Abstract
A broad beam (Kaufman) ion source has been used for the ion beam cleaning and oxidation of sputter-deposited Nb films with the aim of producing NbNb 2O 5Pb alloy Josephson junctions. When attempting ion beam cleaning with an Ar + ion beam followed by ion beam oxidation with an Ar +O 2 mixture, suitable Nb 2O 5 barrier layers could not be formed. In situ X-ray photoelectron spectroscopy (XPS) analyses of the surface of the Nb films immediately after ion beam processing have been made as well as in situ secondary ion mass spectroscopy (SIMS) and ion analysis of the beam. It was found that a NbC layer was formed during ion beam etching as a result of C contamination from the graphite grids. This layer prevented the growth of a Nb 2O 5 layer during the ion beam oxidation step. Possible solutions to this problem are considered.
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