Structural aspects of tunnel‐junction coupled granular lead films

Granular lead films were deposited using the technique of reactive ion beam sputtering of a lead target with argon ions in the presence of an oxygen background. The superconducting properties of these films reveal that the primary means of electron transport is by tunneling across insulating lead oxide barriers separating clusters of lead grains. Results of x‐ray and TEM studies confirm this interpretation and show that the films consist of randomly‐oriented lead grains, less than 500 A in diameter, embedded in an insulating matrix which contains at least two identifiable oxides of lead. These unique structural properties are most likely responsible for the excellent mechanical and electrical stability observed for these films.