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Title: Dynamics of charged excitons in electronically and morphologically homogeneous single-walled carbon nanotubes

Authors:
; ; ; ; ORCiD logo
Publication Date:
Sponsoring Org.:
USDOE
OSTI Identifier:
1416093
Grant/Contract Number:
SC0001517
Resource Type:
Journal Article: Published Article
Journal Name:
Proceedings of the National Academy of Sciences of the United States of America
Additional Journal Information:
Journal Volume: 115; Journal Issue: 4; Related Information: CHORUS Timestamp: 2018-04-16 15:58:04; Journal ID: ISSN 0027-8424
Publisher:
Proceedings of the National Academy of Sciences
Country of Publication:
United States
Language:
English

Citation Formats

Bai, Yusong, Olivier, Jean-Hubert, Bullard, George, Liu, Chaoren, and Therien, Michael J. Dynamics of charged excitons in electronically and morphologically homogeneous single-walled carbon nanotubes. United States: N. p., 2018. Web. doi:10.1073/pnas.1712971115.
Bai, Yusong, Olivier, Jean-Hubert, Bullard, George, Liu, Chaoren, & Therien, Michael J. Dynamics of charged excitons in electronically and morphologically homogeneous single-walled carbon nanotubes. United States. doi:10.1073/pnas.1712971115.
Bai, Yusong, Olivier, Jean-Hubert, Bullard, George, Liu, Chaoren, and Therien, Michael J. Mon . "Dynamics of charged excitons in electronically and morphologically homogeneous single-walled carbon nanotubes". United States. doi:10.1073/pnas.1712971115.
@article{osti_1416093,
title = {Dynamics of charged excitons in electronically and morphologically homogeneous single-walled carbon nanotubes},
author = {Bai, Yusong and Olivier, Jean-Hubert and Bullard, George and Liu, Chaoren and Therien, Michael J.},
abstractNote = {},
doi = {10.1073/pnas.1712971115},
journal = {Proceedings of the National Academy of Sciences of the United States of America},
number = 4,
volume = 115,
place = {United States},
year = {Mon Jan 08 00:00:00 EST 2018},
month = {Mon Jan 08 00:00:00 EST 2018}
}

Journal Article:
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  • A 1 {mu}m long, field emitting, (5, 5) single-walled carbon nanotube (SWCNT) closed with a fullerene cap, and a similar open nanotube with hydrogen-atom termination, have been simulated using the modified neglect of diatomic overlap quantum-mechanical method. Both contain about 80 000 atoms. It is found that field penetration and band bending, and various forms of chemically and electrically induced apex dipole play roles. Field penetration may help explain electroluminescence associated with field emitting CNTs. Charge-density oscillations, induced by the hydrogen adsorption, are also found. Many of the effects can be related to known effects that occur with metallic ormore » semiconductor field emitters; this helps both to explain the effects and to unify our knowledge about FE emitters. However, it is currently unclear how best to treat correlation-and-exchange effects when defining the CNT emission barrier. A new form of definition for the field enhancement factor (FEF) is used. Predicted FEF values for these SWCNTs are significantly less than values predicted by simple classical formulae. The FEF for the closed SWCNT decreases with applied field; the FEF for the H-terminated open SWCNT is less than the FEF for the closed SWCNT but increases with applied field. Physical explanations for this behavior are proposed but the concept of FEF is clearly problematical for CNTs. Curved Fowler-Nordheim plots are predicted. Overall, the predicted field emission performance of the H-terminated open SWCNT is slightly better than that of the closed SWCNT, essentially because a C-H dipole is formed that reduces the height of the tunneling barrier. In general, the physics of a charged SWCNT seems much more complex than hitherto realized.« less
  • Molecular dynamics studies are carried out to investigate electron-irradiation effects in single-walled carbon nanotubes. We have proposed a simulation model which includes the interaction between a high-energy incident electron and a carbon atom, based on Monte Carlo method using the elastic-scattering cross section. The atomic level behavior of a single-walled carbon nanotube under electron irradiation is demonstrated in nanosecond time scale. The incident electron energy, tube diameter, and tube temperature dependences of electron-irradiation effects are studied with the simulation.
  • Photoluminescent defect states introduced by sp 3 functionalization of semiconducting carbon nanotubes are rapidly emerging as important routes for boosting emission quantum yields and introducing new functionality. Knowledge of the relaxation dynamics of these states is required for understanding how functionalizing agents (molecular dopants) may be designed to access specific behaviors. We measure photoluminescence (PL) decay dynamics of sp 3 defect states introduced by aryl functionalization of the carbon nanotube surface. Results are given for five different nanotube chiralities, each doped with a range of aryl functionality. We find the PL decays of these sp 3 defect states are biexponential,more » with both components relaxing on timescales of ~ 100 ps. Exciton trapping at defects is found to increases PL lifetimes by a factor of 5-10, in comparison to those for the free exciton. A significant chirality dependence is observed in the decay times, ranging from 77 ps for (7,5) nanotubes to > 600 ps for (5,4) structures. The strong correlation of time constants with emission energy indicates relaxation occurs via multiphonon decay processes, with close agreement to theoretical expectations. Variation of the aryl dopant further modulates decay times by 10-15%. The aryl defects also affect PL lifetimes of the free E 11 exciton. Shortening of the E 11 bright state lifetime as defect density increases provides further confirmation that defects act as exciton traps. A similar shortening of the E11 dark exciton lifetime is found as defect density increases, providing strong experimental evidence that dark excitons are also trapped at such defect sites.« less
  • We report a detailed study of ultrafast exciton dephasing processes in semiconducting single-walled carbon nanotubes (SWNTs) employing a sample highly enriched in a single tube species, the (6,5) tube. Systematic measurements of femtosecond pump-probe, two-pulse photon echo and three-pulse photon echo peak shift over a broad range of excitation intensities and lattice temperature (from 4.4 to 292 K) enable us to quantify the timescales of pure optical dephasing (T ∗ 2 ), along with exciton-exciton and exciton-phonon scattering, environmental effects as well as spectral diffusion. While the exciton dephasing time (T2 ) increases from 205 fs at room temperature tomore » 320 fs at 70 K, we found that further decrease of the lattice temperature leads to a shortening of the T2 times. This complex temperature dependence was found to arise from an enhanced relaxation of exciton population at lattice temperatures below 80 K. By quantitatively accounting the contribution from the population relaxation, the corresponding pure optical dephasing times increase monotonically from 225 fs at room temperature to 508 fs at 4.4 K. We further found that below 180 K, the inverse of the pure dephasing time (1/T ∗ 2 ) scales linearly with temperature with a slope of 6.7 ±0.6 μeV/K, which suggests dephasing arising from one-phonon scattering (i.e. acoustic phonons). In view ofthe large dynamic disorder of the surrounding environment, the origin of the long room temperature pure dephasing time is proposed to result from reduced strength of exciton-phonon coupling by motional narrowing over nuclear fluctuations. This consideration further suggests the occurrence of remarkable initial exciton delocalization, and makes nanotubes ideal to study many-body effects in spatially confined systems.« less