Organic molecular tuning of many-body interaction energies in air-suspended carbon nanotubes
S. Tanaka K. Otsuka K. Kimura A. Ishii H. Imada Y. Kim Y. K. Kato




Quantum Optoelectronics Research Team, RIKEN Center for Advanced Photonics, Saitama 351-0198, Japan
Nanoscale Quantum Photonics Laboratory, RIKEN Cluster for Pioneering Research, Saitama 351-0198, Japan

Quantum Optoelectronics Research Team, RIKEN Center for Advanced Photonics, Saitama 351-0198, Japan
Nanoscale Quantum Photonics Laboratory, RIKEN Cluster for Pioneering Research, Saitama 351-0198, Japan

Surface and Interface Science Laboratory, RIKEN Cluster for Pioneering Research, Saitama 351-0198, Japan
Department of Advanced Materials Science, School of Frontier Sciences, The University of Tokyo, Chiba 277-8561, Japan

Quantum Optoelectronics Research Team, RIKEN Center for Advanced Photonics, Saitama 351-0198, Japan
Nanoscale Quantum Photonics Laboratory, RIKEN Cluster for Pioneering Research, Saitama 351-0198, Japan

Surface and Interface Science Laboratory, RIKEN Cluster for Pioneering Research, Saitama 351-0198, Japan

Surface and Interface Science Laboratory, RIKEN Cluster for Pioneering Research, Saitama 351-0198, Japan

[Corresponding author. ]yuichiro.kato@riken.jp
Quantum Optoelectronics Research Team, RIKEN Center for Advanced Photonics, Saitama 351-0198, Japan
Nanoscale Quantum Photonics Laboratory, RIKEN Cluster for Pioneering Research, Saitama 351-0198, Japan




We investigate adsorption effects of copper phthalocyanine molecules on excitons and trions in air-suspended carbon nanotubes. Using photoluminescence excitation spectroscopy, we observe that exciton energy redshifts gradually with the molecular deposition thickness. The trion emission is also observed at large deposition amounts, which indicates charge transfer between the phthalocyanine molecules and carbon nanotubes. Analysis of the spectra for individual tubes reveal a correlation between the exciton-trion energy separation and the exciton emission energy, showing that the many-body interaction energies scale similarly with the molecular dielectric screening.   


Organic molecular tuning of many-body interaction energies in air-suspended carbon nanotubes
    Y. K. Kato
    December 30, 2023
============================================================================================



Single-walled carbon nanotubes (CNTs) have attracted considerable attention due to their remarkable physical and electronic properties, and much effort has been devoted to functionalize CNTs for expanding their capabilities <cit.>. In particular, non-covalent functionalization with organic molecules is a powerful strategy for developing CNT based devices such as photovoltaics and photodetectors <cit.>. The interactions between the organic molecules and CNTs are considered to be less perturbative compared to covalent modification, and therefore the outstanding properties of CNTs can be preserved. Organic molecules such as porphyrin and phthalocyanine couple to nanotubes through π-π interactions to modify the charge density of CNTs, while the emission energy is reduced due to the molecular screening <cit.>. Furthermore, there are unique exciton dynamics at the organic molecule/CNT interface including energy and charge transfer <cit.>. 

In the measurements performed for nanotubes in solutions, however, the existence of solvent molecules inevitably complicate the interpretation by influencing the interactions. 
Additionally, the solvents themselves provide molecular screening, reducing the dielectric effects of the organic molecules. Investigation of molecular adsorption on air-suspended nanotubes would provide invaluable information towards fundamental understanding of the adsorption effects, as thermal evaporation techniques <cit.> allow for molecular deposition without introducing other molecules. 
The use of pristine tubes should further enable drastic dielectric modification for developing non-covalently functionalized CNT devices.

Here, we demonstrate control over many-body interaction energies in air-suspended carbon nanotubes by copper phthalocyanine (CuPc) molecule adsorption. The molecules are deposited on chirality-assigned CNTs by thermal evaporation, and we perform photoluminescence (PL) spectroscopy of the CuPc/CNT hybrid. From the averaged PL and PL excitation (PLE) spectra for various chiralities, we find that the E_11 and E_22 resonances redshift with increasing deposition thickness. Furthermore, a new emission peak is observed at an energy below the E_11 peak, which is attributed to trion emission. Data from individual tubes reveal a good correlation between exciton-trion energy separation and the E_11 energy, suggesting the existence of a universal relationship.  We consider a model assuming power law scaling of the interaction energies with dielectric constant to explain the observed correlation.

Our suspended CNTs are grown over trenches on bare Si substrates [Fig. <ref>(a)]. We perform electron beam lithography and dry etching to form the trenches, and another electron beam lithography step defines catalyst areas near the trenches. Fe(III) acetylacetonate and fumed silica dispersed in ethanol are spin coated as catalyst for CNT growth. CNTs are synthesized by alcohol chemical vapor deposition at 800^∘C for 1 minute <cit.>.



 We characterize the suspended nanotubes with a home-built sample scanning microspectroscopy system <cit.>. A wavelength tunable Ti:sapphire laser is used for excitation, and the laser polarization is rotated using a half-wave plate. The beam with a power P is focused onto the nanotube by an objective lens, which is also used to collect the PL from the nanotubes. The PL signal is detected by an InGaAs photodiode array detector attached to a spectrometer. For PLE maps and PL images, the laser polarization is parallel to the tube axis, and all measurements are conducted at room temperature in dry nitrogen.

Carbon nanotubes are located by line scans along the trenches, and PLE measurements are performed. We check whether only a single peak is observed in the emission spectrum and whether the E_11 and E_22 resonance energies match tabulated data for air-suspended nanotubes <cit.>. If a nanotube satisfies these conditions, the position and the chirality for the nanotube is recorded into a list for further measurements. 

After the characterization, the sample is placed in a vacuum chamber for evaporation of CuPc (Sigma-Aldrich) and is kept at about 80^∘C for ten minutes to remove air molecules before the evaporation. CuPc molecules are deposited on suspended CNTs in the chamber at room temperature using an evaporator heated to 480–520^∘C under a vacuum of less than 10^-4 Pa. A glass slide is also placed in the chamber to quantify the deposition thickness from absorbance of CuPc peak at 2.0 eV <cit.>. Calibration is performed by measuring the actual thickness by a surface profiler for two of the films. Four samples with different deposition amounts are prepared by changing the evaporation time, with nominal thickness on the substrate of 3 nm, 7 nm, 16 nm, and 26 nm. A scanning electron microscope image of a typical CNT after the evaporation is shown in Fig. <ref>(b). Bright spots are observed sparsely on the suspended CNTs, indicating inhomogeneous adsorption of CuPc. 

In order to investigate the molecular adsorption effects, we characterize the nanotubes after the deposition. We compare PL spectra, PL images, and polarization dependence for a suspended CNT before and after CuPc deposition for the 26 nm sample [Figs. <ref>(c)–(h)]. In the PLE map before the deposition [Fig. <ref>(c)], the emission occurs at the E_11 energy and the E_22 transition can be observed as a resonance in the excitation energy. The values for the E_11 and E_22 resonances are consistent with those for a (9,7) air-suspended nanotube <cit.>, indicating that air-molecules such as water are adsorbed <cit.>. Figure <ref>(f) shows a PLE map of the same tube after the deposition, and we find differences in the peak energy, the line width, and the intensity. Both of the E_11 and E_22 resonances show redshift as well as broadening, and the PL intensity decreases significantly with the molecular adsorption. Additionally, a new emission band appears in an energy region below the E_11 emission. The PL image of the molecular adsorbed nanotube is slightly smaller compared to that before the evaporation [Figs. <ref>(g),(d)], which is likely due to the inhomogeneous adsorption as observed in Fig. <ref>(b). In comparison, the laser polarization dependence does not change before and after the deposition [Figs. <ref>(e),(h)].


The PLE maps of the nanotubes for the four samples are measured to examine the deposition amount dependence of the adsorption effects. We integrate the PLE maps for each nanotube along the excitation and emission energy axes to obtain PL and PLE spectra, respectively, and the spectra for nanotubes with the same chiralities are averaged within each sample. The ensemble averaged PL and PLE spectra for (9,7) tubes are shown in Figs. <ref>(a) and <ref>(b), respectively. In the PL spectra [Fig. <ref>(a)], the intensity decreases and the E_11 resonance energy redshifts with the increase of the deposition thickness. Two peaks are observed for the 3 nm sample, corresponding to emission from regions of nanotubes with and without the CuPc molecule adsorption.
At large deposition amounts, the new emission band is observed as in Fig. <ref>(f). We will refer to this peak as the T emission, whose intensity does not seem to depend much on the amount of CuPc molecules. In the PLE spectra [Fig. <ref>(b)], the E_22 resonance also redshifts with increasing deposition thickness, and the simultaneous redshifts for the E_11 and E_22 resonances can be explained by the molecular dielectric screening <cit.>. For the 26 nm sample, the E_22 resonance peak is on top of a broad background slope, which may be attributed to the tail of the CuPc absorption peak at 2.0 eV <cit.>. Exciton transfer from CuPc aggregates to CNTs would be consistent with the appearance of the absorption tail in the PLE spectra <cit.>. 




To evaluate the E_11 and E_22 resonance shifts for each sample, we extract the peak positions by fitting the ensemble averaged PL and PLE spectra. A Lorentz function is used to fit the E_11 resonance in the PL spectra, except for the 3 nm sample where two Lorentz functions are used to obtain a weighted average of the E_11 emission energy. In the case of the PLE spectra, we extract the E_22 resonance energy by fitting with a Lorentzian on top of a linear function. In Fig. <ref>(c), we plot the energy shifts of the E_11 and E_22 resonances for (9,7) nanotubes relative to the energies before the evaporation. They show similar behavior, and the energies decrease monotonically with the deposition thickness. The E_11 energy shifts by more than 60 meV, which is considerably larger than the shift caused by organic molecule adsorption in solutions (∼ 20 meV) <cit.>.
The peak areas obtained from the fitting are also shown in Fig. <ref>(d), drastically decreasing as the thickness increases. A possible cause for the intensity reduction is carrier-induced PL quenching<cit.> as charge transfer between a metal-phthalocyanine and a CNT has been predicted by a density functional calculation <cit.>.

Using the same analysis procedure, the E_11 and E_22 resonance energies for various chiralities are obtained [Fig. <ref>(a)]. Redshifts of both resonances are observed for all chiralities measured, consistent with the dielectric screening effects due to the adsorbed molecules. The molecule-induced shifts of the E_11 and E_22 resonances for the 26 nm sample are plotted as a function of nanotube diameter in Fig. <ref>(b). Although we expect that the shifts become gradually smaller as the diameter increases <cit.>, there is no clear dependence.  The scatter of the data points is likely caused by large tube-to-tube deviations of adsorption amounts. Averaging the shifts of the E_11 and E_22 resonances for all chiralities, we obtain values of -58 meV and -67 meV, respectively. Comparable emission energy shifts have been observed for nanotubes under dielectric screening by solvents <cit.>, explaining why the shifts due to organic molecule adsorption in solutions are suppressed.



We evaluate the change in the exciton resonance energy by considering the reduction of the electronic many-body interactions due to molecular adsorption. The E_11 exciton energy is determined by E_11=E_sp+E_se-E_eb, where E_sp is the single-particle bandgap, E_se is the self-energy from repulsive electron interactions, and E_eb is the exciton binding energy from the attractive electron-hole interactions <cit.>. Because the magnitude of the self-energy is larger than that of the exciton binding energy, the E_11 exciton energy is higher than E_sp by the net many-body correlation energy E_se-E_eb. Assuming that these interactions scale by the same factor C_X, the shift of the E_11 exciton energy Δ E_11 relative to the air-molecule-adsorbed state is given by Δ E_11 =(E_se-E
_eb)× (C_X-1). For air-molecule adsorbed nanotubes with 1-nm diameter, E_se and E_eb have been estimated to be 910 meV and 660 meV, respectively <cit.>. From the average Δ E_11 of -58 meV for the 26 nm sample, C_X is calculated to be 0.77, which corresponds to a reduction of the many-body interactions with the molecular adsorption by 23%. The average Δ E_22 is slightly larger than the average Δ E_11, which is reasonable because the net many-body correlation energy for the E_22 excitons is larger than that for the E_11 excitons <cit.>. 

We now turn our attention to the low energy T emission. Figure  <ref>(a) is a PLE map for a (9,7) nanotube in the 26 nm sample, and there are two peaks at 0.81 eV and 0.92 eV corresponding to the T and E_11 emission, respectively. The absorption resonance energies for both emission are almost the same, and the PL images at the T and E_11 energies overlap spatially [Figs. <ref>(b),(c)]. The spectral and spatial coincidence indicates that the T emission comes from the same tube. 
We define the energy separation between the T and E_11 peaks to be Δ E_X-T, for example Δ E_X-T=0.11 eV in Fig. <ref>(a). The T emission energy for various chiralites are obtained by fitting the ensemble averaged PL spectra with a Lorentz function, and Δ E_X-T is plotted as a function of the diameter in Fig. <ref>(d). Since the K-momentum exciton emission should appear at 0.13–0.14 eV below the E_11 emission peak <cit.>, it cannot explain the T emission with Δ E_X-T=0.10–0.12 eV. In addition, intensity of the K-momentum exciton emission is typically 1% of the bright E_11 exciton emission <cit.>, but the T emission intensity can be comparable to the E_11 emission <cit.>. A more plausible interpretation would be emission from trions, as the energy separation can be 0.10–0.14 eV under dielectric screening within the diameter range shown in Fig. <ref>(d) <cit.>. The observed Δ E_X-T tends to become smaller as the diameter increases, consistent with the behavior for the exciton-trion energy separation <cit.>. As a trion is a bound state of a carrier and an exciton <cit.>, we expect trion formation if there is charge transfer between CuPc molecules and CNTs. Such a picture can also explain the E_11 intensity reduction with the molecular adsorption.



The exciton-trion energy separation for the CuPc adsorbed state is smaller than that for the air molecule adsorbed state by about 70 meV for tubes with diameter d=1 nm, indicating that exciton-carrier interactions are considerably screened by the CuPc molecules. It is known that the exciton-trion energy separation Δ E_X-T follows the relation Δ E_X-T=E_tb+E_st, where E_tb=A/d is the trion binding energy and E_st= B/d^2 is the singlet-triplet splitting energy while A and B are proportionality constants <cit.>. For the air molecule adsorbed state, A=105 meV· nm and B=70 meV· nm^2 <cit.>. We fit the data by Δ E_X-T = (A/d+ B/d^2)× C_T, under an assumption that both A and B scale by the same factor C_T upon the organic molecule adsorption. The result is shown as a blue line in Fig. <ref>(d), giving C_T =0.67, which is comparable to the value of C_X.

So far we have been discussing the ensemble spectra, but data for the individual tubes provide additional insights to molecular screening effects on the many-body interactions. By fitting the PL spectra for each nanotube, we obtain the energies for the T and E_11 emission in various molecular screening environments. In Fig. <ref>(a), Δ E_X-T for (9,7) individual nanotubes are plotted as a function of the E_11 exciton emission energy. We find that there is a good correlation between Δ E_X-T and E_11, where Δ E_X-T becomes smaller as the E_11 emission energy redshifts. We also plot data points for (9,7) suspended nanotubes with and without air-molecule adsorption from ref  as green and blue points, respectively. These data points also follow the trend, suggesting that there is a universal relation applicable to nanotubes under different surface conditions.  Similar correlation is observed for (13,2) and (11,3) nanotubes [Figs. <ref>(b) and <ref>(c), respectively], as well as for the other chiralities. We note that CuPc adsorption can shift the E_11 energy by ∼ 100 meV compared to the pritine state, offering flexible tunability over the emission energy



The correlation can be understood in terms of the molecular dielectric screening [Fig. <ref>(d)]. In general, the many-body interactions determining the T and E_11 exciton energies are sensitive to environment, which can simply be parameterized as the environmental dielectric constant ε. Assuming that interaction energies scale as ε^-α with α being a constant <cit.>, Δ E_X-T=E_tb^ε =1ε^-α+E_st^ε =1ε^-α and E_11=E_sp+E_se^ε =1ε^-α-E_eb^ε =1ε^-α, where E_tb^ε =1, E_st^ε =1, E_se^ε =1, and E_eb^ε =1 are the trion binding energy, singlet-triplet splitting energy, self energy, and exciton binding energy at ε =1, respectively. The slope for the correlation is then given by ∂Δ E_X-T/∂ E_11=E_tb^ε =1+E_st^ε =1/E_se^ε =1-E_eb^ε =1, indicating a linear relation between Δ E_X-T and E_11. The experimentally observed correlation therefore implies that the many-body interactions energies scale similarly within the experimental conditions explored, which is reasonable since the scaling factor for the E_11 exciton C_X is comparable to that for the trion C_T.


Using the reported values for pristine suspended nanotubes of E_tb^ε =1=117 meV, E_st^ε =1=78 meV, E_se^ε =1=980 meV, and E_eb^ε =1=725 meV for 1 nm-diameter tubes <cit.>, the proportionality coefficient is about 0.8. To compare this value with the experimental results, we fit the data points for the organic molecule adsorbed state with a linear function. We impose the line to go through a data point for the air-molecule adsorbed state, where the E_11 emission energy is obtained from the table in ref  and Δ E_X-T is determined from the equation given in ref . The obtained coefficients range from 0.8 to 1.2 [Fig. <ref>(e)], which is a reasonable agreement considering the large uncertainty in the absolute value of E_se^ε =1. 

In summary, we have investigated adsorption effects of CuPc molecules on excitons and trions in air-suspended CNTs by measuring PL spectra of the CuPc/CNT hybrids. By averaging the PLE spectra for tubes with the same chiralities, the redshift of the E_11 and E_22 resonances have been observed with increasing deposition thickness due to the molecular screening. The E_11 energy modification from the pristine state to the CuPc adsorbed state can reach 100 meV, which is significantly larger than the energy shift with organic molecule adsorption in solutions. Furthermore, we find that the trion emission emerges at an energy lower than the E_11 exciton emission, which is likely due to charge transfer between CuPc molecules and CNTs. The spectra from individual tubes show that there is a good correlation between the exciton-trion energy separation and the exciton emission energy. A model assuming power law scaling of the many-body interactions with dielectric constant can quantitatively explain the observed correlation, which should be able to describe nanotubes with different surface conditions in a universal manner. Our findings show that organic molecule adsorption significantly affects many-body interaction energies of suspended CNTs, which opens up a pathway to CNT devices utilizing noncovalent molecular functionalization.



Work supported in part by JSPS (KAKENHI JP16H05962 and JP17H07359) and MEXT (Photon Frontier Network Program, Nanotechnology Platform).  We thank Advanced Manufacturing Support Team at RIKEN for technical assistance.










35
fxundefined [1]
 ifx#1

fnum [1]
 #1firstoftwo
 secondoftwo
 
fx [1]
 #1firstoftwo
 secondoftwo
 





noop [0]secondoftwo

ref[1]@startlink#1@href
href[1]#1@endlink
anitize@url [0]`
12`$12`&12`#12`1̂2`_12`%12
startlink[1]
endlink[0]

rl [1]href #1












@bib@innerbibempty

[Hirsch(2002)]Hirsch:2002
  author author A. Hirsch, title title Functionalization of
  single-walled carbon nanotubes, https://www.onlinelibrary.wiley.com/doi/abs/10.1002/1521-3773
  journal journal Angew. Chem. Int. Ed. volume 41, pages 1853 (year
  2002)NoStop
[Miyauchi et al.(2013)Miyauchi, Iwamura, Mouri, Kawazoe, Ohtsu, and Matsuda]Miyauchi:2013
  author author Y. Miyauchi, author M. Iwamura,
  author S. Mouri, author T. Kawazoe, author
  M. Ohtsu,  and author
  K. Matsuda, title title Brightening of excitons in carbon nanotubes on dimensionality
  modification, 10.1038/nphoton.2013.179 journal journal Nat. Photon. volume
  7, pages 715 (year 2013)NoStop
[He et al.(2017)He,
  Hartmann, Ma, Kim,
  Ihly, Blackburn, Gao,
  Kono, Yomogida, Hirano,
  Tanaka, Kataura, Htoon, and  Doorn]He:2017
  author author X. He, author N. F. Hartmann,
  author X. Ma, author
  Y. Kim, author R. Ihly, author J. L.  Blackburn, author W. Gao, author J. Kono, author Y. Yomogida, author
  A. Hirano, author T. Tanaka, author H. Kataura, author H. Htoon,  and author S. K.  Doorn, title title Tunable
  room-temperature single-photon emission at telecom wavelengths from sp^3
  defects in carbon nanotubes, http://dx.doi.org/10.1038/nphoton.2017.119 journal journal Nat. Photon. volume 11, pages 577 (year 2017)NoStop
[Guldi et al.(2005)Guldi,
  Rahman, Zerbetto, and Prato]Prato:2005
  author author D. M. Guldi, author G. M. A. Rahman, author F. Zerbetto,   and author M. Prato, title title Carbon nanotubes in electron donor-acceptor
  nanocomposites, https://doi.org/10.1021/ar040238i journal journal Acc. Chem. Res. volume
  38, pages 871 (year 2005)NoStop
[Ehli et al.(2009)Ehli,
  Oelsner, Guldi, Mateo-Alonso,
  Prato, Schmidt, Backes,
  Hauke, and Hirsch]Hirsch:2009
  author author C. Ehli, author C. Oelsner,
  author D. M. Guldi, author A. Mateo-Alonso, author
  M. Prato, author C. Schmidt, author C. Backes, author F. Hauke,  and author A. Hirsch, title title
  Manipulating single-wall carbon nanotubes by chemical doping and charge
  transfer with perylene dyes, https://www.nature.com/articles/nchem.214#supplementary-information
  journal journal Nat. Chem. volume 1, pages 243 (year 2009)NoStop
[Malic et al.(2011)Malic,
  Weber, Richter, Atalla,
  Klamroth, Saalfrank, Reich,  and Knorr]Knorr:2011
  author author E. Malic, author C. Weber,
  author M. Richter, author V. Atalla, author
  T. Klamroth, author
  P. Saalfrank, author
  S. Reich,  and author
  A. Knorr, title title Microscopic model of the optical absorption of carbon nanotubes
  functionalized with molecular spiropyran photoswitches, 10.1103/PhysRevLett.106.097401 journal journal
  Phys. Rev. Lett. volume 106, pages
  097401 (year 2011)NoStop
[Bartelmess et al.(2010)Bartelmess, Ballesteros, de la Torre,
  Kiessling, Campidelli, Prato,
  Torres, and Guldi]Guldi:2010
  author author J. Bartelmess, author B. Ballesteros, author G. de la
  Torre, author D. Kiessling,
  author S. Campidelli, author M. Prato, author
  T. Torres,  and author
  D. M. Guldi, title title Phthalocyanine-pyrene conjugates: A powerful approach toward carbon
  nanotube solar cells, https://doi.org/10.1021/ja107131r journal journal J. Am. Chem. Soc. volume 132, pages 16202 (year
  2010)NoStop
[Hecht et al.(2006)Hecht,
  Ramirez, Briman, Artukovic,
  Chichak, Stoddart, and Grüner]Gruner:2006
  author author D. S. Hecht, author R. J. A. Ramirez, author M. Briman,
  author E. Artukovic, author K. S. Chichak, author
  J. F. Stoddart,  and author
  G. Grüner, title title Bioinspired detection of light using a porphyrin-sensitized
  single-wall nanotube field effect transistor, https://doi.org/10.1021/nl061231s journal journal Nano Lett. volume 6, pages
  2031 (year 2006)NoStop
[Alam et al.(2017)Alam,
  Dehm, Hennrich, Zakharko,
  Graf, Pfohl, Hossain,
  Kappes, Zaumseil, Krupke,  and Flavel]Flavel:2017
  author author A. Alam, author S. Dehm, author F. Hennrich, author
  Y. Zakharko, author
  A. Graf, author M. Pfohl, author I. M.  Hossain, author M. M.  Kappes, author J. Zaumseil, author R. Krupke,   and author B. S. Flavel,  title title Photocurrent spectroscopy of
  dye-sensitized carbon nanotubes, 10.1039/C7NR04022A
  journal journal Nanoscale volume 9, pages 11205 (year
  2017)NoStop
[Roquelet et al.(2010)Roquelet, Garrot, Lauret, Voisin, Alain-Rizzo, Roussignol,
  Delaire, and Deleporte]Deleporte:2010
  author author C. Roquelet, author D. Garrot,
  author J. S. Lauret, author C. Voisin, author
  V. Alain-Rizzo, author
  P. Roussignol, author
  J. A. Delaire,  and author
  E. Deleporte, title title Quantum efficiency of energy transfer in noncovalent carbon
  nanotube/porphyrin compounds, https://doi.org/10.1063/1.3496470
  journal journal Appl. Phys. Lett. volume 97, pages 141918 (year
  2010)NoStop
[Correa and Orellana(2012)]Orellana:2012
  author author J. D. Correa and author W. Orellana, title title Optical response of
  carbon nanotubes functionalized with (free-base, zn) porphyrins, and
  phthalocyanines: A dft study, 10.1103/PhysRevB.86.125417
  journal journal Phys. Rev. B volume 86, pages 125417 (year
  2012)NoStop
[Orellana(2014)]Orellana:2014
  author author W. Orellana, title title Strong π-π
  interaction of porphyrins on (6,5) carbon nanotubes with full surface
  coverage: Ab-initio calculations, https://doi.org/10.1063/1.4890591 journal journal Appl. Phys. Lett. volume 105, pages 023110 (year 2014)NoStop
[Garrot et al.(2011)Garrot,
  Langlois, Roquelet, Michel,
  Roussignol, Delalande, Deleporte, Lauret, and Voisin]Voisin:2011
  author author D. Garrot, author B. Langlois,
  author C. Roquelet, author T. Michel, author
  P. Roussignol, author
  C. Delalande, author
  E. Deleporte, author
  J. S. Lauret,  and author
  C. Voisin, title title Time-resolved investigation of excitation energy transfer in carbon
  nanotube-porphyrin compounds, https://doi.org/10.1021/jp207267e
  journal journal J. Phys. Chem. C volume 115, pages 23283 (year
  2011)NoStop
[Casey et al.(2008)Casey,
  Bachilo, and Weisman]Bruce:2008
  author author J. P. Casey, author S. M. Bachilo,
   and author R. B. Weisman,  title title Efficient photosensitized energy
  transfer and near-ir fluorescence from porphyrin-swnt complexes, 10.1039/B716649D journal journal J.
  Mater. Chem. volume 18, pages 1510
  (year 2008)NoStop
[Zhong et al.(2013)Zhong,
  Diev, Roberts, Antunez,
  Brutchey, Bradforth, and Thompson]Thompson:2013
  author author Q. Zhong, author V. V. Diev,
  author S. T. Roberts, author P. D. Antunez, author
  R. L. Brutchey, author
  S. E. Bradforth,  and author
  M. E. Thompson, title
  title Fused porphyrin-single-walled carbon nanotube hybrids:
  Efficient formation and photophysical characterization, https://doi.org/10.1021/nn400362e journal journal ACS Nano volume 7, pages
  3466 (year 2013)NoStop
[Sarkar et al.(2018)Sarkar,
  Habib, Pal, and Prezhdo]Prezhdo:2018
  author author R. Sarkar, author M. Habib,
  author S. Pal,  and author O. V. Prezhdo, title title Ultrafast, asymmetric charge transfer and slow
  charge recombination in porphyrin/cnt composites demonstrated by time-domain
  atomistic simulation, http://dx.doi.org/10.1039/C8NR02544D
  journal journal Nanoscale volume 10, pages 12683 (year
  2018)NoStop
[Stranks et al.(2011)Stranks, Sprafke, Anderson, and  Nicholas]Nichola:2011
  author author S. D. Stranks, author J. K. Sprafke, author H. L. Anderson,  and author R. J. Nicholas, title title Electronic and
  mechanical modification of single-walled carbon nanotubes by binding to
  porphyrin oligomers, 10.1021/nn103588h journal journal ACS Nano volume 5,  pages 2307 (year 2011)NoStop
[Lozzi et al.(2008)Lozzi,
  Santucci, Bussolotti, and La Rosa]Rosa:2008
  author author L. Lozzi, author S. Santucci,
  author F. Bussolotti,  and  author S. La Rosa, title title Investigation on copper phthalocyanine/multiwalled
  carbon nanotube interface, https://doi.org/10.1063/1.2961325
  journal journal J. Appl. Phys. volume 104, pages 033701 (year
  2008)NoStop
[Basiuk et al.(2018)Basiuk,
  Flores-Sánchez, Meza-Laguna, Flores-Flores, Bucio-Galindo, Puente-Lee,  and Basiuk]Basiuk:2018
  author author V. A. Basiuk, author L. J. Flores-Sánchez, author V. Meza-Laguna, author J. O. Flores-Flores, author L. Bucio-Galindo, author I. Puente-Lee,  and author E. V. Basiuk, title title Noncovalent
  functionalization of pristine cvd single-walled carbon nanotubes with 3d
  metal(ii) phthalocyanines by adsorption from the gas phase, https://doi.org/10.1016/j.apsusc.2017.12.122 journal
  journal Appl. Surf. Sci. volume 436,  pages 1123  (year 2018)NoStop
[Ishii et al.(2015)Ishii,
  Yoshida, and Kato]Ishii:2015
  author author A. Ishii, author M. Yoshida,   and author Y. K. Kato,  title title Exciton diffusion, end quenching, and
  exciton-exciton annihilation in individual air-suspended carbon nanotubes,  10.1103/PhysRevB.91.125427 journal journal Phys. Rev. B volume 91, pages 125427 (year 2015)NoStop
[Tang(1986)]Tang:1986
  author author C. W. Tang, title title Two-layer organic
  photovoltaic cell, https://doi.org/10.1063/1.96937 journal journal Appl. Phys. Lett. volume 48, pages 183 (year 1986)NoStop
[Uda et al.(2018)Uda,
  Tanaka, and Kato]Uda:2018a
  author author T. Uda, author S. Tanaka,  and  author Y. K. Kato, title title Molecular screening effects on exciton-carrier
  interactions in suspended carbon nanotubes, https://doi.org/10.1063/1.5046433 journal journal Appl. Phys. Lett. volume 113, pages 121105 (year 2018)NoStop
[Lefebvre and Finnie(2008)]Lefebvre:2008
  author author J. Lefebvre and author P. Finnie, title title Excited excitonic states
  in single-walled carbon nanotubes, 10.1021/nl080518h
  journal journal Nano Lett. volume 8, pages 1890 (year 2008)NoStop
[Larsen et al.(2012)Larsen,
  Deria, Holt, Stanton,
  Heben, Therien, and Blackburn]Blackburn:2012
  author author B. A. Larsen, author P. Deria,
  author J. M. Holt, author I. N. Stanton, author
  M. J. Heben, author
  M. J. Therien,  and author
  J. L. Blackburn, title
  title Effect of solvent polarity and electrophilicity on quantum
  yields and solvatochromic shifts of single-walled carbon nanotube
  photoluminescence, https://doi.org/10.1021/ja2114618 journal journal J. Am. Chem. Soc. volume 134, pages 12485 (year
  2012)NoStop
[Yasukochi et al.(2011)Yasukochi, Murai, Moritsubo, Shimada, Chiashi, Maruyama, and  Kato]Yasukochi:2011
  author author S. Yasukochi, author T. Murai,
  author S. Moritsubo, author T. Shimada, author
  S. Chiashi, author S. Maruyama,  and author Y. K. Kato, title title
  Gate-induced blueshift and quenching of photoluminescence in suspended
  single-walled carbon nanotubes, 10.1103/PhysRevB.84.121409 journal journal Phys.
  Rev. B volume 84, pages 121409(R)
  (year 2011)NoStop
[Yoshida et al.(2016)Yoshida, Popert, and Kato]Yoshida:2016
  author author M. Yoshida, author A. Popert,   and author Y. K. Kato,  title title Gate-voltage induced trions in
  suspended carbon nanotubes, 10.1103/PhysRevB.93.041402
  journal journal Phys. Rev. B volume 93, pages 041402(R) (year
  2016)NoStop
[Schuettfort et al.(2009)Schuettfort, Nish, and Nicholas]Nicholas:2009
  author author T. Schuettfort, author A. Nish,   and author R. J. Nicholas,  title title Observation of a type ii
  heterojunction in a highly ordered polymer-carbon nanotube nanohybrid
  structure, https://doi.org/10.1021/nl902081t journal
  journal Nano Lett. volume 9,  pages 3871 (year 2009)NoStop
[Choi and Strano(2007)]Strano:2007
  author author J. H. Choi and author M. S. Strano, title title Solvatochromism in
  single-walled carbon nanotubes, https://doi.org/10.1063/1.2745228
  journal journal Appl. Phys. Lett. volume 90, pages 223114 (year
  2007)NoStop
[Ohno et al.(2007)Ohno,
  Iwasaki, Murakami, Kishimoto,
  Maruyama, and Mizutani]Ohno:2007
  author author Y. Ohno, author S. Iwasaki,
  author Y. Murakami, author S. Kishimoto, author
  S. Maruyama,  and author
  T. Mizutani, title title Excitonic transition energies in single-walled carbon nanotubes:
  Dependence on environmental dielectric constant, 10.1002/pssb.200776124 journal journal Phys.
  Status Solidi B volume 244, pages
  4002 (year 2007)NoStop
[Walsh et al.(2007)Walsh,
  Vamivakas, Yin, Cronin,
  Ünlü, Goldberg, and Swan]Swan:2007
  author author A. G. Walsh, author A. N. Vamivakas, author Y. Yin,
  author S. B. Cronin, author M. S. Ünlü, author
  B. B. Goldberg,  and author
  A. K. Swan, title title Screening of excitons in single, suspended carbon nanotubes,  https://doi.org/10.1021/nl070193p journal journal Nano Lett. volume 7, pages
  1485 (year 2007)NoStop
[Miyauchi et al.(2015)Miyauchi, Zhang, Takekoshi, Tomio, Suzuura, Perebeinos, Deshpande, Lu, Berciaud, Kim, Hone, and Heinz]Miyauchi:2015
  author author Y. Miyauchi, author Z. Zhang,
  author M. Takekoshi, author Y. Tomio, author
  H. Suzuura, author V. Perebeinos, author V. V.  Deshpande, author C. Lu, author S. Berciaud,
  author P. Kim, author
  J. Hone,  and author
  T. F. Heinz, title title Tunable electronic correlation effects in nanotube-light
  interactions, 10.1103/PhysRevB.92.205407 journal journal Phys. Rev. B volume
  92, pages 205407 (year 2015)NoStop
[Sato et al.(2007)Sato,
  Saito, Jiang, Dresselhaus,  and Dresselhaus]Dresselhaus:2007
  author author K. Sato, author R. Saito,
  author J. Jiang, author G. Dresselhaus,  and author M. S. Dresselhaus, title title Discontinuity in the family pattern of single-wall
  carbon nanotubes, 10.1103/PhysRevB.76.195446 journal journal Phys. Rev. B volume
  76, pages 195446 (year 2007)NoStop
[Matsunaga et al.(2010)Matsunaga, Matsuda, and Kanemitsu]Matsunaga:2010
  author author R. Matsunaga, author K. Matsuda,
   and author Y. Kanemitsu,  title title Origin of low-energy photoluminescence
  peaks in single carbon nanotubes: K-momentum dark excitons and triplet
  dark excitons, 10.1103/PhysRevB.81.033401 journal journal Phys. Rev. B volume
  81, pages 033401 (year 2010)NoStop
[Matsunaga et al.(2011)Matsunaga, Matsuda, and Kanemitsu]Matsunaga:2011
  author author R. Matsunaga, author K. Matsuda,
   and author Y. Kanemitsu,  title title Observation of charged excitons in
  hole-doped carbon nanotubes using photoluminescence and absorption
  spectroscopy, 10.1103/PhysRevLett.106.037404 journal journal Phys. Rev. Lett. volume 106, pages 037404 (year
  2011)NoStop
[Santos et al.(2011)Santos,
  Yuma, Berciaud, Shaver,
  Gallart, Gilliot, Cognet,  and Lounis]Santos:2011
  author author S. M. Santos, author B. Yuma,
  author S. Berciaud, author J. Shaver, author
  M. Gallart, author P. Gilliot, author L. Cognet,  and author B. Lounis, title title
  All-optical trion generation in single-walled carbon nanotubes, 10.1103/PhysRevLett.107.187401 journal journal Phys. Rev. Lett. volume 107, pages 187401 (year 2011)NoStop



