Elemental and phase composition analysis of hydrogen-sensitive Pd/Mg-Ni films

A magnesium-nickel (Mg-Ni) film with a palladium (Pd) overcoat is switchable between a conducting metallic state and a semiconducting state through hydridation and dehydridation processes. The Pd overcoat is added to suppress possible oxidation of the alloy layer. However, some Pd and oxygen (O) atoms are still able to diffuse into the alloy layer, such that the distributions of elemental and phase compositions along the direction of depth are quite complicated. In this work, we propose a method to obtain more detailed information on the elemental and phase compositions in a Pd/Mg-Ni film by means of analyzing Pd 3d5/2, Pd 3p3/2, Ni 2p3/2, Mg 1s and O 1s photoelectron spectra. The method was applied to analyze a typical Pd/Mg-Ni film sample. Results verified that Pd can diffuse into the alloy layer. An Mg-O phase is formed near the surface. An Mg-Ni alloy phase dominates at deeper regions. The Mg-Ni phase contains 80% of the total number of atoms in the film, and is non-stoichiometric and highly disordered. Nevertheless, it can give a remarkable change of electrical resistivity during hydridation- dehydridation processes.