Variation of the take-off angle in XPS permits one to obtain information on chemical composition of very thin films as a function of depth without the use of ion sputtering. The method together with Auger depth profiling was applied to the study of nickel surfaces subjected to transpassive dissolution in nitrate solution. Obtained results indicate the presence of thin oxide films containing nitrogen which is present in a reduced form.
Dr. Madhav Datta, Mathieu, H. J., and Landolt, D., “Application of angle resolved XPS and AES depth profiling to the study of transpassive films on nickel”, in Passivity of metals and semiconductors, Amsterdam (Netherlands): Elsevier, 1983, pp. 113-118.