Optical transmittance and microgravimetric studies of the oxidation of 〈100〉 single crystal films of copper

Thin single crystal copper films have been grown and oxidized on (100) faces of cleaved sodium chloride discs suspended from a vacuum ultramicrobalance. Optical transmittance measurements between 400–800 nm and electron microscopic investigations were also used to characterize the oxidation process. Polycrystalline copper films grown at room temperature are substantially the same as those grown previously on glass substrates. Single crystalline growth at 325 ° C on rock salt produces a characteristic transmittance curve due to the “island” nature of the films. These curves compare favorably with other previously published results. Single crystal copper films oxidized to CuO_0.67 at temperatures of 117–159°C in 100 Torr of oxygen for films less than 500 A thick. For films 378 to 1000 Å thick, compositions of CuO_0.52 to CuO_0.62 were obtained between 123–176°C. The oxidation to less than CuO_0.67 is attributed to the existence of islands in these films which are thicker than the average film thickness, and require higher temperatures or thinner films to permit oxidation to CuO_0.67 before the nucleation of CuO sets in.