The surface metal-insulator transition in MBE magnetite thin films

The (100) and (111) MBE thin-film surfaces of magnetite have been investigated by low-energy ion scattering (LEIS) in the small-angle geometry and in the temperature range of 85-300 K. Distinct anomalies in the temperature dependence of scattering ion yield R+(T) in the temperature range 100-125 K are attributed to the metal-insulator phase transition of this material. A strong dependence of the R+(T) curve on the primary energy of incoming ions and on the geometrical structure of the surface semi-channels was observed. Three processes are taken into account: the Auger neutralization of ions related to the electron localization at the Verwey transition, the re-ionization of bombarding particles in the zigzag collisions from the topmost atomic rows, and the re-ionization in a collision cascade with the atomic rows lying inside the semi-channel. The latter one plays a more important role in the case of the (100) surface with a larger channel width. The change of the scattered-ion yield with increasing primary energy for both two surfaces is considered as indication of a dominant contribution from the Auger neutralization. (C) 2002 Elsevier Science B.V. All rights reserved.