Growth mechanisms of mixed oxides on alumina

In this paper the growth mechanisms of mixed oxides on alumina are examined. Two combinations of both LaCeCuO/alumina and MgMnCoO/alumina were processed by the atomic layer epitaxy (ALE) technique by carrying out from five to nine reaction cycles. Each cycle of growth consisted of the reaction sequences of the corresponding metal beta-diketonate and air. The layer-by-layer growth was followed by element determinations and FTIR spectroscopy. X-ray diffraction (XRD), scanning electron microscopy with elemental mapping (SEM-EDS) and surface area measurements were carried out on the mixed oxides after the growth was completed. It was shown that mixed oxides can be processed on alumina in a reproducible fashion by ALE using the metal beta-diketonates as precursors. Owing to the high alumina surface area, a submonolayer of atoms bound on a surface could be precisely determined and the growth rate followed stepwise after each reaction sequence. In addition, during the growth, the stability and also the tendency of the metal beta-diketonates to etch the oxide layers could be evaluated. Although etching played an important role in the growth, it was also found to be reproducible. On the whole, it is suggested that the growth on high surface area materials can be used as a tool to deepen our understanding of the growth mechanisms involved in ALE.