Weak thermal reduction of biphase Fe₂O₃(0001) films grown on Pt(111): Sub-surface Fe²⁺ formation

The initial thermal reduction of biphase Fe2O3(0001) films grown on Pt(111) has been studied with HREELS, LEED, TDS, and synchrotron-based valence band photoelectron spectroscopy. Ab initio calculations of the electronic excitation energies of Fe2+ and Fe3+ ions in different oxidic environments were carried out to support the experimental studies. Annealing the biphase Fe2O3(0001) at 1000 K results in the desorption of oxygen and a concomitant significant change of the electronic excitation spectra measured with HREELS. On the other hand, studies employing more surface sensitive methods like LEED, vibrational spectroscopy of adsorbates, and surface-sensitive valence band photoelectron spectroscopy reveal barely any changes induced by the desorption of oxygen. Based on these experimental findings we propose that the thermal reduction of biphase Fe2O3(0001) occurs mostly below the surface under the chosen conditions