Optical properties of SiC nanotubes: A systematic $\textit{ab initio}$ study

TL;DR

This systematic ab initio study investigates the electronic and optical properties of various SiC nanotubes, revealing their semiconducting nature, diameter-dependent band gaps, and characteristic dielectric spectra for different electric field orientations.

Contribution

The paper provides a comprehensive first-principles analysis of SiC nanotubes' optical properties, highlighting their semiconducting behavior and the influence of diameter and chirality on their dielectric response.

Findings

Most SiC nanotubes are semiconductors, except small zigzag tubes which are metallic.

Band gaps decrease with diameter and can become zero for small tubes.

Optical spectra show characteristic peaks at ~3 eV and broad features at ~7 eV depending on orientation.

Abstract

The band structure and optical dielectric function $\epsilon$ 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 DFT with the LDA. 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 \AA$ $ is almost independent of diameter. For the electric field parallel to the tube axis ($E\parallel \hat{z}$), the $\epsilon''$ for all the SiC-NTs with a moderate diameter (say, $D$ $>$ 8 \AA$ $) 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 $\epsilon''$ spectrum does deviate markedly from this general behavior. In the high-energy region (from 6 eV upwards), the $\epsilon''$ for all the SiC-NTs exhibit a broad peak centered at ~7 eV. For the electric field perpendicular to the tube axis ($E\perp \hat{z}$), the $\epsilon''$ 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 whilst 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 half of the magnitude of the corresponding ones for $E\parallel \hat{z}$.