Collection of Czechoslovak Chemical Communications - digital archive 

Abstract

X-Ray photoelectron spectroscopy (XPS) has been used to study the adsorption of carbon monoxide on Pd dispersed on oxidized Si(111) surface. A fraction of the deposited Pd diffusing at room temperature to the SiO₂/Si interface increases with decreasing SiO₂ thickness. For oxide layers thinner than ≈1 nm, almost all deposited Pd diffuses to SiO₂/Si interface forming there Si silicide. Consequently, the amount of adsorbed CO is dependent on the thickness of the thermally grown SiO₂ layer. Two different chemical states of adsorbed carbon atoms, the population of which depends on the amount of the Pd deposited, are observed in the C (1s) spectra of adsorbed CO. Adsorption activity of Pd clusters does not depend on whether n- or p-type Si is used. Comparison of the experimental Pd/CO concentration ratios with those calculated assuming several different modes of the Pd growth on SiO₂/Si points to the pseudo-Stranski-Krastanow mode (flat clusters with incomplete condensation of the first layer) at 300 K. Changes in charge balance across the Pd/SiO₂/Si interface caused by CO adsorption are discussed in terms of the surface photovoltage effect and work function variation.

Keywords: X-ray photoelectron spectroscopy; Pd/SiO2/Si(111); Pd-Clusters; Palladium; CO Adsorption.