STM imaging of MBE-grown pseudomorphic (100) Fe3O4 surfaces reveals te
rrace widths that are typically a few hundred angstroms broad, and can
be as broad as 1000 Angstrom. These terraces are separated by steps t
hat are 1/4 of the spinel lattice constant high, corresponding to the
distance (2.1 Angstrom) between planes of oxygen (or equivalent iron)
atoms. The images show that the p(1 x 1) surface reconstruction is cau
sed by a clustering of atoms in the unit cell. These clusters are alig
ned along a [110] direction, and change direction an alternate terrace
s. The reconstruction is driven by the tetrahedral iron atoms, which h
ave dangling bonds that rotate by 90 degrees from one atomic plane to
the next. Some regions of the surface also show a high-symmetry close-
packed structure with 3 Angstrom spacing between atoms. The presence o
f stacking faults is revealed by the orientation of the unit cells. In
one image, the two possible orientations of the unit cells are presen
t on the same terrace, separated by a disordered band, which must cont
ain a stacking fault. In another case, the unit cells are oriented in
the same direction on two terraces separated by a 2.1 Angstrom step. A
gain a disordered region appears at the boundary between the two terra
ces. Single-domain regions are as large as a few hundred angstroms wid
e, which indicates that the surface diffusion length of the iron atoms
during the initiation of growth on the higher symmetry MgO substrate
is of this same order. (C) 1997 Elsevier Science B.V.