Journal of physics. Condensed matter : an Institute of Physics journal, Jan 14, 2016
Graphene nanoribbons are quasi-one-dimensional planar graphene allotropes with diverse properties... more Graphene nanoribbons are quasi-one-dimensional planar graphene allotropes with diverse properties dependent on their width and types of edges. Graphene nanoribbons anchored to substrates is a hybrid system, which offers novel opportunities for property modifications as well as experimental control. Here we present electronic structure calculations of zigzag graphene nanoribbons chemically attached via the edges to the Si or C terminated surfaces of a SiC substrate. The results show that the edge characteristics are rather robust and the properties are essentially determined by the individual nanoribbon. While the localized spin polarization of the graphene nanoribbon edge atoms is not significantly affected by the substrate, secondary energy gaps in the highest conduction and lowest valence region may emerge in the anchored structures. The van der Waals interaction together with the electrostatic interactions due to the polarity of the surface bonds are found to be important for the...
... One more NH vibration (seems N3) shows an increase of the intensity and shift from 3206 (Thy)... more ... One more NH vibration (seems N3) shows an increase of the intensity and shift from 3206 (Thy) to 3212 cm"^ (Thy-SWCNT). ... 7, 45 (2007). 16. S. Gowtham, RH Scheicher, R. Ahuja, R. Pandey, Sh. Kama, Physical Review B 76, 33401-33404 (2007). 17. Handbook. ...
2008 Conference on Lasers and Electro Optics and 2008 Conference on Quantum Electronics and Laser Science, May 3, 2008
We study theoretically the interactions of excitonic states with surface electromagnetic modes of... more We study theoretically the interactions of excitonic states with surface electromagnetic modes of a single-walled carbon nanotube. We show that these interactions result in the exciton-plasmon coupling that is significant in its strength due to the presence of weakly-dispersive low-energy (~0.5-2 eV) interband surface plasmon modes and large exciton excitation energies ~1 eV in small-diameter nanotubes. We estimate the exciton-plasmon Rabi splitting to be ~0.1 eV which is close to that in organic semiconductors and much larger than that in hybrid semiconductor-metal nanoparticle molecules. We calculate the exciton absorption lineshape and show the line splitting effect as the exciton is tuned to the nearest interband surface plasmon resonance of the nanotube.
We calculate the energy exchange between phonons and electrons in a metal for very low temperatur... more We calculate the energy exchange between phonons and electrons in a metal for very low temperatures. Our results can be applied to quantum-dot refrigerators. The formula of Allen^1 applies to the usual processes of absorption or emission of one phonon. Here we consider the energy exchange due to two phonon processes. Second order processes are expected to be important at temperatures less than 1 K. We include two different second-order processes: (i) the Compton-like scattering of phonons, and (ii) the electron-dual-phonon scattering from the second-order electron-phonon interaction. In the Compton-like process an electron emits (or absorbs) a phonon thereby making a transition into a virtual state, and then absorbs (or emits) another phonon. We have found that the process contains a singular energy denominator. The singularity is removed by introducing quasiparticle damping. Then the final formula for the energy exchange depends upon the lifetime of the electrons. For pure metals the thermal relaxation depends on the temperature of the lattice according to T^8. We perform the same calculation for electron-dual-phonon scattering and we find that the temperature dependence is T^9. A comparison with the result for an electron - single-phonon process^1 is also presented. 1. P.B.Allen, Phys.Rev.Lett. 59, 1460 (1987)
Journal of physics. Condensed matter : an Institute of Physics journal, Jan 14, 2016
Graphene nanoribbons are quasi-one-dimensional planar graphene allotropes with diverse properties... more Graphene nanoribbons are quasi-one-dimensional planar graphene allotropes with diverse properties dependent on their width and types of edges. Graphene nanoribbons anchored to substrates is a hybrid system, which offers novel opportunities for property modifications as well as experimental control. Here we present electronic structure calculations of zigzag graphene nanoribbons chemically attached via the edges to the Si or C terminated surfaces of a SiC substrate. The results show that the edge characteristics are rather robust and the properties are essentially determined by the individual nanoribbon. While the localized spin polarization of the graphene nanoribbon edge atoms is not significantly affected by the substrate, secondary energy gaps in the highest conduction and lowest valence region may emerge in the anchored structures. The van der Waals interaction together with the electrostatic interactions due to the polarity of the surface bonds are found to be important for the...
... One more NH vibration (seems N3) shows an increase of the intensity and shift from 3206 (Thy)... more ... One more NH vibration (seems N3) shows an increase of the intensity and shift from 3206 (Thy) to 3212 cm"^ (Thy-SWCNT). ... 7, 45 (2007). 16. S. Gowtham, RH Scheicher, R. Ahuja, R. Pandey, Sh. Kama, Physical Review B 76, 33401-33404 (2007). 17. Handbook. ...
2008 Conference on Lasers and Electro Optics and 2008 Conference on Quantum Electronics and Laser Science, May 3, 2008
We study theoretically the interactions of excitonic states with surface electromagnetic modes of... more We study theoretically the interactions of excitonic states with surface electromagnetic modes of a single-walled carbon nanotube. We show that these interactions result in the exciton-plasmon coupling that is significant in its strength due to the presence of weakly-dispersive low-energy (~0.5-2 eV) interband surface plasmon modes and large exciton excitation energies ~1 eV in small-diameter nanotubes. We estimate the exciton-plasmon Rabi splitting to be ~0.1 eV which is close to that in organic semiconductors and much larger than that in hybrid semiconductor-metal nanoparticle molecules. We calculate the exciton absorption lineshape and show the line splitting effect as the exciton is tuned to the nearest interband surface plasmon resonance of the nanotube.
We calculate the energy exchange between phonons and electrons in a metal for very low temperatur... more We calculate the energy exchange between phonons and electrons in a metal for very low temperatures. Our results can be applied to quantum-dot refrigerators. The formula of Allen^1 applies to the usual processes of absorption or emission of one phonon. Here we consider the energy exchange due to two phonon processes. Second order processes are expected to be important at temperatures less than 1 K. We include two different second-order processes: (i) the Compton-like scattering of phonons, and (ii) the electron-dual-phonon scattering from the second-order electron-phonon interaction. In the Compton-like process an electron emits (or absorbs) a phonon thereby making a transition into a virtual state, and then absorbs (or emits) another phonon. We have found that the process contains a singular energy denominator. The singularity is removed by introducing quasiparticle damping. Then the final formula for the energy exchange depends upon the lifetime of the electrons. For pure metals the thermal relaxation depends on the temperature of the lattice according to T^8. We perform the same calculation for electron-dual-phonon scattering and we find that the temperature dependence is T^9. A comparison with the result for an electron - single-phonon process^1 is also presented. 1. P.B.Allen, Phys.Rev.Lett. 59, 1460 (1987)
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