Electronic excitations at the plasmon–molecule interface

The recent rise of plasmonic materials for solar-to-chemical energy conversion places a focus on the mechanisms associated with charge and energy flow at the metal–molecule interface. Understanding the connection between these effects and their roles in the plasmonic excitations of adsorbed molecules has been challenging. In this Review, we strive to provide a general framework—based on the concept of electron scattering—that encompasses the most important effects at the plasmonic metal–molecule interface. First we use the model of adsorbate-induced surface resistivity to understand the chemical specificity of the electron scattering process. We then analyse two of the most prominent effects in plasmonics through the lens of the electron scattering model: chemical interface damping and the chemical model of surface-enhanced Raman scattering. We show how most metal–adsorbate charge- or energy-transfer interactions can be mapped into two major classes—electron scattering through molecular resonances and direct non-resonant electron scattering.