Oxygen pressure dependence of the alpha-Fe2O3(0001) surface structure

The dependence of the alpha-Fe2O3(0001) hematite surface structure on ambie nt oxygen gas pressure was investigated with scanning tunneling microscopy and low energy electron diffraction. For this, thin epitaxial alpha-Fe2O3(0 001) films grown onto a Pt(111) substrate were prepared in oxygen partial p ressures between 10(-6) and 1 mbar at temperatures around 830 degrees C. In high pressures of 1 mbar an oxygen-terminated surface structure covers alm ost the whole sample surface. At pressures between 10(-4) and 10(-1) mbar c omparable amounts of oxygen and iron-terminated surface areas coexist in ne ighboring domains. The lateral size of these domains decreases from values of 200-900 Angstrom for pressures between 10(-3) and 10(-1) mbar to values around 30 Angstrom at 10(-4) mbar. At 10(-5) mbar the oxygen-terminated sur face areas completely vanish and an iron-terminated alpha-Fe2O3(0001) surfa ce structure is formed, which is partly covered by disordered patches with lateral sizes of 10-20 A. Further decreasing the oxygen pressure to 10-6 mb ar results in a partial reduction of the surface region and the formation o f coexisting alpha-Fe2O3(0001) and FeO1-x(111) domains that are arranged in an ordered manner forming a superstructure known as 'biphase structure'. ( C) 1999 Elsevier Science B.V. All rights reserved.