A first-principles study of the size-dependent electronic properties of SiC nanotubes

We investigate the structural and electronic properties of SiC nanotubes (NTs) with hexagonal cross sections by a first-principles calculation using plane-wave ultra-soft pseudo-potential technology based on the density-functional theory. Our results reveal that surface-layer C and Si atoms relax significantly upon decreasing the tube-wall thickness because of surface-size and quantum-size effects. We also find that all relaxed SiC NTs stay stably on the nanoscale because of an admixture of sp 2 and sp 3 hybridization between C and Si atoms and a strong covalent, and that the band gap tends to decrease with increasing tube-wall thickness. Our calculations further indicate that both C and Si atoms on the inner and outer surface of SiC NTs contribute to defect states at the top of the valence band and at the bottom of the conduction band. These results provide reference information for a thorough understanding of the properties of SiC nanostructures and also enable more precise monitoring and control of the growth of SiC nanostructures.