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Abstract

The surface structure formed on epitaxial Fe₃O₄(111) magnetite films grown onto Pt(111) was re-examined by a full dynamical low energy electron diffraction (LEED) intensity analysis. Prior to the LEED measurements the films were investigated with scanning tunneling microscopy regarding their surface defect concentrations and the possible coexistence of different surface terminations. 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 surface defect concentrations the best fit structure reveals a Pendry R-factor of 0.20 based on a data set with a total energy range of 1300 eV. It corresponds to an unreconstructed bulk termination of Fe₃O₄(111), which exposes 1/4 monolayer of iron atoms over a hexagonal close-packed oxygen layer underneath. The outermost iron plane is relaxed inward towards the underlying oxygen plane by 41±7% of the corresponding bulk spacing, followed by strong relaxations of the next three interlayer spacings. The same surface termination with slightly different relaxations was obtained in an earlier analysis, which corresponded to a local R-factor minimum in parameter space [W. Weiss et al., Phys. Rev. Lett. 71 (1993) 1848]. The energetics of the Fe₃O₄(111) surface structure is discussed considering the mixed iono-covalent bond character in this oxide.