On the Formation of Very Thin Oxide Films on Metals: Contact Potential Measurements During the Oxidation of Different Crystallographic Faces of Copper

Abstract

The low temperature oxidation of copper is treated in terms of a model in which the surface reaction involving the formation of copper ion vacancies at the gas-oxide interface is rate controlling. The predictions of the model are compared with experimental observations of the change in contact potential difference when clean (100), (110), and (111) copper surfaces are oxidized at room temperature. A value of 0.75±0.03 eV for the activation energy for formation of a copper ion vacancy is derived from the process of fitting experiment to theory. The interpretation of the observed changes in contact potential difference is made in terms of surface states located at the metal-oxide interface and at the gas-oxide interface. A reaction rate anisotropy that is in agreement with the observations of Young, Cathcart, and Gwathmey follows naturally from the model.