Hydrogen in Nb and Nb Ti Nb thin films

Epitaxial Nb and Nb Ti Nb films on sapphire substrates were prepared by e beam evaporation and sealed with thin Pd or Au layers to avoid oxidation. Hydrogen charging was performed from the gas phase and the concentration in the films was measured by the N 15 nuclear reaction method. For the single Nb layer the hydrogen concentration in the film as a function of the external hydrogen pressure solubility was investigated. For the Nb Ti Nb sandwich samples the distribution of hydrogen among the different layers was studied. In both cases deviations from the bulk behavior were observed. They are attributed to restrictions in the lateral expansion of epitaxial films. In addition interface effects were studie