Ion-beam-deposited films for refractory-metal tunnel junctions

We report on the application of a Kaufman ion source to the deposition of Nb and Ta thin films. We find that high quality Nb films (T
c
= 9.1 K) can be produced by this technique under tolerant deposition conditions. In addition, substantial, systematic improvement in the I-V characteristics of Nb tunnel junctions has been realized by depositing, in situ, thin (≥10Å) Ta layers on the Nb film surface.