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Abstract

The dependence of the α-Fe₂O₃(0001) hematite surface structure on ambient oxygen gas pressure was investigated with scanning tunneling microscopy and low energy electron diffraction. For this, thin epitaxial α-Fe₂O₃(0001) films grown onto a Pt(111) substrate were prepared in oxygen partial pressures between 10⁻⁶ and 1 mbar at temperatures around 830°C. In high pressures of 1 mbar an oxygen-terminated surface structure covers almost the whole sample surface. At pressures between 10⁻⁴ and 10⁻¹ mbar comparable amounts of oxygen and iron-terminated surface areas coexist in neighboring domains. The lateral size of these domains decreases from values of 200–900 Å for pressures between 10⁻³ and 10⁻¹ mbar to values around 30 Å at 10⁻⁴ mbar. At 10⁻⁵ mbar the oxygen-terminated surface areas completely vanish and an iron-terminated α-Fe₂O₃(0001) surface structure is formed, which is partly covered by disordered patches with lateral sizes of 10–20 Å. Further decreasing the oxygen pressure to 10⁻⁶ mbar results in a partial reduction of the surface region and the formation of coexisting α-Fe₂O₃(0001) and FeO_1−x(111) domains that are arranged in an ordered manner forming a superstructure known as ‘biphase structure’.