Effect of halide ion adsorption upon plasmon-mediated photoelectron emission at the silver/solution interface

The effect of the roughening of the silver surface upon photoemission observed in the presence of two different scavengers dissolved in an aqueous solution, CO2 and NO3- ions, was re-examined. The quantum yield of the photocurrent exhibits a sharp maximum at 370-380 nm in the frequency range of surface plasmons on silver. These photoyields were strongly affected by the extent of the roughening of the AE surface and reached an unusually large value of 0.05 electron per incident photon. Electrochemical oxidation/reduction roughening performed in the presence of Cl-, Br-, and ClO4- ions, similar to that employed in enhanced Raman scattering (SERS) experiments, affected the maximum of the photocurrent and in some cases also its onset potential, Photocurrents arising al potentials more negative than the potential of zero charge (pzc) of silver were principally influenced by changing morphology of the surface resulting from more or less deep roughening performed in different solutions. On the other hand, the photoelectrochemical behavior of silver at potentials positive with respect to the pzc was clearly affected by the specific adsorption of anions of the supporting electrolyte, It was, Ln particular, the Br- anion that caused in this potential region the strongest enhancement of the photocurrent, associated with the reduction of scavengers and led to an apparent positive shift of the onset potential. The role played by the specifically adsorbed anions is interpreted in terms of slowing down the reverse reactions of solvated electrons and of reaction intermediates (such as, for example, the NO32- anion) returning to the electrode.