Influence of the nature of the (0001) alumina surface on thin film growth

The bulk lattice of alpha-alumina can, in principle, be terminated parallel to the (0001) plane in different ways. The influence of the different structures of this surface on the overgrowth of thin films has been investigated using transmission electron microscopy and scanning electron microscopy. Results are presented for the cases of pulsed-laser deposited NiO, Cu2O and TiO2 films. Growth of NiO produces continuous films consisting of two twin-related variants irrespective of the surface termination; observations show both variants grow on the same (0001) terraces and cross to adjacent terraces. For depositions of Cu2O, the size and morphology of copper oxide islands that evolved showed two distinct variants depending on the surface terrace on which they grew. In the growth of TiO2, an additional phase was found to nucleate on one set of terraces. These observations can be understood if the film-growth process is influenced by the lattice termination at the (0001) alumina surface; conversely, they also confirm that the termination can indeed occur at distinctly different points within the unit cell. (C) 1997 Elsevier Science B.V.