Study of Cuprous Oxide formed in Air at 0.5 mm of Hg between 200° C and 1030° C and its rectification

Abstract

Oxides of copper formed at an air pressure 0.5 mm of Hg in the temperature range 200° C to 1030° C and for a time of formation of one hour have been studied. Their composition structure by the method of electron diffraction and X-ray reflection, rectification, and magnetic susceptibility — all these as a function of the subsequent heat treatment and the thickness of the film — have been investigated. The films formed at 500° C just begin to show rectification, it becomes appreciable at 800° C and then increases rapidly with the temperature of formation of the film. The rectifying films are all Cu2O films but with a peculiar structure. The appearance of an appreciable amount of rectification is accompanied by changes in the surface structure, body structure and the susceptibility of the films. For a rectifying film the surface layer consists of large Cu2O crystals showing 111 orientation. Below this small crystallites of Cu2O, including an excess of oxygen, and showing a zinc blende structure, are present. The effect of the subsequent heat treatment is to reduce the amount of oxygen and increase the diamagnetic susceptibility. A maximum rectification is obtained, when the Cu2O crystallites are fairly small and contain on an average an excess of one atom of oxygen per crystallite. A plausible mechanism for the changes is suggested.