An electron-microscopy study of the A15 Nb₃Ge substrate interface

Electron microscopy has been used to study very thin Nb-Ge films sputtered-deposited onto copper substrates. Micrographs and selected-area electron-diffraction patterns reveal an interface region between the substrate and the first A15 Nb₃Ge to form. This interface consists of microcrystalline Nb-N-O and a two-phase region consisting of Nb-N-O grains and an unidentifiable tetragonal Nb-Ge phase. The A15 Nb₃Ge grains which form later in the growth of the film exhibit the same grain size and shape as the Nb-N-O grains. From the results a model for the role of the interface in the initial formation of A15 Nb₃Ge is proposed.