STRUCTURE OF METAL ELECTROLYTE INTERFACES - COPPER ON GOLD(111), WATER ON SILVER(111)

Two examples are presented of the application of in situ structure and composition sensitive techniques to elucidating the nature of the ele ctrode-electrolyte interface. One case is the underpotentially deposit ed submonolayer of Cu on Au(111). Despite extensive electrochemical, L EED, RHEED, STM, AFM, and EXAFS investigations, the structure of the c opper adlayer is still controversial. In situ surface EXAFS, surface X -ray scattering, and quartz crystal microbalance (QCM) data lead to th e conclusion that the adlayer adopts a (root 3 x root 3)R30 degrees he xagonal honeycomb arrangement of Cu atoms in which the Cu coverage is 2/3 and the sulfate coverage 1/3. The other case is the structure of w ater at the Ag(111)-aqueous sodium fluoride interface. Analysis of X-r ay scattering shows that the interfacial water molecules exhibit poten tial dependent layering and reorientation and a markedly increased den sity (twice bulk water) in the inner layer.