Exceptional spatial variation of charge injection energies on plasmonic surfaces

Abstract: Charge injection into a molecule on a metallic interface is a key step in many photo-activated reactions. The energy barrier for injection is paralleled with the lowest particle and hole addition energies. We employ Green's function formalism of the many-body perturbation theory and compute the excitation energies, which include non-local correlations due to charge density fluctuations on the surface, i.e., the plasmons. We explore a prototypical system: CO$_2$ molecule on nanoscale plasmonic Au infinite and nanoparticle surface with nearly 3,000 electrons. In contrast to widely used density functional theory, we demonstrate that the energy barrier varies significantly depending on the molecular position on the surface, creating "hot spots" for possible carrier injection. These areas arise due to an intertwined competition between purely plasmonic couplings (charge density fluctuations on the substrate surface alone) and the degree of hybridization between the molecule and the substrate. There are multiple positions found with the lowest energy barrier for the electron/hole injection. We identify that the charge injection barrier to the adsorbate on the plasmonic surface trends down from the facet edge to the facet center -- here, the change in molecular orbitals overshadows the role of the charge fluctuations in the substrate. This finding contrasts the typical picture in which the electric field enhancement on the nanoparticle edges is considered the most critical factor.