Oxygen chemisorption on transition-metal carbide (100) surfaces studied by X-ray photoelectron spectroscopy and low-energy He⁺ scattering

The mechanism for oxidation of the (100) surfaces of TiC, VC, ZrC, and TaC has been studied using X-ray photoemission and low-energy He⁺ ion scattering. The oxidation of TiC(100) is found to proceed into the bulk even at room temperature by replacing a part of the surface carbon atoms with oxygen and subsequent diffusion of oxygen into the bulk via carbon vacancies suggesting that the preferential bonding of oxygen with carbon exists at the surface. In case of the (100) surfaces of VC and TaC oxidation into the bulk is prevented by formation of an additional metal-oxygen bond at the surface. These significant differences will be elucidated on the basis of the electronic band structures characteristic of the transition-metal carbides.