Fig. 4

XPS spectra of the Ru(0001) after various chemical treatments. The spectra were logically grouped by means of shifting along a vertical axis (intensity in arbitrary units). The group of two curves in the lower part of the plot contains spectra of the sample before oxidation (initial substrate) and after full reduction of the previously existing oxide film (fully reduced by CO). The group of three curves in the middle part of the plot contains spectra of the surface covered by non-continuous oxide film as a result of oxide growth (partially oxidized) and reduction of the previously existing oxide film (partially reduced by HCl, partially reduced by CO). A single curve in the upper part of the plot (fully oxidized) is the spectrum obtained on the Ru(0001) sample, which was oxidized to saturation