XPS depth profile analysis of non‐stoichiometric NiO films

Abstract

Abstract Antiferromagnetic NiO films used for pinning layers in spin valve systems were prepared by reactive sputtering from an NiO target with variation of the oxygen/argon mixture in the sputter gas. Using XPS depth profiling we investigated the NiO x overstoichiometry ( x > 1) in the films that was found by other methods and the chemical changes in the films during annealing. A direct detection of Ni 3+ failed because of strong preferential sputtering with the formation of metallic Ni during sputtering. By means of factor analysis a qualitative description of the overstoichiometry is possible. Indirectly it could be shown that metallic Ni is already formed in the oxide layers during annealing. It can be concluded that the stability of the NiO x films decreases with increasing deviation from stoichiometry ( x > 1). Copyright © 2004 John Wiley & Sons, Ltd.