Morphology and stability of chemically modified electrode surfaces without -SH and -SS- structures studied by scanning tunneling microscopy

Abstract The morphology of chemically modified Au(111) substrate was investigated by scanning tunneling microscopy (STM). 4,4′-Bipyridine and 3,3′-thiodipropionic acid were used as surface modifiers. Both molecules formed adlayers although they have no -SH or -SS-groups. In addition, we checked the stability of the modified substrate using STM. In case of 4,4′-bipyridine, the structure was substantially changed when the sample was kept in ethanol for 1 h. It is suggested that the molecules kept a high mobility on the substrate. In case of 3,3′-thiodipropionic acid, on the other hand, no changes were observed after storing in ethanol. Surface plasmon measurements supported the STM data. From these results, we concluded as follows: even if the molecules have no -SH or -SS-group, they can form uniform layers on the gold substrate. However, the stability of the layers depends on the structures of the compounds.