The reduction of copper oxide thin films with hydrogen plasma generated by an atmospheric-pressure glow discharge

The reduction of copper oxide thin films by a hydrogen plasma generated by an atmospheric-pressure glow (APG) discharge was investigated. The copper oxide films were prepared by heating the sputtered copper films to 150 degrees C in the air (heat-formed copper oxide) or by sputtering (sputtered copper oxide). Both films were composed of Cu2O. The reduction occurs first on the surface, then the Cu/Cu2O interface gradually shifts from the surface into the inner region and finally the whole layer is reduced to metallic copper. This process is approximately explained by assuming that the diffusion of the atomic hydrogen in the reduced layer is the rate-deyermining step. By transmission electron microscopic (TEM) observation, a layer of 3-5 nm thickness composed of many Cu2O microcrystals was observed along the surface of the heat-formed copper oxide. After the APG hydrogen plasma treatment, the crystal Cu2O layer disappeared and the crystalline lattice was re-arranged to form large crystal Cu grains.