Irreversible Change in the NO Adsorption State on Pt(111) under High Pressure Studied by AP-XPS, NEXAFS, and STM

Ambient pressure X-ray photoelectron spectroscopy (AP-XPS) has been applied to the investigation of NO adsorption on Pt(111) under various pressures of NO (up to 1 Torr) at room temperature. Under 10 −7 Torr, molecular NO occupies the most stable fcc-hollow sites and partially occupies the energetically unfavorable atop sites. NO reversibly desorbs from the atop sites after evacuation. At NO pressures higher than 10 −6 Torr, however, irreversible adsorption of atomic oxygen takes place via NO dissociation, leading to the formation of NO+O domains. This result is consistent with near-edge X-ray absorption fine structure (NEXAFS) and scanning tunneling microscopy (STM) results.