Ab Initio Theory of Chemical Interface Damping of Surface Plasmons

Metallic nanostructures exhibit fascinating optical properties made possible by surface plasmons, which are collective oscillations of the conduction electrons. The properties of surface plasmons can be modified by functionalizing the metallic nanostructures with molecular adsorbates. For example, a significant reduction in the surface plasmon propagation length has been experimentally observed after functionalization. This phenomenon is known as chemical interface damping (CID). However, the physical origin behind CID remains unclear, with two proposed mechanisms being: (1) excitation of electron-hole pairs involving the adsorbate orbitals, and (2) electronic scattering by adsorbate-induced dipoles.

To resolve this issue, we perform first-principles density-functional theory calculations for different molecules adsorbed on on Au(111) surfaces. We calculate the density of states projected onto the adsorbate orbitals to analyze surface-plasmon decay channels associated with mechanism (1). We also use cluster models of the surface to compute adsorbate-induced dipole moments relevant to mechanism (2). These results are compared to experimental measurements, offering insights into the origin of CID and guiding future efforts to control properties of surface plasmons.