Structural changes in ZnO/NiO artificial superlattices made by ion beam sputtering

ZnO thin films, NiO thin films and ZnO/NiO artificial superlattices were fabricated on alpha-Al2O3(001) substrates by ion beam sputtering (IBS). Reflection high-energy electron diffraction (RHEED) patterns observed during the depositions indicated that these films were grown epitaxially on the substrates by a two-dimensional layer-by-layer growth. RHEED intensity oscillation was also observed during the deposition. The period of the oscillation corresponded to the deposition of one atomic layer of ZnO or NiO. From the changes in spacing of lattice plane measured on RHEED patterns, it was found that the structure of ZnO on NiO was NaCl-type if the number of ZnO layers was less than 8, but it changed to Wurtzite-type structure with increasing number of ZnO layers. Satellite peaks corresponding to the period of superlattice were observed in X-ray diffraction patterns when the number of ZnO layers was less than 8, which indicated that oxide artificial superlattices could be made by IBS. However, the satellite peaks and an epitaxial relationship between ZnO and NiO were found to disappear when NaCl-type and Wurtzite-type structures were mixed in one superlattice. (C) 1997 Elsevier Science S.A.