Plasmon-induced electron-hole separation at metal-semiconductor interfaces is an essential step in photovoltaics, photochemistry, and optoelectronics. Despite its importance in fundamental understandings and technological applications, the mechanism and dynamics of the charge separation under plasmon excitations have not been well understood. Here, the plasmon-induced charge separation between a Ag20 nanocluster and a TiO2(110) surface is investigated using time-dependent density functional theory simulations. It is found that the charge separation dynamics consists of two processes: during the first 10 fs an initial charge separation resulting from the plasmon-electron coupling at the interface and a subsequent charge redistribution governed by the sloshing motion of the charge-transfer plasmon. The interplay between the two processes determines the charge separation and leads to the inhomogeneous layer-dependent distribution of hot carriers. The hot electrons are more efficient than the hot holes in the charge injection, resulting in the charge separation. Over 40% of the hot electron-hole pairs are separated spatially from the interface. Finally, the second TiO2 layer receives the most net charges from the Ag nanocluster rather than the interfacial layer. These results reveal the mechanism and dynamics of the charge separation driven by the surface plasmon excitation and have broad implications in plasmonic applications.
Keywords: direct charge injection; electron−hole separation; hot carriers; plasmonics; time-dependent density functional theory.