Initial oxidation of 3C-SiC (111) in oxidizing atmosphere containing water vapor: H₂O adsorption from first-principles calculations

First-principles calculation based on density-functional theory (DFT) were employed to investigate H₂O adsorption on 3C-SiC (111) surface for understanding atomic initial oxidation mechanism of CVD-SiC in oxidizing atmosphere containing water vapor. Firstly, Si-terminated 3C-SiC (111) slabs with intense surface states were constructed. Then, adsorption energy calculations demonstrated that the optimized structure of total dissociation of H₂O molecule (SO structure) is relatively stable. The charge density difference plots of the corresponding O and Si atoms also indicated that the O and Si atoms in SO structure are more stable than those in the other structures. Besides, all orbital energies of relevant atoms in three stable structure shifted to the lower energy levels. From energy barrier analysis, the complete dissociation of H₂O molecule on the SiC (111) surface had to overcome higher energy barrier than the partial dissociation, meaning that H₂O molecules preferred to partially dissociate into OH radicals and H atoms on Si-terminated 3C-SiC (111) surface. By the analyses of geometry, charge transfer and bond population, O–H⋯O hydrogen bond network gradually was generated on the surface with increasing H₂O coverage. Furthermore, the bond energy of the formed O–H⋯O hydrogen bond between two *OH radicals is higher than that between *OH and *O–2H group, owing to electronegativity difference of corresponding O atoms.