First-Principles Study of Faceted Single-Crystalline Silicon Carbide Nanowires and Nanotubes

The energetics and atomic and electronic structures of silicon carbide (SiC) nanowires (NWs) and nanotubes (NTs) with radii ranging from 0.45 to 2.9 nm are investigated using density functional theory in conjunction with an atomistic band-order potential. It is found that the formation energy ( E form ) of the NWs decreases with the increase of wire radius, and that of the NTs decreases with the increase of wall thickness, irrespective of the tube radius. NTs with faceted single-crystalline walls are energetically more favorable than the cylindrical single- or multiwalled SiC NTs. Due to the surface states, the faceted NWs and NTs possess indirect band gaps, which are narrower than that of bulk SiC crystal. The highest valence band and the lowest conduction band mainly arise from the undercoordinated C and Si atoms on the facets. The surface states can be passivated by surface hydrogenation, and the hydrogenated SiC NWs and NTs become direct-band gap semiconductors with wider band gaps than that of bulk SiC crystal.