Low temperature oxidation of Fe2+ surface sites on the (2 x 1) reconstructed surface of α-Fe2O3(01(1)over-bar2)

Temperature programmed desorption (TPD), electron energy loss spectroscopy (ELS) and low energy electron diffraction (LEED) were used to study the interaction of molecular oxygen with the (2 x 1) reconstructed surface of hematite alpha-Fe2O3(01 (1) over bar2) under UHV conditions. The (2 x 1) surface is formed from vacuum annealing of the 'ideal' (1 x 1) surface and possesses Fe2+ surface sites based on ELS. While O-2 does not stick to the (1 x 1) surface at 120 K, the amount of O-2 that can be reversibly adsorbed at 120 K on the (2 x 1) surface was estimated to be similar to 0.5 ML (where 1 ML is defined as the Fe3+ surface coverage on the ideal (1 x 1) surface), with additional O-2 that is irreversibly adsorbed based on subsequent H2O TPD. Molecularly and dissociatively adsorbed O-2 modifies the surface chemistry of H2O both in terms of enhanced OH stability (relative to either the (1 x 1) or (2 x 1) surfaces) and in the blocking of H2O adsorption sites. While O-2 adsorption at 120 to 300 K does not transform the (2 x 1) surface into the (1 x 1) surface, the influence of O-2 on the (2 x 1) surface involves both charge transfer from surface Fe2+ sites and formation of an ordered c(2 x 2) structure resulting from O-2 dissociation. (C) 2010 Elsevier B.V. All rights reserved.