On the evolution of copper oxide films grown on α-Al<inf>2</inf>O<inf>3</inf> by pulsed-laser ablation

Pulsed-laser ablation was used to deposit copper oxide onto single-crystal substrates of (0001) α-Al2O3 at temperatures ranging up to 900°C. Prior to deposition, the substrates were chemically cleaned and annealed to create a surface structure of low-index terraces separated by crystallographic steps. After deposition, the samples were characterized using transmission electron microscopy and scanning electron microscopy. The deposited film evolved by an island growth process, with the morphology of the particles being dependent on the growth condition, substrate orientation, and nature of the substrate surface. Both CuO and Cu2O were produced by the depositions. The phase observed changed from CuO to Cu2O with increasing deposition temperature, as would be expected based on the equilibrium phase diagram. In deposition s performed on (0001) alumina substrates with widely spaced surface steps, it was found that on some surface terraces one characteristic particle morphology was produced whereas on others a second morphology was dominant. This suggests that the plane of surface termination in the alumina lattice, which consists of a layer of either Al or O in this orientation, is influencing the growth process.