The surface metal–insulator transition in MBE magnetite thin films

Abstract

The (1 0 0) and (1 1 1) 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 (1 0 0) 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.