Study of the Oxides of Copper Formed in Air

Abstract

Oxides of copper formed in air at temperatures between 150°C and 1030°C, and for times of formation up to one hour have been studied. Their composition, structure by electron reflection and rectification - all these as a function of the thickness of the film - have been investigated. At first small crystallites of Cu2O are formed, then they increase in size and get oriented. These crystallites of Cu2O gradually change over to those of CuO showing a three ring pattern, definite orientation and finally a fibrous structure. At high temperatures and appreciable times of formation a layer of Cu2O is formed below the CuO layer. Rectification of CuO films showing orientation and of the composite film Cu2O + CuO has been studied in detail. A plausible mechanism for the formation of the various oxides is suggested. The following special points have been observed: (1) Cu2O changes into CuO, crystallite by crystallite, (2) The three ring pattern is due to oriented monoclinic CuO, (3) CuO oriented shows a small rectification in a direction opposite to that of Cu2O, (4) At high temperatures, when a change of orientation of CuO can occur, a Cu2O film is formed below the CuO film, (5) The composite layer Cu2O + CuO shows a rectification comparable with Cu2O but with a higher voltage response.