The (0 0 1) surface and morphology of thin Fe3O4 layers grown by O2-assisted molecular beam epitaxy

We have investigated the termination and the surface reconstruction of Fe3O4 prepared by oxygen-assisted molecular beam epitaxy on MgO(0 0 1). The epitaxial Fe3O4 layer consists of two structural domains as a result of the fact that its lattice parameter is twice that of MgO. The domains with a lateral size of about 150 nm were observed to be slightly rotated (by an angle of about 1°) around the normal [0 0 1] axis. The surface was investigated with low-energy electron diffraction (LEED) and with low-energy ion scattering (LEIS). We performed 3-D calculations of the ion trajectories in the computer simulations of LEIS, using the program match. The azimuthal scans of scattered and recoiled particles measured in LEIS were compared with computer simulations for many trial structures, including those published in the recent literature. Good agreement was found for a relaxed Fe terminated surface in which every second Fe atom is missing. The topmost layer has an inward relaxation of about 40%. This model explains the symmetry seen in LEED, and it fulfills the criterion of charge neutrality of this polar surface.