Structural and chemical characterisation of titanium deuteride films covered by nanoscale evaporated palladium layers

Thin titanium deuteride (TiDy) films, covered by an ultra-thin palladium layer, have been compared with the corresponding titanium and palladium films using a combination of scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The TiDy layers were prepared under ultra-high vacuum (UHV) conditions by precisely controlled deuterium sorption at 298 K on a Ti film evaporated onto a Si(100) substrate. Both Ti and TiDy films were then covered in situ by a nanoscale Pd layer. It was found that a 10- to 12-nm-thick Pd layer protects the TiDy films efficiently against extensive air interaction. The morphology of both the surface and bulk Pd/TiDy (Ti) films have been observed using SEM and cross-sectional TEM analysis, respectively. A polycrystalline bulk morphology in both Ti and TiDy films accompanied by a fine-grained Pd surface was observed. High-magnification cross-sectional TEM images reveal the TiDy film to be plastically deformed leading to an increase in the roughness of the top Pd layer. Complex structures, including Moiré patterns, have been identified within the Pd/TiDy interface. The chemical nature of this interface has been analysed after partial sputtering of the Pd top layer using XPS. Besides TiDy and Pd, TiO and PdO were found to be the main chemical species in the interface region of the Pd/TiHy film. The XPS valence-band spectra of the Pd/TiDy interface reveal electronic features characteristic of a Pd–Ti bimetallic structure.