Superconducting Properties of Crystalline Films of Aluminum on Silicon

Abstract

For some years the properties of disordered and ultrathin films have been the subject of active investigation (see, e.g., Refs. 1). Until the work reported here there have been, as far as we know, no investigations of superconductivity in well-ordered and well-characterized ultrathin films. Perhaps the most significant feature of the present results is that the transition temperature of the Al films is not very much higher than the bulk value, even down to thicknesses near 30 Å. Films evaporated with more gas have higher T _c ’s and films oxidized by exposure to air also have increased T _c ’s. Another interesting feature of these results is the effect of the initial stages of nucleation on the film properties. Films grown epitaxially have lower R_□ than films that are less crystalline. However, although the higher-resistance films have broader transitions, the T _c ’s are the same. These experiments will be described more fully later.