MG/PD AND BA/PD INTERFACES WITH AND WITHOUT HYDROGEN

X-ray photoelectron spectroscopy was used to study alloying and interdiffusion of Mg and Ba overlayers and of their hydrides with Pd and with PdHx substrates, respectively. Mg and Ba films were prepared by evaporation on Pd foils. To avoid the problem of very low reaction rate of gaseous H-2 on alkaline metals we have prepared Mg- and Ba-hydrides by deposition of metallic Mg and Ba, respectively, on previously hydrided Pd-foils. The analysis of spectral changes in core levels of these metals (Mg 1s, Ba 3d and Pd 3d) compared with those of the bulk materials indicated the formation of a 1-3 monolayers thick interface alloy for the Mg/Pd system at 300 K, while the Ba/Pd system exhibited a considerably longer range of intermixing/alloying at 300 K. The range of Ba/Pd interdiffusion decreased at 120 K. Hydrogen diffused from the Pd substrate across the interface into the overlayers and inhibited intermixing of the metal components in both cases. From spectral changes of the Ba, Mg and the Pd core levels on PdH. substrate we conclude that all Ba was transformed into Ba-hydride. Contrary, part of the Mg layers remained metallic. The sticking coefficient of Mg vapour on Mg-hydride turned out to be low.