Epitaxial growth of thin oxide and sulphide films on copper

Abstract

The paper reports an electron-diffraction study of the formation and growth of epitaxial cuprous oxide, cupric oxide and cuprous sulphide films formed by heating copper single crystal, (100), (110) and (111) faces, in air or in the presence of sulphur vapour carried by a stream of oxygen free nitrogen. It has been observed that the initial oxide films formed on copper, at all temperatures and ambient air pressures, consisted of cuprous oxide which grew with parallel orientations on the (110) and (111) faces, while on the (100) face the initial orientation was (111), <110> Cu2O || (100) <100> Cu, at lower temperatures; and (111) <110> + (100) increase in film thickness, the growing crystals changed their orientations relative to the substrate surface. This has been shown to be caused by extensive and multiple twinning. At about 300°C, at atmospheric pressure, cupric oxide was formed over the epitaxially grown cuprous oxide films with its (110) (111) and (111) planes parallel to the (110), (111) and (100) planes of the copper substrate; the orientations with respect to the cuprous oxide films being (110) CuO || (110) Cu2O and (111) CuO (111) Cu2O. The initial sulphide films formed on a copper single crystal (110) face were cubic having an orientation of (211)<111>|| (110)<111> Cu, and having a lattice parameter of a=33.51 A, which may be ascribed to a superstructure form of the cubic copper glance (ao = 5.587 A). With increase in film thickness, this epitaxially grown cubic sulphide film was covered by polycrystallite (CuS). Epitaxial growth is discussed in relation to lattice misfits, and the effects of multiple twinning in crystal growth are discussed in some detail. (Dr. Y.N. Trehan, Scientist, National Metallurgical Laboratory)