Geometric and electronic structures of graphitic-like and tubular silicon carbides: Ab-initio studies

The optimized structures of graphitic-like sheets (i.e., single and multilayered) as well as tubular structures (i.e., both single-wall and double-wall) of SiC including their electronic structures are investigated using ab-initio simulations within the framework of the density-functional theory. We find that: (i) SiC graphitic-like structures form sp(2)-like bonding, although the bulk phases of SiC exhibit sp(3) bonding, (ii) the interplanar spacing in a multilayer graphitic sheet depends on how the atoms are arranged in adjacent SiC bilayers (e.g., Si-C or C-C interplanar order). It is smaller for the Si-C ordering (similar to 3.7 angstrom) than for the C-C ordering (similar to 4.5 angstrom). Our analysis indicates that the electrostatic interaction between the bilayers is responsible for the smaller interplanar spacing exhibited by the Si-C ordering. These findings provide the basis for the interpretation of experimental observations that display two different values for intershell distances (similar to 3.8 angstrom or similar to 4.8 angstrom) in SiC-based multiwall nanotubes.