Scanning tunneling microscopy (STM) study of benzene and its coadsorption with carbon monoxide on Rh(111)

The surface structures of benzene and coadsorbed benzene/carbon monoxide on a Rh(lll) surface have been studied using scanning tunneling microscopy (STM). Benzene does not form a well-ordered overlayer on Rh(111), even at saturation coverage. When the coverage is approximate to 0.5 monolayer, only the benzene molecules at the top side of the step edges were imaged, while those on the terraces could not be detected by the STM owing to rapid diffusion. Coadsorption of carbon monoxide decreased the mobility of benzene which could then be imaged by STM. It was also found that carbon monoxide enhanced the surface ordering by formation of coadsorbed benzene/CO overlayers. The attractive interaction between benzene and carbon monoxide on Rh(111) surface contributes to the inhibition of the benzene diffusion and the enhancement of the surface overlayer ordering. (C) 1997 Elsevier Science B.V.