Plasmoelectric potentials in colloidal Ag and Au nanoparticles

Abstract

The resonant plasmonic properties of metallic nanostructures depend strongly on charge carrier d. While researchers have reported shifts of the resonant absorption frequency of plasmonic nanostructures due to electrostatically induced changes of charge d., the converse -the dependence of charge d. and electrostatic potential on optical absorption- has been largely overlooked. Here, we report a theor. framework and provide exptl. evidence for a 'plasmoelec. effect', a newly described mechanism for generating electrochem. potentials in plasmonic nanostructures via narrowband absorption. A simple thermodn. model shows that, unlike the more familiar thermoelec. or photovoltaic effects, the magnitude and sign of the plasmoelec. potential depends on the frequency difference between the plasmon resonance and incident radiation.We exptl. test our predictions by characterizing the elec. and optical response of colloids of monodisperse Au or Ag nanoparticles spin-cast on ITO films. Scanning Kelvin probe force microscopy (KPFM) dets. the surface potential of device structures while varying the frequency of incident radiation near the plasmon resonance. Under 1000 mW cm^(-2) single-frequency illumination, we measure induced potentials of ± 15 mV from 60 nm Au particles, with a characteristic sign change for illumination blue or red of the particle absorption max. Addnl., power and frequency-dependent increases of optical absorption from samples under monochromatic illumination indicate shifts of the plasmon resonance when compared with the spectral response of samples under white light illumination. We observe clear evidence for the size-dependent and frequency-dependent trends consistent with our theor. framework, providing deeper mechanistic insight and highlighting potential applications of this plasmoelec. effect for optoelectronic and photoelectrochem. power conversion.

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