Comparative study of the electron–electron interactions on optoelectronic properties of carbon nanotube within orthogonal and nonorthogonal tight-binding model (original) (raw)
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Physical Review Letters, 2004
We report correlated-electron calculations of optically excited states in ten semiconducting single-walled carbon nanotubes with a wide range of diameters. Optical excitation occurs to excitons whose binding energies decrease with the increasing nanotube diameter, and are smaller than the binding energy of an isolated strand of poly-(paraphenylene vinylene). The ratio of the energy of the second optical exciton polarized along the nanotube axis to that of the lowest exciton is smaller than the value predicted within single-particle theory. The experimentally observed weak photoluminescence is an intrinsic feature of semiconducting nanotubes, and is consequence of dipole-forbidden excitons occurring below the optical exciton.
Optoelectronic Properties of Single-Wall Carbon Nanotubes
Advanced Materials, 2012
diffraction is a powerful technique for the determination of atomic structure of individual nano-objects, as was demonstrated in Iijima's original work on multiwall [ 187 ] and singlewall [ 1 ] carbon nanotubes. However, it is not suited for studying a large number of carbon nanotubes. Therefore, optical spectroscopy has emerged in the last decade as the most convenient means for determining the chirality indices (n , m) of SWCNTs in macroscopic ensembles of SWCNTs. There is now a wellestablished correlation between optical transition energies, diameters, and (n , m) indices, as shown in Figure 2 a. [ 188 ] RRS spectroscopy has served as the most commonly used tool for (n , m) determination for both metallic and semiconducting SWCNTs for many years. [ 189 ] For semiconducting, or ν = ± 1, SWCNTs, PLE spectroscopy [ 24-35 ] can provide accurate information on the E 11 and E 22 energies from the emission and excitation photon energies, respectively, as shown in Figure 2 b. One can also combine PLE and RRS spectroscopies to determine E 33 and E 44 in semiconducting nanotubes. [ 190 ] Furthermore, as detailed in Section 3, coherent phonon spectroscopy has several advantages for simultaneously determining (n , m) indices and phonon frequencies for both semiconducting and metallic SWCNTs (see Figure 2 c). Finally, Section 4 presents how aligned SWCNT fi lms can be used to develop optoelectronic devices, ranging from state-of-the-art terahertz polarizers to large-area, broadband photodetectors. 2. Enrichment and Spectroscopy of Armchair Carbon Nanotubes Because of their excellent electrical properties, metallic SWCNTs are considered to be promising candidates for a variety of future electronic applications such as nanocircuit interconnects and power transmission cables. In particular, (n , n)-chirality, or 'armchair,' metallic nanotubes are theoretically predicted to be truly gapless and intrinsically insensitive to disorder, [ 191-192 ] consistent with experimentally observed ballistic conduction behavior at the single-tube level. Unfortunately, progress towards creating such ballistic-conducting armchair devices in bulk quantities has been slowed by the inherent problem of nanotube synthesis, whereby both semiconducting and metallic nanotubes are produced. Sébastien Nanot received his Ph.D. from Université de Toulouse (France) in 2009 under supervision by Profs. Bertrand Raquet and Jean-Marc Broto. His thesis focused on individual carbon nanotube properties under a very high magnetic fi eld. He moved to Rice University where he is appointed as a postdoctoral researcher in Prof. Junichiro Kono's group. His current research focuses on optoelectronic properties of carbon nanotubes ensembles.
Nano Letters, 2003
The electronic properties of carbon nanotubes (NTs) in a uniform transverse field are investigated within a single orbital tight-binding (TB) model. For doped nanotubes, the dielectric function is found to depend not only on symmetry of the tube, but also on radius and Fermi level position. Bandgap opening/closing is predicted for zigzag tubes, while it is found that armchair tubes always remain metallic, which is explained by the symmetry in their configuration. The bandstructures for both types are considerably modified when the field strength is large enough to mix neighboring subbands.
Excitonic Effects and Optical Spectra of Single-Walled Carbon Nanotubes
Physical Review Letters, 2004
Many-electron effects often dramatically modify the properties of reduced dimensional systems. We report calculations, based on an ab initio many-electron Green's function approach, of electronhole interaction effects on the optical spectra of small-diameter single-walled carbon nanotubes. Excitonic effects qualitatively alter the optical spectra of both semiconducting and metallic tubes. Excitons are bound by ∼ 1 eV in the semiconducting (8,0) tube and by ∼ 100 meV in the metallic (3,3) tube. These large many-electron effects explain the discrepancies between previous theories and experiments.
Local electronic properties of carbon nanotube heterojunctions
Physical Review B, 2000
Local electronic properties of metallic-semiconducting carbon nanotube heterostructures are investigated by studying the behavior of the one-electron local density of states ͑LDOS͒ along the tubes. We determine how these properties change from the metallic to the semiconducting side of a nanotube junction. We show that Friedel oscillations may not always be evident on the metallic side, and we found clear exponential decay of the LDOS on the semiconducting side. The exponential rates of decay as well as the absence of the oscillations are explained in terms of a simple picture that relates the LDOS to the bulk electronic structure of the constituent parts of the heterostructures.
The Electronic Structure of Short Carbon Nanotubes: The Effects of Correlation
Advances in Condensed Matter Physics, 2015
This paper presents atight bindingandab initiostudy of finite zig-zag nanotubes of various diameters and lengths. The vertical energy spectra of such nanotubes are presented, as well as their spin multiplicities. The calculations performed using thetight bindingapproach show the existence of quasi-degenerate orbitals located around the Fermi level, thus suggesting the importance of high-qualityab initiomethods, capable of a correct description of the nondynamical correlation. Such approaches (Complete Active Space SCF and Multireference Perturbation Theory calculations) were used in order to get accurate ground and nearest excited-state energies, along with the corresponding spin multiplicities.
We investigate the electron-electron (e-e) interactions effect on the optoelectronic properties of zigzag silicon hexagonal nanotubes (Si h-NTs). Analytic expressions for the band structure and optical absorption of Si h-NTs have been derived based on orthogonal tight-binding (OTB) method. We combine OTB method and Hubbard model and show electron-electron interactions effect on the band structure of metallic and semiconducting zigzag nanotubes for the first and second-nearest neighbor. Moreover, the optical matrix elements and optical absorption are analytically derived for light polarization parallel to the tube axis in low energy for first nearestneighbor (1NN) and second nearest-neighbor (2NN) approximation. It is found that the electron-electron interactions do not modify the optical absorption spectrum of zigzag Si h-NTs. These results can be beneficial for the explanation of resonant Raman Spectra of nanotube samples.
Effect of electric field on the electronic structures of carbon nanotubes
Applied Physics Letters, 2001
We have investigated the electronic structures of a capped single-walled carbon nanotube under the applied electric field using density functional calculations. The capped tube withstands field strengths up to 2 V/Å. When the electric field is applied along the tube axis, charges are transferred from the occupied levels localized at the top pentagon of the cap, and not from the highest occupied level localized at the side pentagon, to the unoccupied levels. We find that the charge densities at the top of the armchair cap show two-or five-lobed patterns depending on the field strength, whereas those of the zigzag cap show a three-lobed pattern. The interpretation for the images of the field emission microscope is also discussed.