Optical and electrical probing of plasmonic metal-molecule interactions

Plasmonic nanostructures enable efficient light-to-chemical energy conversion by concentrating optical energy into nanoscale volumes. A key mechanism in this process is chemical interface damping (CID), where surface plasmons are damped by adsorbed molecules, enabling the transfer of charge to adsorbed molecules. Here, we investigate the relationship between CID and adsorbate-induced changes in dc electrical resistivity for four molecular adsorbates on gold surfaces. Our results reveal two distinct CID regimes. On one hand, CID takes place via direct resonant electronic transitions to the lowest unoccupied molecular orbital. This mechanism is dependent on plasmon energy. In the second regime, plasmon damping takes place through inelastic electron scattering at the metal-molecule interface. This regime shows a weaker dependency on plasmon energy. This mechanism also leads to adsorbate-induced changes in dc resistivity. These findings provide previously unidentified insights into the microscopic origins of plasmon damping and offer a unified framework for understanding metal-adsorbate energy transfer.