Electric strength of aluminium oxide films

Abstract

FRÖHLICH'S theory of dielectrics predicts an increase in the electric strength as the thickness of the dielectric specimen approaches the electronic mean free path. This prediction has been verified experimentally for certain crystalline materials, such as mica and the alkali halides. Recent work with thin films of amorphous aluminium oxide shows that its electric strength also increases if the film thickness is less than 10-5 cm. The oxide was formed by 'anodic oxidation' of aluminium which had been evaporated in a vacuum on a glass optical flat, the film thickness being measured by means of multiple reflexion fringes. The potential difference across the film was applied through small steel bearings. Some of the results obtained at 290° K. in a vacuum of 10-5 mm. of mercury are as follow: "equation presented" © 1950 Nature Publishing Group.