Adatom Fe(III) on the hematite surface: Observation of a key reactive surface species

Carrick M Eggleston¹ , Andrew G Stack² , Kevin M Rosso³ and Angela M Bice⁴

¹Department of Geology and Geophysics, University of Wyoming, Laramie, Wyoming 82071-3006

²Department of Land, Air and Water Resources, University of California, Davis, California 95616

³William R. Wiley Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, P.O. Box 999, MSIN K8-96, Richland, Washington 99352

⁴Department of Geology and Geophysics, University of Wyoming, Laramie, Wyoming 82071-3006

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Geochemical Transactions 2004, 5:33doi:10.1186/1467-4866-5-33


Published:	30 June 2004

Abstract

The reactivity of a mineral surface is determined by the variety and population of different types of surface sites (e.g., step, kink, adatom, and defect sites). The concept of "adsorbed nutrient" has been built into crystal growth theories, and many other studies of mineral surface reactivity appeal to ill-defined "active sites." Despite their theoretical importance, there has been little direct experimental or analytical investigation of the structure and properties of such species. Here, we use ex-situ and in-situ scanning tunneling microcopy (STM) combined with calculated images based on a resonant tunneling model to show that observed nonperiodic protrusions and depressions on the hematite (001) surface can be explained as Fe in an adsorbed or adatom state occupying sites different from those that result from simple termination of the bulk mineral. The number of such sites varies with sample preparation history, consistent with their removal from the surface in low pH solutions.