  Superconducting films of alpha-Ta are promising candidates for the
fabrication of advanced superconducting qubits. However, alpha-Ta films suffer
from many growth-induced structural inadequacies that negatively affect their
performance. We have therefore explored a new synthesis method for alpha-Ta
films which allows the growth of these films with unprecedented quality. Using
this method, high quality alpha-Ta films are deposited at a comparably high
substrate temperature of 1150 C. They are single-phase alpha-Ta and have a
single out-of-plane (110) orientation. They consist of grains above 2 um that
have one of three possible in-plane orientations. As shown by scanning
transmission electron microscopy and electron energy loss studies the
substrate-film interfaces are sharp with no observable intermixing. The
obtained insights into the epitaxial growth of body-centered-cubic films on
quasi-hexagonal substrates lay the basis for harnessing the high structural
coherence of such films in various applications.
