Mass-spectrographic analysis of high-Tc Nb-Ge sputtered films

Abstract
Secondary ion mass spectroscopy (SIMS) has been used to determine the concentration profiles of niobium and germanium in high‐Tc (22 K) Nb‐Ge films which were deposited onto polished sapphire substrates by a low‐energy sputtering technique. X‐ray lattice parameter data on such films indicate that in some cases their average composition is Nb‐rich nonstoichiometric Nb3Ge. The SIMS analysis reveals a nonuniform composition within these sputtered films. The Ge concentration increases with film thickness but at least a portion of the film has the stoichiometric Nb3Ge composition. The occurrence of high critical temperatures in such films is thus still compatible with the hypothesis that the highest Tc’s in the Nb‐Ge system are due to the presence of the stoichiometric or near‐stoichiometric Nb3Ge compound.

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