Silicon-carbon nanocomposites: Theoretical investigations

The geometrics, cohesive and strain energies, and band gaps of silicon carbide nanotubes as a function of the nanotube diameter were studied using a self-consistent-charge density-functional tight-binding method. It is verified that C atoms moved slightly inwards and Si atoms outwards, resulting in an inner C cylinder and a outer Si cylinder due to the difference in hybridization of Si and C atoms. The buckling diminishes as the diameter of the tube increases. Both the cohesive and the strain energies vary inversely proportional to the square of the nanotube diameter, irrespective of the type (zigzag, armchair or chiral) of the SiCNTs. In contrast, the energy gap is very sensitive to both the diameter and the type of the nanotube. All the zigzag, armchair and chiral SiCNTs were found to be semiconductors with small band gaps (∼1 eV). However, the zigzag and chiral SiCNTs considered here indicate a n = 3k anomaly, with the band gaps of zigzag (n, 0) SiNTs being considerably smaller and approaching those of the armchair (n, n) SiCNT.