Influence of a superimposed film on the electrical conductivity of thin metal films

Abstract

The resistance of thin continuous (100-1000 Å thick) Au, Ag, Cu, and Al films as influenced by super-imposed thin layers of conducting, semiconducting, and insulating materials has been studied. An overlay of SiO or Permalloy increases the resistance of Au films, but has little effect on Ag films. An overlay of Ge increases the resistance of Ag films by about 25%, but has negligible effect on Al films. The resistance of Cu films first increases with the thickness of the Ge and Cr overlay and then decreases rapidly to a saturation value. The changes in the resistance are markedly dependent on the thickness of the overlay; saturation values are obtained for an average thickness of less than 10 Å. Changes are observed for both diffuse and specular films. The observed changes are a function of the ratio of the thickness to the mean free path of conduction electrons and can be explained only by a change in the amount of diffuse scattering at the surface rather than in the specularity parameter. The data suggest that the formation of a new interface modifies the nature of the surface potential making both enhanced as well as reduced scattering of electrons possible and thus an increase or decrease of the resistance can result.