Fe3O4(111) surface structure determined by LEED crystallography

The surface structure formed on epitaxial Fe3O4(111) magnetite films grown onto Pt(111) was re-examined by a full dynamical low energy electron diffra ction (LEED) intensity analysis. Prior to the LEED measurements the films w ere investigated with scanning tunneling microscopy regarding their surface defect concentrations and the possible coexistence of different surface te rminations. After a final oxidation at 1000 K in 10(-6) mbar oxygen partial pressure one defined surface structure is formed, and for films with low s urface defect concentrations the best fit structure reveals a Pendry R-fact or of 0.20 based on a data set with a total energy range of 1300 eV. It cor responds to an unreconstructed bulk termination of Fe3O4(111), which expose s 1/4 monolayer of iron atoms over a hexagonal close-packed oxygen layer un derneath. The outermost iron plane is relaxed inward towards the underlying oxygen plane by 41 +/- 7% of the corresponding bulk spacing, followed by s trong relaxations of the next three interlayer spacings. The same surface t ermination with slightly different relaxations was obtained in an earlier a nalysis, which corresponded to a local R-factor minimum in parameter space [W. Weiss et al., Phys. Rev. Lett. 71 (1993) L548]. The energetics of the F e3O4(111) surface structure is discussed considering the mixed iono-covalen t bond character in this oxide. (C) 1999 Elsevier Science B.V. All rights r eserved.