A.C. effects in asymmetric discontinuous metal films

Abstract

Although the thermally activated electrical conduction mechanism in discontinuous metal island films on insulating substrates has been studied for many years, it still defies resolution at a detailed quantitative level. There is widespread (but not unanimous) agreement that the basic mechanism is by interisland tunneling, that the activation energy has electrostatic origins, and that percolation processes must be involved, although no simple percolation formalism has yet passed external criticism. The observatioh of strongly polarity-dependent resistances in asymmetrically deposited films suggests that the contact regions dominate film properties and a.c. measurements were performed to verify this model. The results support the concept fully, but at extreme asymmetries a pseudo-inductive effect develops, which leads to an extension of the basic model to include time-dependent space charge effects. With independent verification, this would be the first advance in the basic conduction model in over ten years.