Surface metal-insulator phase transition of a single crystalline magnetite(001)

The single crystalline Fe3O4 (0 0 1) surface has been investigated by, using a low-energy ion scattering (LEIS) in the temperature range of 85-300 K. An Ar+ ion beam with primary energies of 4-8 keV was used. Two distinguished peaks in the LEIS spectra were attributed to the Ar+-Fe scattering and the Fe-recoil atoms. An enormous increase of the Ar+-Fe peak-intensity and an enhanced influence from the azimuthal angle on the Fe-recoil peak were found at low temperature. In the metal-insulator phase transition region, the temperature-dependent curve of the scattering ion yield, R+(T), have revealed two step-like increases. The first step-rise was always found at 138 K. The second step-rise was found at 123 K under 5 ke-V Ar+ ion bombardment, which moved to lower temperature with increasing primary energies implying a widening of the plateau between two steps. The characteristics of the R+(T) curves were explained as a complex interplay between dominant Auger and resonant neutralizations related to the change in the electronic state in the octahedral-Fe sites and the re-ionization of neutralized particles in a collision with atoms in the deeper layers than the surface layer. The later one was influenced largely by the change in the crystal transparency of magnetite at the phase transition. (C) 2003 Elsevier B.V. All rights reserved.