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 Ag 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 at 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, in 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 NO3
2- anion) returning to the
electrode.