CHARACTERIZATION BY AUGER-SPECTROSCOPY OF NIOBIUM ALUMINUM-OXIDE NIOBIUM SANDWICHES FOR JOSEPHSON-JUNCTIONS

Auger electron spectroscopy (AES) combined with ion sputtering was use d to study the chemical composition of Nb-Al2O3-Nb thin film sandwiche s. Attention was focused on the interfaces between the aluminum oxide and the two niobium films, because they are responsible for the electr ical quality of the Josephson junctions based on these sandwiches. The real composition of the analyzed interfaces as a function of thicknes s was reconstructed from the AES signal intensities versus time data t hrough an approximate conversion method. The obtained results show tha t the niobium layers adjacent to these interfaces are less pure than t he rest of the films, due to aluminum and oxygen diffusion: a gradual aluminum diffusion up to 10-20 nm in the base niobium film was found.