Room-temperature epitaxial growth of NiO(111) thin films by pulsed laser deposition

The room-temperature epitaxial growth of NiO(1 1 1) thin films was successfully achieved on alpha-Al2O3(0 0 0 1) substrates using a pulsed laser deposition method. The epitaxial growth mechanism and the effect of oxygen pressure on the film quality were investigated using X-ray diffraction, X-ray pole figure, reflection high-energy electron diffraction and atomic force microscopy. The orientation relationships of the films with respect to the substrates were NiO[1 1 1] parallel to alpha-Al2O3[0 0 0 1], NiO[1 0 (1) over bar] parallel to alpha-Al2O3 [1 0 (1) over bar 0], and NiO[2 (1) over bar (1) over bar ] parallel to alpha-Al2O3[1 1 (2) over bar 0]. The films consisted of a lot of domains and showed sixfold symmetry. These results can be explained by the higher-order epitaxy mechanism enabling the fourfold longer in-plane lattice parameters of NiO(1 1 1) to match the threefold longer parameters of alpha-Al2O3(0 0 0 1) with <4.5% misfit. The crystallinity of the epitaxial films was significantly improved by expanding the in plane lattice parameter. This is due to the relaxation of the lattice misfit between the film and the substrate at the initial growth. (C) 2002 Elsevier Science B.V. All rights reserved.