Electronic structure and surface kinetics of palladium hydride studied with x-ray photoelectron spectroscopy and electron-energy-loss spectroscopy

X-ray photoelectron spectra and electron-energy-loss spectra (EELS) are presented and interpreted for Pd${\mathrm{H}}_{\mathrm{\sim }0.8}$ prepared by in situ loading and cleaning of a 10-μm foil cooled to 80 K. Hydrogenation induces new states with considerable $d$ character 8 eV in the valence band, a slight narrowing of the valence-band spectrum, and a shift of the Fermi level out of the $d$ manifold of states. In the core-line spectra a +0.17-eV binding-energy shift occurs, the asymmetry is reduced, and a shake-up satellite at 6 eV essentially disappears. In the EELS spectra a 7-eV plasmon loss is attenuated and shifted to 5 eV. During degassing experiments, no significant surface depletion is found, and two different rates occur: For concentrations ${\mathrm{H}}_x\gtrsim 0.65$ atomic fraction hydrogen (($\beta$ phase) an activation energy of 8.1-kcal/mole ${\mathrm{H}}_2$ is found, while for ${\mathrm{H}}_x\gtrsim 0.65$ (two-phase region) the rate is ${10}^5$ slower, but has a similar activation energy of 9.0-kcal/mole ${\mathrm{H}}_2$. During this time the surface contains both $\beta$ and $\alpha$ phases.