ORIGINAL PAPER Microstructural and chemical transformation of thin Ti/Pd and TiDy/Pd bilayer films induced by vacuum annealing

Abstract Using a combination of scanning electron mi-croscopy, transmission electron microscopy (TEM), X-ray diffraction and X-ray photoelectron spectroscopy (XPS), we made a comparative study of the high-temperature annealing impact on thin titanium deuteride (TiDy) films covered by an ultrathin Pd layer, and on Ti/Pd bilayer films. The bilayer films were prepared under ultrahigh vacuum conditions and were in situ annealed using the same anneal-ing procedure. It was found that the surface and the bulk morphology of both films undergo different annealing-induced transformations, leading to an extensive intermix-ing between the Ti and Pd layers and the formation of a new PdTi2 bimetallic phase. Energy-filtered TEM imaging and energy-dispersive X-ray spectrometry analysis, as well as XPS depth profiling all provided evidence of a different distribution of Pd and Ti in the annealed TiDy/Pd film compared with the annealed Ti/Pd film. Our results show that thermal decomposition of TiDy, as a consequence of annealing the TiDy/Pd film, modifies the intermixing process, thereby promoting Ti diffusion into the Pd-rich top layer of the TiDy film and thus providing a more likely path for the formation of the PdTi2 phase than in an annealed Ti/Pd film