Ion scattering and Auger electron spectrometry of superconducting ’’Nb3Ge’’ sputtered films

Abstract

Low‐energy ion scattering spectrometry (ISS) in conjunction with Auger electron spectrometry (AES) has been applied to the analysis of a series of superconducting ’’Nb₃Ge’’ thin films deposited on alumina substrates by rf sputtering. ISS was used to determine the Nb/Ge ratio as a function of depth, while AES in combination with ISS was used to determine the impurities. No gradients in composition with depth were observed except in a thin (∼13% of the film thickness) niobium‐deficient region near the film‐alumina interface. The applicability of ISS to quantitative measurements of the Nb/Ge ratio was shown by comparing the variation of this ratio with lattice parameter a₀ with a similar analysis performed on the same samples using electron microprobe (EMP) measurements on the Nb and Ge composition. Comparison of the Nb/Ge ratio determined by ISS with EMP data showed that no preferential sputtering of Ge from the films occurred during neon ion bombardment. The variation of T_c with the Nb/Ge ratios determined by ISS and EMP supports the idea that for ’’Nb₃Ge’’, T_c increases as the composition approaches the stoichiometric ratio of 3:1.