloidal quantum dot solids.
Colloidal quantum dots (CQDs) are attractive materials for inexpensive, room-temperature-, and solution-processed optoelectronic devices. A high carrier diffusion length is desirable for many CQD device applications. In this work we develop two new experimental methods to investigate charge carrier diffusion in coupled CQD solids under charge-neutral, i.e., undepleted, conditions. The methods take advantage of the quantum-size-effect tunability of our materials, utilizing a smaller-bandgap population of quantum dots as a reporter system. We develop analytical models of diffusion in 1D and 3D structures that allow direct extraction of diffusion length from convenient parametric plots and purely optical measurements. We measure several CQD solids fabricated using a number of distinct methods and having significantly different doping and surface ligand treatments. We find that CQD materials recently reported to achieve a certified power conversion efficiency of 7% with hybrid organic-inorganic passivation have a diffusion length of 80 � 10 nm. The model further allows us to extract the lifetime, trap density, mobility, and diffusion coefficient independently in each material system. This work will facilitate further progress in extending the diffusion length, ultimately leading to high-quality CQD solid semiconducting materials and improved CQD optoelectronic devices, including CQD solar cells. PMID:23701285
Zhitomirsky, David; Voznyy, Oleksandr; Hoogland, Sjoerd; Sargent, Edward H
Charge Transfer and Transport in DNA
We explore charge migration in DNA, advancing two distinct mechanisms of charge separation in a donor (d)-bridge ({Bj})-acceptor (a) system, where {Bj} = B1,B2,\\\\cdots ,BN are the N-specific adjacent bases of B-DNA: (i) two-center unistep superexchange induced charge transfer, d*{Bj}a -> dmp{Bj}a�, and (ii) multistep charge transport involves charge injection from d* (or d+) to {Bj}, charge hopping within {Bj},
Joshua Jortner; Mordechai Bixon; Thomas Langenbacher; Maria E. Michel-Beyerle
Correlated charge transport in bilinear tunnel junction arrays
NASA Astrophysics Data System (ADS)
We study theoretically the nature of correlations in space and time of the current in a one-dimensional bilinear array of tunnel junctions in the normal conduction limit, using the kinetic Monte Carlo method. The bilinear array consists of two parallel rows of tunnel junctions, capacitively coupled in a ladder configuration. The electrostatic potential landscape and the charge-charge interaction length both depend on the circuit capacitances, which in turn influence transport and charge correlations in the array. We observe the formation of stationary charge states when only one rail is voltage biased. When a symmetric bias is applied to both rails, the site at which the positive and negative charge carriers recombine can drift throughout the array. We also calculate charge densities and auto- and cross-correlation functions.
Walker, Kelly A.; Cole, Jared H.
Surface states of charge carriers in epitaxial films of the topological insulator Bi2Te3
NASA Astrophysics Data System (ADS)
The galvanomagnetic properties of p-type bismuth telluride heteroepitaxial films grown by the hot wall epitaxy method on oriented muscovite mica substrates have been investigated. Quantum oscillations of the magnetoresistance associated with surface electronic states in three-dimensional topological insulators have been studied in strong magnetic fields ranging from 6 to 14 T at low temperatures. The cyclotron effective mass, charge carrier mobility, and parameters of the Fermi surface have been determined based on the results of analyzing the magnetoresistance oscillations. The dependences of the cross-sectional area of the Fermi surface S( k F), the wave vector k F, and the surface concentration of charge carriers n s on the frequency of magnetoresistance oscillations in p-type Bi2Te3 heteroepitaxial films have been obtained. The experimentally observed shift of the Landau level index is consistent with the value of the Berry phase, which is characteristic of topological surface states of Dirac fermions in the films. The properties of topological surface states of charge carriers in p-type Bi2Te3 films obtained by analyzing the magnetoresistance oscillations significantly expand fields of practical application and stimulate the investigation of transport properties of chalcogenide films.
Luk'yanova, L. N.; Boikov, Yu. A.; Danilov, V. A.; Usov, O. A.; Volkov, M. P.; Kutasov, V. A.
Order induced charge carrier mobility enhancement in columnar liquid crystal diodes.
Discotic molecules comprising a rigid aromatic core and flexible side chains have been promisingly applied in OLEDs as self-organizing organic semiconductors. Due to their potentially high charge carrier mobility along the columns, device performance can be readily improved by proper alignment of columns throughout the bulk. In the present work, the charge mobility was increased by 5 orders of magnitude due to homeotropic columnar ordering induced by the boundary interfaces during thermal annealing in the mesophase. State-of-the-art diodes were fabricated using spin-coated films whose homeotropic alignment with formation of hexagonal germs was observed by polarizing optical microscopy. The photophysical properties showed drastic changes at the mesophase-isotropic transition, which is supported by the gain of order observed by X-ray diffraction. The electrical properties were investigated by modeling the current-voltage characteristics by a space-charge-limited current transport with a field dependent mobility. PMID:24191748
Eccher, Juliana; Faria, Greg�rio C; Bock, Harald; von Seggern, Heinz; Bechtold, Ivan H
Microscopic Simulations of Charge Transport in Disordered Organic Semiconductors
Charge carrier dynamics in an organic semiconductor can often be described in terms of charge hopping between localized states. The hopping rates depend on electronic coupling elements, reorganization energies, and driving forces, which vary as a function of position and orientation of the molecules. The exact evaluation of these contributions in a molecular assembly is computationally prohibitive. Various, often semiempirical, approximations are employed instead. In this work, we review some of these approaches and introduce a software toolkit which implements them. The purpose of the toolkit is to simplify the workflow for charge transport simulations, provide a uniform error control for the methods and a flexible platform for their development, and eventually allow in silico prescreening of organic semiconductors for specific applications. All implemented methods are illustrated by studying charge transport in amorphous films of tris-(8-hydroxyquinoline)aluminum, a common organic semiconductor.
Local charge carrier mobility in disordered organic field-effect transistors
In conventional field-effect transistors, the extracted mobility does not take into account the distribution of charge carriers. However, in disordered organic field-effect transistors, the local charge carrier mobility decreases from the semiconductor\\/insulator interface into the bulk, due to its dependence on the charge carrier density. It is demonstrated that the conventional field-effect mobility is a good approximation for the local
C. Tanase; E. J. Meijer; P. W. M. Blom; D. M. de Leeuw
Transient effects controlling the charge carrier population of organic field effect transistor channels
NASA Astrophysics Data System (ADS)
We present device simulations exploring the effects of traps during transient processes in the conducting channel of organic field effect transistors (OFETs). The device structure explored resembles a typical organic thin-film transistor with one of the channel contacts removed. However, the channel length is much longer than in typical OFETs in order to increase the transit time. By measuring the displacement current in these long-channel capacitors, transient effects in the carrier transport in organic semiconductors may be studied. When carriers are injected into the device, a conducting channel is established while traps, which are initially empty, are being populated. The filling of the traps then modifies the transport characteristics of the injected charge carriers. In contrast, dc experiments as they are typically performed to characterize the transport properties of organic semiconductor channels investigate a steady state with traps partially filled. Numerical and approximate analytical models for the formation of the conducting channel and the resulting displacement current are discussed here. The temperature dependence of the effective mobility arising from the temperature dependence of the trap emission rate is explored, and calculated results are compared with experimental data. We show that displacement current measurements on OFET structures provide unique opportunities for the study of trap dynamics involving a wide range of time scales.
Chang, Hsiu-Chuang; Ruden, P. Paul; Liang, Yan; Frisbie, C. Daniel
Monte Carlo modeling of the spatially dispersive carrier transport in P3HT and P3HT:PCBM blends
The presence of traps, arising from morpohological or chemical defects, can be critical to the performance of organic semiconductor devices. Traps can reduce the charge carrier mobility, disturb the internal electrical field, drive recombination, and reduce the overall device efficiency as well as operational stability. In this work, we investigate the role of traps in determining charge transport properties of
Xin Jiang
Morphogenesis of post-Golgi transport carriers
The trans-Golgi network (TGN) is one of the main, if not the main, sorting stations in the process of intracellular protein trafficking.\\u000a It is therefore of central importance to understand how the key players in the TGN-based sorting and delivery process, the\\u000a post-Golgi carriers (PGCs), form and function. Over the last few years, modern morphological approaches have generated new\\u000a insights
Alberto Luini; Alexander A. Mironov; Elena V. Polishchuk; Roman S. Polishchuk
The effect of carrier gas contaminants on the charging probability of aerosols under bipolar charging conditions
This work concentrates on the experimental determination of the properties of ionic molecular clusters that are produced in the bipolar ionic atmosphere of a radioactivity based 241Am charger. The main scope of this study was to investigate the dependency of the ions' properties on carrier gas contaminants caused by the evaporation of trace gases from different kinds of frequently encountered tubing materials. A recently developed high resolution mobility spectrometer allows the precise determination of the ions' electrical mobility; an empirical mass-mobility relationship was used to approximate the corresponding ion masses. It was found that impurities in the carrier gas dramatically change the pattern of the ion mobility/size distribution, resulting in very different ion properties that strongly depend on the carrier gas composition. Since the ion properties control the charging process of aerosols, it was further investigated how the different ion properties affect the calculation of the charging probabilities of aerosols. The results show that despite large variations of the ions' properties, only a minor effect on the calculated charging probabilities can be found.
Steiner, Gerhard; Reischl, Georg P.
Low temperature carrier transport properties in isotopically controlled germanium
Investigations of electronic and optical properties of semiconductors often require specimens with extremely homogeneous dopant distributions and precisely controlled net-carrier concentrations and compensation ratios. The previous difficulties in fabricating such samples are overcome as reported in this thesis by growing high-purity Ge single crystals of controlled {sup 75}Ge and {sup 70}Ge isotopic compositions, and doping these crystals by the neutron transmutation doping (NTD) technique. The resulting net-impurity concentrations and the compensation ratios are precisely determined by the thermal neutron fluence and the [{sup 74}Ge]/[{sup 70}Ge] ratios of the starting Ge materials, respectively. This method also guarantees unprecedented doping uniformity. Using such samples the authors have conducted four types of electron (hole) transport studies probing the nature of (1) free carrier scattering by neutral impurities, (2) free carrier scattering by ionized impurities, (3) low temperature hopping conduction, and (4) free carrier transport in samples close to the metal-insulator transition.
Itoh, K.
Valley-polarized massive charge carriers in gapped graphene
NASA Astrophysics Data System (ADS)
The lifting of the fourfold degeneracy of the zeroth Landau level in graphene under high magnetic fields has been the subject of numerous experimental studies, and attributed to various mechanisms such as pure spin splitting, spin splitting combined with subsequent valley splitting, or the formation of a quantum Hall insulator. Unexplored, however, is the influence of an energy gap on the quantum Hall effect (QHE) states in graphene. Here we demonstrate, using measurements of the magnetoresistance of graphene antidot lattices (GALs) in magnetic fields up to 30 T and temperatures between 2 and 100 K, that gap opening in these samples is accompanied by valley polarization and a change from linear to parabolic band structure at low carrier energies. The emergence of a massive character of the carriers profoundly alters the transport characteristics of the zeroth Landau level, which manifests itself in a linear increase of the activated gap with magnetic field. Furthermore, samples of the highest quality display spin splitting on top of the valley splitting, albeit of significantly smaller magnitude.
Peters, E. C.; Giesbers, A. J. M.; Zeitler, U.; Burghard, M.; Kern, K.
Proton-irradiation effects on the charge transport in highly oriented pyrolytic graphite
NASA Astrophysics Data System (ADS)
We have investigated the proton-irradiation effects on the electrical resistivity and magnetoresistance of highly oriented pyrolytic graphite (HOPG). The temperature- and magnetic field-dependent measurements indicate that the carrier mobility rather than the carrier density dictates the charge transport in the HOPG systems.
Kim, Jinsoo; Kim, Dowan; Lee, Kyu Won; Choi, E. H.; Noh, S. J.; Kim, H. S.; Lee, Cheol Eui
Quantitative characterization of carrier transport in nanowire photodetectors
NASA Astrophysics Data System (ADS)
Scanning photocurrent microscopy was used to study carrier transport processes in semiconductor nanowire photodetectors. Under high-level local carrier injection in CdS nanowire devices, spatially non-uniform photocurrent distributions were observed and explained in terms of bipolar transport with spatially separated electrons and holes. The mobility-lifetime product, (�t)*, for both electrons and holes was determined in intrinsic CdS nanowire photodetectors under high-level injection. (�t)* was enhanced compared to the bulk values as a result of the carrier spatial separation. Local time-resolved photocurrent measurements supported this interpretation of the enhanced (�t)*. Global timeresolved photocurrent measurements were used to establish a 10%-90% rise time of ~ 6ns (limited by the instrument response) and a 90%-10% fall time of ~ 20ns for the nanowire photodetectors. A small fraction of the total photocurrent exhibited a long power-law decay attributed to carrier trapping/detrapping processes, and characteristic shallow trap energy of 60meV was extracted. Spatially uniform photocurrent profiles were observed in Si nanowire photodetectors under low-level injection conditions, consistent with unipolar minority carrier transport. Under varying biases, consistent variations in the photocurrent profiles were observed and attributed to the effect of the applied electric fields on drift and diffusion of minority carriers.
Gu, Y.; Romankiewicz, J. P.; Lauhon, L. J.
75 FR 18255 - Passenger Facility Charge Database System for Air Carrier Reporting
Federal Register 2010, 2011, 2012, 2013
...FAA-2010] Passenger Facility Charge Database System for Air Carrier Reporting AGENCY...the Passenger Facility Charge (PFC) database system to report PFC quarterly report...The FAA has developed a national PFC database system in order to more easily...
Energy resolution and related charge carrier mobility in LaBr{sub 3}:Ce scintillators
The scintillation response of LaBr{sub 3}:Ce scintillation crystals was studied as function of temperature and Ce concentration with synchrotron X-rays between 9 keV and 100 keV. The results were analyzed using the theory of carrier transport in wide band gap semiconductors to gain new insights into charge carrier generation, diffusion, and capture mechanisms. Their influence on the efficiency of energy transfer and conversion from X-ray or ?-ray photon to optical photons and therefore on the energy resolution of lanthanum halide scintillators was studied. From this, we will propose that scattering of carriers by both the lattice phonons and by ionized impurities are key processes determining the temperature dependence of carrier mobility and ultimately the scintillation efficiency and energy resolution. When assuming about 100 ppm ionized impurity concentration in 0.2% Ce{sup 3+} doped LaBr{sub 3,} mobilities are such that we can reproduce the observed temperature dependence of the energy resolution, and in particular, the minimum in resolution near room temperature is reproduced.
Khodyuk, I. V.; Quarati, F. G. A.; Alekhin, M. S.; Dorenbos, P. [Luminescence Materials Research Group, Faculty of Applied Sciences, Delft University of Technology, Mekelweg 15, Delft, 2629JB (Netherlands)] [Luminescence Materials Research Group, Faculty of Applied Sciences, Delft University of Technology, Mekelweg 15, Delft, 2629JB (Netherlands)
Influence of ionizing dopants on charge transport in organic semiconductors.
Ionizing chemical dopants are widely used in organic semiconductors to enhance the charge transport properties by increasing the number of mobile charge carriers. However, together with mobile charges, chemical doping produces anion-cation pairs in the organic matrix. In this work we use experimental and computational analysis to study the influence of these ionic species on the charge transport. We show that the anion-cation pairs introduced upon doping have a detrimental, doping-level dependent effect on charge mobility. For doping levels of 0.02-0.05% molar ratio with respect to the molecular organic semiconductor, the increase in conductivity from the extra mobile charges is partially cancelled by a reduction in charge mobility from traps introduced by the anion-cation pairs. As the doping concentration increases, anion-cation pairs start to overlap, resulting in a comparatively smoother potential landscape, which increases the charge mobility to values closer to the undoped semiconductor. This result has a significant, practical impact, as it shows the need to dope at or slightly above a threshold level, which depends on the specific host-dopant combination. PMID:24287888
Abate, Antonio; Staff, Daniel R; Hollman, Derek J; Snaith, Henry J; Walker, Alison B
Charge Transport Simulations for Amorphous Organic Thin Film Devices
NASA Astrophysics Data System (ADS)
We employ Monte Carlo simulations to analyze charge transport through amorphous organic thin films using the well-established ``Miller-Abrahams'' hopping model within a disordered manifold of molecular energies. Whereas most existing studies calculate non-dispersive, equilibrium mobilities at low carrier concentrations, in this work we instead calculate current densities for film thicknesses (i.e. 10 to 100 nm) and applied voltages (i.e. 0.1 to 100 V) typical of common thin film devices (e.g. organic light emitting devices and photovoltaics). We find that at these thicknesses one can not assume the non-dispersive, equilibrium condition. Also, since conduction typically occurs at high carrier concentrations and is space charge limited, we must employ simulations which treat both conditions. We compare our results with those predicted by existing analytic theories, and find that the analytic theories are often highly inaccurate, mainly due to faulty use of Fermi statistics and improper calculation of backward hopping.
Madigan, Conor; Bulovic, Vladimir
Electric Properties of Obsidian: Evidence for Positive Hole Charge Carriers
NASA Astrophysics Data System (ADS)
The blackness of obsidian is due to the presence of oxygen anions in the valence state 1-, creating broad energy levels at the upper edge of the valence band, which absorb visible light over a wide spectral range. These energy states are associated with defect electrons in the oxygen anion sublattice, well-known from "smoky quartz", where Al substituting for Si captures a defect electron in the oxygen anion sublattice for charge compensation [1]. Such defect electrons, also known as positive holes, are responsible for the increase in electrical conductivity in igneous rocks when uniaxial stresses are applied, causing the break-up of pre-existing peroxy defects, Si-OO-Si [2]. Peroxy defects in obsidian cannot be so easily activated by mechanical stress because the glassy matrix will break before sufficiently high stress levels can be reached. If peroxy defects do exist, however, they can be studied by activating them thermally [3]. We describe experiments with rectangular slabs of obsidian with Au electrodes at both ends. Upon heating one end, we observe (i) a thermopotential and (ii) a thermocurrent developing at distinct temperatures around 250�C and 450�C, marking the 2-step break-up of peroxy bonds. [1] Schnadt, R., and Schneider, J.: The electronic structure of the trapped-hole center in smoky quartz, Zeitschrift Physik B Condensed Matter 11, 19-42, 1970. [2] Freund, F. T., Takeuchi, A., and Lau, B. W.: Electric currents streaming out of stressed igneous rocks - A step towards understanding pre-earthquake low frequency EM emissions, Physics and Chemistry of the Earth, 31, 389-396, 2006. [3] Freund, F., and Masuda, M. M.: Highly mobile oxygen hole-type charge carriers in fused silica, Journal Material Research, 8, 1619-1622, 1991.
Nordvik, R.; Freund, F. T.
Carrier-density and field-dependent charge-carrier mobility in organic semiconductors with correlated Gaussian disorder
Recently, it has been demonstrated that for organic semiconductors with a Gaussian density of states (DOS) and with on-site energies that are spatially uncorrelated the hopping mobility of charge-carriers can be strongly carrier-density-dependent (extended Gaussian disorder model, EGDM). In the literature, it has been argued that for some materials, the on-site energies are actually spatially correlated. In this paper, we
M. Bouhassoune; S. L. M. van Mensfoort; P. A. Bobbert; R. Coehoorn
Mean free paths of charge carriers in CZT crystal
NASA Astrophysics Data System (ADS)
The asymmetrical distortion of the Cadmium Zinc Telluride ((CZT) energy spectrum is mainly caused by the hole trapping in the CZT crystal, and it can be characterized by the mean free path of hole. The mean free paths of the charge carriers in the CZT crystal can be extracted from fitting the peak shape of the measured energy spectrum. The energy spectra of ?-rays from 241Am, and that of ? particles from 238Pu were measured with a CZT with 5�5�5 mm 3. The mean free path of the electron was determined from the bias dependence of ?-particle response. The energy spectra of ?-ray were simulated with EGSnrc code, in which Hecht equation was included, and the mean free path of the hole was determined by comparing the measured spectrum with the simulated one. The energy spectrum of 662 keV ?-ray was measured with the CZT detector, and it was compared with the simulated spectrum, in which newly determined mean free paths of the electron and the hole were used.
Park, Se-Hwan; Kim, Yong-Kyun; Jeon, Sung-Dae; Ha, Jang-Ho; Hong, Duk-Geun
Life Time of Charge Carriers in Double Walled Carbon Nanotubes.
NASA Astrophysics Data System (ADS)
We investigate the nature of low-energy excitations in double walled carbon nanotubes, DWNT, by pumping the states using fs IR pulses. The temporal evolution of the population is examined by ionizing the resulting population with delayed fs UV pulses. The electron time of flight of the ionized electrons is recorded for a range of energies above EF to investigate the relaxation dynamics of the charge carriers. The initial, fast relaxation is attributed to the internal thermalization of the electronic system, and is primarily driven by electron-electron (e-e) scattering processes. After the system returns to a Fermi-Dirac distribution it continues to decay with a slower rate associated with electron gas cooling electron-phonon (e-ph) interactions. We specifically want to see if the (e-e) scattering in DWNT follow a Fermi-liquid behavior, as observed in our previous study of MWNT^1. 1. Zamkov, M.; Woody, N.; Shan, B.; Chang, Z.; Richard, P. Phys. Rev. Lett. 2005, 94, 056803.
Chatzakis, Ioannis; Habib, Arifa; Zamkov, Mikhail; Lithvinuk, Igor; Richard, Patrick
Nanotubes in polar environments: Solvated charge carriers and their dynamics
NASA Astrophysics Data System (ADS)
Excess charge carriers on semiconducting nanotubes immersed in sluggish polar environments (such as common solvents) can undergo self-localization into polaronic states whose properties are profoundly different from the free band states. We explore such solvated states within the adiabatic continuum framework using a simplified picture of an electron or a hole confined to a cylindrical surface in the 3D polar medium. At the static level, the binding energy of a polaron is evaluated and found to be a sizable fraction (� 0.3) of the corresponding Wannier- Mott exciton binding energy, which is expected to substantially decrease the thermal activation energy for the exciton dissociation. We discuss the diffusion and mobility of polarons caused by the dielectric fluctuations of the medium and applied electric fields, as well as the local dielectric relaxation modes in the vicinity of the polaron. We also discuss the electronic (optical) transitions between the localized electronic states within a self-consistent potential well due to the orientational polarization pattern. [1] Yu.N. Gartstein, Phys. Lett. A 349, 377 (2006). [2] Yu.N. Gartstein, T.D. Bustamante, S. Ortega Castillo, J. Phys.: Cond. Matter 17, 156210 (2007).
Ussery, Geoffrey; Gartstein, Yuri
Airline Transport Pilot-Airplane (Air Carrier) Written Test Guide.
ERIC Educational Resources Information Center
Presented is information useful to applicants who are preparing for the Airline Transport Pilot-Airplane (Air Carrier) Written Test. The guide describes the basic aeronautical knowledge and associated requirements for certification, as well as information on source material, instructions for taking the official test, and questions that are�
Federal Aviation Administration (DOT), Washington, DC. Flight Standards Service.
Transport properties of carbon dioxide through amine functionalized carrier membranes
CO� facilitated transport was studied using a membrane with amine sites covalently bound to the polymer backbone and ion exchange membranes which have amine complexing agents (carrier) as counterions. The two types of membranes were compared, and several amine functionalities for the ion-exchange membrane were studied. Although the covalently bonded membranes had a larger absorption capacity than amine functionalized Nafion
Takeo Yamaguchi; Lars M. Boetje; Carl A. Koval; Richard D. Noble; Christopher N. Bowman
Carrier transport in dichromatic color-coded semipolar (2021) and (2021) III-N LEDs
NASA Astrophysics Data System (ADS)
Simulation of III-nitride color-coded multiple quantum well (MQW) LED structures was performed using as an experimental benchmark dichromatic semipolar LEDs grown in Ga-polar and N-polar crystallographic orientations (Y. Kawaguchi et.al, APL 100, 231110, 2012). Different QW depths in the color-coded LEDs and opposite interface polarization charges in Ga-polar and N-polar structures provide different conditions for carrier transport across the LED active regions. Combination of several effects was crucial for adequate reproduction of the emission spectra experimentally observed in color-coded structures with violet-aquamarine and aquamarine-violet active region layouts. A standard drift-diffusion transport model wascompleted with rate equations for nonequilibrium QW populations and several high-energy transport features, including the effects of QW carrier overshoot and Auger-assisted QW depopulation. COMSOL-based Optoelectronic Device Modeling Software (ODMS) developed at Ostendo Technologies Inc. was utilized for device simulation.
Kisin, Mikhail V.; Huang, Chih-Li; El-Ghoroury, Hussein S.
Carrier Transport and Related Effects in Detectors of the Cryogenic Dark Matter Search
NASA Astrophysics Data System (ADS)
The Cryogenic Dark Matter Search (CDMS) is searching for weakly-interacting massive particles (WIMPS), which could explain the dark matter problem in cosmology and particle physics. By simultaneously measuring signals from deposited charge and the energy in non-equilibrium phonons created by particle interactions in intrinsic germanium crystals at a temperature of 40
Sundqvist, Kyle Michael
Ambipolar charge transport in microcrystalline silicon thin-film transistors
Hydrogenated microcrystalline silicon ({mu}c-Si:H) is a promising candidate for thin-film transistors (TFTs) in large-area electronics due to high electron and hole charge carrier mobilities. We report on ambipolar TFTs based on {mu}c-Si:H prepared by plasma-enhanced chemical vapor deposition at temperatures compatible with flexible substrates. Electrons and holes are directly injected into the {mu}c-Si:H channel via chromium drain and source contacts. The TFTs exhibit electron and hole charge carrier mobilities of 30-50 cm{sup 2}/V s and 10-15 cm{sup 2}/V s, respectively. In this work, the electrical characteristics of the ambipolar {mu}c-Si:H TFTs are described by a simple analytical model that takes the ambipolar charge transport into account. The analytical expressions are used to model the transfer curves, the potential and the net surface charge along the channel of the TFTs. The electrical model provides insights into the electronic transport of ambipolar {mu}c-Si:H TFTs.
Knipp, Dietmar; Marinkovic, M. [Electronic Devices and Nanophotonics Laboratory, Jacobs University Bremen, 28759 Bremen (Germany); Chan, Kah-Yoong [IEF5-Photovoltaics, Research Center Juelich, 52425 Juelich (Germany); Faculty of Engineering, Multimedia University, Cyberjaya, 63100 Selangor (Malaysia); Gordijn, Aad [IEF5-Photovoltaics, Research Center Juelich, 52425 Juelich (Germany); Stiebig, Helmut [IEF5-Photovoltaics, Research Center Juelich, 52425 Juelich (Germany); Malibu Solar GmbH and Co. KG, 33609 Bielefeld (Germany)
Charge generation, charge transport, and residual charge in the electrospinning of polymers: A review of issues and complications
NASA Astrophysics Data System (ADS)
Electrospinning has become a widely implemented technique for the generation of nonwoven mats that are useful in tissue engineering and filter applications. The overriding factor that has contributed to the popularity of this method is the ease with which fibers with submicron diameters can be produced. Fibers on that size scale are comparable to protein filaments that are observed in the extracellular matrix. The apparatus and procedures for conducting electrospinning experiments are ostensibly simple. While it is rarely reported in the literature on this topic, any experience with this method of fiber spinning reveals substantial ambiguities in how the process can be controlled to generate reproducible results. The simplicity of the procedure belies the complexity of the physical processes that determine the electrospinning process dynamics. In this article, three process domains and the physical domain of charge interaction are identified as important in electrospinning: (a) creation of charge carriers, (b) charge transport, (c) residual charge. The initial event that enables electrospinning is the generation of region of excess charge in the fluid that is to be electrospun. The electrostatic forces that develop on this region of charged fluid in the presence of a high potential result in the ejection of a fluid jet that solidifies into the resulting fiber. The transport of charge from the charge solution to the grounded collection device produces some of the current which is observed. That transport can occur by the fluid jet and through the atmosphere surrounding the electrospinning apparatus. Charges that are created in the fluid that are not dissipated remain in the solidified fiber as residual charges. The physics of each of these domains in the electrospinning process is summarized in terms of the current understanding, and possible sources of ambiguity in the implementation of this technique are indicated. Directions for future research to further articulate the behavior of the electrospinning process are suggested.
Collins, George; Federici, John; Imura, Yuki; Catalani, Luiz H.
Improved hydrodynamical model for carrier transport in semiconductors
A set of closed hydrodynamiclike equations is derived from Boltzmann's transport equation (BTE) describing charge transport in semiconductors. The production terms are modeled as relaxation terms consistently with the Onsager reciprocity principle. Stationary and homogeneous solutions are explicitly treated. The form of the production terms is checked by applying the Grad method of moments to the BTE. Finally the model
A. M. Anile; O. Muscato
Charge and spin transport in mesoscopic superconductors.
Background: Non-equilibrium charge transport in superconductors has been investigated intensely in the 1970s and 1980s, mostly in the vicinity of the critical temperature. Much less attention has been paid to low temperatures and the role of the quasiparticle spin. Results: We report here on nonlocal transport in superconductor hybrid structures at very low temperatures. By comparing the nonlocal conductance obtained by using ferromagnetic and normal-metal detectors, we discriminate charge and spin degrees of freedom. We observe spin injection and long-range transport of pure, chargeless spin currents in the regime of large Zeeman splitting. We elucidate charge and spin transport by comparison to theoretical models. Conclusion: The observed long-range chargeless spin transport opens a new path to manipulate and utilize the quasiparticle spin in superconductor nanostructures. PMID:24605283
Wolf, M J; H�bler, F; Kolenda, S; Beckmann, D
Relation between charge carrier density and lifetime in polymer-fullerene solar cells
NASA Astrophysics Data System (ADS)
The recombination kinetics of photo-generated charge carriers in polymer-fullerene solar cells has been studied. The transition between bimolecular to monomolecular (trap-assisted) recombination has been investigated by transient open-circuit voltage decay and intensity dependence of open-circuit voltage at different temperatures to quantify the trap delimitation energy. It has been observed that the critical parameter underpinning the transition between bimolecular to monomolecular recombination is the density of photo-generated charge carriers and their lifetime. The correspondence between carrier lifetime and density of photo-carriers has been experimentally observed for the first time.
Thakur, Anil K.; Baboz, Henri; Wantz, Guillaume; Hodgkiss, Justin; Hirsch, Lionel
An alternative approach to charge transport in semiconducting electrodes
NASA Technical Reports Server (NTRS)
The excess-carrier charge transport through the space-charge region of a semiconducting electrode is analyzed by a technique known as the flux method. In this approach reflection and transmission coefficients appropriate for a sheet of uniform semiconducting material describe its transport properties. A review is presented of the flux method showing that the results for a semiconductor electrode reduce in a limiting case to those previously found by Gaertner if the depletion layer is treated as a perfectly transmitting medium in which scattering and recombination are ignored. Then, in the framework of the flux method the depletion layer is considered more realistically by explicitly taking into account scattering and recombination processes which occur in this region.
Thomchick, J.; Buoncristiani, A. M.
Time-resolved measurements of charge carrier dynamics and optical nonlinearities in narrow-bandgap semiconductors
NASA Astrophysics Data System (ADS)
All-optical time-resolved measurement techniques provide a powerful tool for investigating critical parameters that determine the performance of infrared photodetector and emitter semiconductor materials. Narrow-bandgap InAs/GaSb type-II superlattices (T2SLs) have shown great promise as a next generation source of these materials, due to superior intrinsic properties and versatility. Unfortunately, InAs/GaSb T2SLs are plagued by parasitic Shockley-Read-Hall recombination centers that shorten the carrier lifetime and limit device performance. Ultrafast pump-probe techniques and time-resolved differential transmission measurements are used here to demonstrate that Ga-free InAs/InAsSb T2SLs and InAsSb alloys do not have this same limitation and thus have significantly longer carrier lifetimes. Measurements at 77 K provided minority carrier lifetimes of 9 mus and 3 mus for an unintentionally doped mid-wave infrared (MWIR) InAs/InAsSb T2SL and InAsSb alloy, respectively; a two order of magnitude increase compared to the 90 ns minority carrier lifetime measured in a comparable MWIR InAs/GaSb T2SL. Through temperature-dependent lifetime measurements, the various carrier recombination processes are differentiated and the dominant mechanisms identified for each material. These results demonstrate that these Ga-free materials are viable options over InAs/GaSb T2SLs for potentially improved infrared photodetectors. In addition to carrier lifetimes, the drift and diffusion of excited charge carriers through the superlattice growth layers (i.e. vertical transport) directly affects the performance of photodetectors and emitters. Unfortunately, there is a lack of information pertaining to vertical transport, primarily due to difficulties in making measurements on thin growth layers and the need for non-standard measurement techniques. However, all-optical ultrafast techniques are successfully used here to directly measure vertical diffusion in MWIR InAs/GaSb T2SLs. By optically generating excess carriers near one end of a MWIR T2SL and measuring the transit time to a thin, 2 lower-bandgap superlattice placed at the other end, the time-of-flight of vertically diffusing carriers is determined. Through investigation of both unintentionally doped and p-type superlattices at 77 K, the vertical hole and electron diffusion coefficients are determined to be 0.04+/-0.03 cm2/s and 4.7+/-0.5 cm2/s, corresponding to vertical mobilities of 6+/-5 cm 2/Vs and 700+/-80 cm2/Vs, respectively. These measurements are, to my knowledge, the first direct measurements of vertical transport properties in narrow-bandgap superlattices. Lastly, the widely tunable two-color ultrafast laser system used in this research allowed for the investigation of nonlinear optical properties in narrow-bandgap semiconductors. Time-resolved measurements taken at 77 K of the nondegenerate two-photon absorption spectrum of bulk n-type GaSb have provided new information about the nonresonant change in absorption and two-photon absorption coefficients in this material. Furthermore, as the nondegenerate spectrum was measured over a wide range of optical frequencies, a Kramers-Kronig transformation allowed the dispersion of the nondegenerate nonlinear refractive index to be calculated.
Olson, Benjamin Varberg
34 nm Charge Transport through DNA
NASA Astrophysics Data System (ADS)
Long-range charge transport through DNA has broad-reaching implications due to its inherent biological recognition capabilities and unmatched capacity to be patterned into precise, nanoscale shapes. We have observed charge transport through 34 nm DNA monolayers (100 base pairs) using DNA-mediated electrochemistry. Cyclic voltammetry of multiplexed gold electrodes modified with 100mer DNAs reveal sizable peaks from distally-bound Nile Blue redox probes for well matched duplexes but highly attenuated redox peaks from 100mer monolayers containing a single base pair mismatch, demonstrating that the charge transfer is DNA-mediated. The 100mers on the gold surface are efficiently cleaved by the restriction enzyme RsaI. The 100mers in the DNA film thus adopt conformations that are readily accessible to protein binding and restriction. The ability to assemble well-characterized DNA films with these 100mers permits the demonstration of charge transport over distances surpassing most reports of molecular wires.
Slinker, Jason; Muren, Natalie; Renfrew, Sara; Barton, Jacqueline
Modeling transport in ultrathin Si nanowires: charged versus neutral impurities.
At room temperature dopants in semiconducting nanowires are ionized. We show that the long-range electrostatic potential due to charged dopants has a dramatic impact on the transport properties in ultrathin wires and can virtually block minority carriers. Our quantitative estimates of this effect are obtained by computing the electronic transmission through wires with either charged or neutral P and B dopants. The dopant potential is obtained from density functional theory (DFT) calculations. Contrary to the neutral case, the transmission through charged dopants cannot be converged within a supercell-based DFT scheme, because the system size implied by the long-ranged electrostatic potential becomes computationally unmanagable. We overcome this problem by modifying the DFT potential with finite element calculations. We find that the minority scattering is increased by a factor of 1,000, while majority transmission is within 50% of the neutral dopant results. PMID:18672945
Rurali, Riccardo; Markussen, Troels; Su��, Jordi; Brandbyge, Mads; Jauho, Antti-Pekka
Theoretical characterization of charge transport in organic molecular crystals
NASA Astrophysics Data System (ADS)
The rapid growth in the interest to explore new synthetic crystalline organic semiconductors and their subsequent device characterization has revived the debate on the development of theoretical models to better understand the intrinsic charge transport mechanisms in organic materials. At the moment, several charge-transport theories for organic molecular crystals have been proposed and have observed a comparable agreement with experimental results. However, these models are limited in scope and restricted to specific ranges of microscopic parameters and temperatures. A general description that is applicable in all parameter regimes is still unavailable. The first step towards a complete understanding of the problem associated with the charge transport in organic molecular crystals includes the development of a first-principles theoretical methodology to evaluate with high accuracy the main microscopic charge-transport parameters and their respective couplings with intra- and intermolecular vibrational degrees of freedom. In this thesis, we have developed a first-principles methodology to investigate the impact of electron-phonon interactions on the charge-carrier mobilities in organic molecular crystals. Well-known organic materials such as oligoacene and oligothienoacene derivatives were studied in detail. To predict the charge-transport phenomena in organic materials, we rely on the Marcus theory of electron-transfer reactions. Within this context, the nature of the intramolecular vibronic coupling in oligoacenes was studied using an approach that combines high-resolution gas-phase photo-electron spectroscopy measurements with first-principles quantum-mechanical calculations. This further led to investigation of the electron interactions with optical phonons in oligoacene single crystals. The lattice phonon modes were computed at both density functional theory (DFT) and empirical force field levels. The low-frequency optical modes are found to play a significant role in dictating the temperature dependence of the charge-transport properties in the oligoacene crystals. A combined classical molecular dynamics and quantum-chemical study on organic molecular crystals revealed that the lattice vibrations are a key component to be taken into account when designing organic materials with improved charge mobilities. Finally, we investigated the microscopic charge-transport parameters in the pentathienoacene, 1,4-diiodobenzene, and 2,6-diiododithieno[3,2- b:2',3'-d]thiophene crystals. In the first case, a combined DFT and gas-phase ultraviolet photoelectron spectroscopy approach revealed that the intrinsic charge transport properties in the pentathienoacene crystal might be higher than that in two benchmark high-mobility organic crystals, i.e., pentacene and sexithienyl. For 1,4-diiodobenzene crystal, a detailed quantum-mechanical study of the electronic and vibrational couplings indicated that its high mobility is primarily associated with the iodine atoms. In the 2,6-diiododithieno[3,2-b:3',2'- d]thiophene crystal, the main source of electronic interactions were found along the pi-stacking direction. For negatively charged carriers, these two halogen-functionalized molecular crystals show a very large polaron binding energy, which suggests significantly low charge-transport mobility for electrons.
Sanchez-Carrera, Roel S.
Quantum-dot infrared photodetector with lateral carrier transport
In this letter, we present a normal-incident quantum-dot infrared photodetector. The detection principle is based on intersubband transition between the p states and the wetting-layer subband in the conduction band of self-assembled In(Ga)As\\/GaAs quantum dots. Carrier transport takes place in a channel next to the quantum-dot layers. The photoresponse is peaked at lambda=6.65 mum (186 meV) and reaches a maximum
L. Chu; A. Zrenner; M. Bichler; G. Abstreiter
The purpose of this analysis is to document the Quality Assurance (QA) classification of the Monitored Geologic Repository (MGR) carrier/cask transport system structures, systems and components (SSCs) performed by the MGR Safety Assurance Department. This analysis also provides the basis for revision of YMP/90-55Q, Q-List (YMP 1998). The Q-List identifies those MGR SSCs subject to the requirements of DOE/RW-0333P, ''Quality Assurance Requirements and Description'' (QARD) (DOE 1998).
S.E. Salzman
A quantum dot infrared photodetector with lateral carrier transport
In this contribution we present a normal-incidence quantum dot (QD) infrared detector structure. It is based on intra-conduction band transitions between the p-states of the QD and the wetting layer subband and lateral transport of photoexcited carriers in a channel next to the quantum dot layers. The photoresponse is peaked at 6.5?m(186meV) and reaches several A\\/W up to 60K. The
L. Chu; A. Zrenner; D. Bougeard; M. Bichler; G. Abstreiter
Impact of the charge transport in the conduction band on the retention of Si-nitride based memories
An improved model for charge injection through ONO gate stacks, that comprises carrier transport in the conduction band of the silicon nitride (Si3N4), is used to investigate the program\\/retention sequence of Si3N4 based (SONOS\\/TANOS) non volatile memories without making assumptions on the initial distribution of the trapped charge at the beginning of retention. We show that carrier transport in the
E. Vianello; F. Driussi; P. Palestri; A. Arreghini; D. Esseni; L. Selmi; N. Akil; M. van Duuren; D. S. Golubovic
Mechanism of charge transport in Si/Al2O3/Al structures
NASA Astrophysics Data System (ADS)
The investigation of current - voltage characteristics of structures Si/Al2O3/Al on the basis of aluminium oxide layers obtained by a method atomic layer deposition is carried out. It is established, that the possible mechanism of charge transport in structure is the space charge limited currents. The charge carrier concentration (Nt), concentration of traps (n0) and electron mobility (?) in Al2O3 layer are calculated.
Borisova, T. M.; Castro,
Thickness dependence of surface morphology and charge carrier mobility in organic field-effect transistors
With the aim of understanding the relationships between organic small molecule field-effect transistors (FETs) and organic conjugated polymer FETs, we investigate the thickness dependence of surface morphology and charge carrier mobility in pentacene and regioregular poly (3-hexylthiophene) (RR-P3HT) field-effect transistors. On the basis of the results of surface morphologies and electrical properties, we presume that the charge carrier mobility is
Xue-Yan Tian; Zheng Xu; Su-Ling Zhao; Fu-Jun Zhang; Guang-Cai Yuan; Jing Li; Qin-Jun Sun; Yun Wang; Xu-Rong Xu
Determining the Drift Time of Charge Carriers in P-Type Point-Contact HPGe Detectors
An algorithm to measure the drift time of charge carriers in p-type point contact (PPC) high-purity germanium (HPGe) detectors from the signals processed with a charge-sensitive preamplifier is introduced. It is demonstrated that the drift times can be used to estimate the distance of charge depositions from the point contact and to characterize losses due to charge trapping. A correction
R. D. Martin; M. Amman; Y. D. Chan; J. A. Detwiler; J. C. Loach; Q. Looker; P. N. Luke; A. W. P. Poon; J. Qian; K. Vetter; H. Yaver
Improved hydrodynamical model for carrier transport in semiconductors
NASA Astrophysics Data System (ADS)
A set of closed hydrodynamiclike equations is derived from Boltzmann's transport equation (BTE) describing charge transport in semiconductors. The production terms are modeled as relaxation terms consistently with the Onsager reciprocity principle. Stationary and homogeneous solutions are explicitly treated. The form of the production terms is checked by applying the Grad method of moments to the BTE. Finally the model is compared with Monte Carlo simulations for silicon.
Anile, A. M.; Muscato, O.
Earthquake lights and the stress-activation of positive hole charge carriers in rocks
Earthquake-related luminous phenomena (also known as earthquake lights) may arise from (1) the stress-activation of positive hole (p-hole) charge carriers in igneous rocks and (2) the accumulation of high charge carrier concentrations at asperities in the crust where the stress rates increase very rapidly as an earthquake approaches. It is proposed that, when a critical charge carrier concentration is reached, the p-holes form a degenerated solid state plasma that can break out of the confined rock volume and propagate as a rapidly expanding charge cloud. Upon reaching the surface the charge cloud causes dielectric breakdown at the air-rock interface, i.e. corona discharges, accompanied by the emission of light and high frequency electromagnetic radiation. ?? 2006 Elsevier Ltd. All rights reserved.
St-Laurent, F.; Derr, J. S.; Freund, F. T.
Charge transport in confined ionic liquids
NASA Astrophysics Data System (ADS)
Charge transport and glassy dynamics in neat and polymerized ionic liquids confined in nanoporous silica are investigated in a wide frequency and temperature ranges by a combination of Broadband Dielectric Spectroscopy and Pulsed Field Gradient Nuclear Magnetic Resonance (PFG NMR). By applying the Einstein-Smoluchowski relations to the dielectric spectra, diffusion coefficients are obtained in quantitative agreement with independent PFG NMR. The impact of geometrical confinement as well as the pore wall-ionic liquid interactions on the overall ionic mobility is explored for diverse categories of ionic liquids. The results are discussed within the framework of dynamic glass transition assisted charge transport in ionic liquids.
Sangoro, Joshua; Iacob, Ciprian; Kipnusu, Wycliffe; Kremer, Friedrich
Organic Semiconductors: A Molecular Picture of the Charge-Transport and Energy-Transport Processes.
NASA Astrophysics Data System (ADS)
Conjugated organic oligomer and polymer materials are being increasingly considered for their incorporation as the active semiconductor elements in devices such as photo-voltaic cells, light-emitting diodes, or field-effects transistors. In the operation of these devices, electron-transfer and energy-transfer processes play a key role, for instance in the form of charge transport (in the bulk or across interfaces), energy transport, charge separation, or charge recombination [1]. Here, we provide a theoretical description of electron-transfer phenomena based on electron-transfer theory, which allows us to provide a molecular, chemically-oriented understanding. In this presentation, we focus on the parameters that impact the mobility of charge carriers [2], that is the electronic coupling within chains and between adjacent chains and the reorganization energy of the chains upon ionization. Materials under study include conjugated oligomers such as oligoacenes, oligothiophene-acenes, oligothiophenes, and oligothienacenes. [1] J.L. Br'edas, D. Beljonne, V. Coropceanu, and J. Cornil, ``Charge-Transfer and Energy-Transfer Processes in pi-Conjugated Oligomers and Polymers'', Chemical Reviews, 104, 4971-5004 (2004). [2] V. Coropceanu, J. Cornil, D.A. da Silva Filho, Y. Olivier, R. Silbey, and J.L. Br'edas, ``Charge Transport in Organic Semiconductors'', Chemical Reviews, 107, xxx (2007).
Br�das, Jean-Luc
Integer charge transfer states in organic light-emitting diodes: Optical detection of hole carriers at the anode|organic interface
Hole carriers that reside at the anode|hole-transport-layer (HTL) interface, creating a dipole layer, have been observed in organic light-emitting diode (OLED) and model devices using charge modulation spectroscopic techniques. These interfacial carriers have been observed with various HTL materials and several anode compositions at voltages such that the HTL is reverse-biased. The cation density at an ITO|CFx|NPB interface is estimated
A. P. Marchetti; K. E. Sassin; R. H. Young; L. J. Rothberg; D. Y. Kondakov
On-Top ?-Stacking of Quasiplanar Molecules in Hole-Transporting Materials: Inducing Anisotropic Carrier Mobility in Amorphous Films.
Dimers of partially oxygen-bridged triarylamines were designed and synthesized as hole-transporting materials. X-ray structural analyses revealed that these compounds form on-top ?-stacking aggregates in the crystalline state. TRMC measurements showed that high levels of anisotropic charge transport were induced in the direction of the ?-stacking. Surprisingly, even in vacuum-deposited amorphous films, these compounds retained some of the face-on ?-stacking, thus facilitating an out-of-plane carrier mobility. PMID:24764307
Wakamiya, Atsushi; Nishimura, Hidetaka; Fukushima, Tatsuya; Suzuki, Furitsu; Saeki, Akinori; Seki, Shu; Osaka, Itaru; Sasamori, Takahiro; Murata, Michihisa; Murata, Yasujiro; Kaji, Hironori
Charge carrier dynamics in hybrid organic-inorganic light emitting devices
NASA Astrophysics Data System (ADS)
We present the results of our research into the charge carrier dynamics of hybrid LEDs. For this, we have used, for the first time in these type of devices, Transient Electroluminescent measurements (TEL) that permit the calculation of charge mobilities from the slow rise of the transient signal originated by single pulses at different voltages.
Martinez-Ferrero, Eugenia; Forneli, Amparo; Palomares, Emilio
Model for intermediate band solar cells incorporating carrier transport and recombination
A model for intermediate band solar cells is presented to assess the effect of carrier transport and recombination (CTR) on the efficiency of these devices. The model includes dependencies of physical parameters including optical absorption, carrier lifetime, and carrier transport on the density of intermediate band electronic states. Simulation results using this model indicate that conversion efficiency degrades when the
Albert S. Lin; Weiming Wang; Jamie D. Phillips
Low Temperature Charge Transport Study in Polypyrrole
NASA Astrophysics Data System (ADS)
Organic polymers were usually considered as electrical insulators but due to the extended ?-backbone system a new class of electrically conductive organic polymers is possible. These ? conjugated polymers have various remarkable properties which leads to their probable use in variety of applications like electronic devices, rechargeable batteries, sensors, corrosion protecting coating etc. Among other conducting polymers polypyrrole has attracted great attension due to high electrical conductivity and good environmental stability. In this study pelletized samples of chemically synthesized polypyrrole using ferric chloride and ammonium peroxydisulphate as oxidizing agents were electrically characterized over wide temperature range of 10-300 K. An effort has been made to explore the charge transport in these doped samples using charge transport models. The analysis of experimental data predicts that hopping and tunneling transports are the dominant mechanism in their respective temperature range.
Taunk, Manish; Chand, Subhash
Nonequilibrium charge carriers and linear galvanomagnetic phenomena in semiconductors
NASA Astrophysics Data System (ADS)
In linear approximations using small electric Ex and magnetic Hy fields, nonequilibrium carriers appear in bounded semiconductors orthogonal to the electric field. An expression for the longitudinal magnetoresistance in a finite bipolar semiconductor is obtained by taking into account the redistribution of the nonequilibrium carriers along the z axis (thickness 2b), the generation and recombination processes assisted by traps (Shockley-Read model), and the different surface recombination velocities. For the first time, it is shown that the redistribution of nonequilibrium carriers generates a change in the conductivity from the classical value. In this case, two new terms appear, which depend on the thickness b. The first contribution to the magnetoresistance exhibits a linear dependence on the magnetic field, where the conductivity of the semiconductor increases or decreases depending on the magnetic field orientation. The second contribution shows a quadratic dependence on the magnetic field. The changes in current density in the cases of strong and weak recombination, and in the cases of intrinsic and extrinsic semiconductors, are also studied.
Molina-Valdovinos, S.; Gurevich, Yu. G.
The influence of negative charged centers on the hole transport in a typical molecularly doped polymer
NASA Astrophysics Data System (ADS)
We have studied effects of the negative charged centers on the time of flight (TOF) curves measured in a typical hole-conducting molecularly doped polymer. The main effects are the unusual TOF (surface generation) current rise in the preflight region (be it a flat plateau or a cusp) due to the accumulated space charge and the current reduction at all times because of the monomolecular recombination. TOF-2 (bulk generation) transients are less sensitive to charged centers. Analysis of these effects has proved that charged centers do not change the carrier mobility provided that the space charge field and bimolecular recombination are properly accounted for in terms of the proposed two-layer MT model. We have shown that combination of TOF, TOF-1a and TOF-2 variants of the electron-gun based technique allows one to establish definitively the character of the charge carrier transport in MDPs.
Tyutnev, Andrey P.; Ikhsanov, Renat Sh.; Saenko, Vladimir S.; Pozhidaev, Evgenii D.
Non-ohmic behavior of carrier transport in highly disordered graphene
NASA Astrophysics Data System (ADS)
We report measurements of disordered graphene probed by both a high electric field and a high magnetic field. By applying a high source-drain voltage, Vsd, we are able to study the current-voltage relation I-Vsd of our device. With increasing Vsd, a crossover from the linear I-Vsd regime to the non-linear one, and eventually to activationless-hopping transport occurs. In the activationless-hopping regime, the importance of Coulomb interactions between charged carriers is demonstrated. Moreover, we show that delocalization of carriers which are strongly localized at low T and at small Vsd occurs in the presence of high electric field and perpendicular magnetic field.
Lo, Shun-Tsung; Chuang, Chiashain; Puddy, R. K.; Chen, T.-M.; Smith, C. G.; Liang, C.-T.
Determining the drift time of charge carriers in p-type point-contact HPGe detectors
NASA Astrophysics Data System (ADS)
An algorithm to determine the drift time of charge carriers in p-type point contact (PPC) high-purity germanium (HPGe) detectors from the signals processed with a charge-sensitive preamplifier is introduced. It is demonstrated that the drift times can be used to estimate the distance of charge depositions from the point contact and to characterize losses due to charge trapping. A correction for charge trapping effects over a wide range of energies is implemented using the measured drift times and is shown to improve the energy resolution by up to 30%.
Martin, R. D.; Amman, M.; Chan, Y. D.; Detwiler, J. A.; Loach, J. C.; Looker, Q.; Luke, P. N.; Poon, A. W. P.; Qian, J.; Vetter, K.; Yaver, H.
Stochastic resonance of charge carriers diffusing in a nonhomogeneous medium with nonhomogeneous temperature
NASA Astrophysics Data System (ADS)
We investigate the dynamics of charge carriers hopping from one trap to the other trap along an n-type semiconductor layer consisting of a spatially nonhomogeneous trap distribution of depth ? assisted by thermal noise. The trap profile is denser at the center and decays as one moves outward. In presence of a uniform background temperature, the charge carriers tend to accumulate around the center. Moreover, applying a nonhomogeneous temperature which is hot at the location of the maximum of trap density, results in a new redistribution of charge carriers which pile up around two points symmetrically positioned with respect to the center of the semiconductor layer making the system to behave like a bistable potential. The thermally activated rate of hopping of charge carriers as a function of the model parameters is studied in the high barrier limit. Using the two-state approximation, the stochastic resonance (SR) of the charge carriers dynamics in the presence of time varying external signal is also investigated.
Aragie, Berhanu; Tatek, Yergou B.; Bekele, Mulugeta
14 CFR 234.13 - Reports by air carriers on incidents involving animals during air transport.
Code of Federal Regulations, 2012 CFR
...incidents involving animals during air transport. 234.13 Section 234.13...incidents involving animals during air transport. (a) Any air carrier that...or death of an animal during air transport provided by the air...
14 CFR 234.13 - Reports by air carriers on incidents involving animals during air transport.
Code of Federal Regulations, 2011 CFR
...incidents involving animals during air transport. 234.13 Section 234.13...incidents involving animals during air transport. (a) Any air carrier that...or death of an animal during air transport provided by the air...
14 CFR 234.13 - Reports by air carriers on incidents involving animals during air transport.
Code of Federal Regulations, 2010 CFR
...incidents involving animals during air transport. 234.13 Section 234.13...incidents involving animals during air transport. (a) Any air carrier that...or death of an animal during air transport provided by the air...
14 CFR 234.13 - Reports by air carriers on incidents involving animals during air transport.
Code of Federal Regulations, 2010 CFR
...incidents involving animals during air transport. 234.13 Section 234.13...incidents involving animals during air transport. (a) Any air carrier that...or death of an animal during air transport provided by the air...
Influence of charged-dislocation density variations on carrier mobility in heteroepitaxial semiconductors: The case of SnO2 on sapphire
NASA Astrophysics Data System (ADS)
In highly mismatched heteroepitaxial systems, the influence of carrier- and dislocation-density variations on carrier mobility is revealed. Transmission electron microscopy reveals the variation of dislocation density through a series of SnO2 films grown by molecular-beam epitaxy on sapphire substrates where the lattice mismatch exceeds 11%. A layer-by-layer parallel conduction treatment of the carrier mobility in SnO2 epilayers is used to illustrate the dominant role of the depth-dependent dislocation density and charge profile in determining the film-thickness dependence of the transport properties.
Vasheghani Farahani, S. K.; Veal, T. D.; Sanchez, A. M.; Bierwagen, O.; White, M. E.; Gorfman, S.; Thomas, P. A.; Speck, J. S.; McConville, C. F.
Characterization of charge carrier lateral conduction in irradiated dielectric materials
NASA Astrophysics Data System (ADS)
A characterization method for surface charging analysis on insulators submitted to electron irradiation has been developed. This method, based on the use of two Kelvin probes (KPs), provides details on the transit time motion for injection of both holes and electrons. It can also be used to assess the isotropy of lateral electrical conduction on the sample. The feasibility of this method was tested on fluorinated ethylene propylene (Teflon� FEP) samples. It was found that central electron injection induces rapid surface charge spreading, in contrast to injection of holes. An electrical anisotropic behaviour of the sample was also detected.
Hanna, R.; Paulmier, T.; Belhaj, M.; Molinie, P.; Dirassen, B.; Payan, D.; Balcon, N.
Electron transport model of dielectric charging
NASA Technical Reports Server (NTRS)
A computer code (SCCPOEM) was assembled to describe the charging of dielectrics due to irradiation by electrons. The primary purpose for developing the code was to make available a convenient tool for studying the internal fields and charge densities in electron-irradiated dielectrics. The code, which is based on the primary electron transport code POEM, is applicable to arbitrary dielectrics, source spectra, and current time histories. The code calculations are illustrated by a series of semianalytical solutions. Calculations to date suggest that the front face electric field is insufficient to cause breakdown, but that bulk breakdown fields can easily be exceeded.
Beers, B. L.; Hwang, H. C.; Lin, D. L.; Pine, V. W.
Charge carrier losses of organic solar cells based on subphthalocyanine/C60 heterojunction
NASA Astrophysics Data System (ADS)
Charge carrier losses of organic solar cells (OSCs) based on Subphthalocyanine (SubPc)/C60 heterojunction have been studied through the measurements of incident light intensity dependent response of the device. The light intensity was varied between 0.03 and 100 mW/cm2. The results showed that short circuit current density follows a linear dependence on light intensity (Pin), while open circuit voltage logarithmically increase with Pin with a slop of 120 mV/decade, indicating that the charge carrier losses are governed by trap-assisted recombination through interface states between donor and acceptor, with an estimated trap density of order 1024 m-3. Moreover, the inverse dependence of shunt resistance (RPA) on light intensity reveals that charge carriers are trapped in the bulk of active layer as well as at the organic/electrode interface, resulting in the decrease of fill factor (FF) with Pin.
Zang, Yue; Yu, Jungsheng; Huang, Jiang; Jiang, Yadong
Variational multiscale models for charge transport
This work presents a few variational multiscale models for charge transport in complex physical, chemical and biological systems and engineering devices, such as fuel cells, solar cells, battery cells, nanofluidics, transistors and ion channels. An essential ingredient of the present models, introduced in an earlier paper (Bulletin of Mathematical Biology, 72, 1562-1622, 2010), is the use of differential geometry theory of surfaces as a natural means to geometrically separate the macroscopic domain from the microscopic domain, meanwhile, dynamically couple discrete and continuum descriptions. Our main strategy is to construct the total energy functional of a charge transport system to encompass the polar and nonpolar free energies of solvation, and chemical potential related energy. By using the Euler-Lagrange variation, coupled Laplace-Beltrami and Poisson-Nernst-Planck (LB-PNP) equations are derived. The solution of the LB-PNP equations leads to the minimization of the total free energy, and explicit profiles of electrostatic potential and densities of charge species. To further reduce the computational complexity, the Boltzmann distribution obtained from the Poisson-Boltzmann (PB) equation is utilized to represent the densities of certain charge species so as to avoid the computationally expensive solution of some Nernst-Planck (NP) equations. Consequently, the coupled Laplace-Beltrami and Poisson-Boltzmann-Nernst-Planck (LB-PBNP) equations are proposed for charge transport in heterogeneous systems. A major emphasis of the present formulation is the consistency between equilibrium LB-PB theory and non-equilibrium LB-PNP theory at equilibrium. Another major emphasis is the capability of the reduced LB-PBNP model to fully recover the prediction of the LB-PNP model at non-equilibrium settings. To account for the fluid impact on the charge transport, we derive coupled Laplace-Beltrami, Poisson-Nernst-Planck and Navier-Stokes equations from the variational principle for chemo-electro-fluid systems. A number of computational algorithms is developed to implement the proposed new variational multiscale models in an efficient manner. A set of ten protein molecules and a realistic ion channel, Gramicidin A, are employed to confirm the consistency and verify the capability. Extensive numerical experiment is designed to validate the proposed variational multiscale models. A good quantitative agreement between our model prediction and the experimental measurement of current-voltage curves is observed for the Gramicidin A channel transport. This paper also provides a brief review of the field.
Wei, Guo-Wei; Zheng, Qiong; Chen, Zhan; Xia, Kelin
Variational multiscale models for charge transport.
This work presents a few variational multiscale models for charge transport in complex physical, chemical and biological systems and engineering devices, such as fuel cells, solar cells, battery cells, nanofluidics, transistors and ion channels. An essential ingredient of the present models, introduced in an earlier paper (Bulletin of Mathematical Biology, 72, 1562-1622, 2010), is the use of differential geometry theory of surfaces as a natural means to geometrically separate the macroscopic domain from the microscopic domain, meanwhile, dynamically couple discrete and continuum descriptions. Our main strategy is to construct the total energy functional of a charge transport system to encompass the polar and nonpolar free energies of solvation, and chemical potential related energy. By using the Euler-Lagrange variation, coupled Laplace-Beltrami and Poisson-Nernst-Planck (LB-PNP) equations are derived. The solution of the LB-PNP equations leads to the minimization of the total free energy, and explicit profiles of electrostatic potential and densities of charge species. To further reduce the computational complexity, the Boltzmann distribution obtained from the Poisson-Boltzmann (PB) equation is utilized to represent the densities of certain charge species so as to avoid the computationally expensive solution of some Nernst-Planck (NP) equations. Consequently, the coupled Laplace-Beltrami and Poisson-Boltzmann-Nernst-Planck (LB-PBNP) equations are proposed for charge transport in heterogeneous systems. A major emphasis of the present formulation is the consistency between equilibrium LB-PB theory and non-equilibrium LB-PNP theory at equilibrium. Another major emphasis is the capability of the reduced LB-PBNP model to fully recover the prediction of the LB-PNP model at non-equilibrium settings. To account for the fluid impact on the charge transport, we derive coupled Laplace-Beltrami, Poisson-Nernst-Planck and Navier-Stokes equations from the variational principle for chemo-electro-fluid systems. A number of computational algorithms is developed to implement the proposed new variational multiscale models in an efficient manner. A set of ten protein molecules and a realistic ion channel, Gramicidin A, are employed to confirm the consistency and verify the capability. Extensive numerical experiment is designed to validate the proposed variational multiscale models. A good quantitative agreement between our model prediction and the experimental measurement of current-voltage curves is observed for the Gramicidin A channel transport. This paper also provides a brief review of the field. PMID:23172978
Wei, Guo-Wei; Zheng, Qiong; Chen, Zhan; Xia, Kelin
A Valence Bond Model to Evaluate Electronic Parameters for Charge Transport in Organic Aggregates
NASA Astrophysics Data System (ADS)
A semi-empirical quantum-chemical model based on a fragment orbital formalism is presented to assess molecular parameters relevant to charge transport in organic crystals. The mixed Valence-Bond/Hartree-Fock approach provides a single and efficient framework to evaluate the electronic polarization effects induced by localized charge carriers and the associated impact on the matrix elements mediating electron migration in the hopping regime. This formalism is applied here to anthracene clusters of increasing sizes.
Aurel, Philippe; Fritsch, Alain; Ducasse, Laurent; Linares, Mathieu; Cornil, J�r�me; Beljonne, David; Castet, Fr�d�ric
Charge transport and glassy dynamics in ionic liquids.
Ionic liquids (ILs) exhibit unique features such as low melting points, low vapor pressures, wide liquidus temperature ranges, high thermal stability, high ionic conductivity, and wide electrochemical windows. As a result, they show promise for use in variety of applications: as reaction media, in batteries and supercapacitors, in solar and fuel cells, for electrochemical deposition of metals and semiconductors, for protein extraction and crystallization, and many others. Because of the ease with which they can be supercooled, ionic liquids offer new opportunities to investigate long-standing questions regarding the nature of the dynamic glass transition and its possible link to charge transport. Despite the significant steps achieved from experimental and theoretical studies, no generally accepted quantitative theory of dynamic glass transition to date has been capable of reproducing all the experimentally observed features. In this Account, we discuss recent studies of the interplay between charge transport and glassy dynamics in ionic liquids as investigated by a combination of several experimental techniques including broadband dielectric spectroscopy, pulsed field gradient nuclear magnetic resonance, dynamic mechanical spectroscopy, and differential scanning calorimetry. Based on Einstein-Smoluchowski relations, we use dielectric spectra of ionic liquids to determine diffusion coefficients in quantitative agreement with independent pulsed field gradient nuclear magnetic resonance measurements, but spanning a broader range of more than 10 orders of magnitude. This approach provides a novel opportunity to determine the electrical mobility and effective number density of charge carriers as well as their types of thermal activation from the measured dc conductivity separately. We also unravel the origin of the remarkable universality of charge transport in different classes of glass-forming ionic liquids. PMID:22082024
Sangoro, Joshua R; Kremer, Friedrich
Charge Transport and Glassy Dynamics in Ionic Liquids
Ionic liquids (ILs) exhibit unique features such as low melting points, low vapor pressures, wide liquidus temperature ranges, high thermal stability, high ionic conductivity, and wide electrochemical windows. As a result, they show promise for use in variety of applications: as reaction media, in batteries and supercapacitors, in solar and fuel cells, for electrochemical deposition of metals and semiconductors, for protein extraction and crystallization, and many others. Because of the ease with which they can be supercooled, ionic liquids offer new opportunities to investigate long-standing questions regarding the nature of the dynamic glass transition and its possible link to charge transport. Despite the significant steps achieved from experimental and theoretical studies, no generally accepted quantitative theory of dynamic glass transition to date has been capable of reproducing all the experimentally observed features. In this Account, we discuss recent studies of the interplay between charge transport and glassy dynamics in ionic liquids as investigated by a combination of several experimental techniques including broadband dielectric spectroscopy, pulsed field gradient nuclear magnetic resonance, dynamic mechanical spectroscopy, and differential scanning calorimetry. Based on EinsteinSmoluchowski relations, we use dielectric spectra of ionic liquids to determine diffusion coefficients in quantitative agreement with independent pulsed field gradient nuclear magnetic resonance measurements, but spanning a broader range of more than 10 orders of magnitude. This approach provides a novel opportunity to determine the electrical mobility and effective number density of charge carriers as well as their types of thermal activation from the measured dc conductivity separately. We also unravel the origin of the remarkable universality of charge transport in different classes of glass-forming ionic liquids.
Sangoro, Joshua R [ORNL; Kremer, Friedrich [University of Leipzig
Fundamentals of Charge Transport through DNA
NASA Astrophysics Data System (ADS)
Achieving charge transport (CT) through DNA comlements its inherent biological recognition capabilities and its unmatched capacity to be patterned into precise, nanoscale shapes. We have probed the length and temperature dependence of DNA charge transport with DNA-mediated electrochemistry. Cyclic voltammetry of 100-mer and 17-mer DNA monolayers on gold revealed sizable peaks from distally-bound Nile Blue redox probes for well matched duplexes, but highly attenuated redox peaks from monolayers containing a single base pair mismatch, demonstrating that the charge transfer is DNA-mediated. The similarity in electron transfer rates through 100-mer and 17-mer monolayers is consistent with fast transport through the DNA and rate-limiting tunneling injection. Temperature dependence studies of 17-mer and 34-mer duplexes showed CT is thermally activated and highly sensitive to the integrity of the DNA base pair pi stack. Activation energies are increased by the presence and identity of single base pair mismatches. Furthermore, the yield of DNA CT with temperature argues that this CT is conformationally gated. These results elucidate the mechanism of DNA CT and direct the use of DNA as molecular wires in electronic applications.
Slinker, Jason; Muren, Natalie; Renfrew, Sara; Barton, Jackie; Wohlgamuth, Chris; McWilliams, Marc
Charge transport in organic crystals: interplay of band transport, hopping and electron-phonon scattering
NASA Astrophysics Data System (ADS)
We present an ab initio description of charge transport in organic semiconductors based on a recently developed theory that goes beyond small-polaron and/or narrow-band models. The mobility expression is evaluated with parameters from density functional theory, and application to naphthalene crystals demonstrates substantial progress in the simulated temperature dependence and relative magnitudes for all transport directions. The scattering by phonons is described in a manner that goes beyond the Holstein model for small polarons and, consequently, significantly improves the temperature dependence and anisotropy of carrier mobility with respect to the previous narrow-band theory. The contributions of coherent and incoherent scattering processes are analyzed. Special emphasis is placed on the origin and understanding of the transition from band transport at low temperatures to hopping at high temperatures, both of which are fully included in the theory. Additionally, in contrast to earlier narrow-band theories, the unphysical divergence at zero temperatures is removed.
Ortmann, Frank; Bechstedt, Friedhelm; Hannewald, Karsten
Dust Charging and Transport on Surfaces
In this paper, we review laboratory studies of dust transport on surfaces in plasmas, performed for a number of different mechanisms: 1) Dust particles were levitated in plasma sheaths by electrostatic forces balancing the gravitational force. 2) Dust was observed to spread over and lift off a surface that repels electrons in a plasma. 3) Dust was transported on surfaces having different secondary electron yields in plasma with an electron beam as a consequence of differential charging. 4) We also report a mechanism of dust transport by electric fields occurring at electron beam impact/shadow boundaries. These processes are candidates to explain the formation of dust ponds that were recently observed in craters on the asteroid Eros by the NEAR Shoemaker spacecraft.
Wang, X. [Colorado Center for Lunar Dust And Atmospheric Studies, University of Colorado, Boulder, CO 80309 (United States); Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, CO 80309 (United States); Robertson, S. [Colorado Center for Lunar Dust And Atmospheric Studies, University of Colorado, Boulder, CO 80309 (United States); Department of Physics, University of Colorado, Boulder, CO 80309 (United States); Horanyi, M. [Colorado Center for Lunar Dust And Atmospheric Studies, University of Colorado, Boulder, CO 80309 (United States); Department of Physics, University of Colorado, Boulder, CO 80309 (United States); Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, CO 80309 (United States)
Carrier transport in amorphous silicon utilizing picosecond photoconductivity
NASA Astrophysics Data System (ADS)
The development of a high-speed electronic measurement capability permitted the direct observation of the transient photoresponse of amorphous silicon (a-Si) with a time resolution of approximately 10ps. This technique was used to measure the initial mobility of photogenerated (2.1eV) free carriers in three types of a-Si having widely different densities of structural defects (i.e., as prepared by: (1) RF glow discharge (a-Si:H); (2) chemical vapor deposition; and (3) evaporation in ultra-high vacuum). In all three types of a-Si, the same initial mobility of approximately 1 cu cm/Vs at room temperature was found. This result tends to confirm the often-made suggestion that the free carrier mobility is determined by the influence of shallow states associated with the disorder in the random atomic network, and is an intrinsic property of a-Si which is unaffected by the method of preparation. The rate of decay of the photocurrent correlates with the density of structural defects and varies from 4ps to 200ps for the three types of a-Si investigated. The initial mobility of a-Si:H was found to be thermally activated. The possible application of extended state transport controlled by multiple trapping and small polaron formation is discussed.
Johnson, A. M.
Enhanced charge carrier mobility in two-dimensional high dielectric molybdenum oxide.
We demonstrate that the energy bandgap of layered, high-dielectric ?-MoO(3) can be reduced to values viable for the fabrication of 2D electronic devices. This is achieved through embedding Coulomb charges within the high dielectric media, advantageously limiting charge scattering. As a result, devices with ?-MoO(3) of ?11 nm thickness and carrier mobilities larger than 1100 cm(2) V(-1) s(-1) are obtained. PMID:23090760
Balendhran, Sivacarendran; Deng, Junkai; Ou, Jian Zhen; Walia, Sumeet; Scott, James; Tang, Jianshi; Wang, Kang L; Field, Matthew R; Russo, Salvy; Zhuiykov, Serge; Strano, Michael S; Medhekar, Nikhil; Sriram, Sharath; Bhaskaran, Madhu; Kalantar-zadeh, Kourosh
Charging and spin-polarization effects in InAs quantum dots under bipolar carrier injection
An ultrafast pump-probe method based on differing polarization properties of neutral and charged excitons in semiconductor quantum dots (QDs) is employed to study carrier dynamics in InGaAs QDs grown in nominally undoped, modulation doped and p-i-n structures. We find that at low temperature even in the nominally undoped samples there are large fractions of charged dots. It is also demonstrated
A. I. Tartakovskii; A. V. Savelyev; M. N. Makhonin; M. S. Skolnick; D. J. Mowbray; M. V. Maximov; V. M. Ustinov; R. P. Seisyan
Charging and spin-polarization effects in InAs quantum dots under bipolar carrier injection
Carrier dynamics in quantum dot p-i-n diodes are studied using an ultrafast polarization-resolved pump-probe technique. It is demonstrated that for bipolar electrical injection there is a high probability of the independent capture of electrons or holes into the dots, resulting in dot charging. Voltage control of the charged exciton population, created via a combination of electrical and optical excitation, which
A. V. Savelyev; A. I. Tartakovskii; M. S. Skolnick; D. J. Mowbray; M. V. Maximov; V. M. Ustinov; R. P. Seisyan
Charging and spin-polarization effects in InAs quantum dots under bipolar carrier injection
NASA Astrophysics Data System (ADS)
Carrier dynamics in quantum dot p-i-n diodes are studied using an ultrafast polarization-resolved pump-probe technique. It is demonstrated that for bipolar electrical injection there is a high probability of the independent capture of electrons or holes into the dots, resulting in dot charging. Voltage control of the charged exciton population, created via a combination of electrical and optical excitation, which exhibits a long lived spin polarization (or spin memory) is demonstrated.
Savelyev, A. V.; Tartakovskii, A. I.; Skolnick, M. S.; Mowbray, D. J.; Maximov, M. V.; Ustinov, V. M.; Seisyan, R. P.
Imaging charge separation and carrier recombination in nanowire p-i-n junctions using ultrafast microscopy.
Silicon nanowires incorporating p-type/n-type (p-n) junctions have been introduced as basic building blocks for future nanoscale electronic components. Controlling charge flow through these doped nanostructures is central to their function, yet our understanding of this process is inferred from measurements that average over entire structures or integrate over long times. Here, we have used femtosecond pump-probe microscopy to directly image the dynamics of photogenerated charge carriers in silicon nanowires encoded with p-n junctions along the growth axis. Initially, motion is dictated by carrier-carrier interactions, resulting in diffusive spreading of the neutral electron-hole cloud. Charge separation occurs at longer times as the carrier distribution reaches the edges of the depletion region, leading to a persistent electron population in the n-type region. Time-resolved visualization of the carrier dynamics yields clear, direct information on fundamental drift, diffusion, and recombination processes in these systems, providing a powerful tool for understanding and improving materials for nanotechnology. PMID:24867088
Gabriel, Michelle M; Grumstrup, Erik M; Kirschbrown, Justin R; Pinion, Christopher W; Christesen, Joseph D; Zigler, David F; Cating, Emma E M; Cahoon, James F; Papanikolas, John M
49 CFR 385.13 - Unsatisfactory rated motor carriers; prohibition on transportation; ineligibility for Federal...
Code of Federal Regulations, 2013 CFR
...TRANSPORTATION FEDERAL MOTOR CARRIER SAFETY REGULATIONS SAFETY FITNESS PROCEDURES General § 385.13 Unsatisfactory rated...carrier is making a good-faith effort to improve its safety fitness, FMCSA may allow the motor carrier to operate for up to...
Theory of radiation-induced and carrier-enhanced conductivity - Space charge and contact effects
NASA Astrophysics Data System (ADS)
The PECK (Parker enhanced carrier kinetics) model is developed for interpreting experimental results on conductivity in dielectrics. In the model, based on steady state solutions of general kinetic equations for electrons and holes, it is assumed that the holes are instantaneously trapped into deep traps, while the electrons hop from shallow trap to shallow trap and are described as quasi-free with a lowered trap-modulated effective mobility. This simplifies the description of the system to the Poisson equation and a single transport equation for the electrons. Raw data on a 6.4-micron biased sample of Kapton, penetrated by a 28-keV incident electron beam, are considered for interpretation. It is shown that current measurements at zero bias can be interpreted in terms of the shape of the excess-charge deposition profile. Measurements at high bias are matched by the model with an appropriate choice for the trap-modulated electron mobility (approximately 7 x 10 to the -15th sq m/V-s), provided injection is assumed to occur at the cathode contact.
Parker, L. W.; Meulenberg, A., Jr.
Exciton transport, charge extraction, and loss mechanisms in organic photovoltaics
NASA Astrophysics Data System (ADS)
Organic photovoltaics have attracted significant interest over the last decade due to their promise as clean low-cost alternatives to large-scale electric power generation such as coal-fired power, natural gas, and nuclear power. Many believe power conversion efficiency targets of 10-15% must be reached before commercialization is possible. Consequently, understanding the loss mechanisms which currently limit efficiencies to 4-5% is crucial to identify paths to reach higher efficiencies. In this work, we investigate the dominant loss mechanisms in some of the leading organic photovoltaic architectures. In the first class of architectures, which include planar heterojunctions and bulk heterojunctions with large domains, efficiencies are primarily limited by the distance photogenerated excitations (excitons) can be transported (termed the exciton diffusion length) to a heterojunction where the excitons may dissociate. We will discuss how to properly measure the exciton diffusion length focusing on the effects of optical interference and of energy transfer when using fullerenes as quenching layers and show how this explains the variety of diffusion lengths reported for the same material. After understanding that disorder and defects limit exciton diffusion lengths, we suggest some approaches to overcome this. We then extensively investigate the use of long-range resonant energy transfer to increase exciton harvesting. Using simulations and experiments as support, we discuss how energy transfer can be engineered into architectures to increase the distance excitons can be harvested. In an experimental model system, DOW Red/PTPTB, we will show how the distance excitons are harvested can be increased by almost an order of magnitude up to 27 nm from a heterojunction and give design rules and extensions of this concept for future architectures. After understanding exciton harvesting limitations we will look at other losses that are present in planar heterojunctions. One of the primary losses that puts stringent requirements on the charge carrier mobilities in these cells is the recombination losses due to space charge build up at the heterojunction. Because electrons are confined to the acceptor and holes to the donor, net charge density always exists even when mobilities are matched, in contrast to bulk heterojunctions wherein matched mobilities lead to zero net charge. This net charge creates an electric field which opposes the built-in field and limits the current that can be carried away from this heterojunction. Using simulations we show that for relevant current densities charge carrier mobilities must be higher than 10-4 cm2/V.s to avoid significant losses due to space charge formation. In the last part of this work, we will focus on the second class of architectures in which exciton harvesting is efficient. We will present a systematic analysis of one of the leading polymer:fullerene bulk heterojunction cells to show that losses in this architecture are due to charge recombination. Using optical measurements and simulations, exciton harvesting measurements, and device characteristics we will show that the dominant loss is likely due to field-dependent geminate recombination of the electron and hole pair created immediately following exciton dissociation. No losses in this system are seen due to bimolecular recombination or space charge which provides information on charge-carrier mobility targets necessary for the future design of high efficiency organic photovoltaics.
Scully, Shawn Ryan
Spin-polarized charge carrier injection by tunneling from ferromagnetic metals into organic semiconductors
Efficient spin-polarized charge carrier injection from a ferromagnetic metal (FM) into a semiconductor is a challenging task. Because of the large differences between the conductivities of metals and semiconductors a spin-dependent injection mechanism, such as tunneling, is a critical requirement. We discuss a new model for such a mechanism for the specific case of organic semiconductors (OS), such as conjugated
Mohammad Yunus; P. Paul Ruden; Darryl L. Smith
Investigation of the charge carrier concentration in highly aluminum doped SiC using Raman scattering
In the production of highly aluminum doped SiC bulk crystals, a need arises for a fast and simple method to estimate the hole concentration in the material for process control and optimization. An approach for a characterization method using Raman spectroscopy is presented. We established a calibration curve along with an empirical function to determine the charge carrier concentration in
R. M�ller; U. K�necke; A. Thuaire; M. Mermoux; M. Pons; P. Wellmann
Charge transport in conducting polymer nanofibers
NASA Astrophysics Data System (ADS)
Here, we present theoretical analysis of electron transport in polyaniline based (PANi) nanofibers assuming the metalic state of the material. To build up this theory we treat conducting polymers as a special kind of granular metals, and we apply the quantum theory of conduction in mesoscopic systems to describe the transport between metallic-like granules. Our results show that the concept of resonance electron tunneling as the predominating mechanism providing charge transport between the grains is supported with recent experiments on the electrical characterization of single PANi nanofibers. By contacting the proposed theory with the experimental data we estimate some important parameters characterizing the electron transport in these materials [1]. Using the Buttiker dephasing model within the scattering matrix formalism we analyze dephasing effects, and we show that these effects could be reduced enough to allow the structure of the electron transmission function to be exposed in the experiments on the electronic transport through fibers [2]. Also, we discuss the origin of rectifying features observed in current-voltage characteristics of fibers with varying cross-sectional areas. 1. N. A. Zimbovskaya, A. T. Johnson, Jr., and N. J. Pinto, Phys. Rev. B 72, 024213 (2005). 2. N. A. Zimbovskaya, J. Chem. Phys. 123, 114708 (2005).
Zimbovskaya, Natalya
Mapping the spatial distribution of charge carriers in quantum-confined heterostructures.
Quantum-confined nanostructures are considered 'artificial atoms' because the wavefunctions of their charge carriers resemble those of atomic orbitals. For multiple-domain heterostructures, however, carrier wavefunctions are more complex and still not well understood. We have prepared a unique series of cation-exchanged HgxCd1-xTe quantum dots (QDs) and seven epitaxial core-shell QDs and measured their first and second exciton peak oscillator strengths as a function of size and chemical composition. A major finding is that carrier locations can be quantitatively mapped and visualized during shell growth or cation exchange simply using absorption transition strengths. These results reveal that a broad range of quantum heterostructures with different internal structures and band alignments exhibit distinct carrier localization patterns that can be used to further improve the performance of optoelectronic devices and enhance the brightness of QD probes for bioimaging. PMID:25080298
Smith, Andrew M; Lane, Lucas A; Nie, Shuming
Charge transport in holography with momentum dissipation
NASA Astrophysics Data System (ADS)
In this work, we examine how charge is transported in a theory where momentum is relaxed by spatially dependent, massless scalars. We analyze the possible IR phases in terms of various scaling exponents and the (ir)relevance of operators in the IR effective holographic theory with a dilaton. We compute the (finite) resistivity and encounter broad families of (in)coherent metals and insulators, characterized by universal scaling behaviour. The optical conductivity at zero temperature and low frequencies exhibits power tails which can violate scaling symmetries, due to the running of the dilaton. At low temperatures, our model captures features of random-field disorder.
Gout�raux, B.
Interface Charge Transport in Organic Transistors as Investigated by Field-Induced Electron Spin Resonance
NASA Astrophysics Data System (ADS)
Most of high-performance organic thin-film transistors (OTFTs) as recently developed is attainable with non-doped, single-component ?-conjugated materials that exhibit high layer crystallinity both for small-molecules and polymers. The layer crystallinity is quite suitable to compose channel transport layers of the OTFTs, although the main origin to hinder the charge transport or the intrinsic carrier mobility is still controversial; intra- or intermolecular electron-phonon coupling, polarization effects by the gate-dielectrics, or thermal or extrinsic disorder effects. Here we discuss the interface charge transport in the OTFTs, as investigated by field-induced electron spin resonance (FESR) technique that probes 1/2 spin of carriers induced by gate voltage. It is shown that the FESR technique is extremely useful especially for OTFTs, because of the fairly small spin-orbit interactions in organic materials as well as of the high layer crystallinity and the anisotropy. The following important aspects of the interface charge transport are presented and discussed: (1) Carrier motion in OTFTs can be understood in terms of the multiple trap-and-release (MTR) transport. The analyses of the motional narrowing effects allow us to estimate the average trap residence time that reaches about 1 ns [1]. (2) Carriers are frozen at the respective trap sites at low temperature. The low-temperature spectral analyses allow us to obtain the distribution of trapped carriers over their degree of localization [2, 3]. (3) We also developed a unique technique to investigate the intra- and inter-domain transport in polycrystalline OTFTs by using anisotropic FESR measurements. The method allows us to evaluate the potential barrier height at the domain boundaries within the films [4].[4pt] [1] Phys. Rev. Lett. 100, 126601 (2008).[0pt] [2] Phys. Rev. Lett. 104, 056602 (2010).[0pt] [3] Phys. Rev. B 85.085211 (2012).[0pt] [4] Phys. Rev. B 85.035308 (2012).
Hasegawa, Tatsuo
Simultaneous Electronic and Ionic Charge Transport in Poly(3-hexylthiophene)-b-Poly(ethylene oxide)
NASA Astrophysics Data System (ADS)
Block copolymers can self-assemble to distinct channels, which allows for simultaneous transport of electronic and ionic charge carriers. A potential polymer system is Poly(3-hexylthiophene)-b-Poly(ethylene oxide) (P3HT-b-PEO). P3HT serves as the electronic conducting channel while the PEO serves as the ionic conducting channel. Both conductive blocks are doped to induce simultaneous electronic and ionic conduction. The PEO phase is doped with LiTFSI while the P3HT is doped with F4TCNQ, which generates hole carriers. In addition, we take into account the case where no electronic dopant is added to P3HT phase. The charge transport properties of the material are analyzed via ac impedance spectroscopy and dc polarization techniques. These experiments provide decoupled electronic and ionic transport in P3HT-b-PEO.
Patel, Shrayesh; Javier, Anna; Balsara, Nitash
Carrier transport in high-efficiency ZnO\\/SiO 2\\/Si solar cells
Carrier transport in ZnO\\/SiO2\\/n-Si solar cell has been theoretically analyzed with a consideration that the photo-carrier transport from silicon to ZnO layer through the barrier is dominated by quantum mechanical tunneling process of minority carrier. It was found that the highest efficiency of the cell could be achieved at SiO2 layer thickness of around 20�. The efficiency of the cells
Wilson W. Wenas; Syarif Riyadi
Current-voltage analysis of PCBM:PCDTBT blend to find out charge transport path
NASA Astrophysics Data System (ADS)
Transport path(s) of charge carrier were identified through I-V measurement within the structure of ITO/PEDOT:PSS/PCDTBT:PCBM/TiO/Ca/Ag in which ohmic regime was enrolled in low bias side while space charge limited conduction mechanism governed at high bias side. Moreover, influence of each constitituent parts of the present device on the dc transport properties was investigated by preparing ITO/PEDOT:PSS/PCDTBT/Ca/Ag and ITO/PEDOT:PSS/ PCBM/Ca/Ag structures and repeating the mentioned experimental techniques.
Saatci, A. Evrim; Kavak, Pelin; Parlak, Elif Alt�rk; G�kdemira, F. P?nar; Menda, U. Deneb; �zdemir, Orhan; Kutlu, Kubilay
A molecule to detect and perturb the confinement of charge carriers in quantum dots.
This paper describes unprecedented bathochromic shifts (up to 970 meV) of the optical band gaps of CdS, CdSe, and PbS quantum dots (QDs) upon adsorption of an organic ligand, phenyldithiocarbamate (PTC), and the use of PTC to map the quantum confinement of specific charge carriers within the QDs as a function of their radius. For a given QD material and physical radius, R, the magnitude of the increase in apparent excitonic radius (?R) upon delocalization by PTC directly reflects the degree of quantum confinement of one or both charge carriers. The plots of ?R vs R for CdSe and CdS show that exciton delocalization by PTC occurs specifically through the excitonic hole. Furthermore, the plot for CdSe, which spans a range of R over multiple confinement regimes for the hole, identifies the radius (R?1.9 nm) at which the hole transitions between regimes of strong and intermediate confinement. This demonstration of ligand-induced delocalization of a specific charge carrier is a first step toward eliminating current-limiting resistive interfaces at organic-inorganic junctions within solid-state hybrid devices. Facilitating carrier-specific electronic coupling across heterogeneous interfaces is especially important for nanostructured devices, which comprise a high density of such interfaces. PMID:22032799
Frederick, Matthew T; Amin, Victor A; Cass, Laura C; Weiss, Emily A
Charge transport parameters of the pentathienoacene crystal.
Pentathienoacene, the thiophene equivalent of pentacene, is one of the latest additions to the family of organic crystal semiconductors with a great potential for use in thin film transistors. By using density functional theory and gas-phase ultraviolet photoelectron spectroscopy, we investigate the microscopic charge transport parameters of the pentathienoacene crystal. We find that the valence band exhibits a stronger dispersion than those in the pentacene and rubrene single crystals with marked uniaxial characteristics within the molecular layer due to the presence of one-dimensional pi-stacks; a small hole effective mass is also found along the direction perpendicular to the molecular layers. In the conduction band, strong intermolecular sulfur-sulfur interactions give rise to a significant interstack electronic coupling whereas the intrastack dispersion is greatly reduced. The intramolecular vibronic coupling (reorganization energy) is stronger than that in pentacene but comparable to that in sexithiophene; it is larger for holes than for electrons, as a result of low-frequency modes induced by the sulfur atoms. The polarization energy is large, but its effect on the vibronic coupling remains small. Charge transport is discussed in the framework of both band and hopping models. PMID:17915865
Kim, Eung-Gun; Coropceanu, Veaceslav; Gruhn, Nadine E; Sanchez-Carrera, Roel S; Snoeberger, Robert; Matzger, Adam J; Br�das, Jean-Luc
Preface: Charge transport in nanoscale junctions
NASA Astrophysics Data System (ADS)
Understanding the fundamentals of nanoscale charge transfer is pivotal for designing future nano-electronic devices. Such devices could be based on individual or groups of molecular bridges, nanotubes, nanoparticles, biomolecules and other 'active' components, mimicking wire, diode and transistor functions. These have operated in various environments including vacuum, air and condensed matter, in two- or three-electrode configurations, at ultra-low and room temperatures. Interest in charge transport in ultra-small device components has a long history and can be dated back to Aviram and Ratner's letter in 1974 (Chem. Phys. Lett. 29 277-83). So why is there a necessity for a special issue on this subject? The area has reached some degree of maturity, and even subtle geometric effects in the nanojunction and noise features can now be resolved and rationalized based on existing theoretical concepts. One purpose of this special issue is thus to showcase various aspects of nanoscale and single-molecule charge transport from experimental and theoretical perspectives. The main principles have 'crystallized' in our minds, but there is still a long way to go before true single-molecule electronics can be implemented. Major obstacles include the stability of electronic nanojunctions, reliable operation at room temperature, speed of operation and, last but not least, integration into large networks. A gradual transition from traditional silicon-based electronics to devices involving a single (or a few) molecule(s) therefore appears to be more viable from technologic and economic perspectives than a 'quantum leap'. As research in this area progresses, new applications emerge, e.g. with a view to characterizing interfacial charge transfer at the single-molecule level in general. For example, electrochemical experiments with individual enzyme molecules demonstrate that catalytic processes can be studied with nanometre resolution, offering a route towards optimizing biosensors at the molecular level. Nanoscale charge transport experiments in ionic liquids extend the field to high temperatures and to systems with intriguing interfacial potential distributions. Other directions may include dye-sensitized solar cells, new sensor applications and diagnostic tools for the study of surface-bound single molecules. Another motivation for this special issue is thus to highlight activities across different research communities with nanoscale charge transport as a common denominator. This special issue gathers 27 articles by scientists from the United States, Germany, the UK, Denmark, Russia, France, Israel, Canada, Australia, Sweden, Switzerland, the Netherlands, Belgium and Singapore; it gives us a flavour of the current state-of-the-art of this diverse research area. While based on contributions from many renowned groups and institutions, it obviously cannot claim to represent all groups active in this very broad area. Moreover, a number of world-leading groups were unable to take part in this project within the allocated time limit. Nevertheless, we regard the current selection of papers to be representative enough for the reader to draw their own conclusions about the current status of the field. Each paper is original and has its own merit, as all papers in Journal of Physics: Condensed Matter special issues are subjected to the same scrutiny as regular contributions. The Guest Editors have deliberately not defined the specific subjects covered in this issue. These came out logically from the development of this area, for example: 'Traditional' solid state nanojunctions based on adsorbed layers, oxide films or nanowires sandwiched between two electrodes: effects of molecular structure (aromaticity, anchoring groups), symmetry, orientation, dynamics (noise patterns) and current-induced heating. Various 'physical effects': inelastic tunnelling and Coulomb blockade, polaron effects, switching modes, and negative differential resistance; the role of many particle excitations, new surface states in semiconductor electrodes, various mechanisms for
Albrecht, Tim; Kornyshev, Alexei; Bj�rnholm, Thomas
Charge Transport Anisotropy in n-Type Disk-Shaped Triphenylene-Tris(aroyleneimidazole)s
NASA Astrophysics Data System (ADS)
Two novel n-type disk-shaped molecules containing a triphenylene core and three fused naphthaleneimide imidazole or peryleneimide imidazole ``arms'' are synthesized and characterized. Their optical and electronic properties are consistent with the pi-extended structural feature of the aromatic cores. The n-type charge carrier mobilities of these molecules are evaluated by both field effect transistors and space-charge limited-current measurements, which show drastically different mobility anisotropy. A strong correlation between film morphology and the charge transport behavior is established by X-ray scattering and atomic force microscopic analyses.
Alvarez, Steven; Zhang, Yue; Hanifi, David; Antonio, Francisco; Pun, Andrew; Klivansky, Liana; Hexemer, Alexander; Ma, Biwu; Liu, Yi
Ultrafast vibrational spectroscopy of charge-carrier dynamics in organic photovoltaic materials.
Ultrafast vibrational spectroscopy is used to examine the dynamics of interfacial electron transfer, free-carrier formation, and bimolecular charge recombination and trapping in an organic photovoltaic material. The carbonyl (C[double bond, length as m-dash]O) stretch of the functionalized fullerene, PCBM, is probed as a local vibrational reporter of the dynamics in a blend with a conjugated polymer, CN-MEH-PPV. Ultrafast interfacial electron transfer from CN-MEH-PPV to PCBM occurs on time scales ranging from less than 100 fs to 1 ps. PCBM molecules at interfaces with the polymer have carbonyl vibrations that are higher in frequency compared to the ensemble. The frequency variation results in part from a vibrational Stark shift arising from an interfacial dipole formed by spontaneous charge transfer from the polymer to PCBM. The Stark shift provides a means to observe directly the formation of free carriers through the spectral evolution of the carbonyl stretch. Free carrier formation occurs surprisingly quickly on the 1-10 ps time scale, suggesting that the charges experience a smaller effective Coulombic binding energy than expected. The interfacial dipole decreases the Coulombic binding energy because the negative pole of the dipole repels electrons at the PCBM domain interface. Following free-carrier formation, electrons diffuse within the material and become trapped on the microsecond time scale resulting in the formation of a distinct peak in the vibrational spectra. The time scale of charge trapping corresponds to the carrier lifetime of similar PPV-based polymer blends that have been reported in the literature on the basis of transient photocurrent measurements. PMID:19421513
Pensack, Ryan D; Banyas, Kyle M; Barbour, Larry W; Hegadorn, Maureen; Asbury, John B
Strong localization of the charge carriers in CdSe nanostructural films
NASA Astrophysics Data System (ADS)
Cadmium selenide nanoparticle films were deposited on usual glass substrate by chemical bath deposition method. Temperature dependence of dc conductivity of the present samples was studied. In the nanocrystalline materials due to small size of grains and confined charge carriers, the electronic states near the Fermi level are localized. When states are localized, the conduction occurs by hopping of carriers between the occupied and unoccupied localized states. Variable range hopping was identified as a predominant conduction mechanism and occurs above room temperature. The density of localized states near the Fermi level was observed to increase with increase of average grain size in the film.
Ghobadi, Nader; Moradian, Rostam
Structures of yeast mitochondrial ADP/ATP carriers support a domain-based alternating-access transport mechanism.
The mitochondrial ADP/ATP carrier imports ADP from the cytosol and exports ATP from the mitochondrial matrix. The carrier cycles by an unresolved mechanism between the cytoplasmic state, in which the carrier accepts ADP from the cytoplasm, and the matrix state, in which it accepts ATP from the mitochondrial matrix. Here we present the structures of the yeast ADP/ATP carriers Aac2p and Aac3p in the cytoplasmic state. The carriers have three domains and are closed at the matrix side by three interdomain salt-bridge interactions, one of which is braced by a glutamine residue. Glutamine braces are conserved in mitochondrial carriers and contribute to an energy barrier, preventing the conversion to the matrix state unless substrate binding occurs. At the cytoplasmic side a second salt-bridge network forms during the transport cycle, as demonstrated by functional analysis of mutants with charge-reversed networks. Analyses of the domain structures and properties of the interdomain interfaces indicate that interconversion between states involves movement of the even-numbered ?-helices across the surfaces of the odd-numbered ?-helices by rotation of the domains. The odd-numbered ?-helices have an L-shape, with proline or serine residues at the kinks, which functions as a lever-arm, coupling the substrate-induced disruption of the matrix network to the formation of the cytoplasmic network. The simultaneous movement of three domains around a central translocation pathway constitutes a unique mechanism among transport proteins. These findings provide a structural description of transport by mitochondrial carrier proteins, consistent with an alternating-access mechanism. PMID:24474793
Ruprecht, Jonathan J; Hellawell, Alex M; Harding, Marilyn; Crichton, Paul G; McCoy, Airlie J; Kunji, Edmund R S
Electrode configuration and signal subtraction technique for single polarity charge carrier sensing in ionization detectors
An ionization detector electrode and signal subtraction apparatus and method provides at least one first conductive trace formed onto the first surface of an ionization detector. The first surface opposes a second surface of the ionization detector. At least one second conductive trace is also formed on the first surface of the ionization detector in a substantially interlaced and symmetrical pattern with the at least one first conductive trace. Both of the traces are held at a voltage potential of a first polarity type. By forming the traces in a substantially interlaced and symmetric pattern, signals generated by a charge carrier are substantially of equal strength with respect to both of the traces. The only significant difference in measured signal strength occurs when the charge carrier moves to within close proximity of the traces and is received at the collecting trace. The measured signals are then subtracted and compared to quantitatively measure the magnitude of the charge and to determine the position at which the charge carrier originated within the ionization detector.
Luke, Paul (Castro Valley, CA) [Castro Valley, CA
High charge carrier mobility and efficient charge separation in highly soluble perylenetetracarboxyl-diimides.
In this communication we report on the synthesis and charge mobility of highly soluble perylenebisimid derivatives. We show that introduction of alkylester side chains results in compounds combining a high solubility with charge mobilities up to 0.22 cm(2) V(-1) s(-1). These materials are therefore interesting as an electron acceptor for solution-processed organic photovoltaics. PMID:24706092
G�nba?, D Deniz; Xue, Chenming; Patwardhan, Sameer; Fravventura, Maria C; Zhang, Hao; Jager, Wolter F; Sudh�lter, Ernst J R; Siebbeles, Laurens D A; Savenije, Tom J; Jin, Shi; Grozema, Ferdinand C
Effects of charge carrier concentration in hybrid conjugated polymer/oxide photovoltaic devices
NASA Astrophysics Data System (ADS)
Organic photovoltaics (OPV) represent an attractive route towards inexpensive, lightweight, and abundant renewable energy. The principal criticisms of OPV are low power conversion efficiency and unstable materials resulting in short device lifetimes. Hybrid OPV (h-OPV) devices with ZnO functioning either as the electron acceptor in the heterojunction, or as an electron transport layer in a polymer/fullerene based heterojunction, present useful device structures for investigating the functional mechanisms within OPV devices and a possible pathway towards air-stable high efficiency devices. Such use allows the vast knowledge surrounding oxide nanostructure morphology, band position, and carrier concentration control to be used in designing bulk-heterojunction OPV devices. The work presented in this thesis explores the effects of carrier concentration modulation in the polymer and/or oxide layers of these devices. Exposure to air is known to induce chemical defects in polymer semiconductors, which act as dopants in OPV devices. This increase in doping density can be used to improve OPV devices, however the low work-function metallic electrodes are often highly air sensitive. Using a silver back electrode and a ZnO interlayer at the transparent front contact in a polymer-based bulk heterojunction device allows for fabrication and testing in air. Relatively efficient devices are fabricated in this manner, but the devices show a characteristic aging time that indicates that air is a requirement to function as a quality diode. Air exposure may be effecting any of the layers in the device, but evidence is presented that shows the increased doping density in the polymer is largely responsible for the change in device quality over this time period. When oxides are used as the electron acceptor material in the device heterojunction, the carrier concentration in both the oxide and the polymer determine the strength of the electric field at the junction. Oxygen related doping of the polymer is a requisite for functional devices, but intentional doping of the oxide provides an additional degree of control over interfacial electric fields. By using planar hybrid heterojunctions, the utility of this effect is shown by increasing the driving force for charge separation. Interfacial barrier layers are required on highly doped ZnO to prevent recombination and preserve high fill factors. The measurable carrier concentration in the depletion region of polymer and polymer-fullerene blend films is shown to be significantly larger under illumination than in the dark. This effect is not related to breaking of the conjugated bonds in the polymer, as is the device aging phenomenon, but stems from low mobility of photo-generated electrons. The depletion width and maximum electric field in devices are influenced by the presence of an increased effective doping density under illumination.
White, Matthew Schuette
Atomic-Scale Charge Transport at the Si(001) Surface.
National Technical Information Service (NTIS)
Scanning tunneling microscopy measurements of local surface photovoltage of the Si(001) surface reveal the existence of local charging produced by the tunneling current. Atomic-scale variations in the charge transport arise at characteristic defects, step...
D. G. Cahill R. J. Hamers
Charge Carrier Dynamics of Quantum Confined Semiconductor Nanoparticles Analyzed via Transient Absorption Spectroscopy
NASA Astrophysics Data System (ADS)
Semiconductor nanoparticles are tiny crystalline structures (typically range from 1 - 100 nm) whose shape in many cases can be dictated through tailored chemical synthesis with atomic scale precision. The small size of these nanoparticles often results in quantum confinement (spatial confinement of wave functions), which imparts the ability to manipulate band-gap energies thus allowing them to be optimally engineered for different applications (i.e., photovoltaics, photocatalysis, imaging). However, charge carriers excited within these nanoparticles are often involved in many different processes: trapping, trap migration, Auger recombination, non-radiative relaxation, radiative relaxation, oxidation / reduction, or multiple exciton generation. Broadband ultrafast transient absorption laser spectroscopy is used to spectrally resolve the fate of excited charge carriers in both wavelength and time, providing insight as to what synthetic developments or operating conditions will be necessary to optimize their efficiency for certain applications. This thesis outlines the effort of resolving the dynamics of excited charge carriers for several Cd and Si based nanoparticle systems using this experimental technique. The thesis is organized into five chapters and two appendices as indicated below. Chapter 1 provides a brief introduction to the photophysics of semiconductor nanoparticles. It begins by defining what nanoparticles, semiconductors, charge carriers, and quantum confinement are. From there it details how the study of charge carrier dynamics within nanoparticles can lead to increased efficiency in applications such as photocatalysis. Finally, the experimental methodology associated with ultrafast transient absorption spectroscopy is introduced and its power in mapping charge carrier dynamics is established. Chapter 2 (JPCC, 19647, 2011) introduces the first of the studied samples: water-solubilized 2D CdSe nanoribbons (NRs), which were synthesized in the Osterloh laboratory (UCD). The measured signals were decomposed into the constituent dynamics of three transient populations: hot tightly bound excitons, relaxed tightly bound excitons, and separated trapped carriers (holes and electrons). The influenes of three external factors affecting the observed dynamics were explored: (1) excitation wavelength, (2) excitation fluence, and (3) presence of the hole scavenger HS -. Both higher-energy excitation photons and higher-intensity excitation induce slower relaxation of charge carriers to the band edge due to the need to dissipate excess excitation energy. Nonlinear decay kinetics of the relaxed exciton population is observed and demonstrated to arise from bimolecular trapping of excitons with low-density trap sites located at CdSe NR surface sites instead of the commonly resolved multiparticle Auger recombination mechanism. This is supported by the observed linear excitation-fluence dependence of the trapped-carrier population that is n umerically simulated and found to deviate from the excitation fluence dependence expected of Auger recombination kinetics. Introducing hole scavenging HS- has a negligible effect on the exciton kinetics, including migration and dissociation, and instead passivates surface trap states to induce the rapid elimination of holes after exciton dissociation. This increases the lifetime of the reactive electron population and increases measured photocatalytic H2 generation activity. A broad (200 nm) and persistent (20 ps) stimulated emission observed in the tightly bound excitons suggests their potential use as broadband microlasers. In chapter 3 (JPCL, 2688, 2011), the photocatalytic H2O splitting activities of CdSe and CdSe/CdS core/shell quantum dots, which were also synthesized in the Osterloh laboratory (UCD) are contrasted. CdSe/CdS core/shell quantum dots constructed from 4.0 nm CdSe quantum dots are shown to be strongly active for visible-light-driven photocatalytic H2 evolution in 0.1M Na 2S/Na2SO3 solution with a turnover number of 9.94 after 5 h at 103.9 ?mol/h. CdSe quantum dots themselv
Thibert, Arthur Joseph, III
Carrier trapping and scattering in amorphous organic hole transporter
NASA Astrophysics Data System (ADS)
The effects of dopants on the hole transporting properties of N,N'-diphenyl-N,N'-bis(1-naphthyl)(1,1'-biphenyl)-4,4'diamine (NPB) have been studied by time of flight. Five dopants: copper phthalocyanine (CuPc), 4-(dicyanomethylene)-2-methyl-6-(p-dimethylaminostyrle)-4H-pyran (DCM1), 4-dicyanomethylene-2-methyl-6-[2-(2,3,6,7-tetra-hydro-1H,5H-benzo[ij] quinolizin-8-yl)vinyl]-4H-pyran (DCM2), 2-(4-biphenyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (tBu-PBD), and 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) are used in this study. The dopant molecules behave like hole traps or scatterers. Their detailed behaviors are determined by their highest occupied molecular orbital relative to that of NPB. Generally, traps are found to induce significant reduction in hole mobility while there is a slight reduction for scattering. Two different underlying charge transport mechanisms are proposed.
Tsung, K. K.; So, S. K.
Charge carrier mobility in organic molecular materials probed by electromagnetic waves.
Charge carrier mobility is an essential parameter providing control over the performance of semiconductor devices fabricated using a variety of organic molecular materials. Recent design strategies toward molecular materials have been directed at the substitution of amorphous silicon-based semiconductors; accordingly, numerous measurement techniques have been designed and developed to probe the electronic conducting nature of organic materials bearing extremely wide structural variations in comparison with inorganic and/or metal-oxide semiconductor materials. The present perspective highlights the evaluation methodologies of charge carrier mobility in organic materials, as well as the merits and demerits of techniques examining the feasibility of organic molecules, crystals, and supramolecular assemblies in semiconductor applications. Beyond the simple substitution of amorphous silicon, we have attempted to address in this perspective the systematic use of measurement techniques for future development of organic molecular semiconductors. PMID:24776977
Seki, Shu; Saeki, Akinori; Sakurai, Tsuneaki; Sakamaki, Daisuke
Printing technique dependent charge carrier velocity distribution in organic thin film transistors
NASA Astrophysics Data System (ADS)
In this study we investigated the influence of the deposition technique on the surface topology and the resulting device performance in organic thin film transistors (OTFT). We varied the parameters of flexographic and gravure printing for the organic semiconductor (OSC) and did multilayer gravure printing for the dielectric, respectively. Therefore, we manufactured transistors in bottom contact top gate architecture and compared them to spin coated samples. As investigation tool for OTFTs, the charge carrier velocity distribution is correlated with the optical characteristics of the printed layers. We found a dependency of the printing technique on the surface topology of the semiconductor and, due to the resulting increase of the channel length, a broadening of the charge carrier velocity distribution. For the dielectric we found a dependency on the layer thickness which seems to be independent from the deposition technique.
Ganz, Simone; Pankalla, Sebastian; Sauer, Hans Martin; Glesner, Manfred; Doersam, Edgar
Charge transport scaling in turbulent electroconvection
NASA Astrophysics Data System (ADS)
We describe a local-power-law scaling theory for the mean dimensionless electric current Nu in turbulent electroconvection. The experimental system consists of a weakly conducting, submicron-thick liquid-crystal film supported in the annulus between concentric circular electrodes. It is driven into electroconvection by an applied voltage between its inner and outer edges. At sufficiently large voltage differences, the flow is unsteady and electric charge is turbulently transported between the electrodes. Our theoretical development, which closely parallels the Grossmann-Lohse model for turbulent thermal convection, predicts the local-power law N?F(?)R?P? . R and P are dimensionless numbers that are similar to the Rayleigh and Prandtl numbers of thermal convection, respectively. The dimensionless function F(?) , which is specified by the model, describes the dependence of Nu on the aspect ratio ? . We find that measurements of Nu are consistent with the theoretical model.
Tsai, Peichun; Daya, Zahir A.; Morris, Stephen W.
The non-random walk of chiral magnetic charge carriers in artificial spin ice
The flow of magnetic charge carriers (dubbed magnetic monopoles) through frustrated spin ice lattices, governed simply by Coulombic forces, represents a new direction in electromagnetism. Artificial spin ice nanoarrays realise this effect at room temperature, where the magnetic charge is carried by domain walls. Control of domain wall path is one important element of utilizing this new medium. By imaging the transit of domain walls across different connected 2D honeycomb structures we contribute an important aspect which will enable that control to be realized. Although apparently equivalent paths are presented to a domain wall as it approaches a Y-shaped vertex from a bar parallel to the field, we observe a stark non-random path distribution, which we attribute to the chirality of the magnetic charges. These observations are supported by detailed statistical modelling and micromagnetic simulations. The identification of chiral control to magnetic charge path selectivity invites analogy with spintronics.
Zeissler, K.; Walton, S. K.; Ladak, S.; Read, D. E.; Tyliszczak, T.; Cohen, L. F.; Branford, W. R.
Charging and spin-polarization effects in InAs quantum dots under bipolar carrier injection
NASA Astrophysics Data System (ADS)
An ultrafast pump-probe method based on differing polarization properties of neutral and charged excitons in semiconductor quantum dots (QDs) is employed to study carrier dynamics in InGaAs QDs grown in nominally undoped, modulation doped and p-i-n structures. We find that at low temperature even in the nominally undoped samples there are large fractions of charged dots. It is also demonstrated that for bipolar electrical injection there is a high probability of the independent capture of electrons or holes into the dots, resulting in dot charging. Voltage-control of the charged exciton population, created via a combination of electrical and optical excitation, which exhibits a long lived spin-polarization (or spin-memory) is demonstrated.
Tartakovskii, A. I.; Savelyev, A. V.; Makhonin, M. N.; Skolnick, M. S.; Mowbray, D. J.; Maximov, M. V.; Ustinov, V. M.; Seisyan, R. P.
Detection of Negative Charge Carriers in Superfluid Helium Droplets: The Metastable Anions He*� and He2*�
Helium droplets provide the possibility to study phenomena at the very low temperatures at which quantum mechanical effects are more pronounced and fewer quantum states have significant occupation probabilities. Understanding the migration of either positive or negative charges in liquid helium is essential to comprehend charge-induced processes in molecular systems embedded in helium droplets. Here, we report the resonant formation of excited metastable atomic and molecular helium anions in superfluid helium droplets upon electron impact. Although the molecular anion is heliophobic and migrates toward the surface of the helium droplet, the excited metastable atomic helium anion is bound within the helium droplet and exhibits high mobility. The atomic anion is shown to be responsible for the formation of molecular dopant anions upon charge transfer and thus, we clarify the nature of the previously unidentified fast exotic negative charge carrier found in bulk liquid helium.
The non-random walk of chiral magnetic charge carriers in artificial spin ice.
The flow of magnetic charge carriers (dubbed magnetic monopoles) through frustrated spin ice lattices, governed simply by Coulombic forces, represents a new direction in electromagnetism. Artificial spin ice nanoarrays realise this effect at room temperature, where the magnetic charge is carried by domain walls. Control of domain wall path is one important element of utilizing this new medium. By imaging the transit of domain walls across different connected 2D honeycomb structures we contribute an important aspect which will enable that control to be realized. Although apparently equivalent paths are presented to a domain wall as it approaches a Y-shaped vertex from a bar parallel to the field, we observe a stark non-random path distribution, which we attribute to the chirality of the magnetic charges. These observations are supported by detailed statistical modelling and micromagnetic simulations. The identification of chiral control to magnetic charge path selectivity invites analogy with spintronics. PMID:23409243
Zeissler, K; Walton, S K; Ladak, S; Read, D E; Tyliszczak, T; Cohen, L F; Branford, W R
Charge transport gap in graphene antidot lattices
NASA Astrophysics Data System (ADS)
Graphene antidot lattices (GALs) offer an attractive approach to band-gap engineering in graphene. Theoretical studies indicate that the size of the opened gap is sensitive to the shape, size, and architecture of the nanoholes introduced into the graphene sheet. We have investigated the temperature-dependent electrical conductivity of GALs comprising 50-nm-diameter nanoholes with a pitch of 80, 100, and 200 nm, respectively. The data reveal the presence of localized states within a transport gap, whose interactions lead to a soft Coulomb gap and associated Efros-Shklovskii variable range hopping (ES-VRH). This conduction type is preserved upon application of magnetic fields up to 1 Tesla, above which a transition to Mott variable range hopping occurs. Such a crossover can alternatively be introduced at zero magnetic fields by increasing either the nanohole spacing or the gate-controlled carrier concentration. Furthermore, at intermediate magnetic fields, the hopping exponent assumes a value of 2/3, as predicted by percolation theory for ES-VRH under this condition.
Giesbers, A. J. M.; Peters, E. C.; Burghard, M.; Kern, K.
Bound and Scattering States of Itinerant Charge Carriers in Complex Magnetic Materials
NASA Astrophysics Data System (ADS)
The concept of magnetic polaron is analyzed and developed to elucidate the nature of itinerant charge carrier states in magnetic semiconductors and similar complex magnetic materials. By contrasting the scattering and bound states of carriers within the s-d exchange model, the nature of bound states at finite temperatures is clarified. The free magnetic polaron at certain conditions is realized as a bound state of the carrier (electron or hole) with the spin wave. Quite generally, a self-consistent theory of a magnetic polaron is formulated within a nonperturbative many-body approach, the Irreducible Green Functions (IGF) method which is used to describe the quasiparticle many-body dynamics at finite temperatures. Within the above many-body approach we elaborate a self-consistent picture of dynamic behavior of two interacting subsystems, the localized spins and the itinerant charge carriers. In particular, we show that the relevant generalized mean fields emerges naturally within our formalism. At the same time, the correct separation of elastic scattering corrections permits one to consider the damping effects (inelastic scattering corrections) in the unified and coherent fashion. The damping of magnetic polaron state, which is quite different from the damping of the scattering states, finds a natural interpretation within the present self-consistent scheme.
Kuzemsky, A. L.
Characterization of the charge transport and electrical properties in solution-processed semiconducting polymers
NASA Astrophysics Data System (ADS)
The conventional charge transport models based on density- and field-dependent mobility, only having a non-Arrhenius temperature dependence, cannot give good current-voltage characteristics of poly (2-methoxy-5-(2'-ethylhexyloxy)-p-phenylene vinylene) (MEH-PPV) hole-only devices. In this paper, we demonstrate that the current-voltage characteristics can give a good unified description of the temperature, carrier density and electric field dependence of mobility based on both the Arrhenius temperature dependence and the non-Arrhenius temperature dependence. Furthermore, we perform a systematic study of charge transport and electrical properties for MEH-PPV. It is shown that the boundary carrier density has an important effect on the current-voltage characteristics. Too large or too small values of boundary carrier density will lead to incorrect current-voltage characteristics. The numerically calculated carrier density is a decreasing function of the distance to the interface, and the numerically calculated electric field is an increasing function of the distance. Both the maximum of carrier density and the minimum of electric field appear near the interface.
Wang, LiGuo; Zhang, HuaiWu; Tang, XiaoLi; Li, YuanXun; Zhong, ZhiYong
Liquid-crystalline semiconducting polymers with high charge-carrier mobility
Organic semiconductors that can be fabricated by simple processing techniques and possess excellent electrical performance, are key requirements in the progress of organic electronics. Both high semiconductor charge-carrier mobility, optimized through understanding and control of the semiconductor microstructure, and stability of the semiconductor to ambient electrochemical oxidative processes are required. We report on new semiconducting liquid-crystalline thieno[3,2-b ]thiophene polymers, the
Iain McCulloch; Martin Heeney; Clare Bailey; Kristijonas Genevicius; Iain MacDonald; Maxim Shkunov; David Sparrowe; Steve Tierney; Robert Wagner; Weimin Zhang; Michael L. Chabinyc; R. Joseph Kline; Michael D. McGehee; Michael F. Toney
Migration of excited charge carriers in arrays of phosphorus-doped silicon nanocrystals
The rate of tunnel migration of excited charge carriers (electrons and holes) in the array of silicon nanocrystals doped with phosphorus is calculated. It is shown that, starting from certain phosphorus concentrations dependent on the relation between the dimensions of the emitting and accepting nanocrystals, the rate of tunneling of electrons sharply decreases (by several orders of magnitude) and becomes lower than the rate of interband radiative recombination
Belyakov, V. A., E-mail: email@example.com; Konakov, A. A.; Burdov, V. A. [Nizhni Novgorod State University (Russian Federation)
Ultrafast charge carrier dynamics and photoelectrochemical properties of ZnO nanowires decorated with Au nanoparticles
This study was designed to examine the possible photosensitization effect of zinc oxide (ZnO) nanowires (NWs) by Au nanoparticles (AuNPs) by directly monitoring the charge carrier lifetime in AuNP-decorated ZnO NWs. ZnO-Au nanocomposite structures showed reduced photocurrent compared to pristine ZnO NWs due to the combined effect of ZnO etching during the AuNPs growth and competitive absorption\\/scattering effects from AuNPs
Jason K. Cooper; Yichuan Ling; Yat Li; Jin Z. Zhang
Activationless charge transport across 4.5 to 22 nm in molecular electronic junctions.
In this work, we bridge the gap between short-range tunneling in molecular junctions and activated hopping in bulk organic films, and greatly extend the distance range of charge transport in molecular electronic devices. Three distinct transport mechanisms were observed for 4.5-22-nm-thick oligo(thiophene) layers between carbon contacts, with tunneling operative when d?< 8 nm, activated hopping when d > 16 nm for high temperatures and low bias, and a third mechanism consistent with field-induced ionization of highest occupied molecular orbitals or interface states to generate charge carriers when d = 8-22 nm. Transport in the 8-22-nm range is weakly temperature dependent, with a field-dependent activation barrier that becomes negligible at moderate bias. We thus report here a unique, activationless transport mechanism, operative over 8-22-nm distances without involving hopping, which severely limits carrier mobility and device lifetime in organic semiconductors. Charge transport in molecular electronic junctions can thus be effective for transport distances significantly greater than the 1-5 nm associated with quantum-mechanical tunneling. PMID:23509271
Yan, Haijun; Bergren, Adam Johan; McCreery, Richard; Della Rocca, Maria Luisa; Martin, Pascal; Lafarge, Philippe; Lacroix, Jean Christophe
Efficiency of extrinsic and intrinsic charge-carrier photogeneration processes obtained from the steady-state photocurrent action spectra of poly( p-phenylene vinylene) derivatives
NASA Astrophysics Data System (ADS)
The efficiency of the charge-carrier photogeneration processes in poly(2,5-bis(3',7'-dimethyl-octyloxy)-1,4-phenylene vinylene) (OC1OC10-PPV) has been analyzed by the spectral response of the photocurrent of devices in ITO/polymer/Al structures. The symbatic response of the photocurrent action spectra of the OC1OC10-PPV devices, obtained for light-excitation through the ITO electrode and for forward bias, has been fitted using a phenomenological model which considers that the predominant transport mechanism under external applied electric field is the drift of photogenerated charge-carriers, neglecting charge-carrier diffusion. The proposed model takes into account that charge-carrier photogeneration occurs via intermediate stages of bounded pairs (excitonic states), followed by dissociation processes. Such processes result in two different contributions to the photoconductivity: The first one, associated to direct creation of unbound polaron pairs due to intrinsic photoionization; and the second one is associated to secondary processes like extrinsic photoinjection at the metallic electrodes. The results obtained from the model have shown that the intrinsic component of the photoconductivity at higher excitation energies has a considerably higher efficiency than the extrinsic one, suggesting a dependence on the photon energy for the efficiency of the photogeneration process.
Cazati, T.; Santos, L. F.; Reis, F. T.; Faria, R. M.
Theoretical characterization of charge transport in one-dimensional collinear arrays of organic conjugated molecules.
A great deal of interest has recently focused on host-guest systems consisting of one-dimensional collinear arrays of conjugated molecules encapsulated in the channels of organic or inorganic matrices. Such architectures allow for controlled charge and energy migration processes between the interacting guest molecules and are thus attractive in the field of organic electronics. In this context, we characterize here at a quantum-chemical level the molecular parameters governing charge transport in the hopping regime in 1D arrays built with different types of molecules. We investigate the influence of several parameters (such as the symmetry of the molecule, the presence of terminal substituents, and the molecular size) and define on that basis the molecular features required to maximize the charge carrier mobility within the channels. In particular, we demonstrate that a strong localization of the molecular orbitals in push-pull compounds is generally detrimental to the charge transport properties. PMID:20217887
Viani, Lucas; Olivier, Yoann; Athanasopoulos, Stavros; da Silva Filho, Demetrio A; Hulliger, J�rg; Br�das, Jean-Luc; Gierschner, Johannes; Cornil, J�r�me
Nanoscale quantification of charge injection and transportation process in Si-nanocrystal based sandwiched structure.
Si nanocrystals are formed by using KrF pulsed laser crystallization of an amorphous SiC/ultrathin amorphous Si/amorphous SiC sandwiched structure. Electrons and holes are injected into Si nanocrystals via a biased conductive AFM tip and the carrier decay and transportation behaviours at the nanoscale are studied by joint characterization techniques of Kelvin probe force microscopy (KPFM) and conductive atomic force microscopy (CAFM). Quantification of the surface charge density is realized by solving the Poisson equation based on KPFM measurements. Besides, the asymmetric barrier height for electrons and holes is considered to play a dominant role in controlling the charge retention and transportation characteristics. The methodology developed in this work is promising for studying the charge injection and transportation process in other materials and structures at the nanoscale. PMID:23989206
Xu, Jie; Xu, Jun; Zhang, Pengzhan; Li, Wei; Chen, Kunji
Simultaneous Electronic and Ionic Charge Transport in Poly(3-hexylthiophene)-b-Poly(ethylene oxide)
Block copolymers can self-assemble to distinct channels, which allows for simultaneous transport of electronic and ionic charge carriers. A potential polymer system is Poly(3-hexylthiophene)-b-Poly(ethylene oxide) (P3HT-b-PEO). P3HT serves as the electronic conducting channel while the PEO serves as the ionic conducting channel. Both conductive blocks are doped to induce simultaneous electronic and ionic conduction. The PEO phase is doped with
Shrayesh Patel; Anna Javier; Nitash Balsara
Temperature and Magnetic Field Effects on the Transport Controlled Charge State of a Single Quantum Dot
Individual InAs/GaAs quantum dots are studied by micro-photoluminescence. By varying the strength of an applied external magnetic field and/or the temperature, it is demonstrated that the charge state of a single quantum dot can be tuned. This tuning effect is shown to be related to the in-plane electron and hole transport, prior to capture into the quantum dot, since the photo-excited carriers are primarily generated in the barrier.
Polymer/Polymer Heterojunctions for Ambipolar Charge Transport in Organic Electronics
NASA Astrophysics Data System (ADS)
Understanding of charge transport in polymer semiconductor heterojunctions is of basic interest in developing high-performance organic optoelectronic devices based on multicomponent polymer semiconductors. We report ambipolar charge transport in thin films of layered heterojunctions and bulk heterojunctions of solution-processable unipolar polymer semiconductors. Selective solubility of the polymer semiconductors, poly(thiazolothiazole)s and ladder-type poly(benzobisimidazo-benzophenanthroline), in organic and acidic solvents enabled the sequential deposition or blending of the polymer semiconductors. Charge carrier mobilities of 0.001-0.01 cm2/Vs were observed for both electrons and holes in the polymer/polymer heterojunction field-effect transistors. Thin film deposition and processing with various solvents are effective to improve charge-carrier mobilities by a factor of 100-1000. We have investigated the effects of the processing methods on morphology, and photophysical and charge transport properties of the polymer semiconductor heterojunctions. Integrated circuits and solar cells based on the polymer semiconductor heterojunctions are also demonstrated.
Kim, Felix; Subramaniyan, Selvam; Jenekhe, Samson
Carrier transport and electronic structure in amorphous oxide semiconductor, a-InGaZnO 4
Carrier transport properties in amorphous oxide semiconductor InGaZnO4 (a-IGZO) thin films were investigated in detail using temperature dependence of Hall measurements. It was found that Hall mobility increased distinctly as carrier concentration increased. Unlikely conventional amorphous semiconductors such as a-Si\\/H, definite normal Hall voltage signals were observed on the films with carrier concentrations (Ne)>1016 cm?3, and Hall mobilities as large
Akihiro Takagi; Kenji Nomura; Hiromichi Ohta; Hiroshi Yanagi; Toshio Kamiya; Masahiro Hirano; Hideo Hosono
14 CFR 234.13 - Reports by air carriers on incidents involving animals during air transport.
Code of Federal Regulations, 2011 CFR
...2014-01-01 2014-01-01 false Reports by air carriers on incidents involving animals during air transport. 234.13 Section 234.13 Aeronautics...PERFORMANCE REPORTS § 234.13 Reports by air carriers on incidents involving animals...
Subsurface Imaging and Sensing of Charge Carrier Movements in the Earth�s Crust
NASA Astrophysics Data System (ADS)
The DUSEL facility will enable unique opportunities for field experiments that would otherwise not be possible at surface facilities (Lesko, K.T., TAUP, 2007) and support a host of undergraduate and graduate educational projects. In this presentation, some of the proposed geophysics experiments will be described as part of the subsurface Imaging and Sensing (SIS) project to study charge carrier movement in crustal rock as a function of various perturbations. The electric conductivity of the Earth�s crust is dominated by positive hole charge carriers, e.g. mobile electron vacancy defects (EVD) in the oxygen anion sublattice of minerals that make up the bulk of crustal rocks. We are interested in (i) coupling of fundamental processes linked to the activation of additional EVDs in rocks deep in the crust subjected to tectonic stresses and the outflow of these charge carriers into the surrounding rocks, (ii) their manifestation across the electromagnetic spectrum and other measuands, (iii) induced forces that arise when these charge carriers are subjected to the episodic or daily magnetic field variations coming from geomagnetic storms or from the ionospheric current vortex, and (iv) in the movement of positive holes in the shallow crust when a thunderstorm system drifts overhead, dragging along a charge cloud in the ground. We propose to conduct active rock stressing experiments in situ using expanding grout technique (performing electrical, electromagnetic, and VolksMeter tilt measurements) and to monitor the electric and magnetic field variations penetrating into the Earth�s crust. Additionally optical phenomena will be investigated (anomalous infrared signatures, visible light arising from atomic oxygen and corona discharge, and infrared imaging). If budget permits, measurement of changes of acoustic velocity, evolution of chemical species (H2, O*, Rn, etc) and radar reflectivity as a function of stresses will also be attempted. We propose to study the charge distribution on the inside walls of cavities or along drifts and how the local electric field is modified when a geomagnetic storm passes overhead or lightning strikes nearby. Detection of signals with this passive experiment at different depths will greatly improve understanding of propagation mechanisms and test predictive capabilities. We have demonstrated with 20 earthquake events that we can provide 1 - 3 day predictions of the earthquakes, using ground-based receivers, a combination of GPS and UHF/VHF satellite signals, and radio-tomography of the ionosphere as the analytical tool. Based on that methodology, we hope to correlate crustal plate boundary, precursory signatures with the sub-surface currents and fields evident at DUSEL.
Dahlgren, R.; Freund, F. T.; Lazarus, M.; Wang, J. S.; Rekenthaler, D.; Peters, R. D.; Duma, G.
EDITORIAL: Charge transport in non-metallic solids
Workers engaged in a wide range of investigations of charge transport in non-metallic solids came together at a meeting of the Institute of Physics Dielectric Group, held in London on 2 April 2008. Topics included both ionic and electronic conduction, investigations of the fundamental mechanisms of charge transport, percolation, modelling the conduction process in both natural and man-made composite electrical
Ian J. Youngs; Darryl P. Almond
Quadrupole transport experiment with space charge dominated cesium ion beam
The purpose of the experiment is to investigate the beam current transport limit in a long quadrupole-focussed transport channel in the space charge dominated region where the space charge defocussing force is almost as large as the average focussing force of the channel.
Faltens, A.; Keefe, D.; Kim, C.; Rosenblum, S.; Tiefenback, M.; Warwick, A.
Ceramic transactions: Mass and charge transport in ceramics. Volume 71
Reports are presented from the meeting on mass and charge transport in ceramics. Topics include defects and charge transport, diffusion, phase transformations, solid-state reactions, sintering, electrical properties, and fracture properties. Individual reports have been processed separately for the United States Department of Energy databases.
Koumoto, Kunihito; Sheppard, L.M.; Matsubara, Hideaki [eds.
Measurement of charge-carrier concentration in indium phosphide by means of an electrolyte-semiconductor contact
An electrolyte-semiconductor contact is used to study the conductivity of epitaxial layers and single crystals of n-type indium phosphide obtained by gas transport. Some of the specimens were alloyed with tin and sulfur. The volt-farad characteristics are used to find the potentials of planar zones, which amount to 0.8-1.3 V for different electrolytes. Values of concentration of charge carriers calculated from measured values of capacitance of the electrolyte-indium-phosphide contact showed good agreement with measurements of the Hall effect on single crystals in the range 10/sup 16/-10/sup 18/ cm/sup -3/. The use of measurements of the capacitance of the electrolyte-semiconductor contact with simultaneous etching of a local region made it possible to study the electron distribution in epitaxial layers of indium phosphide.
Asanov, O.M.; Gaman, V.I.; Zorkal'tseva, N.N.; Korableva, T.V.; Petrova, N.G.
Measurement of Minority Charge Carrier Diffusion Length in Gallium Nitride Nanowires Using Electron Beam Induced Current (EBIC).
National Technical Information Service (NTIS)
Electron Beam Induced Current (EBIC) measurements were performed on GaN nanowires to determine minority charge carrier diffusion length, Ld. Although EBIC has been used to characterize bulk and thin film materials, very little is known about near contact ...
C. P. Ong
Enhanced Carrier Transport of N-Doped TiO2 for Photoelectrochemical Cells
The carrier transport kinetics of the TiO2 film doped with N (TiO2:N) were investigated by measuring the current and open circuit potential transients under light on\\/off illumination. These measurements were compared to an undoped film. The N in TiO2 not only shifted the light absorption into a longer wavelength region (known effect) but also enhanced the carrier transport. The combination
Jae-Hong Kim; Tae Kwan Yun; Jae-Yung Bae; Kwang-Soon Ahn
Carrier control via charge transfer at the topological-insulator/organic-molecule interface
NASA Astrophysics Data System (ADS)
A topological insulator is a material that behaves as an insulator as a bulk state, while permitting metallicity on its Dirac cone surface state. One of the most serious issues of recent researches in this field, however, has been the fact that the Fermi levels in many TIs actually fall in either the conduction or valence band due to the naturally occurring defects and must be controlled by further doping. We report here that the major electron carriers on the SS of a Bi2-xSbxTe3-ySey(BSTS) single crystal can be converted to the hole carriers via interface control using 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane(F4-TCNQ), with strong electron affinity. The evidence can be elucidated using a detailed three-carrier model. The results apparently demonstrate that the charge transfer at the TI/organic-molecule interface is very efficient in order to control the carrier density of TIs, particularly on the SS. Our present results will be very important for studying the fundamental aspects of TIs as well as their future device applications.
Tanigaki, Katsumi; Tanabe, Yoichi; Kuynh, Khuong; Urata, Takahiro; Nouchi, Ryo; Heguri, Satoshi; Shimotani, Hidekazu
Consequence of silver nanoparticles embedment on the carrier mobility and space charge limited conduction in doped polyaniline
NASA Astrophysics Data System (ADS)
The present study depicts a one-pot strategy to fabricate silver-polyaniline hybrid nanocomposites with superior and tunable electrical properties, supported by structural characterizations and detail analysis of their temperature dependent current density (J)-voltage (V) characteristics. TEM micrographs clearly reveal that the nanocomposites synthesized by this one-pot strategy contain higher dispersion of sliver nanoparticle within the polyaniline matrix with respect to that obtained from the embedment of externally pre-synthesized silver nanoparticles. The results obtained from the analysis of J-V characteristics indicate the prevalence of trapped charge-limited conduction mechanism in doped polyaniline and its nanocomposites. For the nanocomposites obtained from one-pot strategy, a transition of charge transport mechanism from deep exponential trap limited to shallow traps limited conduction has been occurred due to higher dispersion of silver nanoparticles within the polyaniline matrix. Such distinct variation of charge conduction is absent in the nanocomposites obtained from the embedment of externally pre-synthesized silver nanoparticles. A direct evaluation of carrier mobility as a function of electric field and temperature illustrates that the incorporation of only �13 to 18 wt% of silver nanoparticles within the polyaniline matrix enhances the carrier mobility in a large extent by reducing the concentration of traps within the polymer matrix. The calculated mobility is consistent with the Poole-Frenkel form for the electrical field up to a certain temperature range. The nonlinear low temperature dependency of mobility of all the nanostructured samples has been explained by Mott variable range hopping conduction mechanisms. Qualitative estimation of various disorder parameters such as optimal hopping distance, localization lengths etc., would help us to outspread the strategies for the fabrication of new organic semiconducting nano-structured devices.
Biswas, Swarup; Dutta, Bula; Bhattacharya, Subhratanu
Charge Transport in Conjugated Materials: From Theoretical Models to Experimental Systems
Charge carrier mobility is the key quantity to characterize the charge transport properties in devices. Based on earlier work of Baessler and co-workers, we set up a Monte-Carlo approach that allows us to calculate mobility using transfer rates derived from Marcus theory. The parameters entering into the rate expression are evaluated by means of different quantum-chemical techniques. Our approach is applied here to a model one-dimensional system made of pentacene molecules as well as to real systems such as crystalline structures and columnar liquid crystal phases.
Olivier, Yoann; Cornil, Jerome [Laboratoire de Chimie des Materiaux Nouveaux, Universite de Mons-Hainaut, 20, Place du Parc, 7000 Mons (Belgium); Muccioli, Luca; Zannoni, Claudio [Dipartimento di Chimica Fisica e Inorganica, Universita di Bologna, 4, Viale Risorgimento, 40136 Bologna (Italy)
DNA charge transport over 34 nm
NASA Astrophysics Data System (ADS)
Molecular wires show promise in nanoscale electronics, but the synthesis of uniform, long conductive molecules is a significant challenge. Deoxyribonucleic acid (DNA) of precise length, by contrast, is synthesized easily, but its conductivity over the distances required for nanoscale devices has not been explored. Here we demonstrate DNA charge transport (CT) over 34 nm in 100-mer monolayers on gold. Multiplexed gold electrodes modified with 100-mer DNA yield sizable electrochemical signals from a distal, covalent Nile Blue redox probe. Significant signal attenuation upon incorporation of a single base-pair mismatch demonstrates that CT is DNA-mediated. Efficient cleavage of these 100-mers by a restriction enzyme indicates that the DNA adopts a native conformation accessible to protein binding. Similar electron-transfer rates measured through 100-mer and 17-mer monolayers are consistent with rate-limiting electron tunnelling through the saturated carbon linker. This DNA-mediated CT distance of 34 nm surpasses that of most reports of molecular wires.
Slinker, Jason D.; Muren, Natalie B.; Renfrew, Sara E.; Barton, Jacqueline K.
TOPICAL REVIEW: Charge transport through molecular switches
NASA Astrophysics Data System (ADS)
We review the fascinating research on charge transport through switchable molecules. In the past decade, detailed investigations have been performed on a great variety of molecular switches, including mechanically interlocked switches (rotaxanes and catenanes), redox-active molecules and photochromic switches (e.g. azobenzenes and diarylethenes). To probe these molecules, both individually and in self-assembled monolayers (SAMs), a broad set of methods have been developed. These range from low temperature scanning tunneling microscopy (STM) via two-terminal break junctions to larger scale SAM-based devices. It is generally found that the electronic coupling between molecules and electrodes has a profound influence on the properties of such molecular junctions. For example, an intrinsically switchable molecule may lose its functionality after it is contacted. Vice versa, switchable two-terminal devices may be created using passive molecules ('extrinsic switching'). Developing a detailed understanding of the relation between coupling and switchability will be of key importance for both future research and technology.
van der Molen, Sense Jan; Liljeroth, Peter
Influence of charge carrier mobility and morphology on solar cell parameters in devices of mono- and bis-fullerene adducts
NASA Astrophysics Data System (ADS)
Herein, we analyze charge carrier mobility and morphology of the active blend layer in thin film organic solar cells and correlate them with device parameters. A low band gap donor-acceptor copolymer in combination with phenyl-C61-butyric acid methyl ester (PCBM) or two bis-adduct fullerenes, bis-PCBM and bis-o-quino-dimethane C60 (bis-oQDMC), is investigated. We study the charge transport of polymer:fullerene blends in hole- and electron-only devices using the space-charge limited current method. Lower electron mobilities are observed in both bis-adduct fullerene blends. Hole mobility, however, is decreased only in the blend containing bis-oQDMC. Both bis-adduct fullerene blends show very high open circuit voltage in solar cell devices, but poor photocurrent compared to the standard PCBM blend for an active layer thickness of 200 nm. Therefore, a higher short circuit current is feasible for the polymer:bis-PCBM blend by reducing the active layer thickness in order to compensate for the low electron mobility, which results in a PCE of 4.3%. For the polymer:bis-oQDMC blend, no such improvement is achieved due to an unfavorable morphology in this particular blend system. The results are supported by external quantum efficiency measurements, atomic force microscopy, transmission electron microscopy and UV/vis spectroscopy. Based on these results, the investigations presented herein give a more scientific basis for the optimization of solar cells.
Muth, Mathis-Andreas; Mitchell, William; Tierney, Steven; Lada, Thomas A.; Xue, Xiang; Richter, Henning; Carrasco-Orozco, Miguel; Thelakkat, Mukundan
Influence of charge carrier mobility and morphology on solar cell parameters in devices of mono- and bis-fullerene adducts.
Herein, we analyze charge carrier mobility and morphology of the active blend layer in thin film organic solar cells and correlate them with device parameters. A low band gap donor-acceptor copolymer in combination with phenyl-C61-butyric acid methyl ester (PCBM) or two bis-adduct fullerenes, bis-PCBM and bis-o-quino-dimethane C60 (bis-oQDMC), is investigated. We study the charge transport of polymer:fullerene blends in hole- and electron-only devices using the space-charge limited current method. Lower electron mobilities are observed in both bis-adduct fullerene blends. Hole mobility, however, is decreased only in the blend containing bis-oQDMC. Both bis-adduct fullerene blends show very high open circuit voltage in solar cell devices, but poor photocurrent compared to the standard PCBM blend for an active layer thickness of 200�nm. Therefore, a higher short circuit current is feasible for the polymer:bis-PCBM blend by reducing the active layer thickness in order to compensate for the low electron mobility, which results in a PCE of 4.3%. For the polymer:bis-oQDMC blend, no such improvement is achieved due to an unfavorable morphology in this particular blend system. The results are supported by external quantum efficiency measurements, atomic force microscopy, transmission electron microscopy and UV/vis spectroscopy. Based on these results, the investigations presented herein give a more scientific basis for the optimization of solar cells. PMID:24196215
Muth, Mathis-Andreas; Mitchell, William; Tierney, Steven; Lada, Thomas A; Xue, Xiang; Richter, Henning; Carrasco-Orozco, Miguel; Thelakkat, Mukundan
Single-step Charge Transport through DNA over Long Distances
Quantum yields for charge transport across adenine tracts of increasing length have been measured by monitoring hole transport in synthetic oligonucleotides between photoexcited 2-aminopurine, a fluorescent analogue of adenine, and N2-cyclopropyl guanine. Using fluorescence quenching, a measure of hole injection, and hole trapping by the cyclopropyl guanine derivative, we separate the individual contributions of single- and multi-step channels to DNA charge transport, and find that with 7 or 8 intervening adenines the charge transport is a coherent, single-step process. Moreover, a transition occurs from multi-step to single-step charge transport with increasing donor/acceptor separation, opposite to that generally observed in molecular wires. These results establish that coherent transport through DNA occurs preferentially across 10 base pairs, favored by delocalization over a full turn of the helix.
Genereux, Joseph C.; Wuerth, Stephanie M.; Barton, Jacqueline K.
Confinement effects and surface-induced charge carriers in Bi quantum wires
NASA Astrophysics Data System (ADS)
We present measurements of Shubnikov-de Haas oscillations in arrays of bismuth nanowires. For 80 nm wires, the hole concentration is less than 30% that of bulk Bi, a finding that is consistent with current models of quantum confinement effects. However, 30-nm-diam nanowires which are predicted to be semiconductors show a nearly isotropic short period of 0.025 T-1, consistent with a heavy carrier concentration five times that of bulk Bi. These results are discussed in terms of surface-induced charge carriers in a spherical Fermi surface pocket that are uniformly distributed in the 30 nm nanowire volume and that inhibit the semimetal-to-semiconductor transition.
Huber, T. E.; Nikolaeva, A.; Gitsu, D.; Konopko, L.; Foss, C. A.; Graf, M. J.
Two-dimensional charge transport in self-organized, high-mobility conjugated polymers
NASA Astrophysics Data System (ADS)
Self-organization in many solution-processed, semiconducting conjugated polymers results in complex microstructures, in which ordered microcrystalline domains are embedded in an amorphous matrix. This has important consequences for electrical properties of these materials: charge transport is usually limited by the most difficult hopping processes and is therefore dominated by the disordered matrix, resulting in low charge-carrier mobilities (<=10-5cm2V-1s-1). Here we use thin-film, field-effect transistor structures to probe the transport properties of the ordered microcrystalline domains in the conjugated polymer poly(3-hexylthiophene), P3HT. Self-organization in P3HT results in a lamella structure with two-dimensional conjugated sheets formed by interchain stacking. We find that, depending on processing conditions, the lamellae can adopt two different orientations-parallel and normal to the substrate-the mobilities of which differ by more than a factor of 100, and can reach values as high as 0.1cm2V-1s-1 (refs 3, 4). Optical spectroscopy of the field-induced charge, combined with the mobility anisotropy, reveals the two-dimensional interchain character of the polaronic charge carriers, which exhibit lower relaxation energies than the corresponding radical cations on isolated one-dimensional chains. The possibility of achieving high mobilities via two-dimensional transport in self-organized conjugated lamellae is important for applications of polymer transistors in logic circuits and active-matrix displays.
Sirringhaus, H.; Brown, P. J.; Friend, R. H.; Nielsen, M. M.; Bechgaard, K.; Langeveld-Voss, B. M. W.; Spiering, A. J. H.; Janssen, R. A. J.; Meijer, E. W.; Herwig, P.; de Leeuw, D. M.
Electron transport and charge induction in cadmium zinc telluride detectors with space charge build up under intense x-ray irradiation
NASA Astrophysics Data System (ADS)
Under intense x-ray irradiation, wide band gap semiconductor radiation detectors fabricated from crystals with low hole transport properties develop a steady-state space charge distribution that results from a dynamic equilibrium between charge carrier dynamics and the incident photon field. At a high enough x-ray flux, this space charge can collapse the electric field within the detector, resulting in the paralyzation of photon counting (i.e., high-flux polarization). However, well before polarization causes a catastrophic device failure, there can be enough space charge present to significantly modify the electric field. A modified field affects the electron transport and, therefore, signal generation within the sensor, which can ultimately degrade the performance of high-rate photon counting electronics. In this study, we analytically solve the fundamental equation of charge conservation to derive the modified electron transport in the presence of an exponential space charge distribution that results from the incident x-rays. We use these space-time solutions to calculate and study the time dependence of the resulting charge-induced signals. The predicted induced signals are compared throughout with numerical solutions of the full charge transport equation. In addition, we present analogous closed-form signals for a uniform distribution relevant to a broader class of ?-ray applications. Finally, we use these solutions to derive a two-parameter family of modified Hecht curves that naturally predict a voltage offset that appears due to the space charge.
Bale, Derek S.; Szeles, Csaba
How high local charge carrier mobility and an energy cascade in a three-phase bulk heterojunction enable >90% quantum efficiency.
Charge generation in champion organic solar cells is highly efficient in spite of low bulk charge-carrier mobilities and short geminate-pair lifetimes. In this work, kinetic Monte Carlo simulations are used to understand efficient charge generation in terms of experimentally measured high local charge-carrier mobilities and energy cascades due to molecular mixing. PMID:24375640
Burke, Timothy M; McGehee, Michael D
Hot Carrier Transport at the Graphene-Metal Interface Induced by Strong Lateral Photo-Dember Effect
NASA Astrophysics Data System (ADS)
Ultrafast photo-excitation in a semiconductor can lead to transient spatial charge gradient if electrons and holes have different drift velocities. The charge gradient builds up the transient electric field and causes the subsequent terahertz pulse emission. This phenomenon, known as the photo-Dember effect, was typically considered insignificant in graphene due to its similar electron and hole mobilities. Here, we observe hot carrier transport at the graphene-metal interface driven by the photo-Dember electric field under femtosecond pulse laser excitation. The polarity of hot carrier transport is determined by the asymmetry of electron and hole mobilities of the graphene device and cannot be flipped sign by tuning graphene doping level. This indicates the formation of strong photo-Dember field, dominating over the graphene/metal built-in electric field or thermal electric field. We further analyze the spatial distribution and temporal evolution of the transient electric field near the contact edge by using the drift-diffusion model. The modeling results suggest that strong photo-Dember effect is caused by the low electronic specific heat of graphene and a huge charge gradient near the graphene-metal interface under pulse laser excitation.
Liu, Chang-Hua; Chang, You-Chia; Dissanayake, Nanditha; Zhang, Yaozhong; Zhong, Zhaohui
Stress Activation and Propagation of Electronic Charge Carriers in Igneous Rocks
NASA Astrophysics Data System (ADS)
Igneous and high-grade metamorphic rocks in the Earth's crust generate electric currents when subjected to deviatoric stresses. The reason is that these rocks contain dormant electronic charge carriers in the form of peroxy links. Peroxy links are sites in the crystal structures of the constituent minerals where oxygen anions have converted from their common 2- valence state to the 1- valence state, O3X-OO-XO3 with X=Si4+, Al3+ etc. As rocks are stressed and dislocations sweep through the mineral grains, the peroxy links break up, activating electrons and pholes ("phole" is an abbreviation for "positive hole", a defect electron on the oxygen sublattice, chemically O- in a matrix of O2-). The pholes are mobile electronic charge carriers that can spread out of the stressed rock into the surrounding unstressed rock. They travel via energy levels at the upper edge of the valence bands, cross grain boundaries and achieve a phase velocity on the order of 200�50 m/sec, consistent with phonon-assisted electron hopping. Due to mutual repulsion inside the rock volume the pholes spread to the surface, where they build up a positive surface charge. The surface charge can be measured with a non-contact capacitive sensor. If a Cu contact is applied to the surface of the rock, electrons are injected from ground into the rock in response to the evolving positive charge on the rock surface. We modeled surface potentials and burst-like electron injections following low and medium velocity impact experiments, 100 m/sec and 1.5 km/sec respectively.
Ling, J.; Freund, F. T.
Minority carrier transport in p-ZnO nanowires
NASA Astrophysics Data System (ADS)
In this work, we explore the minority carrier diffusion length in zinc oxide nanowires, using the electron beam-induced current technique. Systematic measurements as a function of temperature were performed on p-type, Sb-doped ZnO film, containing a 4 ?m thick nanowire layer. The minority carrier diffusion length exhibits a thermally activated increase with the energy of 74+/-5 meV. Electron beam irradiation also causes the diffusion length increase with the activation energy of 247+/-10 meV, likely related to SbZn-2VZn acceptor-complex.
Lin, Y.; Shatkhin, M.; Flitsiyan, E.; Chernyak, L.; Dashevsky, Z.; Chu, S.; Liu, J. L.
Probing the electronic structure at semiconductor surfaces using charge transport in nanomembranes
NASA Astrophysics Data System (ADS)
The electrical properties of nanostructures are extremely sensitive to their surface condition. In very thin two-dimensional crystalline-semiconductor sheets, termed nanomembranes, the influence of the bulk is diminished, and the electrical conductance becomes exquisitely responsive to the structure of the surface and the type and density of defects there. Its understanding therefore requires a precise knowledge of the surface condition. Here we report measurements, using nanomembranes, that demonstrate direct charge transport through the ?* band of the clean reconstructed Si(001) surface. We determine the charge carrier mobility in this band. These measurements, performed in ultra-high vacuum to create a truly clean surface, lay the foundation for a quantitative understanding of the role of extended or localized surface states, created by surface structure, defects or adsorbed atoms/molecules, in modifying charge transport through semiconductor nanostructures.
Peng, Weina; Aksamija, Zlatan; Scott, Shelley A.; Endres, James J.; Savage, Donald E.; Knezevic, Irena; Eriksson, Mark A.; Lagally, Max G.
Electronic-Structure Theory of Organic Semiconductors: Charge-Transport Parameters and Metal/Organic Interfaces
NASA Astrophysics Data System (ADS)
We focus this review on the theoretical description, at the density functional theory level, of two key processes that are common to electronic devices based on organic semiconductors (such as organic light-emitting diodes, field-effect transistors, and solar cells), namely charge transport and charge injection from electrodes. By using representative examples of current interest, our main goal is to introduce some of the reliable theoretical methodologies that can best depict these processes. We first discuss the evaluation of the microscopic parameters that determine charge-carrier transport in organic molecular crystals, i.e., electronic couplings and electron-vibration couplings. We then examine the electronic structure at interfaces between an organic layer and a metal or conducting oxide electrode, with an emphasis on the work-function modifications induced by the organic layer and on the interfacial energy-level alignments.
Coropceanu, Veaceslav; Li, Hong; Winget, Paul; Zhu, Lingyun; Br�das, Jean-Luc
Coherently controlled spin-dependent charge carrier transitions in organic semiconductors: Properties and applications
NASA Astrophysics Data System (ADS)
This thesis is focused on the investigation of the fundamental physical nature and potential technical applications of spin-dependent charge carrier recombination in poly[2-methoxy-5-(2'-ethyl-hexyloxy)-1,4-phenylene vinylene (MEH-PPV), a pi conjugated polymer which has been utilized as organic thin film semiconductor. Pulsed electrically detected magnetic resonance (pEDMR) spectroscopy was used to observe how coherent spin motion of paramagnetic charge carrier states (so called polarons) control the macroscopic conductivity of thin (�100nm) MEH-PPV layers under different charge carrier injection regimes. The pEDMR experiments were conducted at frequencies covering almost three orders of magnitude (�20MHz to �10GHz) and at temperatures between �5K and �300k. The measurements revealed that under balanced bipolar injection, the conductivity of MEH-PPV is influenced at any temperature by the polaron pair (PP) mechanism, a spin-dependent process previously described in the literature. The experiments showed that PPs are weakly exchange- and dipolar-coupled pairs but they are strongly influenced by proton induced hyperfine fields. Electrical detection of coherent polaron-spin motion revealed extraordinary long coherence times (order of mus) at room temperature which could qualify PPs for quantum information applications. The PP mechanism was also demonstrated to work as an extraordinary sensitive (< 50 nT Hz-1/2) organic thin film probe which uses the polarons gyromagnetic ratio gamma as magnetic field standard. gamma was observed to be independent of temperature, device-current, and -bias, and degradation of the MEH-PPV device. In addition to the PP mechanism, another spin-dependent process previously described in the literature was confirmed to significantly influence conductivity in MEH-PPV: Triplet-exciton polaron recombination.
Baker, William J.
Study on charge carrier recombination zone with ultrathin rubrene layer as probe
NASA Astrophysics Data System (ADS)
The characteristic of charge carrier recombination zone in N,N'-bis-(1-naphthyl)-N,N'-biphenyl-1,1'-biphenyl-4,4'-diamine (NPB) based OLEDs is studied using an ultrathin 5,6,11,12-tetraphenylnaphthacene (rubrene) as a probe. By adjusting the rubrene thickness and location in NPB light-emitting layer, the luminescent spectra and electrical properties of the devices are investigated. The results show that when the thickness ranges from 0.2 to 0.8 nm, the surface morphology of rubrene exists as the discontinuous island-like state locating on the surface of NPB film and seldom affect the electrical characteristics. While the location of rubrene shifted from the interface of NPB/2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) to NPB side, the maximum exciton concentration is found within 2 nm away from the interface, which is the main charge carrier recombination zone. With an optimized structure of indium-tin-oxide (ITO)/NPB (40nm)/rubrene (0.3nm)/NPB (7nm)/BCP (30nm)/Mg:Ag, the device exhibits a turn on voltage as low as 3 V and stable white light. The peaks of EL spectra are located at 431 and 555 nm corresponding to the Commissions Internationale De L'Eclairage (CIE) coordinates of (0.32, 0.32), which are relatively stable under the bias voltage from 5 to 15 V. A maximum luminance of 5630 cd/m2 and a maximum power efficiency of 0.6 lm/W is achieved. The balanced spectra are attributed to the stable confining of charge carriers and exciton by the thin emitting layers.
Wen, Wen; Yu, Jungsheng; Li, Yi; Li, Lu; Jiang, Yadong
Ambipolar charge transport in non-peripherally substituted octahexyl zinc phthalocyanine
NASA Astrophysics Data System (ADS)
Time-of-flight measurements on 2\\ \\mu\\text{m} thick drop-cast films of 1,4,8,11,15,18,22,25-octakis(hexyl)phthalocyaninato zinc complex in a sandwich configuration between transparent indium tin oxide and aluminum metal electrodes have been performed. The results show that intrinsic ambipolar transport characteristics are exhibited by this very stable compound having values in the order of 10^{-4}\\ \\text{cm}^{2}\\,\\text{V}^{-1}\\,\\text{s}^{-1} for both types of charge carrier. Both electron and hole transport are dispersive due to a high degree of positional disorder of the molecules.
Chaure, Nandu B.; Barard, Seema; Ray, Asim K.; Cammidge, Andrew N.; Cook, Michael J.
Charge and Shape Effects on the Carrier Dynamics of 25 Atom Au Nanoclusters
NASA Astrophysics Data System (ADS)
We study a series of semiconducting gold clusters that exhibit strong quantum confinement effects on their optical properties. In contrast to larger metallic nanoparticles, the surface plasmon resonance disappears a large optical gap (> 1.3 eV) is formed. Recent synthetic advances have permitted the study of truly monodisperse clusters with precise control on the atomic scale. Using femtosecond and nanosecond transient absorption spectroscopy, we have investigated the excited state relaxation dynamics of spherical and prolate 25 atom isomers. We have determined that these particles exhibit long excited state lifetimes and that the carrier dynamics that are strongly influenced by the charge state and the physical arrangement of the atoms.
Sfeir, Matthew; Qian, Huifeng; Jin, Rongchao
Photosensitive Properties and a Mechanism for Photogeneration of Charge Carriers in Polymeric Layers Containing Organometallic Complexes
New polyamide acids (prepolymers of polybenzoxazinimides) containing 2,2-biquinolyl units in their main chain are synthesized. It is shown that these polymers form stable complexes with acids derived from the transition and rare-earth metals. The results of photophysical studies support the assumption that the process of generation of free charge carriers via a state of a pair bound by a Coulomb interaction includes two stages and that metal-polymer complexes are involved in this process. The quantum yield of photogeneration amounts to 0.007-0.05.
Aleksandrova, E.L. [Ioffe Physicotechnical Institute, Russian Academy of Sciences, Politekhnicheskaya ul. 26, St. Petersburg, 194021 (Russian Federation); Goikhman, M.Ya.; Podeshvo, I.V.; Kudryavtsev, V.V. [Institute of Macromolecular Compounds, Russian Academy of Sciences, Bol'shoi proezd 31, St. Petersburg, 199004 (Russian Federation)
Efficient calculation of Coulomb matrix elements for bilayers of confined charge carriers with arbitrary spatial separation
NASA Astrophysics Data System (ADS)
We describe a practical procedure to calculate the Coulomb matrix elements of 2D spatially separated and confined charge carriers, which are needed for detailed theoretical descriptions of important condensed matter finite systems. We derive an analytical expression, for arbitrary separations, in terms of a single infinite series and apply a u-type Levin transform in order to accelerate the resulting infinite series. This procedure has proven to be efficient and accurate. Direct consequences concerning the functional dependence of the matrix elements on the separation distance, transition amplitudes and the diagonalization of a single electron-hole pair in vertically stacked parabolic quantum dots are presented.
Mondragon-Shem, Ian; Rodr�guez, Boris A.; L�pez, Francisco E.
Localized excited charge carriers generate ultrafast inhomogeneous strain in the multiferroic BiFeO3.
We apply ultrafast x-ray diffraction with femtosecond temporal resolution to monitor the lattice dynamics in a thin film of multiferroic BiFeO3 after above-band-gap photoexcitation. The sound-velocity limited evolution of the observed lattice strains indicates a quasi-instantaneous photoinduced stress which decays on a nanosecond time scale. This stress exhibits an inhomogeneous spatial profile evidenced by the broadening of the Bragg peak. These new data require substantial modification of existing models of photogenerated stresses in BiFeO3: the relevant excited charge carriers must remain localized to be consistent with the data. PMID:24655276
Schick, Daniel; Herzog, Marc; Wen, Haidan; Chen, Pice; Adamo, Carolina; Gaal, Peter; Schlom, Darrell G; Evans, Paul G; Li, Yuelin; Bargheer, Matias
Charge carrier relaxation and effective masses in silicon probed by terahertz spectroscopy
NASA Astrophysics Data System (ADS)
Charge transport in silicon is investigated on a metal-oxide-semiconductor structure, which is driven into depletion, accumulation, or inversion. Terahertz electromodulation spectroscopy provides momentum relaxation times as well as conductivity effective masses of electrons and holes. At room temperature the conductivity effective masses of electrons and holes are close to those values reported for cryogenic temperatures.
Engelbrecht, S. G.; Reichel, A. J.; Kersting, R.
Cis- and trans-isomerization-induced transition of charge transport property in PPV oligomers
NASA Astrophysics Data System (ADS)
Photoisomerization of vinylenes is well known to cause remarkable changes in the photophysical properties of poly (p-phenylene vinylene) (PPV) derivatives. C is-/ trans- isomerization is also expected to induce significant changes in their charge transport properties. In this study, the charge transport properties of cis- and trans-isomers of 2,5-diphenyl-1,4-distyrylbenzene (DPDSB, model compound of PPV) were investigated using a Marcus hopping model. As expected, this conformational transition from cis- to trans-isomer gives rise to a significant difference between hole and electron transport properties. Cis-DPDSB demonstrates an overwhelmingly superior hole transport ( ? h/ ? e = 51), which is even higher than that of trans-DPDSB. By contrast, trans-DPDSB exhibits approximately balanced carrier transport property ( ? h/ ? e = 1.79). These results are understood on a molecular level by considering the structure-transport relationship through two key parameters: transfer integral and reorganization energy. This finding may be helpful in understanding and extrapolating the structure-property relationship and charge transport property of the corresponding PPV polymers derivatives.
Liu, Dandan; Yin, Shiwei; Xu, Hai; Liu, Xiaodong; Sun, Guannan; Xie, Zengqi; Yang, Bing; Ma, Yuguang
Simulation of carrier capture in semiconductor quantum wells: Bridging the gap from quantum to classical transport
The effects of lost phase coherence on carrier capture by semiconductor quantum wells are simulated using Schro�dinger Equation Monte Carlo. Results are shown for polar-opticalphonon-induced capture of both electrons and holes, and for both monoenergetic and thermal distributions of incident charge carriers. Results suggest that semiclassical modeling of hole capture may be sufficient, provided that quantum mechanical reflection from the
Leonard F. Register; Karl Hess
Electronic charge injection and transport in organic field-effect transistors
NASA Astrophysics Data System (ADS)
Electronic devices based on organic semiconductors, such as field-effect transistors (FETs) and light emitting diodes have attracted much interest as possible inexpensive and flexible alternatives to inorganic devices. Despite considerable improvement in device properties, a better understanding of the nature of charge transport in these devices and the physics of contacts is crucial to further development of optoelectronic organic devices. This work outlines our findings in understanding and characterizing the injection and transport mechanisms of charge carriers in solution processed poly (3-hexylthiophene) (P3HT) field-effect devices. We measured hole transport in P3HT FETs with Au electrodes at submicron channel lengths as a function of gate voltage and a wide range of temperatures. The strongly nonlinear and gate modulated transport is shown to be consistent with a model of Poole-Frenkel-like hopping mechanism in the space-charge limited current regime. Charge injection from different source/drain electrodes such as Au, Cu and Cr was examined over a broad temperature range, and the contact current-voltage characteristics were extracted from the dependence of conductance on channel length. The differences between linear vs. nonlinear charge injection were carefully studied and compared to recently developed models of charge injection. In addition, the effect of doping-dependent charge injection in devices with Au and Pt contacts was studied, revealing large contact resistances and marked non-Ohmic transport at low dopant concentrations. Ultraviolet photoemission spectroscopy (UPS) reveals that metal/P3HT band alignment is rearranged as samples are dedoped, leading to an increased injection barrier for holes, with a greater shift for Au/P3HT. We also performed a study using dipole-containing self-assembled monolayers on the Au source and drain electrodes to strongly manipulate the charge injection process across the metal/organic interface. We have shown that chemically increasing the injecting electrode work function significantly improves hole injection relative to untreated Au electrodes.
Hamadani, Behrang Homayoun
Charge transport in organic semiconductors: Assessment of the mean field theory in the hopping regime
NASA Astrophysics Data System (ADS)
The performance of the mean field theory to account for charge transfer rate in molecular dimers and charge transport mobility in molecular stacks with small intermolecular electronic coupling and large local electron-phonon coupling (i.e., in the hopping regime) is carefully investigated against various other approaches. Using Marcus formula as a reference, it is found that mean field theory with system-bath interaction and surface hopping approaches yield fully consistent charge transfer rates in dimers. However, in contrast to the dimer case, incorporating system-bath interaction in the mean field approach results in a completely wrong temperature dependence of charge carrier mobility in larger aggregates. Although the mean field simulation starting from the relaxed geometry of a charged molecule and neglecting system-bath interaction can reproduce thermally activated transport, it is not able to characterize properly the role of additional nonlocal electron-phonon couplings. Our study reveals that the mean field theory must be used with caution when studying charge transport in the hopping regime of organic semiconductors, where the surface hopping approach is generally superior.
Wang, Linjun; Beljonne, David
Enhanced charge transport kinetics in anisotropic, stratified photoanodes.
The kinetics of charge transport in mesoporous photoanodes strongly constrains the design and power conversion efficiencies of dye sensitized solar cells (DSSCs). Here, we report a stratified photoanode design with enhanced kinetics achieved through the incorporation of a fast charge transport intermediary between the titania and charge collector. Proof of concept photoanodes demonstrate that the inclusion of the intermediary not only enhances effective diffusion coefficients but also significantly suppresses charge recombination, leading to diffusion lengths two orders of magnitude greater than in standard mesoporous titania photoanodes. The intermediary concept holds promise for higher-efficiency DSSCs. PMID:24467298
Yazdani, Nuri; Bozyigit, Deniz; Utke, Ivo; Buchheim, Jakob; Youn, Seul Ki; Patscheider, J�rg; Wood, Vanessa; Park, Hyung Gyu
Charge transport properties of nanocrystals studied by electrostatic force microscopy
NASA Astrophysics Data System (ADS)
Charge transport in semiconductor and metal nanocrystal multilayers between two electrodes is probed by electrostatic force microscopy. The in-plane charge diffusion coefficients are deduced from the charge distribution imaged in real time. Temperature dependence of the transport properties and effects of photoionization and oxidation are also investigated. Implications of these results on the transport mechanisms will be discussed. This work was supported by the ONR Young Investigator Award N000140410489, the American Chemical Society (ACS) PRF award # 41256-G10, and the startup funds at the University of Pennsylvania. MF acknowledges funding from the NSF IGERT program (Grant #DGE-0221664) and SENS.
Hu, Zonghai
The Role of Surface Ligands in Electronic Charge Transport in Semiconductor Nanocrystal Arrays
NASA Astrophysics Data System (ADS)
The long, insulating ligands commonly used in the synthesis of colloidal semiconductor nanocrystals (NCs) inhibit strong interparticle coupling and charge transport once NCs are assembled in the solid state into NC arrays. We introduce ammonium thiocyanate (NH4SCN) and its derivatives, ammonium selenocyanate and selenourea to exchange the long, insulating ligands commonly used in the synthesis of colloidal semiconductor NCs. NCs may be exchanged with the new ligand in solution to form dispersions from which NC arrays are deposited or NC arrays with the long, insulating ligands may be exchanged in the solid state with the new ligands. The new compact ligands enhance interparticle coupling and charge transport in thin film, NC arrays as seen by red-shifts in the optical absorption and concomitant increases in carrier mobilities. Thiocyanate-capped CdSe thin film, NC arrays form sensitive photodetectors and n-type field-effect transistors with electron mobilities of �10 cm^2/Vs and current modulation of >10^6, while preserving NC quantum confinement. Temperature-dependent transport measurements reveal band-like transport in NC arrays, overcoming carrier hopping that has typified transport in NC arrays until recently. The non-caustic, chemically benign nature of the ammonium thiocyanate treatment enables the fabrication of NC thin film devices and circuits on flexible plastics.
Kagan, Cherie
Effect of reduction of trap charge carrier density in organic field effect transistors by surface treatment of dielectric layer
NASA Astrophysics Data System (ADS)
In this work, we have studied the effect of surface treatment of SiO2 dielectric layer on the reduction of the trap charge carrier density at dielectric/semiconducting interface by fabricating a metal-insulator-semiconductor (MIS) device using ?, ?-dihexylcarbonylquaterthiophene as semiconducting layer. SiO2 dielectric layer has been treated with 1,1,1,3,3,3-hexamethyldisilazane (HMDS) to modify the chemical group acting as charge traps. Capacitance-voltage measurements have been performed on MIS devices fabricated on SiO2 and HMDS treated SiO2. These data have been used for the calculation of trap charge carrier density and Debye length at the dielectric-semiconductor interface. The calculated trap charge carrier density has been found to reduce from (2.925 � 0.049) � 1016 cm-3 to (2.025 � 0.061) � 1016 cm-3 for the MIS device with HMDS treated SiO2 dielectric in comparison to that of untreated SiO2. Next, the effect of reduction in trap charge carrier density has been studied on the performance of organic field effect transistors. The improvement in the device parameters like mobility, on/off ratio, and gate leakage current has been obtained with the effect of the surface treatment. The charge carrier mobility has been improved by a factor of 2 through this treatment. Further, the influence of the treatment was observed by atomic force microscope and Fourier transform infrared spectroscopy techniques.
Dagar, Janardan; Yadav, Vandana; Tyagi, Priyanka; Kumar Singh, Rajiv; Suman, C. K.; Srivastava, Ritu
Polarized recombination of acoustically transported carriers in GaAs nanowires
The oscillating piezoelectric field of a surface acoustic wave (SAW) is employed to transport photoexcited electrons and holes in GaAs nanowires deposited on a SAW delay line on a LiNbO3 crystal. The carriers generated in the nanowire by a focused light spot are acoustically transferred to a second location where they recombine. We show that the recombination of the transported carriers occurs in a zinc blende section on top of the predominant wurtzite nanowire. This allows contactless control of the linear polarized emission by SAWs which is governed by the crystal structure. Additional polarization-resolved photoluminescence measurements were performed to investigate spin conservation during transport.
Inorganic/organic hybrid solar cells: optimal carrier transport in vertically aligned silicon nanowire arrays
NASA Astrophysics Data System (ADS)
Inorganic/organic hybrid radial heterojunction solar cells that combine vertically-aligned n-type silicon nanowires (SiNWs) with poly(3,4-ethylenedioxythiophene):poly(styrene-sulfonate) (PEDOT:PSS) have great potential for replacing commercial Si solar cells. The chief advantage of such solar cells is that they exhibit higher absorbance for a given thickness than commercial Si solar cells, due to incident light-trapping within the NW arrays, thus enabling lower-cost solar cell production. We report herein on the effects of NW length, annealing and surface electrode on the device performance of SiNW/PEDOT:PSS hybrid radial heterojunction solar cells. The power conversion efficiency (PCE) of the obtained SiNW/PEDOT:PSS hybrid solar cells can be optimized by tuning the thickness of the surface electrode, and the etching conditions during NW formation and post-annealing. The PCE of 9.3% is obtained by forming efficient transport pathways for photogenerated charge carriers to electrodes. Our approach is a significant contribution to design of high-performance and low-cost inorganic/organic hybrid heterojunction solar cells.Inorganic/organic hybrid radial heterojunction solar cells that combine vertically-aligned n-type silicon nanowires (SiNWs) with poly(3,4-ethylenedioxythiophene):poly(styrene-sulfonate) (PEDOT:PSS) have great potential for replacing commercial Si solar cells. The chief advantage of such solar cells is that they exhibit higher absorbance for a given thickness than commercial Si solar cells, due to incident light-trapping within the NW arrays, thus enabling lower-cost solar cell production. We report herein on the effects of NW length, annealing and surface electrode on the device performance of SiNW/PEDOT:PSS hybrid radial heterojunction solar cells. The power conversion efficiency (PCE) of the obtained SiNW/PEDOT:PSS hybrid solar cells can be optimized by tuning the thickness of the surface electrode, and the etching conditions during NW formation and post-annealing. The PCE of 9.3% is obtained by forming efficient transport pathways for photogenerated charge carriers to electrodes. Our approach is a significant contribution to design of high-performance and low-cost inorganic/organic hybrid heterojunction solar cells. Electronic supplementary information (ESI) available. See DOI: 10.1039/c4nr00733f
Sato, Keisuke; Dutta, Mrinal; Fukata, Naoki
Ultrafast dynamics of charge carrier photogeneration and geminate recombination in conjugated polymer:fullerene solar cells
NASA Astrophysics Data System (ADS)
We investigate the nature of ultrafast exciton dissociation and carrier generation in acceptor-doped conjugated polymers. Using a combination of two-pulse femtosecond spectroscopy with photocurrent detection, we compare the exciton dissociation and geminate charge recombination dynamics in blends of two conjugated polymers, MeLPPP [methyl-substituted ladder-type poly( p -phenylene)] and MDMO-PPV [poly(2-methoxy,5-(3,7-dimethyloctyloxy)-1,4-phenylenevinylene], with the electron accepting fullerene derivative PCBM [1-(3-methoxycarbonyl)-propyl-1-phenyl- (6,6)C61 ]. This technique allows us to distinguish between free charge carriers and Coulombically bound polaron pairs. Our results highlight the importance of geminate pair recombination in photovoltaic devices, which limits the device performance. The comparison of different materials allows us to address the dependence of geminate recombination on the film morphology directly at the polymer:fullerene interface. We find that in the MeLPPP:PCBM blend exciton dissociation generates Coulombically bound geminate polaron pairs with a high probability for recombination, which explains the low photocurrent yield found in these samples. In contrast, in the highly efficient MDMO-PPV:PCBM blend the electron transfer leads to the formation of free carriers. The anisotropy dynamics of electronic transitions from neutral and charged states indicate that polarons in MDMO-PPV relax to delocalized states in ordered domains within 500fs . The results suggest that this relaxation enlarges the distance of carrier separation within the geminate pair, lowering its binding energy and favoring full dissociation. The difference in geminate pair recombination concurs with distinct dissociation dynamics. The electron transfer is preceded by exciton migration towards the PCBM sites. In MeLPPP:PCBM the exciton migration time decays smoothly with increasing PCBM concentration, indicating a trap-free exciton hopping. In MDMO-PPV:PCBM, however, the exciton migration time is found to show a threshold-like dependence on the PCBM concentration. This observation is explained by efficient interchain energy transfer in ordered MDMO-PPV domains in conjunction with exciton trapping.
M�ller, J. G.; Lupton, J. M.; Feldmann, J.; Lemmer, U.; Scharber, M. C.; Sariciftci, N. S.; Brabec, C. J.; Scherf, U.
Direct observation and measurement of mobile charge carriers in a monolayer organic semiconductor on a dielectric substrate.
We report the electrical characterization of a single layer of an organic semiconductor grown on a dielectric surface. The dynamic response of the charge carriers in the monolayer film of pentacene was characterized through the electrostatic interactions between an electric force microscope (EFM) probe and pentacene islands of various sizes. These islands were formed in situ by segmenting a coalesced pentacene monolayer into separated regions. The size-dependent dielectric responses of the pentacene islands suggest that mobile charges exist in the organic monolayer. Local capacitance spectroscopy revealed that the charge carriers in the p-type pentacene monolayer could be depleted at high bias voltages, enabling a further determination of the charge-carrier concentration in the organic semiconductor ultrathin film. PMID:21740011
Jiang, Yeping; Qi, Qiong; Wang, Rui; Zhang, Jun; Xue, Qikun; Wang, Chen; Jiang, Chao; Qiu, Xiaohui
Electrical Conductivity of Rocks and Dominant Charge Carriers. Part 1; Thermally Activated Positive Holes
NASA Technical Reports Server (NTRS)
The prevailing view in the geophysics community is that the electrical conductivity structure of the Earth's continental crust over the 5-35 km depth range can best be understood by assuming the presence of intergranular fluids and/or of intragranular carbon films. Based on single crystal studies of melt-grown MgO, magma-derived sanidine and anorthosite feldspars and upper mantle olivine, we present evidence for the presence of electronic charge carriers, which derive from peroxy defects that are introduced during cooling, under non-equilibrium conditions, through a redox conversion of pairs of solute hydroxyl arising from dissolution of H2O.The peroxy defects become thermally activated in a 2-step process, leading to the release of defect electrons in the oxygen anion sublattice. Known as positive holes and symbolized by h(dot), these electronic charge carriers are highly mobile. Chemically equivalent to O(-) in a matrix of O(2-) they are highly oxidizing. Being metastable they can exist in the matrix of minerals, which crystallized in highly reduced environments. The h(dot) are highly mobile. They appear to control the electrical conductivity of crustal rocks in much of the 5-35 km depth range.
Freund, Friedemann T.; Freund, Minoru M.
Conductivity, charge carrier mobility and ageing of ZnPc/C60 solar cells
NASA Astrophysics Data System (ADS)
We have investigated conductivity and ageing of ZnPc/C60 solar cells as they are influenced by the charge carrier mobility and variation of the potential barrier height. The test structures with a reasonable energy conversion efficiency of �1.5% were investigated. The samples were aged for 1300 h upon illumination by the blue LED with peak emission at 475 nm. Upon ageing the devices showed a strong and fast degradation of the efficiency, short circuit current and of the fill factor within several hours followed by a much slower decrease of them. The reference samples kept in the dark at the room temperature did show only very small changes in their I- V curves. Carrier mobility dependencies on electric field strength at different temperatures were measured by the Charge Extraction by Linearly Increasing Voltage (CELIV) method. It was demonstrated that mobility values decrease during degradation as compared to the reference samples. Nevertheless only mobility changes cannot explain the observed drop of device current. The increase of the effective barrier height by about 0.1 eV from �0.55 eV up to �0.65 eV was observed in the aged samples. Meanwhile thermal activation energy values of the electrical conductivity grew from about 0.28 eV prior to degradation up to about 0.34 eV after ageing.
Ka�ukauskas, V.; Arlauskas, A.; Pranaitis, M.; Lessmann, R.; Riede, M.; Leo, K.
Perturbation theory for charged-particle transport in one dimension
NASA Technical Reports Server (NTRS)
Perturbation theory, when applied to charged-particle transport, generates a series solution that requires a double quadrature per term. The continuity of higher-order terms leads to numerical evaluation of the series. The high rate of convergence of the series makes the method a practical tool for charged-particle transport problems. The coupling of the neutron component in the case of proton transport in tissue does not greatly alter the rate of convergence. The method holds promise for a practical high-energy proton transport theory.
Wilson, J. W.; Lamkin, S. L.
Contactless Probing of the Carrier Transport in Carbon Nanotubes Using Dielectric Force Microscopy
NASA Astrophysics Data System (ADS)
We have developed a scanning probe microscopy (SPM) based technique which is named as dielectric force microscopy (DFM) to manipulate and probe the majority carriers in 1-dimentional nanoelectronic materials. We have demonstrated its success in distinguishing semiconducting single-walled carbon nanotubes (SWNTs) from metallic ones, locating semiconducting-metallic junction in SWNTs, determining the majority carrier types in SWNTs and ZnO nanowires, and detecting the electronic doping of SWNTs by gaseous ammonia. To achieve a quantitative measure of the intrinsic carrier transport, we have performed DFM measurement on individual SWNTs, fabricated field effect transistor devices with the individual SWNT serving as the channel, and carried out electrical transport experiment. The results from DFM and transport measurements are quantitatively correlated in an almost perfect fashion allowing the extraction of intrinsic carrier transport properties especially carrier mobility from DFM data without making metal contacts. Furthermore, we have successfully detected the location and behavior of local transport barriers in SWNTs utilizing the nanometer scale resolution feature of DFM.
Li, Yize; Ge, Jun; Liu, Jia; Zhang, Jie; Lu, Wei; Chen, Liwei
41 CFR 302-7.103 - How are the charges calculated when a carrier charges a minimum weight, but the actual weight of...
Code of Federal Regulations, 2013 CFR
...actual weight of HHG, PBP&E and temporary storage is less than the minimum weight charged...RELOCATION ALLOWANCES TRANSPORTATION AND STORAGE OF PROPERTY 7-TRANSPORTATION AND TEMPORARY STORAGE OF HOUSEHOLD GOODS AND PROFESSIONAL...
Accessing the transport properties of graphene and its multi-layers at high carrier density
We present a comparative study of high carrier density transport in mono-, bi-, and trilayer graphene using electric-double-layer transistors to continuously tune the carrier density up to values exceeding 10^{14} cm^{-2}. Whereas in monolayer the conductivity saturates, in bi- and trilayer flling of the higher energy bands is observed to cause a non-monotonic behavior of the conductivity, and a large
J. T. Ye; M. F. Craciun; M. Koshino; S. Russo; S. Inoue; H. T. Yuan; H. Shimotani; A. F. Morpurgo; Y. Iwasa
Carrier Transport in InGaN MQWs of Aquamarine and Green-Laser Diodes
We studied experimentally and theoretically the substrate-orientation impact on carrier transport and capture in InGaN multiple quantum well (MQW) laser diodes (LDs) with emission in the aquamarine-green spectral range. A new simula- tion approach was developed to analyze this behavior of LEDs and LDs emitting at these wavelengths. We show that due to deep carrier confinement, the thermal escape from
Dmitry S. Sizov; Rajaram Bhat; Aramais Zakharian; Kechang Song; Donald E. Allen; Sean Coleman; Chung-en Zah
Triboelectric charging of polymer powders in fluidization and transport processes
In this paper, we investigated the role of tribocharging in fluidization, flowability, and q\\/m distribution as functions of particle size distribution (PSD), fluidization time, and transport tubes of different materials. A charge separator was used to determine mass fractions of powder that had positive, zero, and negative charges. For the two acrylic powders tested, one (Sample A) had volume median
Malay K. Mazumder; Robert A. Sims; David L. Wankum; Tony Chasser
The charge transport in an electrostatic belt generator
The fluctuations in the charge transport system of an EN Tandem Van de Graaff accelerator have been investigated by means of a frequency spectrum analyser. Frequency spectra of the terminal ripple, the short-circuit current and the voltage at the belt charge screen have been measured. Also the correlation function is examined between the last two signals. The mechanisms which can
A. Vermeer; B. A. Strasters
An acoustic charge transport imager for high definition television applications
NASA Technical Reports Server (NTRS)
In this report we present the progress during the second six month period of the project. This includes both experimental and theoretical work on the acoustic charge transport (ACT) portion of the chip, the theoretical program modelling of both the avalanche photodiode (APD) and the charge transfer and overflow transistor and the materials growth and fabrication part of the program.
Hunt, William D.; Brennan, Kevin F.; Summers, Chris J.
Models of long-distance transport: how is carrier-dependent auxin transport regulated in the stem?
� This paper presents two models of carrier-dependent long-distance auxin transport in stems that represent the process at different scales. � A simple compartment model using a single constant auxin transfer rate produced similar data to those observed in biological experiments. The effects of different underlying biological assumptions were tested in a more detailed model representing cellular and intracellular processes that enabled discussion of different patterns of carrier-dependent auxin transport and signalling. � The output that best fits the biological data is produced by a model where polar auxin transport is not limited by the number of transporters/carriers and hence supports biological data showing that stems have considerable excess capacity to transport auxin. � All results support the conclusion that auxin depletion following apical decapitation in pea (Pisum sativum) occurs too slowly to be the initial cause of bud outgrowth. Consequently, changes in auxin content in the main stem and changes in polar auxin transport/carrier abundance in the main stem are not correlated with axillary bud outgrowth. PMID:22443265
Renton, Michael; Hanan, Jim; Ferguson, Brett J; Beveridge, Christine A
Measurement of carrier transport and recombination parameter in heavily doped silicon
NASA Technical Reports Server (NTRS)
The minority carrier transport and recombination parameters in heavily doped bulk silicon were measured. Both Si:P and Si:B with bulk dopings from 10 to the 17th and 10 to the 20th power/cu cm were studied. It is shown that three parameters characterize transport in bulk heavily doped Si: the minority carrier lifetime tau, the minority carrier mobility mu, and the equilibrium minority carrier density of n sub 0 and p sub 0 (in p-type and n-type Si respectively.) However, dc current-voltage measurements can never measure all three of these parameters, and some ac or time-transient experiment is required to obtain the values of these parameters as a function of dopant density. Using both dc electrical measurements on bipolar transitors with heavily doped base regions and transients optical measurements on heavily doped bulk and epitaxially grown samples, lifetime, mobility, and bandgap narrowing were measured as a function of both p and n type dopant densities. Best fits of minority carrier mobility, bandgap narrowing and lifetime as a function of doping density (in the heavily doped range) were constructed to allow accurate modeling of minority carrier transport in heavily doped Si.
Swanson, Richard M.
RoF transport systems with OSNR enhanced multi-band optical carrier generator.
A combination of an economic multi-band optical carrier generator and a novel optical signal to noise ratio (OSNR) enhancement circuit is proposed and demonstrated for radio over fiber (RoF) transport systems. Different from normal RoF transport systems which a central station (CS) needs multiple dedicate wavelength laser diodes (LDs) to support various base stations (BSs), the proposed scheme can employ a single LD to provide multiple optical carriers for various BSs. To verify this scheme, 8 coherent optical carriers are firstly generated using a single LD and a local oscillator (LO). Subsequently, their OSNR values are optimized by the developed OSNR enhancement circuit. An up to 15 dB OSNR enlargement in those optical carriers is experimentally achieved. To demonstrate the practice of the proposal, a pair of those optical carriers is employed to experimentally achieve frequency up-conversion process in a RoF transport system. Clear eye diagram and error free transmission reveal that with a proper carrier selector the proposed scheme can be employed to support multiple RoF transmissions. Furthermore, this proposal also presents a high possibility to achieve 60 GHz RoF transmission using a 10 GHz LO, a LD and a low frequency external modulator. PMID:21935221
Su, Heng-Sheng; Li, Chung-Yi; Lu, Hai-Han; Chang, Ching-Hung; Peng, Peng-Chun; Wu, Po-Yi; Chen, Hwan-Wen
Negative differential resistance and carrier transport of electrically bistable devices based on poly(N-vinylcarbazole)-silver sulfide composites.
An electrically bistable device has been fabricated based on poly(N-vinylcarbazole) (PVK)-silver sulfide (Ag2S) composite films using a simple spin-coating method. Current-voltage (I-V) characteristics of the as-fabricated devices exhibit a typical electrical bistability and negative differential resistance (NDR) effect. The NDR effect can be tuned by varying the positive charging voltage and the charging time. The maximum current ratio between the high-conducting state (ON state) and low-conducting state (OFF state) can reach up to 104. The carrier transport mechanisms in the OFF and ON states are described by using different models on the basis of the experimental result. PMID:24641989
Li, Jiantao; Tang, Aiwei; Li, Xu; Cao, Yapeng; Wang, Miao; Ning, Yu; Lv, Longfeng; Lu, Qipeng; Lu, Yunzhang; Hu, Yufeng; Hou, Yanbing; Teng, Feng
Negative differential resistance and carrier transport of electrically bistable devices based on poly(N-vinylcarbazole)-silver sulfide composites
An electrically bistable device has been fabricated based on poly(N-vinylcarbazole) (PVK)-silver sulfide (Ag2S) composite films using a simple spin-coating method. Current�voltage (I-V) characteristics of the as-fabricated devices exhibit a typical electrical bistability and negative differential resistance (NDR) effect. The NDR effect can be tuned by varying the positive charging voltage and the charging time. The maximum current ratio between the high-conducting state (ON state) and low-conducting state (OFF state) can reach up to 104. The carrier transport mechanisms in the OFF and ON states are described by using different models on the basis of the experimental result.
Polaron effects and electric field dependence of the charge carrier mobility in conjugated polymers
NASA Astrophysics Data System (ADS)
Charge transport in conjugated polymers has been investigated using Monte Carlo simulations implemented on top of the Marcus theory for donor-acceptor transition rates. In particular, polaron effects and the dependency of the mobility on the temperature and the applied electric field have been studied. The conclusions are that while the qualitative temperature dependence is similar to that predicted by Miller-Abrahams theory in the Gaussian disorder model (GDM), the electric field dependence is characterized by a crossover into the Marcus inverted region, not present in the GDM. Furthermore, available analytical approximations to describe the electric field dependence of the mobility in Marcus theory fail to fit the simulation data and hence cannot be used to directly draw conclusions about the importance of polaron effects for charge transport in conjugated polymers.
Jakobsson, Mattias; Stafstr�m, Sven
Essential physics of carrier transport in nanoscale MOSFETs
The device physics of nanoscale MOSFETs is explored by numerical simulations of a model transistor. The physics of charge control, source velocity saturation due to thermal injection, and scattering in ultrasmall devices are examined. The results show that the essential physics of nanoscale MOSFETs can be understood in terms of a conceptually simple scattering model
Mark Lundstrom; Zhibin Ren
The stress-affected carrier injection and transport in organic semiconductor devices
NASA Astrophysics Data System (ADS)
The current-voltage (I-V) characteristics of the thin films of methoxy-5-(2'-ethylhexyloxy)-1,4-phyenylenevinylene] (MEH-PPV) and tris-(8-hydroxyquinoline) aluminum (Alq) under different stresses have been measured, together with their Young's modulus, hardness, and loading curve. We propose a model on stress-affected carrier injection and transport to explain the experimental results. The model is based on the well-built space-charge-limited current (SCLC) and injection-limited current (ILC) model, together with the electrical and mechanic properties of organic semiconductor. By Monte Carlo simulation, we investigated the relationship between the conductance and strain. We found two trends in the current variation with the stress. One is fast at low current density, and the other is relatively slower at high current density, which may due to the SCLC in the bulk and the ILC at the interface, respectively. The working voltage of the present device with the highest sensitivity is about 1 V.
Dai, Weifeng; Zhang, Bin; Kang, Yonglong; Chen, Huamin; Zhong, Gaoyu; Li, Yuesheng
Inorganic/organic hybrid solar cells: optimal carrier transport in vertically aligned silicon nanowire arrays.
Inorganic/organic hybrid radial heterojunction solar cells that combine vertically-aligned n-type silicon nanowires (SiNWs) with poly(3,4-ethylenedioxythiophene):poly(styrene-sulfonate) (PEDOT:PSS) have great potential for replacing commercial Si solar cells. The chief advantage of such solar cells is that they exhibit higher absorbance for a given thickness than commercial Si solar cells, due to incident light-trapping within the NW arrays, thus enabling lower-cost solar cell production. We report herein on the effects of NW length, annealing and surface electrode on the device performance of SiNW/PEDOT:PSS hybrid radial heterojunction solar cells. The power conversion efficiency (PCE) of the obtained SiNW/PEDOT:PSS hybrid solar cells can be optimized by tuning the thickness of the surface electrode, and the etching conditions during NW formation and post-annealing. The PCE of 9.3% is obtained by forming efficient transport pathways for photogenerated charge carriers to electrodes. Our approach is a significant contribution to design of high-performance and low-cost inorganic/organic hybrid heterojunction solar cells. PMID:24789210
Sato, Keisuke; Dutta, Mrinal; Fukata, Naoki
All Electronic Charge Carrier Transit Time Mobility Measurements and Data Analysis in Pentacene Organic Field Effect Transistors
In organic field-effect transistors (OFETs), the most common method of estimating mobility is to extract it from the transfer characteristics (e.g., Id-Vds and Id-Vdg curves). Time-of-flight measurements via optical excitation of charge carriers in the organic material are also used, but this technique measures the mobility of carriers perpendicular to their motion in the OFET geometry. Additionally, in some polycrystalline
Lawrence Dunn; Debarshi Basu; Liang Wang; Ananth Dodabalapur
Heating of charge carriers and rectification of current in asymmetrical p-n junction in a microwave field
The emf U{sub oc} of hot charge carriers generated in an asymmetrical p-n junction in a microwave electromagnetic field is determined by hot holes despite the fact that the temperature of electrons is much higher than that of holes. It is established that the open-circuit voltage depends on the temperature of the carriers, which determine the total current through p-n junction.
Dadamirzayev, M. G., E-mail: email@example.com [Namangan Engineering Pedagogical Institute (Uzbekistan)
Numerical Simulation on the Charge Transport in Tris(8-hydroxyquinolinato)aluminum-Based Organic Light-Emitting Diode Structure
NASA Astrophysics Data System (ADS)
In this paper, we report on our theoretical study on the charge transport of a multilayer structure for organic light-emitting diodes (OLEDs). Our simulation structure comprises a hole transport layer (HTL), an emission layer (EML), and an electron transport layer (ETL) between two electrodes wherein the HTL is N,N\\aku '-bis(3-methylphenyl)-N,N\\aku '-bis(phenyl)benzidine (TPD) and the ETL includes tris(8-hydroxyquinolinato)aluminum (Alq3). We discuss the carrier transport mechanism of the Alq3-based two-layer structure and thereby propose a high-efficiency device structure. We also report our investigation on the transient response during the turn-on/off period and the carrier transport in response to the variation of the injection barrier and applied voltage. This paper also reports the effect of the insertion of the EML layer and the efficiency dependence on the difference in the internal barrier height.
Kim, Kwangsik; Won, Taeyoung
Accessing the transport properties of graphene and its multilayers at high carrier density.
We present a comparative study of high carrier density transport in mono-, bi-, and trilayer graphene using electric double-layer transistors to continuously tune the carrier density up to values exceeding 10(14) cm(-2). Whereas in monolayer the conductivity saturates, in bi- and trilayer filling of the higher-energy bands is observed to cause a nonmonotonic behavior of the conductivity and a large increase in the quantum capacitance. These systematic trends not only show how the intrinsic high-density transport properties of graphene can be accessed by field effect, but also demonstrate the robustness of ion-gated graphene, which is crucial for possible future applications. PMID:21828007
Ye, Jianting; Craciun, Monica F; Koshino, Mikito; Russo, Saverio; Inoue, Seiji; Yuan, Hongtao; Shimotani, Hidekazu; Morpurgo, Alberto F; Iwasa, Yoshihiro
Observation of enhanced carrier transport properties of Si ?100?-oriented whiskers under uniaxial strains
NASA Astrophysics Data System (ADS)
In this study, enhancements of the carrier transport properties of p-type ?100?-oriented Si whiskers are observed under uniaxial tensile and compressive strains. It has been found that over 400% enhancement of electrical conductivity is achieved under a 2% tensile strain, while a 2% compressive strain can only cause �80% conductivity enhancement. The enhancements are mainly attributed to the breaking of the degeneracy of the v2 and v1 valence bands induced a reduction of the hole effective mass. This study provides an important insight of how the carrier mobility variation caused by the strain impact on their transport properties.
Zheng, Kun; Shao, Ruiwen; Deng, Qingsong; Zhang, Yuefei; Li, Yujie; Han, Xiaodong; Zhang, Ze; Zou, Jin
Accessing the transport properties of graphene and its multilayers at high carrier density
We present a comparative study of high carrier density transport in mono-, bi-, and trilayer graphene using electric double-layer transistors to continuously tune the carrier density up to values exceeding 1014�cm-2. Whereas in monolayer the conductivity saturates, in bi- and trilayer filling of the higher-energy bands is observed to cause a nonmonotonic behavior of the conductivity and a large increase in the quantum capacitance. These systematic trends not only show how the intrinsic high-density transport properties of graphene can be accessed by field effect, but also demonstrate the robustness of ion-gated graphene, which is crucial for possible future applications.
Ye, Jianting; Craciun, Monica F.; Koshino, Mikito; Russo, Saverio; Inoue, Seiji; Yuan, Hongtao; Shimotani, Hidekazu; Morpurgo, Alberto F.; Iwasa, Yoshihiro
Charge accumulation due to spin transport in magnetic multilayers
NASA Astrophysics Data System (ADS)
Starting with the Valet-Fert theory of the current-perpendicular-to-plane giant magnetoresistance, we studied the charge accumulation due to spin transport in magnetic multilayers by solving Poisson's equation analytically. Our results show that, in ferromagnetic layers, the charge accumulation has two exponential terms with opposite signs and different decaying lengths: the Thomas-Fermi screening length (on the order of angstrom) and the spin diffusion length (tens of nm in 3d ferromagnetic metals). The charge accumulation on the scale of the screening length is spin-unpolarized and also present in spin-independent transport in nonmagnetic multilayers. However, the charge accumulation on the scale of the spin diffusion length is spin-polarized and shows up only in ferromagnetic layers. Our analysis also provides new insights into the widely used quasi-neutrality approximation, which neglects the charge accumulation.
Zhu, Yao-Hui; Xu, Deng-Hui; Geng, Ai-Cong
Lifetime of charge carriers in Hg1-xCdxTe (x=0.20) crystals
NASA Astrophysics Data System (ADS)
We examine the mechanisms for Auger recombination in narrow-gap semiconductors of the Hg1-xCdxTe type, connected with collision between two electrons in the Ec band followed by transition of one of them to the Ev1 band and collision between two holes in the Ev1 band followed by transition of one of them to the Ev2 band. In analyzing the contributions from different recombination mechanisms over broad concentration and temperature range, we used the models of P. E. Petersen and B. L. Gel'mont, taking into account the specific characteristics of the band structure of Hg1-xCdxTe crystals. We determined the temperature and concentration ranges for n- and p-type semiconductors in which different recombination mechanisms are realized, including a radiative mechanism. We compare the experimental data on charge carrier lifetime with the calculation results using different recombination models in the crystals under study.
Voitsekhovskii, A. V.
Effect of uniaxial compression on traps of excitons and charge carriers in poly(9-vinylcarbazole) films
NASA Astrophysics Data System (ADS)
The effect of uniaxial pressure (1 � 108 Pa) on the photoluminescence spectra and thermally stimulated luminescence curves of poly(9-vinylcarbazole) has been investigated in the temperature range of 5-295 K. The thermally stimulated luminescence curve of crystalline carbazole has been measured for comparison. The high-temperature wings of the thermally stimulated luminescence curves are approximated by a Gaussian function, the half-width of which characterizes the disorder of energy states of deep structural traps. It is concluded that the pressure inhibits conformational changes of polymer chains of poly(9-vinylcarbazole), which leads to the formation of sandwich-like excimers as well as to an ordering of the spatial arrangement of the side carbazolyl groups. As a result, the concentration of "excimer-forming" centers increases, whereas the degree of disorder of energy states of deep structural traps of charge carriers is reduced by almost half and remains unchanged after the depressurization.
Skryshevski, Yu. A.
Electrical phase transition of poly(4,4'-aminotriphenylene hexafluoroisopropylidenediphthalimide) by photogenerated charged carrier injection
NASA Astrophysics Data System (ADS)
We show a set-up of poly(4,4'-aminotriphenylene hexafluoroisopropylidenediphthalimide) (6F-TPA PI)/Al sample in which holes are injected by photoelectron emission process instead of direct charge carrier injection via metal electrode. In this process, an irreversible electrical phase transition of 6F-TPA PI is found in contrast to the Al/6F-TPA PI/Al structure, leading to a write-once-read-many behavior. The photoelectron spectroscopy results measured before and after the switching process revealed that the irreversible electrical phase transition of 6F-TPA PI is attributed to the chemical modification of the carbonyl group in phthalimide moiety.
Lee, Kyoung-Jae; Min Kim, Dong; Ihm, Kyuwook; Ree, Moonhor; Kang, Tai-Hee; Chung, Sukmin
Confinement Effects and Surface-Induced Charge Carriers in Bi Quantum Wires
NASA Astrophysics Data System (ADS)
For small diameters, less than about 200 nanometers, Bi nanowires display modifications of the band structure due to quantum confinement and a transformation from semimetal-to-semiconductor is predicted to occur for diameters of around 60 nm. We have measured the Shubnikov-de Haas oscillations of the magnetoresistance in arrays of bismuth nanowires for various orientations of the magnetic field with respect to the wirelength. For wires of diameter larger than 80 nm, the hole concentration, which is less than that for bulk Bi, is found to decrease for decreasing wire diameters (a decrease from the bulk Bi hole concentration by 70 finding that is consistent with current models of quantum confinement effects. However, 30-nm-diameter nanowires, which are predicted to be semiconductors, show a nearly isotropic short period of 0.025 T-1, consistent with a heavy carrier concentration five times that of bulk Bi. These results are discussed in terms of surface-induced charge carriers in a spherical Fermi surface pocket that are uniformly distributed in the 30-nm nanowire volume and that inhibit the semimetal-to-semiconductor transition. Support by the U.S. Army Research Office through DAAD19-02-1-0303 and by the National Science Foundation through DMR-0072847 is acknowledged.
Huber, T. E.; Graf, M. J.; Foss, J. R.
Electrodeless measurement of charge carrier mobility in pentacene by microwave and optical spectroscopy techniques
NASA Astrophysics Data System (ADS)
Photoinduced transient conductivity of pentacene thin films prepared by thermal vapor deposition is investigated using time-resolved microwave conductivity (TRMC) measurements, giving intrinsic charge carrier mobility in highly ordered structures without any electrode attached. The real and imaginary conductivity values are analyzed and compared with those predicted by molecular orbital calculations. The effects of substrate surface treatment by hexamethyldisilazane are discussed on the basis of kinetic traces of conductivity and morphology. A mobility of >0.7 cm2/V s was obtained from the TRMC measurements and analysis of transient absorption spectra. The measurement of field-effect-transistor mobility in single-crystal domains requires not only complicated fabrication techniques but also many assumptions on the carrier channels, density, injection, etc. The combination of TRMC and transient optical spectroscopy provides an approach for addressing this issue. The present technique is applicable to a wide variety of organic semiconducting materials. Moreover, it is the only technique revealing the intrinsic potentials of mobility in materials that is supported by complete experimental and quantitative procedures not based on any assumptions.
Saeki, Akinori; Seki, Shu; Tagawa, Seiichi
Quantifying charge carrier concentration in ZnO thin films by Scanning Kelvin Probe Microscopy
NASA Astrophysics Data System (ADS)
In the last years there has been a renewed interest for zinc oxide semiconductor, mainly triggered by its prospects in optoelectronic applications. In particular, zinc oxide thin films are being widely used for photovoltaic applications, in which the determination of the electrical conductivity is of great importance. Being an intrinsically doped material, the quantification of its doping concentration has always been challenging. Here we show how to probe the charge carrier density of zinc oxide thin films by Scanning Kelvin Probe Microscopy, a technique that allows measuring the contact potential difference between the tip and the sample surface with high spatial resolution. A simple electronic energy model is used for correlating the contact potential difference with the doping concentration in the material. Limitations of this technique are discussed in details and some experimental solutions are proposed. Two-dimensional doping concentration images acquired on radio frequency-sputtered intrinsic zinc oxide thin films with different thickness and deposited under different conditions are reported. We show that results inferred with this technique are in accordance with carrier concentration expected for zinc oxide thin films deposited under different conditions and obtained from resistivity and mobility measurements.
Maragliano, C.; Lilliu, S.; Dahlem, M. S.; Chiesa, M.; Souier, T.; Stefancich, M.
Nitrogen-doped graphene sheets grown by chemical vapor deposition: synthesis and influence of nitrogen impurities on carrier transport.
A significant advance toward achieving practical applications of graphene as a two-dimensional material in nanoelectronics would be provided by successful synthesis of both n-type and p-type doped graphene. However, reliable doping and a thorough understanding of carrier transport in the presence of charged impurities governed by ionized donors or acceptors in the graphene lattice are still lacking. Here we report experimental realization of few-layer nitrogen-doped (N-doped) graphene sheets by chemical vapor deposition of organic molecule 1,3,5-triazine on Cu metal catalyst. When reducing the growth temperature, the atomic percentage of nitrogen doping is raised from 2.1% to 5.6%. With increasing doping concentration, N-doped graphene sheet exhibits a crossover from p-type to n-type behavior accompanied by a strong enhancement of electron-hole transport asymmetry, manifesting the influence of incorporated nitrogen impurities. In addition, by analyzing the data of X-ray photoelectron spectroscopy, Raman spectroscopy, and electrical measurements, we show that pyridinic and pyrrolic N impurities play an important role in determining the transport behavior of carriers in our N-doped graphene sheets. PMID:23879622
Lu, Yu-Fen; Lo, Shun-Tsung; Lin, Jheng-Cyuan; Zhang, Wenjing; Lu, Jing-Yu; Liu, Fan-Hung; Tseng, Chuan-Ming; Lee, Yi-Hsien; Liang, Chi-Te; Li, Lain-Jong
The interaction of charge carriers with excitons and plasmons within colloidal and epitaxial semiconductor nanostructures
NASA Astrophysics Data System (ADS)
This dissertation describes the influence of the presence of charges--both bound electron and hole charge pairs (excitons) as well as free carriers--on the optical properties of semiconductor nanostructures. In a characterization of the evolution of the electronic structure of semiconductor nanostructures with increasing shape anisotropy, transient absorption (TA) and photoluminescence excitation (PLE) anisotropy measurements revealed that the band-edge absorptive and emissive transitions of CdSe nanorods contain both linear (z) and planar (xy) polarization character. The degree of planar character at the band-edge, modulated by classical local field effects arising from the dielectric contrast between the nanorod and the solvent, limits the degree of photoselection at this wavelength, while variation in the magnitude of the xy projection of the absorptive transitions within states above the band-edge is responsible for the observed wavelength-dependence of the absorption and emission anisotropies. The interaction of excess charge with the excitonic states of CdSe quantum dots (QDs) was probed with steady-state photoluminescence (PL) and ultrafast transient absorption measurements. The results of these experiments were utilized to construct a model for photobrightening (PB) - an increase in PL quantum yield with photoexcitation - based on migration of photoexcited electrons within the film. The basis for this model is that PB is limited by the rate of migration of electrons among surface-localized energetically shallow traps in the film, and not by the rate of creation of surface-trapped charge carriers. Finally, TA and transient third harmonic generation probe (THG-probe) spectroscopies were used to investigate the response of the localized surface plasmon resonances (LSPRs) of vertically aligned ITO nanowires (NWs) upon UV excitation. Both TA and THG-probe experiments show an increase in the frequency of the LSPR upon population of the conduction band of the ITO. The LSPR shifts back to its original energy on the single-picosecond lifetime of the photoexcited electrons. These results indicate that UV excitation modulates the plasma frequency of ITO on the ultrafast timescale by the injection of electrons into, and their subsequent decay from, the conduction band of the NWs, with ~13% changes to the electron concentration in the conduction band achievable in these experiments.
Tice, Daniel Boitnott
Temperature dependence of charge carrier mobility in single-crystal chemical vapour deposition diamond
NASA Astrophysics Data System (ADS)
Measurements of the temperature dependence of the charge carrier mobility in single-crystal chemical vapour deposition diamond using the transient current technique are presented in a temperature range from 2 K to room temperature. An ?-source is used to create free charge carriers in the diamond bulk. The evolution of the current signal induced by their drift under the influence of an externally applied field is studied as a function of the temperature and the electric field strength. The electric field strength is varied by a factor of 30. The measurements are used to extract the transit time, the drift velocity, the saturation velocity, and the low-field mobility in terms of which the results are interpreted. Three samples have been studied which show the same behaviour. For holes, the mobility increases with decreasing temperature due to the acoustic phonon scattering, but it saturates for ultra-cold temperatures. The low-field mobility for holes at room temperature is measured as ?0h(295K)=(2534+/-20) cm2/Vs saturating against ?0h(-->2K)=(11130+/-120) cm2/Vs. For electrons, only a lower limit on the low-field mobility can be given. It is measured as ?0e(295K)=(1802+/-14) cm2/Vs saturating against ?0e(-->2K)=(3058+/-27) cm2/Vs. The electron transit time at low fields shows a different behaviour than the hole transit time and is not following the expected behaviour. This is likely to be caused by a high temperature valley re-population effect.
Jansen, Hendrik; Dobos, Daniel; Eisel, Thomas; Pernegger, Heinz; Eremin, Vladimir; Wermes, Norbert
The key role of charge carriers scattering on polar optical phonons in semiconductors for thermoelectric energy conversion
NASA Astrophysics Data System (ADS)
The Boltzmann equation for charge carriers in n-type InSb is solved by numerical procedure. Temperature and donor atoms concentration dependences of kinetic coefficients are studied with respect to the thermoelectric energy conversion efficiency. It is found that the mechanism of the charge carriers scattering on polar optical phonons is of crucial importance for thermoelectric figure of merit of semiconductors. High thermoelectric efficiency of compounds and alloys comprising such heavy atoms as Pb or Bi is explained by weakening of the above mentioned scattering mechanism due to gigantic values of dielectric constants of substances caused by high polarizability of heavy atoms.
Orlov, V. G.; Sergeev, G. S.
Jahn-Teller assisted polaronic hole hopping as a charge transport mechanism in CuO nanograins
NASA Astrophysics Data System (ADS)
Impedance spectroscopy has been employed to investigate the dielectric and electric transport phenomena in sol-gel synthesized CuO nanograins. Semiconducting features of the grains and grain boundaries have been endorsed to the thermal activation of the localized charge carriers. On cooling below 303 K, a transition from Jahn-Teller polaron hopping mechanism to the Mott's variable range hopping mechanism has been observed owing to random potential fluctuations among localized sites. Activation energies for conduction and relaxation processes at grain boundaries provide strong signatures for the involvement of Jahn-Teller adiabatic small polarons as a charge transport mechanism in CuO nanograins.
Younas, M.; Nadeem, M.; Idrees, M.; Akhtar, M. J.
The ADP and ATP transport in mitochondria and its carrier
Different from some more specialised short reviews, here a general although not encyclopaedic survey of the function, metabolic role, structure and mechanism of the ADP\\/ATP transport in mitochondria is presented. The obvious need for an �old fashioned� review comes from the gateway role in metabolism of the ATP transfer to the cytosol from mitochondria. Amidst the labours, 40 or more
Martin Klingenberg
Effect of Cooling Rate on Microstructure and Charge Transport in Semiconducting Polymer Thin Films
NASA Astrophysics Data System (ADS)
Thermal annealing of polymer thin films often enhances charge carrier mobility which can be attributed to self-healing of the film morphology. We have investigated the effect of cooling rate following the annealing treatment on the thin film microstructure and the charge transport properties using a high performance semiconducting polymer, poly(2,5-bis(3-alkylthiophen-2-yl)thieno[3,2-b]thiophene) (PBTTT). The cooling rate plays a key role in determining the microstructure and performance of polymer thin films. Differential scanning calorimeter measurement shows that fast cooling suppresses the crystallization process. The microstructure of thin films is investigated by using 2D X-ray diffraction and atomic force microscopy. Slow cooling results in well-connected large domains with enhanced three dimensional ordering whereas fast cooling leads to misalignment of small domains with relatively rough surface. Transport characteristics at various temperatures show increase in the charge carrier mobility and decrease in the activation energy when the cooling rate is slowed. This change in the mobility and activation energy becomes saturated with cooling rate below 15 C/min.
Kang, Evan; Kim, Eunseong
Transport in Ballistic Diodes Fabricated in p-GaAs Quantum Wells with Negative Effective Mass Carriers
Theory predicts that the ballistic transport within a quantum well of a system where carrier dispersion has a region of negative effective mass (NEM) will form unstable self-organized carrier distributions. In a diode with a sufficiently short source-drain distance L, the NEM carriers predominate, causing an instability that should result in oscillations analogous to the Gunn effect, but at much
B. R. Perkins; Jun Liu; A. Zaslavsky; M. Shayegan; Z. S. Gribnikov; V. V. Mitin
Ultrahigh-frequency surface acoustic wave generation for acoustic charge transport in silicon
NASA Astrophysics Data System (ADS)
We demonstrate piezo-electrical generation of ultrahigh-frequency surface acoustic waves on silicon substrates, using high-resolution UV-based nanoimprint lithography, hydrogen silsequioxane planarization, and metal lift-off. Interdigital transducers were fabricated on a ZnO layer sandwiched between two SiO2 layers on top of a Si substrate. Excited modes up to 23.5 GHz were observed. Depth profile calculations of the piezoelectric field show this multilayer structure to be suitable for acoustic charge transport in silicon at extremely high frequencies with moderate carrier mobility requirements.
B�y�kk�se, S.; Vratzov, B.; van der Veen, J.; Santos, P. V.; van der Wiel, W. G.
Charged particles time-dependent transverse transport
NASA Astrophysics Data System (ADS)
We discuss an analytical derivation for the temporal dependence of the transverse transport coefficient for times smaller than the correlation time of the magnetic turbulence, as seen by the particle, where the quasi-linear theory is not valid. The transverse transport is assumed to be dominated by the guiding center motion. Contributions of wavelengths shorter and longer than the coherence length to particle drift from the local magnetic field lines and to the magnetic field lines random walk are assessed for slab and 3D isotropic turbulence. Extensions of this model will allow for a study of solar wind physically motivated anisotropy.
Fraschetti, F.; Jokipii, J. R.
Evidence for a Carrier-Mediated Mechanism for Thiamine Transport to Human Jejunal Basolateral Membrane Vesicles
Recent studies from our laboratory have demonstrated the presence of a pH-dependent, amiloride-sensitive, electroneutral carrier-mediated exchange for thiamine absorption in the human small intestinal brush-border membrane vesicles. However, the mechanism of thiamine transport across the human small intestinal basolateral membrane is not understood. The present study was aimed to characterize the mechanism of thiamine transport across the basolateral membranes of
Pradeep K. Dudeja; Sangeeta Tyagi; Ravinder Gill; Hamid M. Said
Modeling charge transport in swept charge devices for x-ray spectroscopy
NASA Astrophysics Data System (ADS)
We present the formulation of an analytical model which simulates charge transport in Swept Charge Devices (SCDs) to understand the nature of the spectral redistribution function (SRF). We attempt to construct the energy-dependent and position dependent SRF by modeling the photon interaction, charge cloud generation and various loss mechanisms viz., recombination, partial charge collection and split events. The model will help in optimizing event selection, maximize event recovery and improve spectral modeling for Chandrayaan-2 (slated for launch in 2014). A proto-type physical model is developed and the algorithm along with its results are discussed in this paper.
Athiray, P. S.; Narendranath, S.; Sreekumar, P.; Gow, J.; Radhakrishna, V.; Babu, B. R. S.
Carrier-mediated transport of actinide ions using supported liquid membranes containing TODGA as the carrier extractant
The transport behavior of Pu{sup 3+} under varying reducing conditions was investigated from a feed containing 3.0 M HNO{sub 3} into a receiver phase containing 0.1 M HNO{sub 3} using TODGA (N,N,N',N' - tetraoctyl-diglycolamide) as the carrier ligand. A mixture of 0.2 M hydroxyl ammonium nitrate and 0.2 M hydrazinium nitrate (used in the feed as the reducing agent) has been found to be effective for quantitative (>99%) transport of the trivalent Pu in about 3 h. Transport of trivalent plutonium in 3 h (>99%) was higher as compared to that of the tetravalent plutonium (94%), though their D values followed an opposite trend. The permeability coefficient (P) of Pu{sup 3+} was (4.63 {+-} 0.26) x 10{sup -3} cm/s as compared to (2.10 {+-} 0.14) x 10{sup -3} cm/s for Pu{sup 4+} and (3.67 {+-} 0.06) x 10{sup -3} cm/s Am{sup 3+}. P values of trivalent actinide ions such as Am{sup 3+}, Pu{sup 3+}, and Cm{sup 3+} are compared with their distribution data. (authors)
Panja, S.; Dakshinamoorthy, A.; Munshi, S.K.; Dey, P.K. [Fuel Reprocessing Division, B.A.R.C., Trombay, Mumbai-400085 (India); Mohapatra, P.K.; Manchanda, V.K. [Radiochemistry Division, B.A.R.C., Trombay, Mumbai-400085 (India)
Role of confinement on carrier transport in Ge-Si(x)Ge(1-x) core-shell nanowires.
We examine the impact of shell content and the associated hole confinement on carrier transport in Ge-Si(x)Ge(1-x) core-shell nanowires (NWs). Using NWs with different Si(x)Ge(1-x) shell compositions (x = 0.5 and 0.7), we fabricate NW field-effect transistors (FETs) with highly doped source/drain and examine their characteristics dependence on shell content. The results demonstrate a 2-fold higher mobility at room temperature, and a 3-fold higher mobility at 77K in the NW FETs with higher (x = 0.7) Si shell content by comparison to those with lower (x = 0.5) Si shell content. Moreover, the carrier mobility shows a stronger temperature dependence in Ge-Si(x)Ge(1-x) core-shell NWs with high Si content, indicating a reduced charge impurity scattering. The results establish that carrier confinement plays a key role in realizing high mobility core-shell NW FETs. PMID:22111925
Nah, Junghyo; Dillen, David C; Varahramyan, Kamran M; Banerjee, Sanjay K; Tutuc, Emanuel
The Onsager reciprocity principle as a check of consistency for semiconductor carrier transport models
During these years several hydrodynamic-like models for simulating carrier transport in semiconductors have been developed. In this paper we check the consistency of these models with the Onsager Reciprocity Principle, which is one of the fundamental principles of Linear Irreversible Thermodynamics. Monte Carlo simulations for silicon in the inhomogeneous case are shown.
Orazio Muscato
A New Carrier Transport Model for Light Emitting Devices with Quantum Well
We present a new carrier transport model for light emitting devices with quantum well. These devices include light emitting diodes (LEDs) and laser diodes (LDs). Nearly all LDs and high efficient LEDs in production contain a quantum well (QW) or multi-quantum well (MQW) in a PN junction. When these devices are driven to produce light, large number of carries, electrons
Chin C. Lee
47 CFR 69.111 - Tandem-switched transport and tandem charge.
Code of Federal Regulations, 2010 CFR
...index for the interconnection charge service category (defined in...tandem-switched transport charges within each study area used for the purpose of jurisdictional separations, in which interconnectors...tandem-switched transport charges within the study area...
47 CFR 69.111 - Tandem-switched transport and tandem charge.
Code of Federal Regulations, 2013 CFR
...index for the interconnection charge service category (defined in...tandem-switched transport charges within each study area used for the purpose of jurisdictional separations, in which interconnectors...tandem-switched transport charges within the study area...
47 CFR 69.111 - Tandem-switched transport and tandem charge.
Code of Federal Regulations, 2010 CFR
...index for the interconnection charge service category (defined in...tandem-switched transport charges within each study area used for the purpose of jurisdictional separations, in which interconnectors...tandem-switched transport charges within the study area...
Unusual two-dimensional electrical charge transport at the surface of polycrystalline perovskite ultrathin films
NASA Astrophysics Data System (ADS)
The discontinuity of the lattice at the surface leads to an inherent presence of dangling bonds and atomic coordinations that differ from that of the bulk. As a consequence of this effect, we report on a two-dimensional confinement of the charge transport at the surface of polycrystalline perovskite oxide. Studying the surface transport separately from the bulk effect was approached by the investigation of ultrathin and stress-free LaCoO3 films that are grown on amorphous and nonconducting substrates using pulsed-spray evaporation chemical vapor deposition. The electrical characterization demonstrates an intriguing surface localization of the charge carriers. This surface trapping, which is observed above room temperature, dominates the electrical transport up to a temperature that depends on the film thickness, e.g., up to 440 K for 8-nm-thick films. This high-temperature effect, which is attributed to the surface adsorption of oxygen, points at a largely ignored surface effect in the study of thin and ultrathin films of transition metal oxides. Desorbing surface oxygen was experimentally shown to disrupt the two-dimensional confinement of the charge transport.
Ngamou, Patrick Herve Tchoua; Kohse-H�inghaus, Katharina; Bahlawane, Naoufal
Narrow-band charge transport in SnI4
Transient photoconductivity techniques have been used to investigate carrier transport in SnI4, a molecular solid. The hole drift mobility is equal to 2.2 cm2 V-1 S-1 at 295 K and varies approximately as T-4 over the temperature range 240 K to 370 K. This unusually rapid diminution with temperature is interpreted in terms of a nonlinear electron-phonon scattering process. It
T. E. Whall; V. Juzova
Charge transport through chains of nanoparticles
NASA Astrophysics Data System (ADS)
We present transport measurements through nanoparticles as well as preparation techniques to contact short chains of nanoparticles. The nanoparticles are deposited onto a mica substrate in a dewetting process of hexane solution containing the nanoparticles. The measurements were done in a self-developed probing tip setup inside a SEM, where the probing tips were driven by piezoelectric motors. The platinum iridium tips were fabricated by anodic dissolving in a drop-off method which results in sharp tip diameters. With this setup it was possible to contact and measure the nanoparticles under vacuum conditions. The I- V characteristics show a power law behavior as expected for low dimensional cluster systems. Transport in the device is expected to be influenced by Coulomb blockade effects and disorder.
L�dtke, T.; Mirovsky, P.; H�ther, R.; Govor, L.; Bauer, G. H.; Parisi, J.; Haug, R. J.
Dynamic disorder in molecular semiconductors: Charge transport in two dimensions
NASA Astrophysics Data System (ADS)
A semiclassical model to study charge transport in molecular semiconductors is extended from one to an arbitrary number of dimensions. The model is applied to the calculation of the charge mobility of the holes in the two dimensional plane of rubrene with the largest charge mobility. The absolute values of the computed mobility tensor, evaluated without adjustable parameters, are in excellent agreement with the experimental results of Podzorov et al. [Phys. Rev. Lett. 95, 226601 (2005)] and have the correct temperature dependence. The localization length and density of states determined by dynamic disorder are analyzed in detail and provide a global description of the charge transport process in agreement with the spectroscopic experiments. The effect of correlation in the modeling of dynamic disorder is also investigated.
Troisi, Alessandro
Monte Carlo modeling of the spatially dispersive carrier transport in P3HT and P3HT:PCBM blends
NASA Astrophysics Data System (ADS)
The presence of traps, arising from morpohological or chemical defects, can be critical to the performance of organic semiconductor devices. Traps can reduce the charge carrier mobility, disturb the internal electrical field, drive recombination, and reduce the overall device efficiency as well as operational stability. In this work, we investigate the role of traps in determining charge transport properties of organic semiconductors and blends such as P3HT and P3HT:PCBM through Monte-Carlo (MC) simulations in conjunction with time-of-flight (TOF) mobility measurements. We employ a Marcus theory description of individual hopping events based on the molecular reorganization energy (lambda) for the MC simulations. Trap states are modeled as diffuse bands that reside at some energy away from the main transport band. This model is used to simulate TOF transients, and the results are compared to experimental data. As is expected from the Marcus theory equation, the mobility is seen to be maximum for an optimal value of lambda. This optimal value is strongly field dependent, but is found to be independent of the trap density. In comparing MC simulations with TOF data, it is found that inclusion of traps results in a much better fit to the data and provides for a mechanism to simulate dispersive transport with a long tail resulting from trapping and detrapping of carriers before they exit the device. We present results for a range of trap densities and statistical distributions and discuss the implications on the operation of bulk heterojunction organic photovoltaic devices.
Jiang, Xin
Mathematical simulation of the distribution of minority charge carriers generated in a multilayer semiconducting structure by a wide electron beam
A method of calculation of the distributions of minority charge carriers generated in a two-layer semiconductor by a wide electron beam with energies 5-30 keV based on the use of the model of independent sources is described.
Burylova, I. V. [Tsiolkovskii Kaluga State Pedagogical University (Russian Federation); Petrov, V. I. [Moscow State University (Russian Federation); Snopova, M. G. [Bauman Moscow State Technical University, Kaluga Branch (Russian Federation); Stepovich, M. A. [Tsiolkovskii Kaluga State Pedagogical University (Russian Federation)
Spin dynamics of charge carriers in the process of their localization in ?'-(BEDT-TTF)2IBr2 single crystals
NASA Astrophysics Data System (ADS)
Sharp changes in the integral intensity and linewidth of the ESR spectrum that accompany the localization of the charge carriers have been revealed in ?'-(BEDT-TTF)2IBr2 crystals. It has been found that the types of localization in two compounds under investigation are different: charge carriers in ??-(BEDT-TTF)4NH4[Cr(C2O4)3] are localized on irregular defects of the crystal lattice, whereas charge carriers in ?'-(BEDT-TTF)2IBr2 are localized at the regular positions of the unit cell. The exchange narrowing of the ESR line and a sharp decrease in the dc and ac magnetic susceptibilities are observed in ?'-(BEDT-TTF)2IBr2 at low temperatures T < 50 K. The dc and ac magnetic susceptibilities observed in ?'-(BEDT-TTF)2IBr2 at high temperatures T > 50 K differ from each other, because the thermally activated hopping frequency of the charge carriers is higher than the frequency of the measuring UHF field of an ESR spectrometer.
Morgunov, R. B.; Dmitriev, A. I.; Chernen'kaya, A. S.; Yakushi, K.; Yamamoto, K.; Tanimoto, Y.
alpha-Isopropylmalate, a leucine biosynthesis intermediate in yeast, is transported by the mitochondrial oxalacetate carrier.
In Saccharomyces cerevisiae, alpha-isopropylmalate (alpha-IPM), which is produced in mitochondria, must be exported to the cytosol where it is required for leucine biosynthesis. Recombinant and reconstituted mitochondrial oxalacetate carrier (Oac1p) efficiently transported alpha-IPM in addition to its known substrates oxalacetate, sulfate, and malonate and in contrast to other di- and tricarboxylate transporters as well as the previously proposed alpha-IPM transporter. Transport was saturable with a half-saturation constant of 75 +/- 4 microm for alpha-IPM and 0.31 +/- 0.04 mm for beta-IPM and was inhibited by the substrates of Oac1p. Though not transported, alpha-ketoisocaproate, the immediate precursor of leucine in the biosynthetic pathway, inhibited Oac1p activity competitively. In contrast, leucine, alpha-ketoisovalerate, valine, and isoleucine neither inhibited nor were transported by Oac1p. Consistent with the function of Oac1p as an alpha-IPM transporter, cells lacking the gene for this carrier required leucine for optimal growth on fermentable carbon sources. Single deletions of other mitochondrial carrier genes or of LEU4, which is the only other enzyme that can provide the cytosol with alpha-IPM (in addition to Oac1p) exhibited no growth defect, whereas the double mutant DeltaOAC1DeltaLEU4 did not grow at all on fermentable substrates in the absence of leucine. The lack of growth of DeltaOAC1DeltaLEU4 cells was partially restored by adding the leucine biosynthetic cytosolic intermediates alpha-ketoisocaproate and alpha-IPM to these cells as well as by complementing them with one of the two unknown human mitochondrial carriers SLC25A34 and SLC25A35. Oac1p is important for leucine biosynthesis on fermentable carbon sources catalyzing the export of alpha-IPM, probably in exchange for oxalacetate. PMID:18682385
Marobbio, Carlo M T; Giannuzzi, Giulia; Paradies, Eleonora; Pierri, Ciro L; Palmieri, Ferdinando
?-Isopropylmalate, a Leucine Biosynthesis Intermediate in Yeast, Is Transported by the Mitochondrial Oxalacetate Carrier*
In Saccharomyces cerevisiae, ?-isopropylmalate (?-IPM), which is produced in mitochondria, must be exported to the cytosol where it is required for leucine biosynthesis. Recombinant and reconstituted mitochondrial oxalacetate carrier (Oac1p) efficiently transported ?-IPM in addition to its known substrates oxalacetate, sulfate, and malonate and in contrast to other di- and tricarboxylate transporters as well as the previously proposed ?-IPM transporter. Transport was saturable with a half-saturation constant of 75 � 4 ?m for ?-IPM and 0.31 � 0.04 mm for ?-IPM and was inhibited by the substrates of Oac1p. Though not transported, ?-ketoisocaproate, the immediate precursor of leucine in the biosynthetic pathway, inhibited Oac1p activity competitively. In contrast, leucine, ?-ketoisovalerate, valine, and isoleucine neither inhibited nor were transported by Oac1p. Consistent with the function of Oac1p as an ?-IPM transporter, cells lacking the gene for this carrier required leucine for optimal growth on fermentable carbon sources. Single deletions of other mitochondrial carrier genes or of LEU4, which is the only other enzyme that can provide the cytosol with ?-IPM (in addition to Oac1p) exhibited no growth defect, whereas the double mutant ?OAC1?LEU4 did not grow at all on fermentable substrates in the absence of leucine. The lack of growth of ?OAC1?LEU4 cells was partially restored by adding the leucine biosynthetic cytosolic intermediates ?-ketoisocaproate and ?-IPM to these cells as well as by complementing them with one of the two unknown human mitochondrial carriers SLC25A34 and SLC25A35. Oac1p is important for leucine biosynthesis on fermentable carbon sources catalyzing the export of ?-IPM, probably in exchange for oxalacetate.
Marobbio, Carlo M. T.; Giannuzzi, Giulia; Paradies, Eleonora; Pierri, Ciro L.; Palmieri, Ferdinando
Grain Boundary Effect on Charge Transport in Pentacene Thin Films
NASA Astrophysics Data System (ADS)
We report on charge transport properties of polycrystalline pentacene films with variable average grain size in the range from 0.1 to 0.3 ?m controlled by the preparation technology. We illustrate with the organic field-effect transistors decrease of the effective mobility and presence of traps with decrease of the grain size. Analysis of the charge transfer excitons reveals decrease of the mobile charge density and the steady-state voltammetry showed significant increase of oxygen- and hydrogen-related defects. We also briefly discuss accumulation of the defects on the grain boundary and show relation between the defect density and grain boundary length.
Weis, Martin; Gmucov�, Katar�na; N�da�dy, Vojtech; Majkov�, Eva; Ha�ko, Daniel; Taguchi, Dai; Manaka, Takaaki; Iwamoto, Mitsumasa
A thermodynamic framework for hydrodynamical models of carrier transport in semiconductors
A set of closed hydrodynamic-like equations is derived from Boltzmann's transport equation (BTE) describing charge transport in semiconductors. The moment hierarchy is closed by using the entropy principle and the production terms are modeled as relaxation terms consistently with the Onsager Reciprocity Principle. Finally the model is compared with Monte Carlo simulations for silicon.
A. M. Anile; O. Muscato
A direct charge pumping technique for spatial profiling of hot-carrier induced interface and oxide traps in MOSFETs
NASA Astrophysics Data System (ADS)
A new charge pumping (CP) technique is proposed to obtain the spatial profile of interface-state density ( Nit) and oxide charges ( Not) near the drain junction of hot-carrier stressed MOSFETs. Complete separation of Nit from Not is achieved by using a direct noniterative method. The pre-stress CP edge is corrected for the charges associated with both the generated Nit and Not. A closed form model is developed to predict the stress-induced incremental CP current. The damage distributions are obtained after fitting the model with experimental data.
Mahapatra, S.; Parikh, C. D.; Vasi, J.; Ramgopal Rao, V.; Viswanathan, C. R.
Positive Hole Charge Carriers and their Role in Generating Pre-Earthquake Phenomena
NASA Astrophysics Data System (ADS)
All minerals that crystallize from a fluid-laden magma or recrystallize in a high-grade metamorphic environment, even nominally anhydrous minerals, incorporate traces of H2O into their matrices: feldspars, pyroxenes, olivines etc. Upon cooling below 600-400�C hydroxyl pairs such as O3Si-OH HO-SiO3 rearrange electronically to form peroxy bonds, O3Si-OO-SiO3 + H2. Thus peroxy defects are introduced into essentially all rocks in the upper portions of the Earth crust. I'll discuss 1. why peroxy defects are thermodynamically allowed; 2. how peroxy defects are activated by stress; 3. what happens when peroxy defects release positive holes and inject them into an otherwise insulating medium; 4. why positive holes have the ability to spread out of the stressed rock volume; 5. why most positive holes are long-lived; 6. how positive holes travel fast and far; 7. what happens when positive holes arrive at the Earth surface; 8. how positive holes can recombine at the surface, returning to the peroxy state and emitting IR radiation with characteristic spectroscopic signature; 9. how positive holes set up microscopic electric fields at rock surfaces, steep enough to field-ionize air molecules and even trigger corona discharges; 10. positive and negative air ionization; 11. selective coupling of positive airborne ions to the ionosphere; 12. how the positive holes flow is not inhibited by the presence of water in rock pores. 13. how positive holes change from electronic charge carriers to highly reactive oxygen radicals when they arrive at rock-water interfaces. The concept of the rock battery is based on the recognition that rocks, which are stressed, turn into a source of positive holes charge carriers. Those positive holes flow out along the self-generated potential gradient. They can generate electric currents, which generate EM signals. However, sustained currents are possible only if and when the battery circuit is closed. Circuit closure in the Earth crust is difficult but not impossible.
Freund, F. T.
Synthesis, Crystal Packing, and Ambipolar Carrier Transport Property of Twisted Dibenzo[g,p]chrysenes.
A versatile method for the synthesis of dibenzo[g,p]chrysene (DBC) derivatives based on regio- and stereoselective stannyllithiation to diarylacetylenes is described. This method affords a variety of DBCs possessing both electron-donating and electron-withdrawing functional groups. These twisted molecules take brickwork packing structures in single crystals. Thus, ambipolar carrier transport properties with mobility values of up to 10(-3) ?cm(2) ?V(-1) ?s(-1) in the amorphous state were achieved. Functional groups on DBC frameworks are considered to increase carrier mobility through the enhancement of intermolecular interactions in the brickwork packing structures. PMID:24764179
Ueda, Yasuyuki; Tsuji, Hayato; Tanaka, Hideyuki; Nakamura, Eiichi
Interaction of charge carriers with lattice vibrations in oligoacene crystals from naphthalene to pentacene.
A key feature of organic ?-conjugated materials is the strong connection between their electronic and geometric structures. In particular, it has been recently demonstrated that nonlocal electron-vibration (electron-phonon) interactions, which are related to the modulation of the electronic couplings (transfer integrals) between adjacent molecules by lattice vibrations, play an important role in the charge-transport properties of organic semiconductors. Here, we use density functional theory calculations and molecular mechanics simulations to estimate the strength of these nonlocal electron-vibration couplings in oligoacene crystals as a function of molecular size from naphthalene through pentacene. The effect of each optical vibrational mode on the electronic couplings is evaluated quantitatively. The results point to a very strong coupling to both intermolecular vibrational modes and intramolecular (including high-frequency) modes in all studied systems. Importantly, our results underline that the amount of relaxation energy associated with nonlocal electron-phonon coupling decreases as the size of the molecule increases. This work establishes an original relationship between chemical structure and nonlocal vibrational coupling in the description of charge transport in organic semiconductor crystals. PMID:20866074
S�nchez-Carrera, Roel S; Paramonov, Pavel; Day, Graeme M; Coropceanu, Veaceslav; Br�das, Jean-Luc
Charge transport properties of spin crossover systems.
The study of spin crossover compounds by means of theoretical or experimental approaches has provided interesting results in recent decades. The main feature of such compounds is the change in the spin state induced by many different external stimuli, i.e. temperature, light, pressure, solvent coordination and the electric field. Spin crossover systems are potentially more useful than other magnetic molecules because their switching behaviour can occur closer to room temperature, and they are thus candidates for use in spintronic devices. Here, I review the state of the art in quantum chemical approaches to the study of such systems and discuss experiments that have focused on transport properties in single-molecule, nano-objects or thin-film spin crossover systems. PMID:24217339
Ruiz, Eliseo
Charge transport in a blue-emitting alternating block copolymer with a small spacer to conjugated segment length ratio
We analyze current versus voltage data obtained using single carrier injection in several metal\\/polymer\\/metal sandwich structures. The polymer used in each case is a soluble blue-emitting alternating block copolymer. Our experimental results demonstrate that the electron transport is space-charge limited by the high density of traps having an exponential energy distribution (temperature dependent characteristic energy) in the copolymer. The electron
Dongge Ma; I. A. H�mmelgen; Xiabin Jing; Zhiyong Hong; Lixiang Wang; Xiaojiang Zhao; Fosong Wang; F. E. Karasz
A new class of carriers that transport selective cargo from the trans Golgi network to the cell surface
We have isolated a membrane fraction enriched in a class of transport carriers that form at the trans Golgi network (TGN) and are destined for the cell surface in HeLa cells. Protein kinase D (PKD) is required for the biogenesis of these carriers that contain myosin II, Rab6a, Rab8a, and synaptotagmin II, as well as a number of secretory and plasma membrane-specific cargoes. Our findings reveal a requirement for myosin II in the migration of these transport carriers but not in their biogenesis per se. Based on the cargo secreted by these carriers we have named them CARTS for CARriers of the TGN to the cell Surface. Surprisingly, CARTS are distinct from the carriers that transport vesicular stomatitis virus (VSV)-G protein and collagen I from the TGN to the cell surface. Altogether, the identification of CARTS provides a valuable means to understand TGN to cell surface traffic.
Wakana, Yuichi; van Galen, Josse; Meissner, Felix; Scarpa, Margherita; Polishchuk, Roman S; Mann, Matthias; Malhotra, Vivek
Charge and spin transport in PEDOT:PSS nanoscale lateral devices
NASA Astrophysics Data System (ADS)
The electrical transport of the highly conductive poly-(3,4-ethylenedioxythiophene):poly(styrenesulfonic acid) (PEDOT:PSS) is investigated with Ohmic and spin-polarized tunnel contacts at nanoscale lateral dimensions. Temperature-dependent charge transport measurements reveal that electrical conductivity scales non-linearly as a function of electrode spacing, which is attributed to the localization of carriers induced by the disorder introduced by the PSS polyelectrolyte. In addition, we demonstrate the integration of this conducting polymer in nanoscale lateral spin-valve devices by increasing the pH of the PEDOT:PSS solution. We present charge and magnetotransport measurement results of NiFe/AlOx/PEDOT:PSS/AlOx/NiFe lateral structures for various thicknesses of the alumina tunnel barriers. We discuss the absence of magnetoresistance of our spin valves within the framework of Valet-Fert theory, and estimate an upper limit for the spin lifetime of carriers in PEDOT:PSS to ?sf ? 50 ns.
de Oliveira, Thales V. A. G.; Gobbi, Marco; Porro, Jos� M.; Hueso, Luis E.; Bittner, Alexander M.
Carrier-mediated system for transport of biotin in rat intestine in vitro
Transport of biotin was examined in rat intestine using the everted sac technique. Transport of 0.1 ..mu..M biotin was linear with time for at least 30 min of incubation and occurred at a rate 3.7 pmol g initial tissue wet wt/sup -1/ min/sup -1/. Transport of biotin was higher in the jejunum than the ileum and was minimum in the colon (85 +/- 6, 36 +/- 6, and 2.8 +/- 0.6 pmol x g initial tissue wet wt/sup -1/ x 25 min/sup -1/, respectively). In the jejunum, transport of biotin was saturable at low concentrations but linear at higher concentrations. The transport of low concentrations of biotin was 1) inhibited by structural analogues (desthiobiotin, biotin methyl ester, diaminobiotin, and biocytin), 2) Na/sup +/ dependent, 3) energy dependent, 4) temperature dependent, and 5) proceeded against a concentration gradient in the serosal compartment. No metabolic alteration occurs to the biotin molecule during transport. This study demonstrates that biotin transport in rat intestine occurs by a carrier-mediated process at low concentrations and by simple diffusion at high concentrations. Furthermore, the carrier-mediated process is Na/sup +/, energy, and temperature dependent.
Said, H.M.; Redha, R.
Unity quantum yield of photogenerated charges and band-like transport in quantum-dot solids.
Solid films of colloidal quantum dots show promise in the manufacture of photodetectors and solar cells. These devices require high yields of photogenerated charges and high carrier mobilities, which are difficult to achieve in quantum-dot films owing to a strong electron-hole interaction and quantum confinement. Here, we show that the quantum yield of photogenerated charges in strongly coupled PbSe quantum-dot films is unity over a large temperature range. At high photoexcitation density, a transition takes place from hopping between localized states to band-like transport. These strongly coupled quantum-dot films have electrical properties that approach those of crystalline bulk semiconductors, while retaining the size tunability and cheap processing properties of colloidal quantum dots. PMID:21946709
Talgorn, Elise; Gao, Yunan; Aerts, Michiel; Kunneman, Lucas T; Schins, Juleon M; Savenije, T J; van Huis, Marijn A; van der Zant, Herre S J; Houtepen, Arjan J; Siebbeles, Laurens D A
On the Structure of the Fixed Charge Transportation Problem
ERIC Educational Resources Information Center
This work extends the theory of the fixed charge transportation problem (FCTP), currently based mostly on a forty-year-old publication by Hirsch and Danzig. This paper presents novel properties that need to be considered by those using existing, or those developing new methods for optimizing FCTP. It also defines the problem in an easier way,�
Kowalski, K.
Synthesis of p -and n-type Gels Doped with Ionic Charge Carriers
NASA Astrophysics Data System (ADS)
In this study, we synthesized the new kinds of semiconducting polymeric gels having negative ( n-type) and positive ( p-type) counter ions as charge carriers. The polyacrylamide gel was doped with pyranine (8-hydroxypyrene-1,3,6-trisulfonic acid, trisodium salt), having {text{SO}}3^{ - } ions as side groups and Na+ as counter ions, so-called p-type semiconducting gel. The doping process was performed during the polymerization where the pyranine binds to the polymer strands over OH group chemically via radical addition. In a similar way, N-isopropylacrylamide (NIPA) gel was doped with methacrylamidopropyltrimethyl ammonium chloride (MAPTAC), having Cl- as counter ions, so-called n-type semiconducting gel. Here MAPTAC was embedded by copolymerization within the polymer network (NIPA). These semiconducting gels can show different electrical properties by changing the concentration of the doping agents, swelling ratio etc. We have shown that the pn junction, formed by combining p-type and n-type gels together in close contact, rectifies the current similar to the conventional Si and Ge diodes.
Alveroglu, E.; Yilmaz, Y.
Computational Confirmation of the Carrier for the "XCN" Interstellar Ice Bank: OCN(-) Charge Transfer Complexes
NASA Technical Reports Server (NTRS)
Recent experimental studies provide evidence that carrier for the so-called XCN feature at 2165 cm(exp -1) (4.62 micron) in young stellar objects is an OCN(-)/NH4(+) charge transfer (CT) complex that forms in energetically processed interstellar icy grain mantles. Although other RCN nitriles and RCN iosonitriles have been considered, Greenberg's conjecture that OCN(-) is associated with the XCN feature has persisted for over 15 years. In this work we report a computational investigation that thoroughly confirms the hypothesis that the XCN feature observed in laboratory studies can result from OCN(-)/NH4(+) CT complexes arising from HNCO and NH3, in a water ice environment. Density functional theory calculations with theory calculations with HNCO, NH3, and up to 12 waters reproduce seven spectroscopic measurements associated with XCN: the band origin of the asymmetric stretching mode of OCN(-), shifts due to isotopic substitutions of C, N, O, and H, and two weak features. However, very similar values are also found for the OCN(-)/NH4(+) CT complex arising from HOCN and NH3. In both cases, the complex forms by barrierless proton transfer from HNCO or HOCN to NH3 during the optimization of the solvated system. Scaled B3LYP/6-31+G** harmonic frequencies for HNCO and HOCN cases are 2181 and 2202 cm(exp -1), respectively.
Park, J.-Y.; Woon, D. E.
Stability of the polaron form of charge carrier localization in misfit titanium disulfide compounds
NASA Astrophysics Data System (ADS)
The behavior of the thermodynamic functions of the silver-intercalated isostructural misfit compounds Ag x PbTi2S5 and Ag x GdTi2S5 is studied. The region of instability of the homogeneous state, which is typical of materials with less than half-filled polaron band, is revealed in the phase diagram of Ag x PbTi2S5. It is shown that the substitution of GdS for PbS gives rise to charge transfer to the TiS2 sublattice, which fills the polaron band above the critical level and suppresses this instability. The behavior of the entropy of silver in both materials fits well the proposed polaron band filling model. It is demonstrated that the peak of the entropy near the boundary of stability of the homogeneous state is universal in character for materials with polaron-type carriers and that it can be associated with a strong variation in the density of states at the Fermi level upon polaron band filling.
Titov, A. N.
Computational Simulation of Charge Transport in Metal Terpyridine Monolayer FETs
NASA Astrophysics Data System (ADS)
Understanding the roles of charge traps and defects in electronic transport in organic materials is becoming increasingly important. Computational studies have been undertaken, using an agent-based Monte Carlo method, of the active region of a monolayer FET. Charge transport is assumed to be due to thermally activated, variable-range hopping between neighboring sites. This model system allows us to probe the role of charge traps/defects both computationally and experimentally. We do this by using multiple metal terpyridine complexes, each having known electronic structure. Using Marcus Theory and quantum calculations, the hopping rate between neighboring complexes can be predicted. Results from computational simulations of this system will be discussed, with special attention being paid to the results that can be experimentally verified, such as voltage-current curves.
Hanwell, Marcus; Hutchison, Geoffrey
Charge transport in 4H-SiC detector structures under conditions of a high electric field
Transport of nonequilibrium charge packets in a structure with a Schottky barrier fabricated on a CVD-grown n-4H-SiC film has been studied at the maximum strength of an electric field at 1.1 MV/cm. The charge was introduced by separate {alpha}-particles and recorded by nuclear spectrometric techniques. A superlinear rise in the recorded charge as a function of the reverse bias applied to the structure was observed. Simultaneously, and also superlinearly increased the scatter in the spectrum of the charge amplitude. The observed effect is attributed to the initial stage of impact ionization. The manifestation of the process at unconventionally low fields ({approx}1 MV/cm) is accounted for by specific features of the process of charge generation. Carriers generated by slowing-down {alpha}-particles are 'hot' from the very beginning.
Ivanov, A. M., E-mail: email@example.com; Mynbaeva, M. G.; Sadokhin, A. V.; Strokan, N. B.; Lebedev, A. A. [Russian Academy of Sciences, Ioffe Physicotechnical Institute (Russian Federation)
Iontophoretic Transport of Charged Macromolecules across Human Sclera
The mechanisms of transscleral iontophoresis have been investigated previously with small molecules in rabbit sclera. The objective of the present study was to examine transscleral iontophoretic transport of charged macromolecules across excised human sclera. Passive and 2-mA iontophoretic transport experiments were conducted in side-by-side diffusion cells with human sclera. The effects of iontophoresis upon transscleral transport of model permeants bovine serum albumin (BSA) and polystyrene sulfonic acid (PSS) as well as a model drug bevacizumab (BEV) were determined. Passive and iontophoretic transport experiments of tetraethylammonium (TEA) and salicylic acid (SA) and passive transport experiments of the macromolecules served as the controls. The results of iontophoresis enhanced transport of TEA and SA across human sclera were consistent with those in a previous rabbit sclera study. For the iontophoretic transport of macromolecules BSA and BEV, higher iontophoretic fluxes were observed in anodal iontophoresis as compared to passive and cathodal iontophoresis. This suggests the importance of electroosmosis. For the polyelectrolyte PSS, higher iontophoretic flux was observed in cathodal iontophoresis compared to anodal iontophoresis. Both electroosmosis and electrophoresis affected iontophoretic fluxes of the macromolecules; the relative contributions of electroosmosis and electrophoresis were a function of molecular size and charge of the macromolecules.
Chopra, Poonam; Hao, Jinsong; Li, S. Kevin
On the advancement of quantum dot solar cell performance through enhanced charge carrier dynamics
NASA Astrophysics Data System (ADS)
The quantum dot solar cell is one of the few solar technologies which promises to compete with fossil fuels, but work is still needed to increase its performance. Electron transfer kinetics at interfaces and limitations of the redox couple within the cell, are responsible for lowering power conversion efficiency. Several techniques which are able to increase electron transfer within the working electrode and at the counter electrode/electrolyte interface are discussed in this dissertation. Trap sites on the surface of CdSe quantum dots are created when mercaptopropionic acid (MPA) is added to the suspension. The trap sites are emissive creating a loss pathway for photogenerated charges which will manifest as reduced photocurrent. MPA displaces amines on the surface of CdSe creating Se vacancies. Emission properties are controlled by the concentration of MPA. Because trap sites are generated, a more successful method to sensitize TiO2 films is the SILAR technique which directly grows quantum dots on the desired surface. Anodically etched TiO2 nanotubes yield photocurrents 20% greater than TiO2 nanoparticles because of longer electron diffusion lengths. Peak incident photon to charge carrier efficiencies of TiO2 nanotube samples show a doubling of photocurrent in the visible region compared to nanoparticles. The TiO2 substrates are sensitized with CdS by the SILAR process which is found to utilize both the inside and outside surfaces of the TiO2 nanotubes. Etched TiO2 nanotubes are removed from the underlying titanium foil in order to use spectroscopic techniques. Ultrafast transient absorption shows the extremely fast nature of charge injection from SILAR CdS into TiO 2 nanotubes. Surface area analysis of TiO2 nanotube powder gives an area of 77m2/g, a value 1.5 times larger than traditional TiO2 nanoparticles. By isolating the counter electrode with a salt bridge the effect of the polysulfide electrolyte is found to act as an electron scavenger on the working electrode. Though activity at the platinum counter electrode increases with the presence of polysulfides, the activity is too low to counteract scavenging at the working electrode. Cu2S, CoS and PbS electrochemically show promise as alternatives to platinum. Cu2S and CoS produce higher photocurrents and fill factors, greatly improving cell performance.
Baker, David R.
Spin and charge transport study in single crystal organic semiconductors
NASA Astrophysics Data System (ADS)
Spin transport studies in amorphous rubrene films have shown exciting and promising results [1]. A large spin diffusion length in these amorphous films has increased the motivation to perform spin transport study in high purity single crystal rubrene. This will provide the fundamental understanding on the spin transport behavior in OS; not influenced by defects or traps. We will present work on small channel single crystal rubrene FET device with magnetic electrodes. For example, our preliminary studies have show mobility for FET with Co electrode to be 0.014cm^2/V-s. A study on the spin and charge transport properties in single crystals of OS with magnetic electrodes is being done and the results will be reported. The influence of gate voltage and applied magnetic field on the transport properties will be discussed. [1] J.H. Shim et al., PRL 100, 226603 (2008)
Raman, Karthik V.; Mulder, Carlijn L.; Baldo, Marc A.; Moodera, Jagadeesh S.
Microscopic model for d-wave charge-carrier pairing and non-Fermi-liquid behavior in a purely repulsive two-dimensional electron system
NASA Astrophysics Data System (ADS)
We investigate a microscopic model for strongly correlated electrons with both on-site and nearest-neighbor Coulomb repulsion on a two-dimensional (2D) square lattice. This exhibits a state in which electrons undergo a ``somersault'' in their internal spin space (spin flux) as they traverse a closed loop in external coordinate space. When this spin-12 antiferromagnetic (AFM) insulator is doped, the ground state is a liquid of charged, bosonic meron vortices, which for topological reasons are created in vortex-antivortex pairs. The magnetic exchange energy of the distorted AFM background leads to a logarithmic vortex-antivortex attraction which overcomes the direct Coulomb repulsion between holes localized on the vortex cores. This leads to the appearance of preformed charged pairs. We use the configuration interaction (CI) method to study the quantum translational and rotational motion of various charged magnetic solitons and soliton pairs. The CI method systematically describes fluctuation and quantum tunneling corrections to the Hartree-Fock approximation. We find that the lowest-energy charged meron-antimeron pairs exhibit d-wave rotational symmetry, consistent with the symmetry of the cuprate superconducting order parameter. For a single hole in the 2D AFM plane, we find a precursor to spin-charge separation in which a conventional charged spin polaron dissociates into a singly charged meron-antimeron bound pair. This model provides a unified microscopic basis for (i) non-Fermi-liquid transport properties, (ii) d-wave preformed charged carrier pairs, (iii) midinfrared optical absorption, (iv) destruction of AFM long-range order with doping and other magnetic properties, and (v) certain aspects of angle-resolved photoemission spectroscopy.
Berciu, Mona; John, Sajeev
Organic single-crystal transistors: development of solution processes and charge transport mechanisms
NASA Astrophysics Data System (ADS)
Patternable solution-crystallized organic transistors are developed with high carrier mobility that exceeds 10 cm2/Vs. We have investigated techniques of crystallization during the fabrication of the organic semiconductor thin films from solution. Regulating direction of the crystal growth in the above process, we successfully formed crystalline films with the mobility as high as 10-12 cm2/Vs from newly developed air-stable organic semiconductor compounds of 2,7-dialkyl[1]benzothieno[3,2-b]benzothiophene (Cn-BTBT) and 2,9-dialkyl-dinaphtho[2,3-b:2',3'-f]thieno[3,2-b]thiophene (Cn-DNTT). Furthermore, comprehensive measurements of Hall-effect and temperature dependent mobility in the solution-crystallized single-crystal transistors tell us that their fundamental charge transport mechanism is band transport.
Uemura, Takafumi; Takeya, Jun
Rational design of charge transport molecules for blue organic light emitting devices
NASA Astrophysics Data System (ADS)
The efficiency and stability of blue OLEDs continue to be the primary roadblock to developing organic solid-state white lighting as well as power efficient displays. It is generally accepted that such high quantum efficiency can be achieved with the use of organometallic phosphor doped OLEDs. The transport layers can be designed to increase the carrier density as a way to reduce the drive voltage. We have developed a comprehensive library of charge transporting molecules using combination of theoretical modeling and experimental evidence. Our work focuses on using chemical structure design and computational methods to develop host, transport, emitter, and blocking materials for high efficiency blue OLEDs, along with device architectures to take advantage of these new materials. Through chemical modification of materials we are able to influence both the charge balance and emission efficiency of OLEDs, and understand the influence of the location of photon emission in OLEDs as a function of minor chemical modifications of host and electron transport materials. Design rules, structure-property relationships and results from state of the art OLEDs will be presented.
Padmaperuma, Asanga; Cosimbescu, Lelia; Koech, Phillip; Polikarpov, Evgueni; Swensen, James; Gaspar, Daniel
An Efficient Scheduling Scheme on Charging Stations for Smart Transportation
NASA Astrophysics Data System (ADS)
This paper proposes a reservation-based scheduling scheme for the charging station to decide the service order of multiple requests, aiming at improving the satisfiability of electric vehicles. The proposed scheme makes it possible for a customer to reduce the charge cost and waiting time, while a station can extend the number of clients it can serve. A linear rank function is defined based on estimated arrival time, waiting time bound, and the amount of needed power, reducing the scheduling complexity. Receiving the requests from the clients, the power station decides the charge order by the rank function and then replies to the requesters with the waiting time and cost it can guarantee. Each requester can decide whether to charge at that station or try another station. This scheduler can evolve to integrate a new pricing policy and services, enriching the electric vehicle transport system.
Kim, Hye-Jin; Lee, Junghoon; Park, Gyung-Leen; Kang, Min-Jae; Kang, Mikyung
Porescale transport phenomena in charge-selective hemofilters
NASA Astrophysics Data System (ADS)
Theoretical models for hindered transport of biomolecules and electrostatic and electrokinetic phenomena in the pressure driven flow of blood simulants in structured nanoporous membranes are developed, motivated by the design requirements for a hemofilter for an implantable artificial kidney. In particular, the selectivity of charged membrane to charged biomolecules of biological interest, the inference of the pore wall surface charge density from streaming potential measurements, when electrical double layers overlap and the pore wall surface charge density is heterogeneous (e.g. due to nonuniformities in the applied surface coatings) and the coupling of intrapore phenomena with mass transfer and fluid flow upstream and downstream of the membrane are discussed. The developed theory is applied to the problem of choosing a hemofilter pore size that provides adequate retention/clearance of desirable/undesirable solutes from blood.
Datta, Subhra; Conlisk, Albert
Investigation of carrier transport properties in semipolar (1122) GaN films with low defect density
NASA Astrophysics Data System (ADS)
We report on the anisotropic carrier transport properties of semipolar (1122) GaN films with low defect density. We utilized the asymmetric lateral epitaxy to obtain various semipolar (1122) GaN films having significantly reduced partial dislocations and basal-plane stacking faults (BPSFs). The directionally dependent carrier transport was observed with the lower sheet resistances (Rsh) along the [1100] direction. The Rsh ratios of semipolar (1122) GaN films were found to be relatively smaller than those of nonpolar a-plane GaN films, possibly due to low BPSF density and the reduced in-plane electric field induced by BPSF along the [1123] direction at wurtzite domain boundaries.
Jang, Soohwan; Kim, Hyonwoong; Soo Kim, Doo; Hwang, Sung-Min; Kim, Jihyun; Hyeon Baik, Kwang
Charge transport measurements of vertically aligned carbon nanofibers
NASA Astrophysics Data System (ADS)
Vertically aligned carbon nanofibers (VACNFs) have found a variety of electronic applications. To further realize these applications, a good understanding of the charge transport properties is essential. In this work, charge transport properties have been systematically measured for three types of VACNF forests with Ni as catalyst, namely VACNFs grown by direct current PECVD, and inductively coupled PECVD at both normal pressure and low pressure. The structure and composition of these nanofibers have also been investigated in detail prior to the charge transport measurements. Four-probe I-V measurements on individual nanofibers have been enabled by the fabrication of multiple metal ohmic contacts on individual fibers that exhibited resistance of only a few kO. An O2 plasma reactive ion etch method has been used to achieve ohmic contacts between the nanofibers and Ti/Au, Ag/Au, Cd/Au, and Cr/Au electrodes. Direct current VACNFs exhibit linear I-V behavior at room temperature, with a resistivity of approximately 4.2 x 10-3 O�cm. Our measurements are consistent with a dominant transport mechanism of electrons traveling through intergraphitic planes in the dc VACNFs. The resistivity of these fibers is almost independent of temperature, and the contact resistance decreases as temperature increases. Further studies reveal that the 10--15 nm thick graphitic outer layer dominates the charge transport properties of do VACNFs. This is demonstrated by comparison of charge transport properties of as-grown VACNFs and VACNFs with the outer layer partially removed by oxygen plasma reactive ion etch. The linear I-V behavior of the fibers does not vary as this outer layer becomes thinner, but displays a drastic shift to a rectifying behavior when this layer is completely stripped away from some regions of the nanofiber. This shift may be related with the compositional differences in the outer layer and the inner core of the nanofibers. Two-probe charge transport measurements on inductively coupled PECVD grown VACNFs indicate linear I-V behavior, and the resistivity of both types of inductively coupled PECVD grown VACNFs is on the order of 10-3 to 10-4 O�cm.
Zhang, Lan
Carrier injection and transport in organic field-effect transistor investigated by impedance spectroscopy
In this research, impedance spectroscopy (IS) has been applied on top-contact pentacene organic field-effect transistors (OFETs) for characterization of the contact resistance and carrier transport properties. The various relaxation processes were analyzed based on the Maxwell�Wagner model, assuming pentacene as a dielectric material. The mobilities obtained from the IS analysis correspond well with that obtained from the current�voltage (I�V) analysis.
Jack Lin; Martin Weis; Dai Taguchi; Takaaki Manaka; Mitsumasa Iwamoto
A two-dimensional DFB laser model accounting for carrier transport effects
A two-dimensional numerical model for DFB semiconductor laser simulation is developed and presented. In this model the transverse carrier transport and longitudinal spatial\\/spectral hole-burning effects in a bulk DFB laser are accounted for rigorously. Comparison with simplified models is made. Methods for improving the accuracy of steady-state and small-signal analyses by the simplified models are proposed and verified
Alexei D. Sadovnikov; Xun Li; Wei-Ping Huang
Carrier transport mechanisms through the metal\\/p-type diamond semiconductor interface
Carrier transport mechanisms at p-diamond\\/metal interfaces were studied by analyzing the dependencies of the specific contact resistivities (?c) on the measurement temperature and the acceptor concentration (NA). A variety of metals, such as Ti, Mo, Cr (carbide forming metals), Pd and Co (carbon soluble metals), were deposited on boron-doped polycrystalline diamond films, and the ?c values were measured by a
Y. Koide; M. Yokoba; A. Otsuki; F. Ako; T. Oku; Masanori Murakami
Carrier transport mechanism of Ohmic contact to p-type diamond
The carrier transport mechanism through the p-diamond\\/metal interface was studied by measuring specific contact resistances (&rgr;c) using a transmission line method for Ti, Mo, and Cr (carbide forming metals) and Pd and Co (carbon soluble metals) metals contacting to the boron-doped polycrystalline diamond films. Schottky barrier heights (?B) of around 0.5 eV were measured for the annealed contacts. The present
M. Yokoba; Yasuo Koide; A. Otsuki; F. Ako; T. Oku; Masanori Murakami
Global seamless network demonstrator: carrier grade automatic switched transport network implementation in realistic telecom field environment
The Global Seamless Network (GSN) Demonstrator is presented, a joint effort of system vendors and Deutsche Telekom Group R&D to demonstrate network functions and management integration and enable, for the first time, experiences with a carrier grade Automatically Switched Transport Network (ASTN) implementation and the envisaged main ASTN clients, IP and Ethernet. For end-to-end monitoring capability, integrating the view on
Hans-Martin Foisel; Norbert Hanik; Ralf-Peter Braun; Georg Lehr; Andreas Gladisch
Voltage-Modulated Millimeter-Wave Spectroscopy on a Polymer Diode: Mesoscopic Charge Transport in Conjugated Polymers
We present a new technique to determine the carrier mobility {mu} in semiconducting, undoped, conjugated polymers in the millimeter-wave frequency range, 10--500GHz. This method probes charge conduction on mesoscopic length scales, a regime inaccessible to other transport experiments. The experiment is based on the detection of millimeter-wave absorption of field-induced charge in polymer diodes, and is applied to poly(p -phenylene vinylene). We demonstrate that locally {mu} can be as high as 10{sup -4} m{sup 2}/V s, and deduce the typical hopping parameters in the mesoscopic high-{mu} regions in the material.
Martens, H. C. F.; Hilt, O.; Brom, H. B.; Blom, P. W. M.; Huiberts, J. N.
Pore network model of electrokinetic transport through charged porous media
NASA Astrophysics Data System (ADS)
We introduce a method for the numerical determination of the steady-state response of complex charged porous media to pressure, salt concentration, and electric potential gradients. The macroscopic fluxes of solvent, salt, and charge are computed within the framework of the Pore Network Model (PNM), which describes the pore structure of the samples as networks of pores connected to each other by channels. The PNM approach is used to capture the couplings between solvent and ionic flows which arise from the charge of the solid surfaces. For the microscopic transport coefficients on the channel scale, we take a simple analytical form obtained previously by solving the Poisson-Nernst-Planck and Stokes equations in a cylindrical channel. These transport coefficients are upscaled for a given network by imposing conservation laws for each pores, in the presence of macroscopic gradients across the sample. The complex pore structure of the material is captured by the distribution of channel diameters. We investigate the combined effects of this complex geometry, the surface charge, and the salt concentration on the macroscopic transport coefficients. The upscaled numerical model preserves the Onsager relations between the latter, as expected. The calculated macroscopic coefficients behave qualitatively as their microscopic counterparts, except for the permeability and the electro-osmotic coupling coefficient when the electrokinetic effects are strong. Quantitatively, the electrokinetic couplings increase the difference between the macroscopic coefficients and the corresponding ones for a single channel of average diameter.
Obliger, Ama�l; Jardat, Marie; Coelho, Daniel; Bekri, Samir; Rotenberg, Benjamin
Pore network model of electrokinetic transport through charged porous media.
We introduce a method for the numerical determination of the steady-state response of complex charged porous media to pressure, salt concentration, and electric potential gradients. The macroscopic fluxes of solvent, salt, and charge are computed within the framework of the Pore Network Model (PNM), which describes the pore structure of the samples as networks of pores connected to each other by channels. The PNM approach is used to capture the couplings between solvent and ionic flows which arise from the charge of the solid surfaces. For the microscopic transport coefficients on the channel scale, we take a simple analytical form obtained previously by solving the Poisson-Nernst-Planck and Stokes equations in a cylindrical channel. These transport coefficients are upscaled for a given network by imposing conservation laws for each pores, in the presence of macroscopic gradients across the sample. The complex pore structure of the material is captured by the distribution of channel diameters. We investigate the combined effects of this complex geometry, the surface charge, and the salt concentration on the macroscopic transport coefficients. The upscaled numerical model preserves the Onsager relations between the latter, as expected. The calculated macroscopic coefficients behave qualitatively as their microscopic counterparts, except for the permeability and the electro-osmotic coupling coefficient when the electrokinetic effects are strong. Quantitatively, the electrokinetic couplings increase the difference between the macroscopic coefficients and the corresponding ones for a single channel of average diameter. PMID:24827338
Obliger, Ama�l; Jardat, Marie; Coelho, Daniel; Bekri, Samir; Rotenberg, Benjamin
Effect of electrically degenerated layer on the carrier transport property of ZnO epitaxial thin films
NASA Astrophysics Data System (ADS)
ZnO films were prepared on (1 1 1) YSZ and (0 0 0 1) sapphire by pulsed laser deposition method. Effect of lattice mismatch on the carrier transport properties of ZnO epitaxial thin films was investigated. The carrier mobility of the ZnO films on YSZ was larger than that of ZnO/sapphire due to smaller lattice mismatch when the thickness was below 150 nm. The effect of electrically degenerated layer on the carrier transport property increased with decreasing the film thickness of ZnO film. The carrier density and electron mobility of 20 nm-thick-ZnO film on either substrate were regardless of the temperature. We concluded that the dominant carrier scattering mechanism in ZnO ultra thin films is double Schottky barriers at the grain boundary and that their height depends on the carrier concentration.
Sakamoto, S.; Oshio, T.; Ashida, A.; Yoshimura, T.; Fujimura, N.
Studies in primary hypomagnesaemia: evidence for defective carrier-mediated small intestinal transport of magnesium.
A 4 year old male with primary hypomagnesaemia was studied using balance and steady-state perfusion techniques. Magnesium balance was negative and could be accounted for by increased faecal losses, renal conservation being normal; calcium balance was normal. After oral magnesium therapy magnesium balance became positive. The perfusion studies demonstrated net loss of magnesium into the intestinal lumen when low concentrations (1 and 2 mmol/l) of magnesium were perfused in contrast with control subjects; whereas at high concentrations (10 mmol/l a net absorption of a magnitude similar to control values was observed. In the control subjects sequential perfusion of increasing concentrations of magnesium demonstrated a curvilinear relationship between rates of absorption and the lower concentrations (1, 2, and 4 mmol/l) with an apparent Km and Vmax of 4.5 mmol/l and 91 nmol/min/cm respectively. At the higher concentrations (6 and 10 mmol/l) the relationship was linear. These data suggest that two separate transport systems participate in the absorption of magnesium from the proximal small intestine; a carrier-mediated system which saturates at low intraluminal concentrations, and a simple diffusional process. The possibility of the second transport system being a carrier-mediated process with a very much higher Km cannot be excluded. In primary hypomagnaesaemia the results suggest that the primary abnormality is a defect in carrier-mediated transport of magnesium from low intraluminal concentrations of magnesium.
Milla, P J; Aggett, P J; Wolff, O H; Harries, J T
950809 Charged particle transport updated multi-group diffusion
In 1974, a charged particle transport scheme was introduced which utilized a multi-group diffusion method for the spatial transport and slowing down of energetic ions in a hot plasma. In this treatment a diffusion coefficient was used which was flux-limited to provide, hopefully, some degree of accuracy when the slowing down of an energetic charged particle is dominated by Coulomb collisions with thermal ions and electrons in a plasma medium. An advantage of this method was a very fast, memory-contained program for calculating the behavior of energetic charged particles which resulted in smoothly varying particle number densities and energy depositions. The main limitation of the original multi-group charged particle diffusion scheme is its constraint to a basic ten group structure; the same ten group structure for each of the five energetic ions tracked. This is regarded as a severe limitation, inasmuch as more groups would be desired to simulate more accurately the corresponding Monte Carlo results of energies deposited over spatial zones from a charged particle source. More generally, it seems preferable to have a different group structure for each particle type since they are created at inherently different energies. In this paper, the basic theory and multi-group description will be given. This is followed by the specific techniques that were used to solve the resultant equations. Finally, the modifications that were made to the cross section data as well as the methods used for energy and momentum deposition are described.
Corman, E.G.; Perkins, S.T.; Dairiki, N.T.
Thermal Transport and Photo-induced Charge Transport in Graphene
NASA Astrophysics Data System (ADS)
The electronic material graphene has attracted much attention for its unique physical properties such as, linear band structure, high electron mobility, and room temperature ballistic conduction. The possibilities for device applications utilizing graphene show great variety, from transistors for computing to chemical sensors. Yet, there are still several basic physical properties such as thermal conductivity that need to be determined accurately. This work examines the thermal properties of graphene grown by the chemical vapor deposition technique. The thermoelectric power of graphene is studied in ambient and vacuum environments and is shown to be highly sensitive to surface charge doping. Exploiting this effect, we study the change in thermoelectric power due to introduction of gaseous species. The temperature dependent thermal conductivity of graphene is measured using a comparison method. We show that the major contribution to the thermal conductivity is the scattering of in-plane phonons. Graphene also shows promise as an optoelectronic material. We probe the Landau level structure of graphene in high magnetic fields using a differential photoconductivity technique. Using this method we observed the lifting of spin and valley degeneracies of the lowest Landau level in graphene.
Benjamin, Daniel K.
Effect of disorder on carrier transport in ZnO thin films grown by atomic layer deposition at different temperatures
NASA Astrophysics Data System (ADS)
We have grown ~200 nm thick ZnO films on (0001) sapphire substrates using atomic layer deposition at different substrate temperatures ranging from ~150 to 350 �C. X-ray diffraction and photoluminescence spectra of these films showed that crystalline and compositional native defects were strongly dependent on the substrate temperature. Room temperature Hall measurement showed that all the films were degenerate with carrier concentration exceeding the Mott's critical density nc required for metallic conduction. The lowest value of room temperature resistivity ~3.6 � 10-3 ? cm was achieved for the film deposited at ~200 �C, which had an estimated carrier concentration ~5.7 � 1019 cm-3 and mobility ~30 cm2/V s. The films deposited both below and above ~200 �C showed increased resistivity and decreased mobility presumably due to the intensified defects and deteriorated crystalline quality of these films. To investigate the effect of disorder on the underlying charge transport mechanisms in these films, the electrical resistivity was measured in the temperature range of ~4.2 to 300 K. The films grown at ~150, 300, and 350 �C were found to be semiconducting in the entire range of the measurement temperature due to the intensified disorder which impeded the metallic transport in these films. However, the films grown at ~200 and 250 �C showed a transition from metallic to semiconducting transport behaviour at lower temperatures due to the reduced defects and improved crystalline quality of these films. The observed semiconducting behaviour below the transition temperature for these films could be well explained by considering quantum corrections to the Boltzmann conductivity which includes the effect of disorder induced weak localization and coulomb electron-electron interactions.
Saha, D.; Das, Amit. K.; Ajimsha, R. S.; Misra, P.; Kukreja, L. M.
Transcellular Transport of Benzole Acid Across Caco-2 Cells by a pH-Dependent and Carrier-Mediated Transport Mechanism
The pH-dependent transcellular transport of [14 C]benzoic acid across a Caco-2 cell monolayer is shown to be mediated by a monocarboxylic acid-specific carrier-mediated transport system, localized on the apical membrane. Evidence for the carrier-mediated transport of benzoic acid includes (a) the significant temperature and concentration dependence, (b) the metabolic energy dependence, (c) the inhibition by unlabeled benzoic acid and other
Akira Tsuji; Hitomi Takanaga; Ikumi Tamai; Tetsuya Terasaki
Carrier-mediated transport of quercetin conjugates: involvement of organic anion transporters and organic anion transporting polypeptides.
Flavonoids modulate cell signaling and inhibit oxidative enzymes. After oral consumption, they circulate in human plasma as amphiphilic glucuronide or sulfate conjugates, but it is unknown how these physiological metabolites permeate into cells. We examined the mechanisms of uptake of these conjugates into hepatocellular carcinoma (HepG2) cells, and found that uptake of quercetin-3'-O-sulfate was saturable and temperature-dependent, indicating the involvement of carrier-mediated transport. Quercetin-3-O-glucuronide was taken up predominantly via passive diffusion in these cells. Quantitative real-time PCR analysis showed high expression of OATP4C1, followed by OAT2, OAT4 and low expression of OATP1B1 in HepG2 cells, and addition of inhibitors of OATs and OATPs resulted in a significant reduction in quercetin-3'-O-sulfate uptake. The accumulation of quercetin-3'-O-sulfate was further evaluated in HEK293 cells expressing OAT2, OAT4 and OATP4C1. Uptake of quercetin-3'-O-sulfate was 2.3- and 1.4-fold higher in cells expressing OAT4 and OATP4C1 at pH 6.0, respectively, than in control HEK293 cells. siRNA knockdown of OATP4C1 expression in HepG2 cells reduced uptake of quercetin-3'-O-sulfate by ?40%. This study highlights a role for OATs and OATPs in the cellular uptake of biologically active flavonoid conjugates. PMID:22634047
Wong, Chi Chun; Akiyama, Yasutoshi; Abe, Takaaki; Lippiat, Jonathan D; Orfila, Caroline; Williamson, Gary
Microstructural effects on charge transport in the molecular semiconductor sexithiophene
NASA Astrophysics Data System (ADS)
This thesis describes experiments probing microstructural effects on charge transport in molecular semiconductor thin films. It reports two techniques of isolating crystalline grains, grain boundaries, and single molecular monolayers, and the experimental results of these techniques on a specific system-sexithiophene (chosen as a model material because of its high charge mobility), but the experiments will be expanded to other molecular materials in future work. Effects of microstructure on transport were probed in two ways: (1) using field-effect devices, and (2) using conducting probe atomic force microscopy (CPAFM). The first technique isolates individual sexithiophene crystals ( � l mum) between closely-spaced electrodes in transistor geometries. Gold electrodes are fabricated on a SiO2 wafer, and trace amounts of sexithiophene are then vacuum-deposited generating thin crystals, 1--6 molecules tall. Electrically-isolated crystals grown between electrodes allowed electrical characterization. Charge transport is observed with: (1) no discernible dependence on film thickness, (2) thermally-activated transport above 100K and temperature insensitive transport below 100K, and (3) time-dependent transport attributable to charge trapping. In cases where a pair of crystals was isolated, the resultant grain boundary severely limited conduction. The second technique uses a modified AFM in which a tip is metal-coated and used as a positionable electrical contact. Individual sexithiophene crystals with one electrical contact made to the substrate can be electrically assessed using the AFM tip as the second. CPAFM allows imaging with minimal applied tip force while allowing current to flow from tip to sample. Monitoring the current/voltage behavior as the tip is repositioned on the sexithiophene crystals allows connection of nanoscale electrical properties to structural features for individual sexithiophene crystals. Experiments isolate conduction through individual layers of a molecular material and discrete grain boundaries. Measured contact and grain boundaries resistances demonstrate that transport in polycrystalline sexithiophene films is likely limited by these features. The combination of electrical and physical characterization of sexithiophene crystals demonstrates the importance of microstructure on transport, and can be generalized to other molecular semiconductors. Furthermore, the ability to electrically contact molecular "sheets" provides a technique for probing the effects of reduced dimensionality on transport in organic systems.
Granstrom, Eric Leroy
Study of the effect of the charge transport layer in the electrical characteristics of the organic photovoltaics
NASA Astrophysics Data System (ADS)
Significant progress in fabrication and optimization of organic photovoltaics (OPVs) has been made during the last decade. The main reason for popularity of OPVs is due to their low production cost, large area devices and compatibility with flexible substrates 1-3. Various approaches including optimizing morphology of the active layers 1, 2, introducing new materials as the donor and acceptor 3,4, new device structures such as tandem structure 5, 6 have been adapted to improve the efficiency of the organic photovoltaics. However, electrical characteristics of the OPVs do not only depend on the active layer materials or device structure. They can also be defined by the interface properties between active layers and the charge transport layers or the metal contacts. Within this paper, the effect of the thickness variation of the charge transport layer in the electrical properties of the bilayer heterojunction OPVs has been studied. Several devices with CuPc/PTCDI-C8 as the donor/acceptor layers have been fabricated with different thicknesses of electron transport layer. MoO3 and Alq3 have been used respectively as the hole transport layer (HTL) and the electron transport layer (ETL). It has been shown that the S-shape effect in the current-voltage curve is attributed to the accumulation of the charge carriers at the interface between the active layer and the charge transport layer 5, 7.
Rahimi, Ronak; Roberts, Alex; Narang, V.; Kumbham, Vamsi Krishna; Korakakis, D.
Study of the effect of the charge transport layer in the electrical characteristics of the organic photovoltaics
NASA Astrophysics Data System (ADS)
Significant progress in fabrication and optimization of organic photovoltaics (OPVs) has been made during the last decade. The main reason for popularity of OPVs is due to their low production cost, large area devices and compatibility with flexible substrates [1-3]. Various approaches including optimizing morphology of the active layers [1,2], introducing new materials as the donor and acceptor [3,4], new device structures such as tandem structure [5,6] have been adapted to improve the efficiency of the organic photovoltaics. However, electrical characteristics of the OPVs do not only depend on the active layer materials or device structure. They can also be defined by the interface properties between active layers and the charge transport layers or the metal contacts. Within this paper, the effect of the thickness variation of the charge transport layer in the electrical properties of the bilayer heterojunction OPVs has been studied. Several devices with CuPc/PTCDI-C8 as the donor/acceptor layers have been fabricated with different thicknesses of electron transport layer. MoO3 and Alq3 have been used respectively as the hole transport layer (HTL) and the electron transport layer (ETL). It has been shown that the S-shape effect in the current-voltage curve is attributed to the accumulation of the charge carriers at the interface between the active layer and the charge transport layer [5,7].
Rahimi, Ronak; Roberts, Alex; Narang, V.; Kumbham, Vamsi Krishna; Korakakis, D.
Monte Carlo simulation of charge transport in disordered organic thin films: Applicability of Meyer-Neldel rule for extracting energetic disorder
NASA Astrophysics Data System (ADS)
Multi-carrier Monte Carlo simulation of charge transport is employed to test the suitability of Meyer-Neldel rule (MNR) in extracting energetic disorder from homogeneous organic thin films in diode geometry. Studies validate the use of MN rule for extracting energetic disorder from homogeneous organic thin films.
Mohan, S. Raj; Singh, Manoranjan P.; Joshi, M. P.; Kukreja, L. M.
Time-of-flight mobility of charge carriers in position-dependent electric field between coplanar electrodes
NASA Astrophysics Data System (ADS)
Time-of-flight measurements of the photocurrent in thin organic semiconductor layers represent an effective way to extract charge carrier mobility. A common method to interpret the time-dependence of the photocurrent in these material systems assumes a position-independent electric field between two coplanar electrodes. In this letter, we compare time-dependence of the photocurrent, measured in the samples comprising thin layers of poly-3-hexylthiophene, with the Monte Carlo simulations. In the simulations, we have used both, a position-independent and a position-dependent electric field. We obtained a favorable agreement between the simulations and the measurements only in the case of position-dependent electric field. We demonstrate that the charge carrier mobility may be underestimated by more than one order of magnitude, if a position-independent electric field is used in the calculations of the mobility.
Pavlica, Egon; Bratina, Gvido
Determination of the charge carrier compensation mechanism in Te-doped GaAs by scanning tunneling microscopy
NASA Astrophysics Data System (ADS)
We identified the charge carrier compensation mechanism in Te-doped GaAs with atomically resolved scanning tunneling microscopy. Three types of defects were found: tellurium donors (TeAs), Ga vacancies (VGa), and Ga vacancy-donor complexes (VGa-TeAs). We show quantitatively that the compensation in Te-doped bulk GaAs is exclusively caused by vacancy-donor complexes in contrast to Si-doped GaAs. This is explained with the Fermi-level effect as the universal mechanism leading to Ga vacancy formation in n-doped GaAs, and a Coulomb interaction leading to the formation of the complexes. The quantification of the carrier compensation yields a -3e charge state of VGa in bulk GaAs.
Gebauer, J.; Weber, E. R.; J�ger, N. D.; Urban, K.; Ebert, Ph.
Thickness dependence of plasmonic charge carrier generation in ultrathin a-Si:H layers for solar cells.
Nanocomposite layers of Ag nanoparticles and a-Si:H film constitute attractive candidates for the realization of ultrathin "two-dimensional" plasmonic solar cells, with an ideal 18% efficiency predicted for an average layer thickness of only 20 nm. By combining optical spectroscopy with photoconductivity measurements, we here characterize different contributions to the light absorption and charge carrier generation in such nanocomposites. We focus in particular on the important role of the absorber layer thickness for these processes, by studying a range of a-Si:H thicknesses from 9 to 67 nm. Through detailed comparison with numerical calculations by the finite element method, observed experimental features are connected to specific resonance modes and charge carrier generation mechanisms. The influence of dipolar and quadrupolar near-field distributions are evaluated with respect to different figures of merit for plasmonic solar cells. We briefly discuss how the present findings may be implemented in practical solar cell configurations. PMID:21732654
Gusak, Viktoria; Kasemo, Bengt; H�gglund, Carl
Effect of temperature and rare-earth doping on charge-carrier mobility in indium-monoselenide crystals
In the temperature range T = 77-600 K, the dependence of the charge-carrier mobility ({mu}) on the initial dark resistivity is experimentally investigated at 77 K ({rho}d{sub 0}), as well as on the temperature and the level (N) of rare-earth doping with such elements as gadolinium (Gd), holmium (Ho), and dysprosium (Dy) in n-type indium-monoselenide (InSe) crystals. It is established that the anomalous behavior of the dependences {mu}(T), {mu}({rho}d{sub 0}), and {mu}(N) found from the viewpoint of the theory of charge-carrier mobility in crystalline semiconductors is related, first of all, to partial disorder in indium-monoselenide crystals and can be attributed to the presence of random drift barriers in the free energy bands.
Abdinov, A. Sh., E-mail: email@example.com [Baku State University (Azerbaijan); Babayeva, R. F., E-mail: firstname.lastname@example.com [Azerbaijan State Economic University (Azerbaijan); Amirova, S. I.; Rzayev, R. M. [Baku State University (Azerbaijan)] [Baku State University (Azerbaijan)
Charge Transport Characteristics Of Cobalt Phthalocyanine Thin Films Grown By Molecular Beam Epitaxy
In the recent times organic semiconductors (OSC) have received attention because of their application in low-cost, flexible, and large area electronics devices. The application of OSC thin films has been limited due to their low charge carrier mobility ({approx}0.1 cm{sup 2}/V-s). We have investigated the effect of substrate on structure and charge transport characteristics of cobalt phthalocyanine (CoPc) films. Thin films have been grown on both single crystal (sapphire and LaAlO{sub 3}) and amorphous (quartz) substrates using molecular beam epitaxy system. The films grown on LaAlO{sub 3} substrates exhibited a higher value of mobility ({approx}4 cm{sup 2}/V-s) while those grown on Al{sub 2}O{sub 3} and quartz showed mobility value of {approx}1 cm{sup 2}/V-s. High mobility for LaAlO{sub 3} substrates has been attributed to the enhanced ordering of the molecules due to natural twin boundaries of substrates. In order to further confirm role of grain boundaries in aligning the CoPc molecules, we measured the charge transport on films deposited at bi-crystal SrTiO{sub 3} substrates. The results showed that current along bi-crystal grain boundary is three orders of magnitude higher than for films on SrTiO{sub 3} substrate without grain boundary, which confirms our hypothesis of ordering of molecules along grain boundaries.
Gupta, S. K.; Singh, Ajay; Samanta, Soumen; Kumar, Arvind; Debnath, A. K.; Aswal, D. K. [Technical Physics Division, Bhabha Atomic Research Center, Mumbai 400 085 (India)
Reduction and transition in thermal activation for charge transport through electrolyte-gated polythiophene thin films with high hole densities
NASA Astrophysics Data System (ADS)
We investigate the activation energy for electrical charge transport through a polythiophene thin film. The results are particularly obtained under high hole density (5.9 � 1020 holes/cm3) through electrolyte-gating and are compared with previous results attained from the same polymer film but with low induced carrier densities. Comparative analyses show that introducing high hole densities into the polymer results in (i) suppression of the transport activation energy and (ii) reduction of the temperature that yields transition in the activation energy. These results are explained based on the formation of bipolaron states, which are generated at such high hole densities.
Lee, Jiyoul; Cho, Boeun; Won Chung, Jong; Sung Kang, Moon
Carrier transport and bandgap shift in n-type degenerate ZnO thin films: The effect of band edge nonparabolicity
NASA Astrophysics Data System (ADS)
Contribution of band edge nonparabolicity to the charge carrier transport in degenerate n-type zinc oxide thin films has been investigated theoretically in order to understand the fundamental aspects of electron scattering in such thin films regardless of precise details of the preparation procedure. To conduct this, the theoretical evaluated results have been compared to the experimental values taken from literatures. The results indicate that the nonparabolicity (introducing through effective mass of charge carriers) has a strong effect on the total mobility of carriers in zinc oxide films so that a satisfactory agreement with experimental data is fulfilled. The dependence of nonparabolicity on bandgap shift is also discussed. Studying the optoelectronic properties of numerous moderately and heavily doped samples revealed that their optical bandgap has lower blueshift than the theoretical value obtained from the well-known Burstein-Moss effect. So, the observed bandgap shift was dependent on the carrier concentration and the total shift of bandgap was evaluated by combining the Burstein-Moss and bandgap narrowing effects. Two different cases were also examined; parabolic and nonparabolic (modified) Burstein-Moss effects. The results show that the modified Burstein-Moss effect leads to great agreement with experimental data.
Abdolahzadeh Ziabari, A.; Rozati, S. M.
Effect of Mg doping on the structural and free-charge carrier properties of InN films
NASA Astrophysics Data System (ADS)
We present a comprehensive study of free-charge carrier and structural properties of two sets of InN films grown by molecular beam epitaxy and systematically doped with Mg from 1.0 � 1018 cm-3 to 3.9 � 1021 cm-3. The free electron and hole concentration, mobility, and plasmon broadening parameters are determined by infrared spectroscopic ellipsometry. The lattice parameters, microstructure, and surface morphology are determined by high-resolution X-ray diffraction and atomic force microscopy. Consistent results on the free-charge carrier type are found in the two sets of InN films and it is inferred that p-type conductivity could be achieved for 1.0 � 1018 cm-3 ? [Mg] ? 9.0 � 1019 cm-3. The systematic change of free-charge carrier properties with Mg concentration is discussed in relation to the evolution of extended defect density and growth mode. A comparison between the structural characteristics and free electron concentrations in the films provides insights in the role of extended and point defects for the n-type conductivity in InN. It further allows to suggest pathways for achieving compensated InN material with relatively high electron mobility and low defect densities. The critical values of Mg concentration for which polarity inversion and formation of zinc-blende InN occurred are determined. Finally, the effect of Mg doping on the lattice parameters is established and different contributions to the strain in the films are discussed.
Xie, M.-Y.; Ben Sedrine, N.; Sch�che, S.; Hofmann, T.; Schubert, M.; Hung, L.; Monemar, B.; Wang, X.; Yoshikawa, A.; Wang, K.; Araki, T.; Nanishi, Y.; Darakchieva, V.
Photogeneration of charge carrier correlated with amplified spontaneous emission in single crystals of a thiophene/phenylene co-oligomer
NASA Astrophysics Data System (ADS)
Thiophene/phenylene co-oligomers have substantial promise for the use of not only organic electronics but also organic optical devices. However, considerably less is known about the correlation between their optical and optoelectronic properties. We have investigated the charge carrier generation in 1,4-bis(5-phenylthiophen-2-yl)benzene (AC5) single crystals by flash-photolysis time-resolved microwave conductivity (TRMC) and transient absorption spectroscopy (TAS). It was found that the dependence of photocarrier generation efficiency on excitation photon density differed from that of emission efficiency once amplified spontaneous emission (ASE) and resultant spectrally narrowed emission occur upon exposure to 355 nm. In contrast, the dependences of emission and photocarrier generation efficiencies were identical when ASE was not involved at a different excitation wavelength (193 nm). An approximated analytical solution of rate equation considering ASE or singlet-singlet annihilation was applied to the experiments, exhibiting good agreement. On the basis of TRMC, TAS, and extinction coefficient of radical cation assessed by pulse radiolysis, the minimum charge carrier mobility was estimated, without electrodes, to be 0.12 cm2 V-1 s-1. The dynamics of charge carrier and triplet excited state is discussed, accompanying with examination by time-dependent density functional theory. The present work would open the way to a deeper understanding of the fate of excited state in optically robust organic semiconducting crystals.
Saeki, Akinori; Seki, Shu; Shimizu, Yasuhiro; Yamao, Takeshi; Hotta, Shu
Computational investigation of charge injection and transport properties of a series of thiophene-pyrrole based oligo-azomethines.
The present study explores the structural, charge carrier injection and transport properties of a series of thiophene-pyrrole based oligo-azomethines using density functional theory (DFT) methods. Our findings show that the presence of a bulky substituent adversely affects these properties. However, the electronic effect of substituents may be utilized to tune these properties by substitutions at suitable positions. Values of frontier orbitals, ionization energies, and electron affinities are calculated for each compound to predict the ease of charge injection from metal electrodes to these azomethines and the stabilities of their ionic forms. In addition to having large injection barriers, lack of stability of the anions may hinder the electron injection. However, most of the compounds have excellent hole injection capability. Computation of reorganization energies and electronic couplings followed by charge transfer rates and mobilities show large carrier mobilities for some of the studied compounds. Considering both the injection capability and carrier mobilities, it is found that a thiophene-pyrrole azomethine without any substituent and substituted azomethines with a methyl, methoxy or amine group at the 3 position of the pyrrole ring may act as efficient materials for the hole transport layer. PMID:24671604
Sahu, Harikrishna; Panda, Aditya N
Flexoelectric rectification of charge transport in strain-graded dielectrics.
Flexoelectricity is emerging as a fascinating means for exploring the physical properties of nanoscale materials. Here, we demonstrated the unusual coupling between electronic transport and the mechanical strain gradient in a dielectric epitaxial thin film. Utilizing the nanoscale strain gradient, we showed the unique functionality of flexoelectricity to generate a rectifying diode effect. Furthermore, using conductive atomic force microscopy, we found that the flexoelectric effect can govern the local transport characteristics, including spatial conduction inhomogeneities, in thin-film epitaxy systems. Consideration of the flexoelectric effect will improve understanding of the charge conduction mechanism at the nanoscale and may facilitate the advancement of novel nanoelectronic device design. PMID:23190011
Lee, Daesu; Yang, Sang Mo; Yoon, Jong-Gul; Noh, Tae Won
Possible role of charge transport in enhanced carbon nanotube growth
NASA Astrophysics Data System (ADS)
We consider the role of electric fields during metal-catalysed thermal chemical vapour deposition growth of carbon nanotubes and show that enhanced growth occurs from a negatively biased electrode. An electric field, applied externally to the growing tubes and/or generated as a result of electron emission or self-biasing, may strongly affect the carbon supply through the catalyst nanoparticle, enhancing the growth rate. Different aspects of the growth process are analysed: the nature of the nanoparticle catalysis, carbon dissolution kinetics, electron emission from the nanotube tips, charge transport in the nanotube catalytic nanoparticle system and carbon drift and diffusion through the catalyst under the action of the electric field. A fundamental tenet for modelling of charge-transport dynamics during the nanotube growth process is proposed.
Bulgakova, N. M.; Bulgakov, A. V.; Svensson, J.; Campbell, E. E. B.
Simulating charge transport in tris(8-hydroxyquinoline) aluminium (Alq(3)).
We present a model of charge transport in organic solids which explicitly considers the packing and electronic structure of individual molecules. We simulate the time-of-flight mobility measurement in crystalline and disordered films of tris(8-hydroxyquinoline) aluminium (Alq(3)). The morphology of disordered Alq(3) is modelled on a molecular scale, and density functional theory is used to determine the electronic couplings between molecules. Without any fitting parameters we predict electron mobilities in the crystalline and disordered phases of approximately 1 and approximately 10(-4) cm(2) V(-1) s(-1), respectively. In good agreement with experiment we find that electron mobilities are two orders of magnitude greater than those of holes. We explain this difference in terms of the spatial extent of the frontier orbitals. Our results suggest that charge transport in disordered Alq(3) is dominated by a few highly conducting pathways. PMID:18368176
Kwiatkowski, J J; Nelson, J; Li, H; Bredas, J L; Wenzel, W; Lennartz, C
Wave-optics applications in charged-particle-beam transport
An overview of electron wave-optics applications to charged-particle-beam transport is presented in the context of the thermal\\u000a wave model (TWM). The quantization of the electron optics is presented both in the configuration space and in the phase space.\\u000a The former provides a description in terms of the Schr�dinger-like equation for a complex function whose squared modulus is\\u000a proportional to the
R. Fedele; M. A. Man'ko; V. I. Man'ko
Charge Transport in Chemically Doped 2D Graphene
We report on a numerical study of electronic transport in chemically doped 2D graphene materials. By using ab initio calculations, a self-consistent scattering potential is derived for boron and nitrogen substitutions, and a fully quantum-mechanical Kubo-Greenwood approach is used to evaluate the resulting charge mobilities and conductivities of systems with impurity concentration ranging within [0.5, 4.0]%. Even for a doping
Aur�lien Lherbier; X. Blase; Yann-Michel Niquet; Fran�ois Triozon; Stephan Roche
Secondary electron emission and self-consistent charge transport in semi-insulating samples
NASA Astrophysics Data System (ADS)
Electron beam induced self-consistent charge transport and secondary electron emission (SEE) in insulators are described by means of an electron-hole flight-drift model (FDM) now extended by a certain intrinsic conductivity (c) and are implemented by an iterative computer simulation. Ballistic secondary electrons (SE) and holes, their attenuation to drifting charge carriers, and their recombination, trapping, and field- and temperature-dependent detrapping are included. As a main result the time dependent ``true'' secondary electron emission rate ?(t) released from the target material and based on ballistic electrons and the spatial distributions of currents j(x,t), charges ?(x,t), field F(x,t), and potential V(x,t) are obtained where V0 = V(0,t) presents the surface potential. The intrinsic electronic conductivity limits the charging process and leads to a conduction sample current to the support. In that case the steady-state total SE yield will be fixed below the unit: i.e., ? = ? + ? < 1.
Fitting, H.-J.; Touzin, M.
Nonlinear charge transport in the helicoidal DNA molecule
NASA Astrophysics Data System (ADS)
Charge transport in the twist-opening model of DNA is explored via the modulational instability of a plane wave. The dynamics of charge is shown to be governed, in the adiabatic approximation, by a modified discrete nonlinear Schr�dinger equation with next-nearest neighbor interactions. The linear stability analysis is performed on the latter and manifestations of the modulational instability are discussed according to the value of the parameter ?, which measures hopping interaction correction. In so doing, increasing ? leads to a reduction of the instability domain and, therefore, increases our chances of choosing appropriate values of parameters that could give rise to pattern formation in the twist-opening model. Our analytical predictions are verified numerically, where the generic equations for the radial and torsional dynamics are directly integrated. The impact of charge migration on the above degrees of freedom is discussed for different values of ?. Soliton-like and localized structures are observed and thus confirm our analytical predictions. We also find that polaronic structures, as known in DNA charge transport, are generated through modulational instability, and hence reinforces the robustness of polaron in the model we study.
Dang Koko, A.; Tabi, C. B.; Ekobena Fouda, H. P.; Mohamadou, A.; Kofan�, T. C.
Nonlinear charge transport in the helicoidal DNA molecule.
Charge transport in the twist-opening model of DNA is explored via the modulational instability of a plane wave. The dynamics of charge is shown to be governed, in the adiabatic approximation, by a modified discrete nonlinear Schro?dinger equation with next-nearest neighbor interactions. The linear stability analysis is performed on the latter and manifestations of the modulational instability are discussed according to the value of the parameter ?, which measures hopping interaction correction. In so doing, increasing ? leads to a reduction of the instability domain and, therefore, increases our chances of choosing appropriate values of parameters that could give rise to pattern formation in the twist-opening model. Our analytical predictions are verified numerically, where the generic equations for the radial and torsional dynamics are directly integrated. The impact of charge migration on the above degrees of freedom is discussed for different values of ?. Soliton-like and localized structures are observed and thus confirm our analytical predictions. We also find that polaronic structures, as known in DNA charge transport, are generated through modulational instability, and hence reinforces the robustness of polaron in the model we study. PMID:23278045
Dang Koko, A; Tabi, C B; Ekobena Fouda, H P; Mohamadou, A; Kofan�, T C
Utilizing carbon nanotube electrodes to improve charge injection and transport in bis(trifluoromethyl)-dimethyl-rubrene ambipolar single crystal transistors.
We have examined the significant enhancement of ambipolar charge injection and transport properties of bottom-contact single crystal field-effect transistors (SC-FETs) based on a new rubrene derivative, bis(trifluoromethyl)-dimethyl-rubrene (fm-rubrene), by employing carbon nanotube (CNT) electrodes. The fundamental challenge associated with fm-rubrene crystals is their deep-lying HOMO and LUMO energy levels, resulting in inefficient hole injection and suboptimal electron injection from conventional Au electrodes due to large Schottky barriers. Applying thin layers of CNT network at the charge injection interface of fm-rubrene crystals substantially reduces the contact resistance for both holes and electrons; consequently, benchmark ambipolar mobilities have been achieved, reaching 4.8 cm(2) V(-1) s(-1) for hole transport and 4.2 cm(2) V(-1) s(-1) for electron transport. We find that such improved injection efficiency in fm-rubrene is beneficial for ultimately unveiling its intrinsic charge transport properties so as to exceed those of its parent molecule, rubrene, in the current device architecture. Our studies suggest that CNT electrodes may provide a universal approach to ameliorate the charge injection obstacles in organic electronic devices regardless of charge carrier type, likely due to the electric field enhancement along the nanotube located at the crystal/electrode interface. PMID:24175573
Xie, Wei; Prabhumirashi, Pradyumna L; Nakayama, Yasuo; McGarry, Kathryn A; Geier, Michael L; Uragami, Yuki; Mase, Kazuhiko; Douglas, Christopher J; Ishii, Hisao; Hersam, Mark C; Frisbie, C Daniel
Semiconductor drift chamber --- An application of a novel charge transport scheme
B The purpose of this paper is to describe a novel charge transport scheme in semiconductors, in which the field responsible for the charge transport is independent of the depletion field. The application of the novel charge transport scheme leads to the following new semiconductor detectors: 1) Semiconductor drift chamber; 2) Ultralow capacitance - large area semiconductor X-ray spectrometers and
Emilio Gatti; Pavel Rehak
Carrier transport in green AlInGaN based structures on c-plane substrates
NASA Astrophysics Data System (ADS)
In this paper, the carrier transport in (Al)InGaN based test structures with In-rich quantum wells on c-plane substrates is investigated under high current operation. To get access to the injection efficiency, the devices are processed as ridge waveguide lasers and examined above threshold. The slope efficiency reveals a slight decrease as a function of current even under pulsed operation that can be related to a reduction of the injection efficiency based on carrier leakage. As the test structure contains an InGaN detection layer on the n-side, it is possible to verify hole overflow across the active region. Moreover, by analysing the current dependence of the radiative recombination in the detection layer, the reduction of slope efficiency can be correlated to increasing hole leakage.
Hager, T.; Binder, M.; Br�derl, G.; Eichler, C.; Avramescu, A.; Wurm, T.; Gomez-Iglesias, A.; Stojetz, B.; Tautz, S.; Galler, B.; Gerhard, S.; Zeisel, R.; Strauss, U.
Space-Charge Transport Limits in Periodic Channels
It has been empirically observed in both experiments and particle-in-cell simulations that space-charge-dominated beams suffer strong emittance growth and particle losses in alternating gradient quadrupole transport channels when the undepressed phase advance {sigma}{sub 0} increases beyond about 85{sup o} per lattice period. Although this criteria has been used extensively in practical designs of intense beam transport lattices, no theory exists that explains the limit. We propose a mechanism for the transport limit resulting from classes of halo particle resonances near the core of the beam that allow near-edge particles to rapidly increase in oscillation amplitude when the space-charge intensity and the flutter of the matched beam envelope are both sufficiently large. Due to a finite beam edge and/or perturbations, this mechanism can result in dramatic halo-driven increases in statistical beam phase space area, lost particles, and degraded transport. A core-particle model for a uniform density elliptical beam in a periodic focusing lattice is applied to parametrically analyze this process.
Lund, S M; Chawla, S R
An acoustic charge transport imager for high definition television applications
NASA Technical Reports Server (NTRS)
The primary goal of this research is to develop a solid-state television (HDTV) imager chip operating at a frame rate of about 170 frames/sec at 2 Megapixels/frame. This imager will offer an order of magnitude improvements in speed over CCD designs and will allow for monolithic imagers operating from the IR to UV. The technical approach of the project focuses on the development of the three basic components of the imager and their subsequent integration. The camera chip can be divided into three distinct functions: (1) image capture via an array of avalanche photodiodes (APD's); (2) charge collection, storage, and overflow control via a charge transfer transistor device (CTD); and (3) charge readout via an array of acoustic charge transport (ACT) channels. The use of APD's allows for front end gain at low noise and low operating voltages while the ACT readout enables concomitant high speed and high charge transfer efficiency. Currently work is progressing towards the optimization of each of these component devices. In addition to the development of each of the three distinct components, work towards their integration and manufacturability is also progressing. The component designs are considered not only to meet individual specifications but to provide overall system level performance suitable for HDTV operation upon integration. The ultimate manufacturability and reliability of the chip constrains the design as well. The progress made during this period is described in detail.
Hunt, W. D.; Brennan, K. F.; Summers, C. J.
An acoustic charge transport imager for high definition television applications
NASA Technical Reports Server (NTRS)
The primary goal of this research is to develop a solid-state high definition television (HDTV) imager chip operating at a frame rate of about 170 frames/sec at 2 Megapixels per frame. This imager offers an order of magnitude improvement in speed over CCD designs and will allow for monolithic imagers operating from the IR to the UV. The technical approach of the project focuses on the development of the three basic components of the imager and their integration. The imager chip can be divided into three distinct components: (1) image capture via an array of avalanche photodiodes (APD's), (2) charge collection, storage and overflow control via a charge transfer transistor device (CTD), and (3) charge readout via an array of acoustic charge transport (ACT) channels. The use of APD's allows for front end gain at low noise and low operating voltages while the ACT readout enables concomitant high speed and high charge transfer efficiency. Currently work is progressing towards the development of manufacturable designs for each of these component devices. In addition to the development of each of the three distinct components, work towards their integration is also progressing. The component designs are considered not only to meet individual specifications but to provide overall system level performance suitable for HDTV operation upon integration. The ultimate manufacturability and reliability of the chip constrains the design as well. The progress made during this period is described in detail in Sections 2-4.
Hunt, W. D.; Brennan, Kevin F.
Towards high charge-carrier mobilities by rational design of the shape and periphery of discotics
NASA Astrophysics Data System (ADS)
Discotic liquid crystals are a promising class of materials for molecular electronics thanks to their self-organization and charge transporting properties. The best discotics so far are built around the coronene unit and possess six-fold symmetry. In the discotic phase six-fold-symmetric molecules stack with an average twist of 30?, whereas the angle that would lead to the greatest electronic coupling is 60?. Here, a molecule with three-fold symmetry and alternating hydrophilic/hydrophobic side chains is synthesized and X-ray scattering is used to prove the formation of the desired helical microstructure. Time-resolved microwave-conductivity measurements show that the material has indeed a very high mobility, 0.2cm2V-1s-1. The assemblies of molecules are simulated using molecular dynamics, confirming the model deduced from X-ray scattering. The simulated structures, together with quantum-chemical techniques, prove that mobility is still limited by structural defects and that a defect-free assembly could lead to mobilities in excess of 10cm2V-1s-1.
Feng, Xinliang; Marcon, Valentina; Pisula, Wojciech; Hansen, Michael Ryan; Kirkpatrick, James; Grozema, Ferdinand; Andrienko, Denis; Kremer, Kurt; M�llen, Klaus
47 CFR 51.909 - Transition of rate-of-return carrier access charges.
Code of Federal Regulations, 2013 CFR
...provision of the Commission's rules: (1) Notwithstanding the rate structure rules set forth in § 69.106 of this chapter or anything else in the Commission's rules, a Rate-of-Return Carrier shall establish separate originating and terminating...
Parameters of the Constant-Energy Surface and Features of Charge Carrier Scattering of Bi2Te3-Based Epitaxial Films
NASA Astrophysics Data System (ADS)
Galvanomagnetic properties of epitaxial Bi0.5Sb1.5Te3 films grown by the hot-wall technique were investigated in magnetic fields of H = 5 T to 14 T through the temperature interval of 10 K to 300 K. The results were analyzed in terms of a many-valley model of the energy spectrum and anisotropic charge carrier scattering. The degeneracy parameter ? d, and ratios of components of the reciprocal effective-mass tensor {leftrightarrow}over ?} and relaxation time tensor {{leftrightarrow}over ? } (\\varepsilon ) were estimated. Substantial anisotropy of charge carrier scattering was observed in the investigated temperature interval. Anisotropy of charge carrier scattering along bisector axes is enhanced, as compared with that of corresponding bulk samples. High charge carrier mobility and higher angular factor of the temperature dependence of mobility promote enhancement of the figure of merit Z of the films as compared with that of corresponding bulk solid solutions.
Lukyanova, L. N.; Boikov, Yu. A.; Danilov, V. A.; Volkov, M. P.; Kutasov, V. A.
Experimental study of the minority-carrier transport at the polysilicon-monosilicon interface
NASA Astrophysics Data System (ADS)
This paper presents the results of an experimental study designed to explore both qualitatively and quantitatively the mechanism of the improved current gain in bipolar transistors with polysilicon emitter contacts. Polysilicon contacts were deposited and heat treated at different conditions. The electrical properties were measured using p-n junction test structures that are much more sensitive to the contact properties than are bipolar transistors. A simple phenomenological model was used to correlate the structural properties with electrical measurements. Possible transport mechanisms are examined and estimates are made about upper bounds on transport parameters in the principal regions of the devices. The main conclusion of this study is that the minority-carrier transport in the polycrystalline silicon is dominated by a highly disordered layer at the polysilicon-monosilicon interface characterized by very low minority-carrier mobility. The effective recombination velocity at the n(+) polysilicon-n(+) monosilicon interface was found to be a strong function of fabrication conditions. The results indicate that the recombination velocity can be much smaller than 10,000 cm/s.
Neugroschel, A.; Arienzo, M.; Isaac, R. D.; Komem, Y.
Extraction of carrier transport parameters from hydrogenated amorphous and nanocrystalline silicon solar cells
NASA Astrophysics Data System (ADS)
Transport properties are very important for solar cells. The efficiency of solar cells is determined by the competition of carrier collection and recombination. The most important parameter is the carrier mobility-lifetime product. However, methods commonly used for measuring transport parameters require specially designed samples. The results are often not easily correlated to solar cell performance. In this paper, we present our studies of extraction of material properties from conventional current-voltage characteristics and quantum efficiency curves. First, we carried out analyses of shunt resistance as a function of the light intensity. For solar cells with no clear parasitic shunt resistance, the shunt resistance is inversely proportional to the short-circuit current, and its proportionality coefficient is related to the effective carrier mobility-lifetime product. For an a-Si:H solar cell made under an optimized condition with high hydrogen dilution, the effective mobility-lifetime product was estimated to be 1.2x10-8 cm2/V. For a-SiGe:H solar cells, the effective mobility-lifetime product depends on Ge content. For optimized a-SiGe:H bottom cells used in high efficiency a-Si:H/a-SiGe:H/a-SiGe:H triple-junction structures, their values are ~5.0x10-9 cm2/V. For high efficiency nc-Si:H solar cells, the effective mobility-lifetime product is ~5.0x10-7 cm2/V. Second, we measured the quantum efficiency as a function of electrical bias and developed an analytical model to deduce the effective mobility-lifetime product. The results obtained from the second method are consistent with the values from the first method. We will present detailed analyses and interpretations of the transport parameters and their correlation to solar cell performance.
Yan, Baojie; Yue, Guozhen; Sivec, Laura; Yang, Jeffrey; Guha, Subhendu
Electron spin resonance study of Er-concentration effect in GaAs;Er,O containing charge carriers
NASA Astrophysics Data System (ADS)
Er-concentration effect in GaAs;Er,O containing charge carriers (n-type, high resistance, p-type) has been studied by X-band Electron spin resonance (ESR) at low temperature (4.7 K < T < 18 K). Observed A, B, and C types of ESR signals were identical to those observed previously in GaAs:Er,O without carrier. The local structure around Er-2O centers is not affected by carriers because similar angular dependence of g-values was observed in both cases (with/without carrier). For temperature dependence, linewidth and lineshape analysis suggested the existence of Er dimers with antiferromagnetic exchange interaction of about 7 K. Moreover, drastic decrease of ESR intensity for C signal in p-type sample was observed and it correlates with the decrease of photoluminescence (PL) intensity. Possible model for the Er-2O trap level in GaAs:Er,O is discussed from the ESR and PL experimental results.
Elmasry, F.; Okubo, S.; Ohta, H.; Fujiwara, Y.
Influence of charge carrier diffusion on the stability of a charged drop of a finite-conductivity liquid
NASA Astrophysics Data System (ADS)
A dispersion relation for the capillary oscillations of a spherical drop of a viscous incompressible liquid with a charge transfer finite rate is derived and analyzed with emphasis on the role of diffusion. It is shown that diffusion has the strongest influence on the stability of rapidly damped quasi-periodic motions of a low-conductivity liquid. The instability growth rate of capillary oscillations grows with the charge diffusion coefficient and decreases with rising conductivity of the liquid.
Artemova, T. K.; Shiryaeva, S. O.; Grigor'ev, A. I.
Ring-Containing Conjugated Polymers: Charge Transport and Electroluminiscence
NASA Astrophysics Data System (ADS)
Conjugated polymers have been studied extensively in the last decade both in the doped conducting state and the undoped semiconducting or insulating form. For the doped conducting polymers, the nature of the metallic state upon doping and the dimensionality of the system have been a hot issue, with improvements in chemical processing playing the key role in clarifying them. For the undoped polymers, particularly the luminescent polymers, the nature of the electronic and optical processes occurring upon charge injection or photoexcitation have been under intense study because they reflect the underlying physics in conjugated polymer based light-emitting (electroluminescent) devices. In this dissertation, both issues are studied. In the conducting state, systematic charge transport and structural studies were performed on hydrochloric and camphor sulfonic acid doped polyaniline and its methyl derivative poly(o-toluidine) (POT) fibers to investigate the role of chemical processing and the nature of the metallic state in conducting polymers. The study shows that the charge transport properties are controlled by the local microstructural order whose formation is very sensitive to chemical processing conditions such as processing temperature, dopant and solvent used. The solvent, or the so-called secondary dopant, has been shown to play a critical role in improving the charge transport properties. As a result of improved chemical processing, high quality camphor sulfonic acid doped poly(o-toluidine) (POT-CSA) fibers have been prepared from m-cresol, enabling a direct experimental test of the random-dimer model (RDM), one of the models proposed to account for the metallic state in polyaniline. The results of the charge transport studies on the POT-CSA fibers and the dielectric response studies of the POT-CSA solutions in formic acid are clearly inconsistent with the RDM. In the semiconducting/insulating states, pyridine-based fluorescent polymers were used to study the electroluminescent processes and properties. Light -emitting diodes based on these polymers were fabricated and characterized in various device configurations. In addition, a new type of electroluminescent device, the symmetrically configured AC light-emitting (SCALE) device, is described. The mechanism for the SCALE device operation is discussed with the emphasis on the role of the interfaces.
Wang, Yunzhang
The solute carrier family 10 (SLC10): beyond bile acid transport
The solute carrier (SLC) family 10 (SLC10) comprises influx transporters of bile acids, steroidal hormones, various drugs, and several other substrates. Because the seminal transporters of this family, namely, sodium/taurocholate cotransporting polypeptide (NTCP; SLC10A1) and the apical sodium-dependent bile acid transporter (ASBT; SLC10A2), were primarily bile acid transporters, the term �sodium bile salt cotransporting family� was used for the SLC10 family. However, this notion became obsolete with the finding of other SLC10 members that do not transport bile acids. For example, the sodium-dependent organic anion transporter (SOAT; SLC10A6) transports primarily sulfated steroids. Moreover, NTCP was shown to also transport steroids and xenobiotics, including HMG-CoA inhibitors (statins). The SLC10 family contains four additional members, namely, P3 (SLC10A3; SLC10A3), P4 (SLC10A4; SLC10A4), P5 (SLC10A5; SLC10A5) and SLC10A7 (SLC10A7), several of which were unknown or considered hypothetical until approximately a decade ago. While their substrate specificity remains undetermined, great progress has been made towards their characterization in recent years. SLC10A4 may participate in vesicular storage or exocytosis of neurotransmitters or mastocyte mediators, whereas SLC10A5 and SLC10A7 may be involved in solute transport and SLC10A3 may have a role as a housekeeping protein. Finally, the newly found role of bile acids in glucose and energy homeostasis, via the TGR5 receptor, sheds new light on the clinical relevance of ASBT and NTCP. The present mini-review provides a brief summary of recent progress on members of the SLC10 family.
da Silva, Tatiana Claro; Polli, James E.; Swaan, Peter W.
Charge Localization and Transport in Lithiated Olivine Phosphate Materials
We report density functional theory (DFT) calculations for olivine-type LiTMPO4 and TMPO4 (TM=Mn, Fe, Co, Ni) structures, using GGA+U and the B3LYP hybrid density functional that includes nonlocal Fock exchange. TM is typically characterized in terms of the formal oxide states of 2+ or 3+, corresponding to TM with localized charge in LiTMPO4 and TMPO4 structures, respectively, in which electron transport would take place by thermally activated hopping of electrons strongly localized on the transition metal (small polarons). In this work, we assess the validity of the concept of formal TM oxidation states in these materials, and conclude that the valence depends in large part on the strength of d-p hybridization. Stable small polaron formation, i.e., mixed 2+ and 3+ valence states, appears to require that the ratio of differences in the metal and oxygen ionic charges (dQTM/dQO) of the two end member phases is larger than 2, corresponding to the mixed-valence TM system. If the ratio of dQTM/dQO is smaller than 2, excess electrons prefer delocalization and the system behaves more single-valence like with charge transport more akin to metallic conduction. The critical ratio emerging from our analysis may turn out to be relevant to other transition metal systems as well, as a criterion to discriminate single-valence or mixed-valence characteristics and hence the predominant conduction mechanism.
Yu, Jianguo; Rosso, Kevin M.; Liu, Jun
Measurement of the drift mobilities and the mobility-lifetime products of charge carriers in a CdZnTe crystal by using a transient pulse technique
NASA Astrophysics Data System (ADS)
In this work we present results on the measurement of the drift mobility and the mobility-lifetime product of charge carriers in a 16-pixellated CdZnTe detector. For the determination of an interaction position based on the pulse rise-time method in a CZT detector, it is necessary to characterize the transport properties governed by drift mobility and lifetime for electrons and holes. In order to extract the transport properties of an electron and a hole, we bombarded 5.5-MeV alpha particles from a 241Am source and 81-keV gamma rays emitted from a 133Ba source on the negatively biased contact of the CZT detector. A time-of-flight (TOF) method was used to measure the electron drift mobility at room temperature whose value turned out to be 906.4 cm2/V? s. With the Hecht's equation, the electron mobility-lifetime product was also determined from the bias-dependent alpha response and was equal to (9.88 � 2.33) � 10-3 cm2/V. On the other hand, the hole mobility-lifetime product was evaluated by a model based on the average charge collection efficiency which accounts for the absorption probability with a given photon energy. By using a single parameter fitting of the model, we obtained the hole mobility-lifetime product of (8.28 � 0.17) � 10-4 cm2/V.
Cho, H. Y.; Lee, J. H.; Kwon, Y. K.; Moon, J. Y.; Lee, C. S.
Extrinsic limiting factors of carrier transport in organic field-effect transistors
Extrinsic factors to disturb the carrier transport in pentacene field-effect transistors (FETs), as a representative of the\\u000a high-mobility organic FETs (OFETs), have been comprehensively analyzed by using atomic-force-microscope potentiometry (AFMP),\\u000a microscopic four-point-probe field-effect transistor (MFPP-FET) measurement, and other techniques. In the first part, by mainly\\u000a using AFMP as a powerful tool to reveal the potential distribution in working OFETs, we
Masakazu Nakamura; Hirokazu Ohguri; Naoyuki Goto; Hiroshi Tomii; Mingsheng Xu; Takashi Miyamoto; Ryousuke Matsubara; Noboru Ohashi; Masaaki Sakai; Kazuhiro Kudo
Mathematical modeling of a carrier-mediated transport process in a liquid membrane.
An analysis of the reaction diffusion in a carrier-mediated transport process through a membrane is presented. A simple approximate analytical expression of concentration profiles is derived in terms of all dimensionless parameters. Furthermore, in this work we employ the homotopy perturbation method to solve the nonlinear reaction-diffusion equations. Moreover, the analytical results have been compared to the numerical simulation using the Matlab program. The simulated results are comparable with the appropriate theories. The results obtained in this work are valid for the entire solution domain. PMID:23670364
Ganesan, Subramanian; Anitha, Shanmugarajan; Subbiah, Alwarappan; Rajendran, Lakshmanan
Charge transport in organic crystals: interplay of band transport, hopping and electron-phonon scattering
We present an ab initio description of charge transport in organic semiconductors based on a recently developed theory that goes beyond small-polaron and\\/or narrow-band models. The mobility expression is evaluated with parameters from density functional theory, and application to naphthalene crystals demonstrates substantial progress in the simulated temperature dependence and relative magnitudes for all transport directions. The scattering by phonons
Frank Ortmann; Friedhelm Bechstedt; Karsten Hannewald
Charge Transport in Azobenzene-Based Single-Molecule Junctions
NASA Astrophysics Data System (ADS)
The azobenzene class of molecules has become an archetype of molecular photoswitch research, due to their simple structure and the significant difference of the electronic system between their cis and trans isomers. However, a detailed understanding of the charge transport for the two isomers, when embedded in a junction with electrodes is still lacking. In order to clarify this issue, we investigate charge transport properties through single Azobenzene-ThioMethyl (AzoTM) molecules in a mechanically controlled break junction (MCB