Oxidation simulation study of silicon carbide nanowires: A carbon-rich interface state

Silicon carbide nanowires (SiCNWs) have attracted increasing attention due to their excellent properties and wide range of potential applications. SiCNWs covered with oxide layer, which can be simply prepared by thermal oxidation, show a number of fascinating functional prospects. However, the oxidation mechanism of the SiCNWs is barely explored. Here we studied oxidation of SiCNWs at 300-1500 K by using the reactive molecular dynamics simulations with ReaxFF potential. The temperature-dependent oxidation processes and the obtained structures were discussed in detail. The results reveal that self-limiting oxidation of the SiCNWs can switch from the rate-determining step of chemical reaction at the interface to diffusion limited oxidation after a definite time. In addition, the SiC vertical bar C vertical bar SiOx core-shell structure was proved to be formed during the oxidation from a theoretical view. A saturation emit mechanism was proposed to explain why the C-rich layer is too thin to be detected. DFT calculations were employed to study electronic structure of the core-shell structures, indicating the SiO2 layer apparently narrows band gaps of the SiCNWs, and the accumulated C at the interface could offset conduction band and valence band, resulting in instability problem during application of the SiCNWs.