  We report on the structural properties of epitaxial FeO layers grown by
molecular beam epitaxy on MgO(111). The successful stabilization of polar FeO
films as thick as 16 monolayers (ML), obtained by deposition and subsequent
oxidation of single Fe layers, is presented. FeO/MgO(111) thin films were
chemically and structurally characterized using low-energy electron
diffraction, Auger electron spectroscopy and conversion electron Mossbauer
spectroscopy (CEMS). Detailed in situ CEMS measurements as a function of the
film thickness demonstrated a size-effect-induced evolution of the hyperfine
parameters, with the thickest film exhibiting the bulk-wustite hyperfine
pattern. Ex situ CEMS investigation confirmed the magnetic ordering of the
wustite thin film phase at liquid nitrogen temperature.
