Nucleation and growth of high-T c Nb3Ge coevaporated films

Results from coevaporation of Nb3Ge using ultrahigh-purity niobium indicate that high-Tc A15 nucleation starts from an initial strongly disordered NbGe layer if the formation of Nb precipitates and other phases is suppressed by adding oxygen, directly during initial growth or via substrate precoating with oxidized surface layers. The influence of oxygen (or other suitable impurities) is assumed to reduce the mobility of the constituents, thus preventing their arrangement in stable formations of Nb or Nb5Ge3. Reduced mobility is supposed to be the condition required for formation of the initial disordered structure from which the high-Tc A15 phase grows.