Reaction mechanisms of the initial steps for the oxidation of (000[formula omitted]) C and (0001) Si faces of SiC with OH radicals

Abstract

The reaction mechanisms of OH radicals on the C and Si faces of SiC were analyzed using density functional theory calculations to understand the difference in reactivity. For the first OH radical, it was shown that the O–H bond dissociation occurs on both faces, but at different spin states, i.e., the reaction proceeds at a lower spin multiplicity on the Si face. Then, the generated surface O atom causes dissociation of a C–Si bond to form a C–O–Si structure on the C face, whereas it binds to two surface Si atoms to form a Si–O–Si structure on the Si face. These differences are explained by the atomic charge and spin density of the surface atoms. The second OH radical generates a CO molecule on the C face, and a second Si–O–Si structure is formed on the Si face. These results shed light on the reasons why the grinding technique using a tribocatalytic abrasive, which is considered to be promoted by oxidation of the surface by oxidants such as the OH radical, is inefficient on the Si face of SiC.