HYDROGEN IN NB AND NB TI NB THIN-FILMS

Epitaxial Nb and Nb/Ti/Nb films on sapphire substrates were prepared b y e-beam evaporation and sealed with thin Pd or Au layers to avoid oxi dation. Hydrogen charging was performed from the gas phase and the con centration in the films was measured by the N-15 nuclear reaction meth od. For the single Nb layer the hydrogen concentration in the film as a function of the external hydrogen pressure (solubility) was investig ated. For the Nb/Ti/Nb sandwich samples the distribution of hydrogen a mong the different layers was studied. In both cases deviations from t he bulk behavior were observed. They are attributed to restrictions in the lateral expansion of epitaxial films. In addition interface effec ts were studied.