CALORIMETRIC AND XPS STUDY OF THE EFFECT OF COPPER ON THE SORPTION PROPERTIES OF DYSPROSIUM

The chemical composition of the surface of bimetallic dysprosium-copper films and their sorption properties towards carbon monoxide at room temperature have been studied by adsorption calorimetry and X-ray photoelectron spectroscopy. The former method has been used to compare the behaviour of carbon monoxide and hydrogen on these films. The surface enrichment in dysprosium occurs in the bimetallic film evaporated from DyCu and DyCu6 Specimens. The uptake of CO is reduced by the presence of copper, but the adsorption heat and the rate of its production are little affected. C 1s spectra of the alloy surface saturated by irreversibly adsorbed CO show the existence of two distinct adsorption states corresponding to dissociated and molecular species. Molecular adsorption likely occurs at dysprosium sites surrounded by copper atoms. Calorimetric measurements with hydrogen have shown that the admixture of copper cuts down not only the uptake, but also the heat of interaction in comparison with pure dysprosium. The results point to rapid penetration of the dissociated H atoms into the bulk of the film and to their bonding to both the Dy and Cu components.