Retardation of oxidation and duplex oxide growth on single crystal nickel after magnesium implantation

Abstract

Rutherford backscattering spectrometry and channeling have been employed to study the oxidation behaviour of single crystal nickel after magnesium implantation and to probe the structural relationship between the substrate and its oxide following oxidation in pure oxygen at 700°C for various times. A two-tier oxide structure, including an oriented inner oxide layer, was found to form during the oxidation of an unannealed implanted sample and a reduction in oxidation rate was observed. Correlations appear to exist between this oxidation behaviour and the presence of a high concentration of magnesium. Results are discussed in terms of the blocking effect of magnesium on the outward diffusion of nickel cations along fast transport paths, such as grain boundaries. It is concluded that the oriented inner oxide layer of the two-tier oxide grows inwards, presumably via an inward diffusion of oxygen. This oxide growth mechanism becomes important when a high concentration of Mg incorporated into a growing oxide retards the outward diffusion of nickel cations and therefore reduces the usual outward growth of oxide.