Pulsed-laser ablation was used to deposit copper oxide onto single-crystal substrates of (0001) OC-AI2O3 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 conditions, 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 depositions 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.
The Cu-Al-O system is of considerable interest for electronic packaging, where thin copper wires are bonded to alumina substrates. In order to optimize the adhesion properties of Cu to alumina, it has been suggested that a ternary bonding environment is necessary at the interface. In comparison to a model oxide system such as NiO/alumina, where NiO is the only stable oxide of Ni and only one phase forms during the reaction, the situation is more complex in the Cu-Al-O system. First, two oxides of copper can form with CuO stable at room temperature and Cu2O stable above 1020°C in air. In addition, two copper aluminate reaction products (CuAl2O4 and CuAlO2) can form in the Cu-Al-O system. In a previous study it was found that both form during reactions in air at 1100°C, with the relative positions of each dependent on the crystallographic orientation of the alumina substrate.
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