Plasmon-Induced Charge Separation (PICS) and Plasmonic Nanoantenna Effects: Similarities and Differences

Metal nanoparticles including gold, silver, and copper nanoparticles absorb visible and near infrared light due to localized surface plasmon resonance (LSPR).  We found plasmon-induced charge separation (PICS)^1,2 at the interface between plasmonic metal nanoparticles and semiconductor such as TiO₂ and applied it to photocatalysis,² photovoltaic cells,^2,3 multicolor photochromism,^1,4 infrared photochromism,⁵ single particle multicolor changes,⁶ and photomorphing gells.⁷  PICS is also applied by other groups in particular to photocatalysis^8,9 and photovoltaic cells.^10,11

However, PICS is often confused with plasmonic nanoantenna effects.  Au or Ag nanoparticles assist semiconductors and dye molecules in light absorption by trapping photons based on LSPR.  As a result, nanoparticles enhance photocurrents, photocatalytic reactions, and other photochemical reactions.  The enhancement based on the plasmonic nanoantenna effects occurs at wavelengths at which both of the semiconductor/dye molecule and the metal nanoparticles absorb light.  In addition, the maximum enhancement is reached when the distance between the metal nanoparticle and the semiconductor/dye is about 10 nm.^12-14 The enhancement is suppressed in the case of direct contact.

On the other hand, PICS occurs at LSPR wavelengths even if those are longer than the absorption edge wavelength of the semiconductor.^1-11  PICS is based on direct electron transfer from the resonant metal nanoparticles to semiconductor^2,15due to external photoelectric effect or hot electron injection.  Therefore, it occurs when the metal nanoparticle is in direct contact with the semiconductor, if electron tunneling or hopping is not possible between them. 

In the paper, recent developments related to PICS would also be described.  This work was supported in part by “R&D on Innovative PV Power Generation Technology” which The University of Tokyo contracted with New Energy and Industrial Technology Development Organization (NEDO) and a Grant-in-Aid for Scientific Research (No. 25288063, No. 25107511).

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