The Formation of Intermediate Oxygen States on Ru(10−10) at High Pressures

Abstract

The reaction of Ru(10−10) with oxygen has been investigated under high-pressure conditions (≤1 bar) with thermal desorption spectroscopy (TDS), low electron energy diffraction (LEED), X-ray photoelectron spectroscopy (XPS), and measurements of the work function changes ΔΦ, derived from ultraviolet photoelectron spectroscopy (UPS). For oxygen exposures between 0.1 and 1000 L, only chemisorption is observed independent of the sample preparation temperature TP (425 K < TP < 750 K). For exposures higher than 1000 L, chemisorption is followed by oxide formation at TP > 525 K. At exposures larger than 1000 L and temperatures below 525 K, the formation of an intermediate oxygen state as a precursor to the actual oxide is observed with XPS and TDS. It is accompanied by a perturbation of the long-range order of the Ru surface structure. Significant changes of the work function, ΔΦ, indicate that a Ru(10−10) surface exposed to oxygen at TP < 525 K resembles properties of a defect-rich Ru(0001) surface. The minimum oxygen exposures required for the formation of oxide as well as the intermediate state are found to be approximately 2 orders of magnitude smaller than on Ru(0001).