COMBINED SCANNING FORCE MICROSCOPY AND ELECTROCHEMICAL QUARTZ MICROBALANCE IN-SITU INVESTIGATION OF SPECIFIC ADSORPTION AND PHASE-CHANGE PROCESSES AT THE SILVER HALOGENIDE INTERFACE/

Specific adsorption of halogenides and silver halogenide phase formati on was investigated by the combination of electrochemical quartz micro balance measurements (EQMB), topographical in-situ scanning force micr oscopy (SFM), and in-situ lateral force microscopy (LFM). In-situ LFM can be employed to monitor specific adsorption and, more generally, ch emical conversion reactions in submonolayers of atomic species which a re inaccessible to topological imaging by SFM. Reorganization of the e lectrochemical double layer during specific adsorption caused nanotrib ological changes. Hydrated anions in the outer Helmholtz plain are not locally bonded to a specific site and give low LFM friction values. S pecifically adsorbed anions and ion pairs, on the other hand, impede t he lateral cantilever translation, resulting in increased friction: EQ MB measurements yielded data corresponding to the formation of up to o ne monolayer of specifically adsorbed cation-halogenide ion pairs. Ano dic dissolution of silver to AgO- and the formation of Ag2O islands in a halogenide-free alkaline solution contributed to a roughening of th e surface. Long range in-situ SFM showed that silver halogenide phases are anodically nonuniformly formed as smooth islands located in no ob servable correspondence to grain surfaces or boundaries suggesting a d issolution-precipitation growth mechanism. AgI and AgBr phases can alm ost reversibly be reduced. Irreversible mass gains after an oxidation- reduction cycle can be associated with Ag deposition near surface step s from soluble AgIn+1n- and AgBrn+1n- species which were dissolved int o the electrolyte bulk during previous anodic scans in the dissolution potential range. In the presence of chloride, the silver surface is v igorously electropolished and soluble AgCln+1n-, species evolve, while AgCl islands precipitate on the newly generated surface regardless of the original silver grain topography.