Carbonate on Ag(1 1 0): a complex system clarified by STM

In the present work we have used scanning tunneling microscopy (STM) in conjunction with temperature programmed reaction spectroscopy (TPRS) to study the formation of surface carbonate on Ag(1 1 0) by the reaction of CO2 with atomic oxygen. Recently, we have found and reported that the STM images attributed previously to carbonate are actually due to chemisorbed CO2. STM images reported here reveal that the surface carbonate species on Ag(1 1 0) has a very different appearance from chemisorbed CO2. Chemisorbed CO2 appears as round protrusions, whereas carbonate forms thick rods along the [1 1̄ 0] direction consisting of double or single chains. An adsorption structure model consistent with the STM observation and the (1×2) reconstruction is suggested. Images recorded at various oxygen coverages show that the carbonate rods form between the –Ag–O– rows and accumulate near step edges. In situ STM imaging during carbonate formation demonstrates that the reaction may initiate at the end or from the side of the –Ag–O– rows. The reaction progresses along the rows.