Surface reduction of ruthenium compounds with long exposure to an X-ray beam in photoelectron spectroscopy

The reduction of Ru at the surface of commercial RuCl3 and RuO2 has been observed during XPS analysis. The experiments have been performed with either a non-monochromatized (Mg K-alpha) or a monochromatized (Al K-alpha) X-ray beam. Ruthenium reduction is enhanced by increasing the X-ray dose, but the residual pressure exerts only a weak influence. The initial composition of commercial ruthenium (III) chloride hydrate is a complex mixture of chloro or chlorohydroxo species rather than pure RuCl3. nH(2)O. RuCl3 is not suitable as a reference compound for ruthenium chloride compounds in XPS analysis, because it contains mainly Ru(IV) which is reduced under X-ray. A similar reduction occurs at the surface of RuO2 samples (by reduction of RuO3 layers), and on the adventitious carbon. (C) 1999 Elsevier Science B.V. All rights reserved.