Adsorption of oxygen and carbon dioxide on cesium-reconstructed Ag(1 1 0) surface

Abstract

The adsorption of oxygen and carbon dioxide on cesium-reconstructed Ag(1 1 0) surface has been studied with scanning tunneling microscopy (STM) and temperature programmed desorption (TPD). At 0.1 ML Cs coverage the whole surface exhibits a mixture of (1 × 2) and (1 × 3) reconstructed structures, indicating that Cs atoms exert a cooperative effect on the surface structures. Real-time STM observation shows that silver atoms on the Cs-covered surface are highly mobile on the nanometer scale at 300 K. The Cs-reconstructed Ag(1 1 0) surface alters the structure formed by dissociative adsorption of oxygen from p(2 × 1) or c(6 × 2) to a p(3 × 5) structure which incorporates 1/3 ML Ag atoms, resulting in the formation of nanometer-sized (10–20 nm) islands. The Cs-induced reconstruction facilitates the adsorption of CO 2, which does not adsorb on unreconstructed, clean Ag(1 1 0). CO 2 adsorption leads to the formation of locally ordered (2 × 1) structures and linear (2 × 2) structures distributed inhomogeneously on the surface. Adsorbed CO 2 desorbs from the Cs-covered surface without accompanied O 2 desorption, ruling out carbonate as an intermediate. As a possible alternative, an oxalate-type surface complex [OOC–COO] is suggested, supported by the occurrence of extensive isotope exchange between oxygen atoms among CO 2(a). Direct interaction between CO 2 and Cs may become significant at higher Cs coverage (>0.3 ML).