Morphological and structural investigation of the early stages of epitaxial growth of alpha-Fe2O3 (0001) on alpha-Al2O3 (0001) by oxygen-plasma-assisted MBE

We have investigated the early stages of alpha-Fe2O3 (0001) film growth on alpha-Al2O3 (0001) using oxygen-plasma-enhanced molecular beam epitaxy alon g with reflection high-energy electron diffraction, non-contact atomic forc e microscopy, and X-ray photoelectron spectroscopy and diffraction. A compr essionally strained, fully stoichiometric alpha-Fe2O3 film three monolayers thick forms prior to the onset of three-dimensional island formation and l attice relaxation. The surface of this film appears to buckle along (<11(2) over bar 0>), giving rise to a new set of inwardly contracted diffraction s pots, which, if not resolved from the substrate spots, could be interpreted as a 12% in-plane lattice parameter expansion. Such an interpretation has led prior investigators to conclude that the interfacial layer consists of a disordered cation layer with an in-plane lattice parameter similar to 6% larger than that of alpha-Fe2Oa3 [T. Fujii, D. Alders, F.C. Voogt, T. Hibma , B.T. Thole, G.A. Sawatzky, Surf. Sci. 366 (1996) 579]. Our interpretation of the diffraction data suggests that the interfacial layer is badly disto rted but commensurate with the substrate. (C) 1999 Elsevier Science B.V. Al l rights reserved.