The nature of copper in thin films of copper iodide grown by laser-assisted molecular beam deposition: comparative ESCA and EDXS studies

Thin molecular films of copper iodide have been grown by direct chemical reaction within a molecular beam using laser-assisted molecular beam deposition. Molecular iodine vapour entrained in a helium carrier gas stream was supersonically expanded into the laser-ablated plasma plume of vaporized copper, producing copper iodide. Films of this material were grown on substrates situated in the path of this molecular beam. The oxidation state of copper and the chemical composition of these films were studied by electron spectroscopy for chemical analysis and energy-dispersive X-ray spectroscopy, and, the results were compared with those of a high-purity Cul powder. The binding energy of the Cu 2p_3/2 photoelectron line and the kinetic energy of the X-ray-induced Cu L₃M_4.5M_4.5 Auger line are determined to be the same for both samples. The surface morphology and extent of surface inhomogeneities in copper iodide films were found to be largely dependent on the fluence of the incident laser and the expansion conditions. Secondary electron images of these films indicate clustering of copper iodide on the surface of the films during film growth. The copper in these films is found to be in the Cu⁺ ionization state.