Epitaxial (111) oxide films were grown onto Pt (111) substrates by repeated cycles of Fe deposition and oxidation in 10-6mbar of O. A previous low-energy electron diffraction intensity analysis had revealed a ¼-monolayer of Fe atoms over a close-packed O layer. By using scanning tunnelling microscopy, an hexagonal lattice of protrusions with an 0.6nm periodicity was observed. The protrusions were attributed to the uppermost Fe atoms, and agreed with the predominant Fe 3d electron density of states near to the Fermi-level which was related to these surface atoms; as revealed by ab initio spin-density functional theory calculations. The most abundant type of point defect which was observed by scanning tunnelling microscopy was an Fe vacancy in the topmost layer. This was confirmed by low-energy electron diffraction intensity calculations in which various types of vacancy defect were simulated. For oxidation temperatures of about 870K, the usual oxide (111) surface coexisted with several different surface structures which covered about 5% of the films. This exposed a ¾-monolayer of Fe atoms, or close-packed Fe and O layers, and resulted in surface domains that were of the forms: FeO (111) and Fe3O4 (111). These domains were arranged periodically on the surface and formed ordered bi-phase superstructures. At an oxidation temperature of 1000K, they vanished and only the normal Fe3O4 (111) surface remained.

Defect Structures on Epitaxial Fe3O4(111) Films. S.K.Shaikhutdinov, M.Ritter, X.G.Wang, H.Over, W.Weiss: Physical Review B, 1999, 60[15], 11062-9