Abstract
It is shown that the surface composition of a binary alloy with known bulk composition can be determined by Auger Electron Spectroscopy, without calibrated reference spectra if an adsorbate is selectively chemisorbed on one of the constituent components. The correctness of the procedure is verified for Pt-Cu alloys using AES data obtained upon exposure to C 2H 4. The accuracy of the method is discussed. The method is applied on a Pt 0.25Rh 0.75(100) surface. Under our experimental conditions oxygen is preferentially adsorbed on Rh at low exposures whereas hydrogen. CO, NO, and C 2H 4 are non-selectively chemisorbed. The results point to a surface enrichment in Pt above 1200 K. Below 1200 K an enrichment in Rh cannot be ruled out. The results are discussed in relation to controversial literature data concerning the surface composition of Pt-Rh alloys.
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