Some oxide surfaces of high structural quality can be epitaxially grown on atomically clean and well ordered metal single crystals by reactive deposition, e.g. MnO/Ag(100) [1,2]. However, the synthesis of iron oxide films with a single crystallographic phase presents a challenge in surface science. FeO, which has the NaCl crystal structure and only the Fe2+ valence state, can be well characterized by LEED, XPS, and as well by Conversion Electron Mössbauer Spectroscopy (CEMS). We have succeeded on growing and characterizing the electronic and surface structure of well ordered FeO(100) and FeO(111) ultra-thin films. Growths have been carried out under ultrahigh vacuum conditions by electron-beam evaporation of 57Fe onto atomically clean and well ordered Ag(100) and Ag(111) surfaces. By varying the oxygen background pressure during in situ oxidation process and the substrates temperature during and after growth, the best conditions to obtain the monoxide films were established. Photoelectron spectroscopy (XPS) was performed on both systems in order to characterize iron oxide films with respect to the chemical states and composition - a temperature induced phase transition, the Fe3O4 → FeO reductions process, was identified. Besides the paramagnetic phase, the antiferromoagnetic phase of FeO films was characterized by low temperature Mössbauer (CEMS) spectra. Qualitative and quantitative electron diffraction (LEED) analysis was performed on both systems. The FeO(100) has an almost bulk termination structure with a very small rumple on the first layer, which agrees with the structure found in other studies carried out on the (0 0 1) surface of oxides that have rock-salt structure. The FeO(111) is as well almost bulk terminated, presenting small relaxations on the first atomic layers.
[1] F. Müller, R. de Masi, D. Reinicke, P. Steiner, S. Hüfner and K. Stöwe, Surf. Sci. 520, 172 (2002).
[2] E. A. Soares, R. Paniago, V. E. de Carvalho, E. L. Lopes, G. J. P. Abreu, and H.-D. Pfannes, Phys. Rev. B 73, 035419 (2006).
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