Ordered Array of Single Adatoms with Remarkable Thermal Stability: Au / Fe₃O₄(001)

Abstract

Gold deposited on the Fe₃O₄(001) surface at room temperature was studied using scanning tunneling microscopy (STM) and x-ray photoelectron spectroscopy (XPS). This surface forms a (√2 × √2)R45° reconstruction, where pairs of Fe and neighboring O ions are slightly displaced laterally producing undulating rows with ‘‘narrow’’ and ‘‘wide’’ hollow sites. At low coverages, single Au adatoms adsorb exclusively at the narrow sites, with no significant sintering up to annealing temperatures of 400 °C. We propose the strong site preference to be related to charge and orbital ordering within the first subsurface layer of Fe₃O₄(001)-(√2 × √2)R45°. Because of its high thermal stability, this could prove an ideal model system for probing the chemical reactivity of single atomic species.