PNNL

Abstract

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 (2x1) reconstructed surface of hematite a-Fe2O3(011bar2) under UHV conditions. The (2x1) surface is formed from vacuum annealing of the ‘ideal’ (1x1) surface and likely possesses Fe2+ surface sites. While O2 does not stick to the (1x1) surface at 120 K and high temperature, the amount of O2 adsorbed at 120 K on the (1x2) surface that can be recovered in TPD was estimated to be ~0.5 ML, with additional O2 irreversibly adsorbed based on subsequent H2O TPD. Molecularly and dissociatively adsorbed O2 is seen to modify the surface chemistry of H2O both in the form of stabilized OH groups and blocking of H2O adsorption sites. While O2 adsorption at low temperature does not transform the (2x1) surface into the (1x1) surface, the influence of O2 on the (2x1) surface involves both charge transfer from surface Fe2+ sites and formation of an ordered c(2x2) structure resulting from O2 dissociation.