A theory of the irreversible electrical resistance changes of metallic films evaporated in vacuum

Abstract

Metallic films prepared by evaporation show characteristic irreversible changes, especially if prepared at low temperatures. The changes can be explained by a decay of lattice distortions. To allow of a mathematical treatment, a set of simplifying assumptions is formulated. To initiate a decomposition of a distortion, a certain energy must be reached, but the observed changes cannot be explained if all distortions have the same decay energy. A characteristic function F₀ expressing the law of distribution of the decay energies is formulated, calculated from measurements available and found to be of the expected order. The shape of this function and the position of its maxima depend on the structure of the support and on the thickness of the film. The resistance measurement at a constant temperature has the disadvantage that it reveals only a small part of F₀. This is overcome if uniformly rising temperature is used. A possibility that the changes are caused by a recombination of interstitial atoms and lattice vacancies is investigated, but as this requires essentially only a single value of the transition energy, the results are inconsistent with the observed changes, so that the decay theory should be preferred, as it gives more consistent results.