Spin-density functional theory was used to investigate various possible structures for the (00•1) haematite surface. It was found that, depending upon the ambient O partial pressure, 2 geometries with (1 x 1) symmetry were particularly stable under thermal equilibrium conditions. One was terminated by Fe, and the other by O. Both of them exhibited enormous surface relaxations. This was -57% in the case of the Fe-terminated surface, and -79% in the case of the O-terminated surface. A large inward relaxation of the first layer of Fe-terminated surface was noted, as well as a huge contraction of the interlayer spacing between the Fe sub-surface layers of the O3-terminated surface. In addition to relaxations along the [00•1] direction, the O layers of both surfaces exhibited a plane rotational reconstruction. This appeared to be the first report of this type of relaxation, and of plane reconstruction of O layers, at a metal oxide surface. Scanning tunnelling microscopy revealed the presence of 2 different surface terminations which coexisted on monocrystalline (00•1) α-Fe2O3 films which had been prepared using an O pressure of 0.001mbar. An unusual electronic structure was predicted for the O3-terminated surface; with a noticeable incidence of states from the sub-surface Fe layer. This resulted in a magnetic polarization of the O.

X.G.Wang, W.Weiss, S.K.Shaikhutdinov, M.Ritter, M.Petersen, F.Wagner, R.Schlögl, M.Scheffler: Physical Review Letters, 1998, 81[5], 1038-41