THERMAL-DESORPTION SPECTROSCOPY INVESTIGATION OF CO ADSORPTION ON CU/PD(111) SURFACES

Thermal desorption spectroscopy (TDS) experiments of CO adsorbates on vacuum deposited, epitaxial Pd(111) and Cu(111)/ Pd(111) bilayer films were carried out under UHV conditions. It was shown in this work that CO adsorption on these films takes place in two steps: the high energy sites (β2) are filled first during early exposure and then one or more low energy sites are filled to saturation. CO adsorption on Cu(111)/Pd(111) 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 peak temperature of the TDS curves decreases linearly with increasing CO coverage and does so more rapidly with increasing Cu coverage. This result shows that the binding energy of CO depends not only on the overlayer coverage but also on the density of CO molecules on the surface. © 1990.