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

Abstract

Thin titanium deuteride (TiD(y)) 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 TiD(y) 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 TiD(y) 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 TiD(y) films efficiently against extensive air interaction. The morphology of both the surface and bulk Pd/TiD(y) (Ti) films have been observed using SEM and cross-sectional TEM analysis, respectively. A polycrystalline bulk morphology in both Ti and TiD(y) films accompanied by a fine-grained Pd surface was observed. High-magnification cross-sectional TEM images reveal the TiD(y) 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/TiD(y) interface. The chemical nature of this interface has been analysed after partial sputtering of the Pd top layer using XPS. Besides TiD(y) and Pd, TiO and PdO were found to be the main chemical species in the interface region of the Pd/TiH(y) film. The XPS valence-band spectra of the Pd/TiD(y) interface reveal electronic features characteristic of a Pd-Ti bimetallic structure.