Quantitative analysis of thin oxide films using x-ray photoelectron spectroscopy and rastered ion bombardment

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Abstract
Using x-ray photoelectron spectroscopy (XPS or ESCA), it is possible to construct a quantitative profile of the composition of a surface film as a function of depth into that film. The factors contributing to distortion of the profile are considered with reference to an oxidized Inconel 600 alloy surface containing metallic and oxidized iron, chromium, and nickel. The ability of XPS to differentiate clearly between metal and oxide components is important since the photoelectron yield can differ for each of these species. Differentiation of oxide from metal is accomplished by automated analysis of the XPS peak shapes together with application of the appropriate, experimentally derived photoelectron yields. Ion bombardment can distort the quantitative information in a depth profile by preferential sputtering of some components and by beam-induced chemical decomposition of the surface. For the oxide mixtures under study, preferential sputtering was not detected. Moreover, ion bombardment of these oxide surfaces did not result in significant reduction of oxide to metal. The appearance of metallic components, observed in some systems during the sputtering of oxides, is attributed to the redeposition of sputtered components on the edge of a sputtered region, and their absence in this work is due to the use of a rastering ion beam to remove the entire analysis region evenly. Thus, the component ratios obtained in profile experiments on Inconel films can be expected to reflect the real concentrations.

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