Abstract
Nb 3 Al thin films have been prepared and characterized with varying deposition parameters, including substrate temperature, deposition rate, gas doping, and epitaxial growth. Nb-Al samples made with the optimum substrate temperature have lattice constants following the prediction of Geller radii and a systematic T c increment with Al composition, namely, a ΔT c /ΔC of 1.9 K/at% Al. Employment of the self-epitaxial method results in extending the A15 phase boundary by 1 at% Al and an enhancement of T c by 2.4 K at a given substrate temperature. By extrapolating from T c =16.7 K, the highest transition temperature observed in this work, stoichiometric Nb 3 Al is predicted to have an T c onset of 20.7 K.