Films of α-Fe2O3(00•1) with a thickness of about 7nm or 70nm were grown epitaxially onto α-Al2O3(00•1) by O plasma-assisted molecular beam epitaxy. The interfaces were characterized by using high-resolution transmission electron microscopy, electron energy-loss spectroscopy, and X-ray diffraction. The interface exhibited coherent regions separated by equally-spaced misfit dislocations. When imaged from the [¯21•0] direction, the dislocation spacing was 7.0nm for the 70nm-thick specimen, and 7.2nm for the 7nm-thick specimen. When imaged from the [01•0] direction, the dislocation spacing was 4.5nm for the 7nm-thick specimen. The experimentally observed dislocation spacings were approximately consistent with those calculated from the lattice mismatch between α-Al2O3 and α-Fe2O3, implying that the lattice mismatch was accommodated mainly by interface misfit dislocations above the critical thickness, which was less than 7nm. This conclusion was also corroborated by the measured residual strain of about 0.5% determined from X-ray diffraction for the 70nm film. Electron energy-loss spectroscopy analysis reveals that the Fe L2,3-edge showed no measurable chemical shift relative to the L2,3-edge of structural Fe+3, indicating complete oxidation of Fe in the as-grown film.

The Characteristics of Interface Misfit Dislocations for Epitaxial α-Fe2O3 on α-Al2O3(0001). C.M.Wang, S.Thevuthasan, F.Gao, D.E.McCready, S.A.Chambers: Thin Solid Films, 2002, 414[1], 31-8