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Volume 100, Issue 7, 01 October 2006
Identification by photoluminescence and positron annihilation of vacancy and interstitial intrinsic defects in ion-implanted silicon100(2006); http://dx.doi.org/10.1063/1.2354332View Description Hide Description
Defect centers generated in crystalline silicon by MeV Si implants have been investigated by a combination of photoluminescence, variable-energy positron annihilation measurements, depth profiling by etching,annealing studies, and the dependence on impurities. The broad photoluminescence band occurs at intrinsic interstitial complexes, the band at small vacancy clusters, and the line at a low concentration of vacancy clusters which are possibly formed by aggregation of the centers.
On the modulation mechanisms in photoreflectance of an ensemble of self-assembled quantum dots100(2006); http://dx.doi.org/10.1063/1.2355551View Description Hide Description
We present the investigation of the modulation mechanisms in photoreflectance (PR) spectroscopy of an ensemble of self-assembled semiconductor quantum dots(QDs). In order to distinguish between possible factors contributing to the total modulation efficiency of QD transitions, a photoreflectance excitation experiment has been performed on an quantum dot structure grown by solid-source molecular beam epitaxy. It has been observed that the intensity of PR features related to QDs changes in a function of the wavelength of the pumping laser, tuned from above-GaAs band gap down to below wetting layer ground state transition. Based on this dependence we have shown that most of the QD PR signal intensity originates from the modulation of the built-in electric field caused by carriers photogenerated in GaAs layers. We also conclude that the modulation of QD transitions related to a possible modification of the dot properties due to filling them with carriers is negligible in PR experiment on an ensemble of dots. An additional confirmation of the PR results has been obtained by using contactless electroreflectance (CER), demonstrating that the line shape of PR and CER QD resonances is almost identical in both spectra. Thus, the QD transitions can be analyzed by using the standard low field line shape functional form applicable in any electromodulation spectroscopy.
Instrumented Taylor anvil-on-rod impact tests for validating applicability of standard strength models to transient deformation states100(2006); http://dx.doi.org/10.1063/1.2354326View Description Hide Description
Instrumented Taylor anvil-on-rod impact tests have been conducted on oxygen-free electronic copper to validate the accuracy of current strength models for predicting transient states during dynamic deformation events. The experiments coupled the use of high-speed digital photography to record the transient deformation states and laser interferometry to monitor the sample back (free surface)velocity as a measure of the elastic∕plastic wave propagation through the sample length. Numerical continuum dynamics simulations of the impact and plastic wave propagation employing the Johnson-Cook [Proceedings of the Seventh International Symposium on Ballistics, 1983, The Netherlands (Am. Def. Prep. Assoc. (ADPA)), pp. 541–547], Zerilli-Armstrong [J. Appl. Phys. C1, 1816 (1987)], and Steinberg-Guinan [J. Appl. Phys. 51, 1498 (1980)]constitutive equations were used to generate transient deformation profiles and the free surfacevelocity traces. While these simulations showed good correlation with the measuredfree surfacevelocity traces and the final deformed sample shape, varying degrees of deviations were observed between the photographed and calculated specimen profiles at intermediate deformation states. The results illustrate the usefulness of the instrumented Taylor anvil-on-rod impact technique for validating constitutive equations that can describe the path-dependent deformation response and can therefore predict the transient and final deformation states.
Crystal structure and thermoelectric properties of type-I clathrate compounds in the Ba–Ga–Ge system100(2006); http://dx.doi.org/10.1063/1.2355443View Description Hide Description
The crystal structure and thermoelectric properties of type-I clathrate compounds in the Ba–Ga–Ge system have been investigated as a function of Ga content. The solid solubility of Ga in the type-I clathrate compounds is determined to be when expressed with the formula of . As the Ga content increases, the crystal structure changes from a superlatticestructure to the normal type-I clathratestructure with the transition occurring at . The density of Gevacancies in the type-I clathrate phase decreases as the Ga content increases. The absolute values of electrical resistivity and Seebeck coefficient increase, while that of lattice thermal conductivity decreases with the increase in the Ga content. The changes in electrical resistivity and Seebeck coefficient are explained in terms of the number of excess electrons, while the change in lattice thermal conductivity is explained in terms of the extent of the rattling motion of Ba atoms encapsulated in the cage structure.
Comparative studies of molecular reorientations in thermal-assisted and photoassisted electric-field poled nonlinear optical polymers100(2006); http://dx.doi.org/10.1063/1.2352810View Description Hide Description
The reorientational mobilities of molecules in nonlinear optical (NLO) polymers poled by thermal-assisted (TAP) and photoassisted (PAP) electric-field polings are compared by measuring the temporal development of the NLO properties under a secondary poling voltage at a temperature below the glass transition temperature of the polymer. By comparing the experimental results with a theoretical model that is based on a distribution of relaxation times, it was found that the experimental poling profile for a polymer poled by PAP showed a good agreement with the theory, while that for a polymer poled by TAP did not. The discrepancy of the behaviors between the two poling methods suggests that the relaxation patterns observed for polymers poled by TAP may not behave in a manner intrinsic to the polymer.
In situ monitoring of the growth of ice films by laser picosecond acoustics100(2006); http://dx.doi.org/10.1063/1.2353125View Description Hide Description
Ultrashort optical pulses are used to excite and probe picosecond acoustic pulses in a sample consisting of an opaque material upon which ice is continuously deposited from the vapor phase at . By analysis of the ultrasonic propagation and reflection inside the submicron icefilm and taking into account the scattering of the probe light by the acoustic waves, the thickness, sound velocity,refractive index,ultrasonic attenuation, and photoelastic constant of the icefilm are derived. This method should find applications for the in situ monitoring of thin transparent films during growth.
NMR relaxation of and single crystals with the electric-quadrupole-type interactions100(2006); http://dx.doi.org/10.1063/1.2354328View Description Hide Description
The spin-lattice relaxation time and spin-spin relaxation time of and single crystals grown by the slow evaporation method were measured over the temperature range of . In the case of the crystal, changes were observed in the near 340, 363, and , which correspond to phase transitions. The abrupt decrease in observed at is due to a shortening in the direction as a result of a phase transition from a tetragonal to a cubic structure. We suggest that the cubic Rb environment is favored above , which causes relaxation and averages out the quadrupolar splittings. On the other hand, the in decreased with increasing temperature, and no phase transitions were observed in the temperature range considered. For both and , the relaxation rate of Rb was found to be proportional to the square of the temperature, indicating that the relaxation proceeds via a Raman process. This behavior for the electric-quadrupolar-type and crystals stands in contrast to a previous report that the relaxations in and crystals with the magnetic relaxation type proceed via single-phonon processes. Therefore, the relaxation mechanism in crystals with an electric quadrupolar NMR interaction mechanism is completely different from that in crystals with magnetic-type NMR behavior.
Study of a nonlinear mechanical response of reentrant spin glass antiferromagnet Mn–Cu alloys100(2006); http://dx.doi.org/10.1063/1.2356900View Description Hide Description
We have studied the relation between the mechanical response and the magnetic susceptibility of -phase Mn–Cu binary alloys, which are reentrant spin glass (RSG) antiferromagnets. A close correlation between the temperature dependency of the hysteretic magnetization due to magnetic freezing and internal friction was observed. When the Cu concentration reached up to , where the antiferromagnetic long-range order disappeared, the magnetically correlated internal friction also disappeared. This composition effect and a remarkable vibration-amplitude dependency of the internal friction suggested that antiferromagneticdomain walls were responsible for these phenomena. Thus, we concluded that RSG freezing influences the dynamics of antiferromagneticdomain walls in a similar way as that of ferromagnets, and leads to internal friction.
Deformation stacking fault probability and dislocation microstructure of cold worked Cu–Sn–5Zn alloys by x-ray diffraction line profile analysis100(2006); http://dx.doi.org/10.1063/1.2356906View Description Hide Description
Plastically deformed (hand-filed) Cu–Sn–5Zn ternary alloys with Sn concentrations 1, 2.5, and are investigated. Microstructural parameters are studied in terms of x-ray diffraction profile fitting analysis. It is observed by Dey et al. [Acta. Mater.53, 4635 (2005)] that the change in stacking fault probability with Sn concentration for ternary Cu–Sn–5Zn alloys is similar to Cu-based binary alloy (Cu–Sn) system but behaves in a different manner from Cu–1Sn–Zn ternary alloy systems. The crystallite size distribution is broader for alloy with Sn and becomes narrower with increasing Sn concentration. Value of dislocation density is of the order of and shows a compositional dependence. Type of dislocation is found to be predominantly screw; ⟨100⟩-type dipoles may also be present in the cold-worked alloys. The dislocation arrangement is found to be more correlated in case of Sn compared to other alloys of higher Sn concentration. The stacking fault energy is obtained from modified Reed-Schramm equation and is of the order of with no significant compositional dependence.
Polymer light emitting diodes and poly(di--octylfluorene) thin films as fabricated with a microfluidics applicator100(2006); http://dx.doi.org/10.1063/1.2349467View Description Hide Description
A microfluidics applicator is used in the fabrication of a polyfluorene based polymer light emitting diode(PLED). This procedure results in a single contiguous polymer trace and, as a consequence of the high deposition speed, shows unusual characteristics in both the film morphology and polymer microstructure. These aspects are studied using fluorescence microscopy, profilometry, and optical absorption and emission spectroscopies. Room temperature analysis of the poly(di--octylfluorene) indicates that the combination of high-speed deposition and rapid drying process traps the polymer into a metastable conformational state. Optical spectroscopy at reduced temperature identifies emission from at least two distinct conformational chromophores. At elevated temperature there is an abrupt, irreversible transition to a more conventional structural form. Electroluminesence data from PLED test devices are shown and this demonstrates some of the unique opportunities afforded by this method of polymer film formation and device fabrication. Device operation is not optimized.
Depth profiling of strain and defects in heterostructures by micro-Raman imaging100(2006); http://dx.doi.org/10.1063/1.2355431View Description Hide Description
We have reported depth and in-plane profiling of strain, Ge composition, and defects in strained-heterostructures using micro-Raman imaging. Raman profiling in the depth direction was carried out with a depth resolution of using a small-angle beveled sample and ultraviolet (UV) excitation. Depth profiles of the Ge composition and Raman bandwidth clearly show that the defect density depends strongly on the Ge-grading rate in a compositionally graded layer. The in-plane strain variation at a given depth in each layer has been evaluated. The in-plane strain variations in the are closely related to clustering of misfit dislocations in the graded layer. For the top strained-Si layer, two-dimensional UV-Raman images of the frequency and bandwidth of the Si band reveal that film crystallinity is correlated with the magnitude of in-plane strain. The close correlation between the frequency and bandwidth is attributed to inhomogeneous strain fields associated with misfit dislocation clusters, which induce complete relaxation of strain in constant composition layers.
Nanostructure and temperature-dependent photoluminescence of Er-doped thin films for micro-optoelectronic integrated circuits100(2006); http://dx.doi.org/10.1063/1.2349477View Description Hide Description
The nanostructure and photoluminescence of polycrystalline Er-doped thin films,deposited by radical-enhanced atomic layer deposition(ALD), were investigated in this study. The controlled distribution of erbium separated by layers of , with erbium concentrations varied from , was confirmed by elemental electron energy loss spectroscopy (EELS) mapping of Er and . This unique feature is characteristic of the alternating radical-enhanced ALD of and . The results are also consistent with the extended x-rayabsorption fine structure(EXAFS) modeling of the Er distribution in the thin films, where the EXAFS data were best fitted to a layer-like structure.X-ray diffraction(XRD) and selected-area electron diffraction (SAED) patterns revealed a preferential film growth in the [111] direction, showing a lattice contraction with increasing Er doping concentration, likely due to of a smaller ionic radius replacing the slightly larger . Room-temperature photoluminescence characteristic of the intra- transition at was observed for the , Er-doped thin film, showing various well-resolved Stark features due to different spectroscopic transitions from the energy manifold. The result indicates the proper substitution of by in the lattice, consistent with the EXAFS and XRD analyses. Thus, by using radical-enhanced ALD, a high concentration of optically active ions can be incorporated in with controlled distribution at a low temperature, , making it possible to observe room-temperature photoluminescence for fairly thin films without a high temperature annealing.
Structural and chemical phase transitions in tungsten carbide films evidenced by the analysis of their stiffness tensors100(2006); http://dx.doi.org/10.1063/1.2356098View Description Hide Description
Brillouin light scattering (BLS) is used to provide a comprehensive study of thin tungstencarbidefilmsdeposited on single crystal silicon substrates whose distinctive nature depends critically on the deposition parameters. The use of stepped films in these slow-on-fast systems provides enhanced data sets and allows the velocity dispersion of the observed surface excitations, including the discrete Rayleigh and Sezawa modes to be studied in detail. Comprehensive and powerful methods of data analysis and interpretation including the recently developed Monte Carlo(MC) method, the surface Green's function, and classical approaches are applied to extract the effective elastic constants and density of each of the films. The MC and Green's function methods are used to remove ambiguities in Sezawa mode assignments and to identify a mode-crossing event. Auger electron spectroscopy and x-ray diffraction investigations confirm conclusions about chemical composition and microstructure obtained by BLS including a structural phase transition, thus leading to a consistent description of elastic,structural, and chemical properties of tungstencarbidefilms as a function of their deposition conditions. The anisotropicelastic tensors of the various films are employed for an analysis of the angular dependent Young's modulus and the shear modulus, suggesting implications for the film performance in wear protection. Finally, an estimate of the elasticanisotropy of the single crystal is provided on the basis of the effective elastic constants of a nanocrystalline film.
Ferroelectric switching of electrically commanded alignment layers for liquid crystal displays100(2006); http://dx.doi.org/10.1063/1.2357416View Description Hide Description
Optical second harmonic generation(SHG) was used to probe the structural and dynamic properties of electrically commanded alignment layers for liquid crystal displays. The layers were thick and were made of siloxane-based side chain ferroelectric liquid crystal polymer (FLCP). The effect of an external dc electric field in the range of on the SHG signal was probed in an empty sandwich cell and in a cell filled with an isotropic liquid (hexadecane). In both cases the nonlinear induced polarization shows characteristics of the "V-shaped" switching, which is associated with a relatively minor reorientational perturbation of the film. This signifies a presence of domain structure, which is strongly pinned to the substrates. The values of switching times deduced from the SHG response are two orders of magnitude larger from the values obtained by optical birefringencemeasurements. This observation suggests that in the top surface layer of the FLCP, which is mainly responsible for the birefringence and also for the so-called electrically commanded surface effect, the reorientation of the polymer side chains takes place much faster than in the regions close to the substrate.
Simulating thermal explosion of octahydrotetranitrotetrazine-based explosives: Model comparison with experiment100(2006); http://dx.doi.org/10.1063/1.2357418View Description Hide Description
A model comparison with measurements for the thermal, chemical, and mechanical behaviors in a thermal explosionexperiment is presented. Confined high explosives (HEs) are heated at a rate of until an explosion is observed. The heating, ignition, and deflagration phases are modeled using an arbitrarily Lagrangian-Eulerian (ALE3D) code that can handle a wide range of time scales that vary from a structural to a hydrodynamic time scale. During the preignition phase, quasistatic mechanics and diffusive thermal transfer from a heat source to the HE are coupled with the finite chemical reactions that include both endothermic and exothermic processes. Once the HE ignites, a hydrodynamic calculation is performed as a burn front propagates through the HE. Two octahydrotetranitrotetrazine (HMX)-based explosives, LX-04 and LX-10, are considered, whose chemical-thermal-mechanical models are constructed based on measurements of thermal and mechanical properties along with small-scale thermal explosionmeasurements. The present HMX modeling work shows the violence calculations with thermal predictions associated with a confined thermal explosion test. The simulated dynamic response of HE confinement during the explosive phase is compared to measurements in larger scale thermal explosion tests. The explosion temperatures for both HEs are predicted to within . Calculated and measured wall strains provide an indication of vessel pressurization during the heating phase and violence during the explosive phase.
Optical properties and local bonding configurations of hydrogenated amorphous silicon nitride thin films100(2006); http://dx.doi.org/10.1063/1.2356915View Description Hide Description
We report on the optical properties and local bonding configurations of both as-deposited and postannealed hydrogenated amorphous silicon nitride thin films grown on crystalline Si substrates with approximately . Ultraviolet optical reflection and infrared (IR) absorption measurements were applied to characterize the films. A method simply based on optical reflectionspectra is proposed for accurate determination of the optical band gap, band tail, wavelength-dependent refractive index and extinction coefficient, as well as the film thickness, suggesting that the Tauc-Lorentz [G. E. Jellison, Jr. and F. A. Modine, Appl. Phys. Lett.69, 371 (1996);69, 2137 (1996)] model with the inclusion of Urbach tail is the optimal one to describe the optical response of films. The yielded optical parameters can be related well to the film microstructure as revealed by the IR absorption analysis. These results have implications for future deposition controlling and device applications.
Interdiffusion in Fe–Pt multilayers100(2006); http://dx.doi.org/10.1063/1.2355552View Description Hide Description
multilayers with modulation periods and and bcc-fcc texture were fabricated by magnetron sputtering on thermally oxidized Si wafers. The structural evolution of the multilayers with annealingtemperature in the range of was studied by in situx-ray diffraction(XRD) and x-ray reflectivity. Two temperature regimes were found from the XRD data. Below slow, short-range diffusion is observed without significant broadening of the satellite peaks or changes in the texture. Above fast, long-range diffusion is observed accompanied by significant broadening of the satellites and rapid increase of the misorientations of the grains. The multilayers crystallize at about into the tetragonal FePt phase with a small degree of ordering and strong [111] texture. The transition resembles a first-order phase transition with a critical exponent which practically does not depend on . The bulk interdiffusion coefficient, determined from the decay of the satellite of the (001) Bragg peak of the multilayers, can be expressed in Arrhenius form as . The gradient-energy coefficient , entering the Cahn-Hilliard diffusion equation [Acta Metallurg.9, 795 (1961),10, 179 (1962);J. Chem. Phys.28, 258 (1959)], was estimated from the dependence of the diffusion coefficient to be .
Void formation and surface energies in100(2006); http://dx.doi.org/10.1063/1.2357422View Description Hide Description
The spontaneous formation of voids has been observed in films deposited by multistage evaporation processes but was not found commonly in single-stage evaporated material. These voids may be isolated in the grains or may occur at the grain boundaries. The voids exhibit strongly faceted geometries with interior surfaces being close-packed {112} planes of the chalcopyrite structure. A model based on the Kirkendal effect [Trans. AIME171, 130 (1947)] and the interdiffusion and phase reaction in the bilayer process is proposed to explain the observation. The void shape is analyzed and an approximate Wulff construction [Z. Kristallogr. Mineral.34, 449 (1901)] is used to estimate the relative surface energies of the predominant facets. Certain dislocation cores are also found to be unstable and convert to nanovoids in the presence of sufficient atomic vacancies moving in the lattice.
Leaky Lamb wave of a piezoelectric plate subjected to conductive fluid loading: Theoretical analysis and numerical calculation100(2006); http://dx.doi.org/10.1063/1.2357648View Description Hide Description
This paper examines in detail the characteristics of a leaky Lamb wave propagating in a piezoelectric plate immersed in a dielectric or conductive fluid. The analysis is based on the partial wave analysis and its numerical calculations. Some corrections have been made so that both the changes in phase velocity and the wave attenuation of leaky Lamb waves caused by fluid's mechanical, dielectric, and conductive loadings are determined accurately. Influences of each material property of the loading fluid such as mass density, wave speed, permittivity, and conductivity on the leaky Lamb wave have been quantitatively characterized. Particular emphasis is placed on the velocity variations and excessive attenuation caused by the fluid's conductivity. The results are important in designing piezoelectricacoustic wave sensors working in liquid phase.
Transmission electron microscopy investigation of the structural damage formed in GaN by medium range energy rare earth ion implantation100(2006); http://dx.doi.org/10.1063/1.2357845View Description Hide Description
The crystallographic nature of the damage created in GaN by rare earth ions has been investigated following implantation at room temperature by varying the fluence of Er, Eu, or Tm from . There is a build up of point defects clusters, which increases in density and depth versus the ion fluence. When a threshold around is reached, a nanocrystalline surface layer is observed. From the lowest fluence, we point out the formation of basal stacking faults, with a majority of . Their density also increases with the fluence, but it is seen to saturate at the onset of the observation of the surface nanocrystalline layer. Extrinsic faults bounded by the partials have also been identified; however, most of the stacking faults transform to which are noticed to fold easily from basal to prismatic planes by switching or not to the Drum atomic configuration.


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8. Why is it necessary for engage in physical activity?
You ought to know of all traits of healthy living.
Weight training includes lifting unique weights to build up hard six pack abs. You should begin by lifting dumbbells and then move on on to lifting bar bells. Do not try and exert a lot of pressure in your body from your first day itself. If you attempt and lift plenty of weight from your first day of your workout you will end up hurting yourself. This can render you motionless for several days. All of the endeavours that you had put in working out will be lost if you're immobile for several days. You need to practice only quick and easy workouts in the initial days of your practice. It isn't feasible to get 6-pack abs within the first few days itself.
Cardiovascular routines enable you to use up more calories and you can slim down definitely. An hour of work out in a health club will aid you to burn up 400 calories. When you shed one pound you've lost 3500 calorie consumption. Which means when you work out in the gym daily then you'll lose 1pound in a month. You need to work hard to strengthen your muscle mass and lessen the amount of fat present in the body. You can perform so through the weight lifting work outs. Resistance training and interval training workout are part of weight lifting. They not only aid to develop 6-pack abs but they also lead to rise in the size of muscle tissues. If your muscles improves your metabolism also increases. When you develop muscle groups you can be burning more calorie consumption in the process. They can burn off calories throughout the day. You may be burning calories even when sleeping. You could lose the body bodyweight faster than expected.
Be respectful, keep it clean.

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