Optical properties of SiC nanotubes: An ab initio study
Journal
Physical Review B - Condensed Matter and Materials Physics
Journal Volume
76
Journal Issue
3
Date Issued
2007
Author(s)
Abstract
The band structure and optical dielectric function of single-walled zigzag [(3,0),(4,0),(5,0),(6,0),(8,0),(9,0),(12,0),(16,0),(20,0),(24,0)], armchair [(3,3),(4,4),(5,5),(8,8),(12,12),(15,15)], and chiral [(4,2),(6,2),(8,4),(10,4)] SiC-NTs as well as the single honeycomb SiC sheet have been calculated within density-functional theory with the local-density approximation. The underlying atomic structure of the SiC-NTs is determined theoretically. It is found that all the SiC nanotubes are semiconductors, except the ultrasmall (3,0) and (4,0) zigzag tubes which are metallic. Furthermore, the band gap of the zigzag SiC-NTs which is direct, may be reduced from that of the SiC sheet to zero by reducing the diameter (D), though the band gap for all the SiC nanotubes with a diameter larger than ∼20 Å is almost independent of diameter. For the electric field parallel to the tube axis (E z), the ″ for all the SiC-NTs with a moderate diameter (say, D>8 Å) in the low-energy region (0-6 eV) consists of a single distinct peak at ∼3 eV. However, for the small diameter SiC nanotubes such as the (4,2), (4,4) SiC-NTs, the ″ spectrum does deviate markedly from this general behavior. In the high-energy region (from 6 eV upwards), the ″ for all the SiC-NTs exhibit a broad peak centered at ∼7 eV. For the electric field perpendicular to the tube axis (E z), the ″ spectrum of all the SiC-NTs except the (4,4), (3,0), and (4,0) nanotubes, in the low-energy region also consists of a pronounced peak at around 3 eV while in the high-energy region is roughly made up of a broad hump starting from 6 eV. The magnitude of the peaks is in general about one-half of the magnitude of the corresponding ones for E z. Interestingly, the calculated static dielectric constant (0) for all the SiC nanotubes is nearly independent of diameter and chirality with (0) for Ez being only about 30% larger than for E z. The calculated electron energy loss spectra of all the SiC nanotubes for both electric field polarizations are rather similar to that of E c of the SiC sheet, being dominated by a broad (π+σ) -electron plasmon peak at near 21 eV and a small π -electron plasmon peak at ∼4 eV. © 2007 The American Physical Society.
Type
journal article