Adsorption and Surface Reaction of NO2 on a Stepped Au(997) Surface: Enhanced Reactivity of Low-Coordinated Au Atoms

Abstract

The adsorption and surface reaction of NO2 on a stepped Au(997) surface were investigated by temperature-programmed desorption, X-ray photoelectron spectroscopy, and ultraviolet photoelectron spectroscopy. At low NO2 exposures, NO2 chemisorbs molecularly and reversibly on the Au(997) surface at 130 K, but low-coordinated Au atoms on the (111) step sites exhibit enhanced reactivity. NO2(a) chemisorbed on the (111) step sites is thermally more stable than that chemisorbed on the (111) terrace sites. At large NO2 exposures, an amorphous physisorbed N2O4 multilayer forms at 130 K. Subsequent heating causes the isomerization of the physisorbed N2O4 multilayer (O2N–NO2) to nitrite–N2O4 (ONO–NO2) and the subsequent transformation of nitrite–N2O4 into nitrosonium nitrate (NO+NO3–) that further decomposes into NO(g) and NO2(g) at elevated temperatures, forming O(a) on the surface. These surface reactions could be utilized to prepare oxygen adatoms on inert Au surfaces under ultrahigh vacuum conditions. Our results broaden the fundamental understanding of the interaction between small molecules and Au surfaces.