Plasmon-induced charge separation (PICS)^1-3 involves electron transfer from plasmonic nanoparticles of Au, Ag, or Cu to a semiconductor such as TiO₂.^1-4 PICS of Ag-TiO₂ systems often involve oxidation of Ag to Ag⁺,⁵ and that this reaction occurs preferentially at resonance sites, at which optical near fields are localized.^6-8 This cannot be ascribed to thermal acceleration of reaction,⁹ but can be explained in terms of ejection of energetic holes from the nanoparticles as Ag⁺ ions.

This hole ejection has been investigated further for Au nanocubes on TiO₂ by using other reactions; Pb²⁺ oxidation to PbO₂ and pyrrole oxidation to polypyrrole. Au nanocubes on TiO₂ show distal mode, in which electron oscillation is localized at the top face of the nanocube, and proximal mode, in which electron oscillation is localized at the bottom face. In the case of Pb²⁺ oxidation, PICS for the distal mode and proximal mode resulted in PbO₂ deposition at around the top face and the bottom face, respectively.¹⁰ However, in the case of pyrrole oxidation, both of the distal mode PICS and proximal mode PICS resulted in polypyrrole deposition at the whole surface of the nanocube.

On the basis of those results, we conclude that the localized oxidation and the delocalized oxidation are ascribed to energetic hole ejection mechanism and positive charge accumulation mechanism, respectively. We have applied energetic hole ejection to fabrication of chiral plasmonic nanostructures¹¹ and near IR photovoltaics.¹²

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