Investigation of Surface Oxide Layers by X-Ray Appearance Potential Spectroscopy

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Abstract
X‐ray appearance potential spectroscopy using low energy electron excitation is a simple method for surface analysis sensitive to light elements. The spectra obtained from many elements show considerable structure which is presumably related to the valence band distribution. The apparatus consisted of a tungsten filament electron source and a large area, windowless, soft x‐ray detector based on the photoelectric yield of a gold surface. The specimen, electron source, and detector were located in an all metal, bakeable vacuum system having demountable, gold wire sealed flanges. Facilities were provided for surface cleaning by ion bombardment and heating the specimen in situ. A 10Aå layer of oxygen on nickel was readily detected using an electron current of 2 mA. The L3,2 structure of iron in pure and known oxide forms was obtained by perfoming in situ oxidation of a pure iron specimen. Slight but reproducible changes in the structure were observed, indicating the potential capability of the technique to distinguish between different valence states of an element. The oxygen spectrum also showed a multiple peaked structure.

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