Time-dependent measurement of plasmon-induced charge separation on a gold nanoparticle/TiO2 interface by electrostatic force microscopy

Abstract

Plasmon-induced charge separation (PICS) is an efficient way to use the hot carriers generated by localized surface plasmon resonance. Although the ultrafast dynamics of hot carrier generation and annihilation itself are well understood, the slow dynamics of PICS are not, despite their importance for the use of hot carriers in chemical reactions. In this work, we directly observed the slow dynamics of PICS on an Au nanoparticle (NP)/TiO2 interface by using electrostatic force microscopy with time-resolved measurements obtained by sideband signal of frequency shift. The change in contact potential difference induced by PICS had a bias voltage dependence, indicating that the number of holes in the Au NPs ([{mathrm{h}}_{mathrm{AuNP}}^{+}]) accumulated by laser irradiation depended on bias voltage. The decay constant for the annihilation of the separated charge on the Au NPs at the Au NP/TiO2 interface was directly determined to be ca. 150 ms, and the annihilation process was discussed in a simple model based on the transient Schottky barrier.