Thermal desorption spectroscopy of CO adsorption on epitaxial Cu(111)-Pd(111) thin film surfaces

Abstract

Thermal desorption spectroscopy experiments of CO adsorbates on vacuum deposited, epitaxial (111)Pd and (111)Cu-(111)Pd bilayer films were carried out under uhv conditions. Auger electron spectroscopy and LEED measurements showed that Cu grows epitaxially on (111)Pd films formed on mica in layer growth mode. CO adsorption on (111)Cu-Pd bilayers occurs in decreasing amounts as the Cu overlayer thickens. Beyond approximately two monolayers (ML) Cu, no CO adsorbs. The saturation CO coverages decrease linearly by approximately 25% for every 1/2 ML Cu deposited. The desorption energy corresponding to the peak of the main desorption line decreased as the Cu and/or CO coverages increased. A simple relationship between Cu coverage and the temperature at the peak of the main CO desorption line for different CO coverages was derived from the data. The results show that thin Cu overlayers on Pd significantly affect the adsorption and desorption characteristics of CO on these thin film bilayers.