Structure of α-Fe2O3 single crystal surfaces following Ar+ ion bombardment and annealing in O2

Abstract

The surface stoichiometry and structure of α-Fe2O3(0001) and (10ovbar|12) natural growth faces has been studied with X-ray photoemission and LEED following room temperature Ar ion bombardment and subsequent annealing in partial pressures of O2 between 400°C and 1000°C. Disordered, oxygen-deficient ion bombardment surfaces were annealed to produce surface structures and stoichiometries approaching the ideal truncation of bulk α-Fe2O3, but only after long, high temperature annealing treatments in 10−6 Torr O2. LEED suggests that a Fe3O4(111) layer initially forms on the (0001) face for annealing temperatures up to 775°C. At higher temperatures, extra diffraction beams are observed which are attributed to multiple scattering across a Fe1−xO(111)/α-Fe2O3(0001) interface. The extra beams disappear after long annealing times at 900°C and are replaced by a (1 × 1) pattern characteristic of α-Fe2O3(0001). On the (10ovbar|12) surface, a (1 × 1) LEED pattern is observed when the surface is annealed in 10−6 Torr O2, but a (1 × 2) reconstruction similar to that observed on the surface of α-Al2O3 is evident in lower O2 partial pressures. The surface phases produced by ion bombardment and annealing treatments are quite different from those predicted by the bulk FeO phase diagram.