Scanning Tunneling Spectroscopy Study Of The Electronic Structure Of Fe3o4 Surfaces

Scanning tunneling spectroscopy (STS) experiments were performed on the (001) and (111) surfaces of single crystalline magnetite. Room temperature spectra exhibit a similar to 0.2 eV gap around E-f. The importance of perfect surface order to the existence of this gap is illustrated. STS is also carried out on the (111) surface, at 140 and 95 K, just above and below the Verwey transition temperature (T-V similar to 120 K), respectively. It is confirmed that above T-V a similar to 0.2 eV gap exists in the surface density of states (DOS) around E-f. Furthermore, broad bands are resolved on both sides of E-f, with peaks centered on similar to+0.5 eV and similar to-0.45 eV. Below T-V it is shown that the value of the gap in the surface DOS remains similar, however, the peaks resolved in the conduction and valence bands shift markedly away from E-f. The similarity of the gap value before and after the transition points away from an ionic charge ordering occurring at the magnetite surface below T-V. However, the shifting of the bands points to a certain degree of electronic ordering or charge disproportionation playing an integral part in the Verwey transition, at the magnetite surface.