The chemistry of hematite {001} surfaces

Natural hematite {001} surfaces, exposed by fracturing large specular samples, were characterized us ing a number of spectroscopic, microscopic, and diffraction methods: X-ray Photoelectron Spectroscopy (XPS), Scanning Force Microscopy (SFM), Scanning Electron Microscopy(SEM), X-ray Diffraction (XRD), and Low-Energy Electron Diffraction (LEED). It was found that the {001} fracture surface represents a terminated growth face, which in all cases is contaminated with adventitious material and/or secondary phases. The contamination is due to air and aqueous solution infiltration along grain boundaries. Exposure experiments, designed to test the stability of hematite surfaces with respect to hydrated phases (particularly goethite),were conducted under N-2 air, humid air, and deionized water for up to three months. Hematite was found to be relatively inert in these exposure experiments, with the exception of the accumulation of adventitious carbon and oxygen. In no instance was goethite observed to form at the expense of hematite, even on the top few monolayers of the sample.