H2O and O2 co-adsorption on 3C-SiC (111) by first-principle calculations: The role of water in initial oxidation

First-principle calculations were employed to investigate the initial oxidation behaviors of CVD-SiC in wet oxygen. The H2O/O-2 co-adsorption behaviors with different H2O/O-2 molecular ratios and coverages on (3 x 3) 3C-SiC (111) surface were studied by geometry optimization and property calculation. The results showed that the O-O bond in Si-O=O structure had higher bond energy than that in Si-O-O-H structure, indicating the weaker bond energy of O-O bond in the formed hydroperoxyl. First-principle molecular dynamic (FPMD) simulations confirmed that the formation of hydroperoxyl as an intermediate was feasible during the dissociation of molecular oxygen, which played an important role in O-2 activation. The static calculation results indicated that the formation of hydroperoxyl needed to experience a lower activation energy barrier (0.35 eV), which demonstrated more likely occurrence than the direct dissociation of molecular oxygen. In brief, the introduction of molecular water could enhance the oxidation rate of 3C-SiC in initial stage by the formation of hydroperoxyl. This work revealed the initial oxidation mechanism of 3C-SiC (111) in wet oxygen and the role of water in initial oxidation, which could also provide a new view to explain the accelerated oxidation rate of SiC in wet oxygen.