M-edge x-ray absorption spectroscopy: A new tool for dilute mixed-valent materials

The valence of Tm compounds is derived from MV x-ray absorption spectra recorded by total electron yield under ultra-high-vacuum conditions. For mixed-valent systems the spectra are superpositions of Tm3+ (three lines) and Tm2+ (one line) components, providing accurate mean valence values even in highly dilute systems, such as TmxY1-xSe, which agree well with those from lattice-constant systematics. A surface valence change on TmS(100) is identified as an initial-state effect. © 1983 The American Physical Society.