Oxidation of Cobalt by Oxygen Bombardment at Room Temperature

Most experiments on thermal oxidation of cobalt have shown the parabolic growth rate consistent with the diffusion of cations through neutral cation vacancies. Here, we present experimental results on the oxidation of Co metal by low-energy oxygen bombardment at room temperature, which scales with the dose of implanted oxygen, Φ, as Φ1/6. This type of oxide growth, predicted theoretically for diffusion of cobalt cations by doubly charged cation vacancies, has not been observed previously in thermal oxidation of Co. Our results demonstrate that oxidation of Co, which involves formation of both monoxide, CoO, and spinel, Co3O4, oxide structures, can be indeed driven by doubly charged vacancies, as predicted theoretically, when oxidation conditions enhance both the production of point defects and the mobilities of cobalt cations and oxygen anions within cobalt oxide.