The oxidation and reduction of Ru thin films grown on a Si(1 0 0) surface were studied by X-ray photoemission spectroscopy (XPS). Ru thin films were oxidized with O-2, plasma generated by an rf discharge, and their XPS spectra were measured. The spectra were decomposed into several components for Ru suboxides attributable to different stages of oxidation. After sufficient exposure to oxygen, a stoichiometric rutile RuO2 layer was found to have formed near the surface. Thermal annealing at 500 K resulted in a thicker RuO2 layer. Experiments demonstrated that the Ru oxide layer can be removed by H(D) atoms via the desorption of water molecules. (c) 2007 Elsevier B.V. All rights reserved.