Fermi level equilibration at the metal-molecule interface in plasmonic systems

TL;DR

This study demonstrates how tuning the Fermi level of plasmonic silver nanoparticles via halide ion adsorption induces charge transfer, affecting plasmonic effects and catalytic behavior at the metal-molecule interface.

Contribution

It provides the first experimental and theoretical quantification of Fermi level upshift effects and their impact on plasmonic phenomena and catalysis.

Findings

Fermi level upshift of ~0.3 eV achieved by halide adsorption

Fermi level shift comparable to plasmoelectric effect and hot-carriers

Halide ions influence catalysis based on surface affinity

Abstract

We highlight a new metal-molecule charge transfer process by tuning the Fermi energy of plasmonic silver nanoparticles (AgNPs) in-situ. The strong adsorption of halide ions upshifts the Fermi level of AgNPs by up to ~0.3 eV in the order: Cl-<Br-<I-, favoring the spontaneous charge transfer to aligned molecular acceptor orbitals until charge neutrality across the interface is achieved. By carefully quantifying experimentally and theoretically the Fermi level upshift, we show for the first time that this effect is comparable in energy to different plasmonic effects such as the plasmoelectric effect or hot-carriers production. Moreover, by monitoring in-situ the adsorption dynamic of halide ions in different AgNP-molecule systems, we show for the first time that the catalytic role of halide ions in plasmonic nanostructures depends on the surface affinity of halide ions compared to that of the target molecule.