Applied Surface Science 51 (1991) 47-60 North-Holland 41 zyxwvutsr An ESCA study of the interaction of oxygen with the surface of ruthenium J.Y. Shen, A. Adnot and S. Kaliaguine * Departmenf zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA of Chemical Engineering and GRAPS, UniversitP Lmnl, Ste-Foy, Quebec, Canada Received 21 July 1990; accepted for publication 21 February 1991 The interaction of oxygen with the surface of a Ru wafer in the range of room temperature to 600 o C was investigated by ESCA. Ru 3d,3p,MW, valence band and 0 1s spectra were recorded. Three different states of oxygen were observed on the Ru wafer surface. Definitive identification of two of the three states was achieved according to the multiplet structure in the photoemission spectra of oxygen and the binding energy of various states of oxygen. The oxygen species identified are 02- and dissolved atomic oxygen. The third oxygen state which gives rise to the peak at a BE of 532.3 eV in the 01s spectrum and 11.7 eV in the photoemission spectrum is tentatively assigned to a chemisorbed hydroperoxy radical. A discussion of the Ru oxidation process is also given. zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA 1. Introduction XPS or electron spectroscopy for chemical an- alysis (ESCA) [1,2] is one of the most widely used techniques for elemental analysis of the near- surface region. Because this near-surface tech- nique has a nominal sampling depth of the order of 40 A, it has been singularly useful in studying the surface of many catalytically important materials. The chemical specificity of the photo- ejected electrons and their semisurface nature are desirable properties which can be used to char- acterize the various catalytic surface species and can also lead to identifying the active sites. Much work has been done in this field [3-71. For exam- ple, Kim and Winograd [3] used XPS to study Ru-0 surfaces. They identified a variety of species on the RuO, surface. Ruthenium metal is an important catalyst in chemical industry [S] and in particular in the electrochemistry of chlorine and oxygen [9]. It can be supported on several materials as SiO,, Al,O,, * Author to whom correspondence should be addressed. or zeolites and its catalytic properties are greatly changed depending on the support and pretreating conditions. In order to interpret these observa- tions, the surface electronic structure of Ru and the interaction of oxygen with the surface of ruthenium have been the subjects of intensive studies during the last 20 years. Almost all surface analysis methods have been applied to clarify the mechanism of oxygen-ruthenium interaction and identify the surface species. Fuggle et al. [lo] used XPS and UPS to study the adsorption and coad- sorption of oxygen and CO on a clean(001) face of a Ru single crystal. They presented data on the shifts of XPS peaks and changes in UPS spectra as a function of adsorbate coverage. The work func- tion and LEED data of Madey et al. [ll] showed the formation of two binding states of oxygen upon oxygen exposure. However, in the TD data of these authors only one peak was observed. The incorporation of oxygen into the Ru lattice was mentioned in numerous papers [12-171. Praline et al. [16] found that oxygen dissolution occurs with a measurable rate at temperatures as low as 400 K, while Sumev et al. [17] found that oxygen diffusion into the Ru lattice began at T 2 1150 K. 0169-4332/91/$03.50 0 1991 - Elsevier Science Publishers B.V. (North-Holland)