Optical and electrical probing of plasmonic metal-molecule interactions

TL;DR

This study explores how different molecules affect plasmon damping on gold surfaces, revealing two distinct mechanisms—resonant electronic transitions and inelastic scattering—that influence energy transfer and electrical resistivity.

Contribution

It uncovers two regimes of chemical interface damping in plasmonic systems and links resistivity changes to plasmon energy transfer mechanisms, providing a unified understanding.

Findings

BPT causes CID via resonant LUMO excitation, dependent on plasmon energy.

ATP, adenine, and DDT induce CID through inelastic electron scattering.

Resistivity changes correlate with plasmon damping mechanisms.

Abstract

Plasmonic nanostructures enable efficient light-to-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. In this study, we investigate the relationship between CID and adsorbate-induced changes in DC electrical resistivity for four molecular adsorbates-adenine, 4-aminothiophenol (ATP), biphenyl thiol (BPT), and 1-dodecanethiol (DDT)-on gold surfaces. Our results reveal two distinct CID regimes. BPT causes CID via direct electronic transitions to the lowest unoccupied molecular orbital (LUMO), which is centered at approx. 2 eV above the Fermi level and can be resonantly excited by the plasmon. This mechanism is dependent on plasmon energy. In contrast, ATP, adenine and DDT lead to plasmon damping through inelastic electron scattering at the metal-molecule interface. This regime shows a weaker dependency on plasmon energy since it does not involve resonant electron excitation between hybridized metal-molecule states. This same mechanism contributes to adsorbate-induced changes in DC resistivity, suggesting that resistivity measurements can serve as a probe of plasmonic energy transfer, as highlighted by the good correlation between the two effects. These findings provide new insights into the microscopic origins of plasmon damping and offer a unified framework for understanding metal-adsorbate energy transfer.