STRUCTURE OF THE FE2O3-AL2O3 (0001) INTERFACE

Misfit dislocation networks at the Fe2O3-Al2O3 (0001) interface have been characterized using weak-beam imaging in the transmission electron microscope. The heterojunctions were prepared by chemical vapour deposition of alpha-Fe2O3 (haematite) directly on to specially prepared electron-transparent sapphire substrates. The haematite grew epitaxially. Two types of hexagonal dislocation network consisting of firstly b=1/3[1120BAR] edge perfect dislocations and secondly b=1/3[1010BAR] edge partial dislocations were formed at the interface to accommodate the 5.5% lattice misfit. The first type of network has been associated with a normal near-SIGMA=1 orientation of the haematite; the second, with twinned near-SIGMA=3-oriented regions of the haematite film. Faceted double-positioning (lateral twin) boundaries and stacking faults are common defects in the haematite film. The stacking faults emanate from kinks in the substrate surface steps. Models of the interaction between the stacking faults and the misfit dislocation network are presented.