# Tracking Molecular Shear at Metal Surfaces Using Enhanced Lamb Wave Scattering in Plasmonic Nanocavities

## TL;DR

This paper shows how plasmonic nanocavities can detect molecular shear vibrations at metal surfaces, revealing new insights into molecular interactions.

## Contribution

The study identifies terahertz Lamb shear modes in plasmonic nanocavities, a novel phenomenon with large cross sections compared to SERS.

## Key findings

- Low-frequency inelastic light scattering reveals terahertz Lamb shear modes in nanogaps.
- These modes have larger cross sections than surface-enhanced Raman scattering (SERS).
- Molecular binding and damping strongly influence these modes at room temperature.

## Abstract

Extreme plasmonic confinement to the nanoscale can be
used to probe
the configuration of molecules at metallic surfaces. Exploring low-frequency
(hν < k
B
T) inelastic light scattering from molecular-monolayer-filled
plasmonic nanocavities reveals additional low-frequency excitations
not previously observed. We identify these as terahertz Lamb shear
modes in the nanogap, exhibiting cross sections even larger than the
surface-enhanced Raman scattering (SERS) of the vibrating molecules.
Comparing different molecules and metals shows the influence on these
Lamb modes of surface binding of the molecular monolayer as well as
the strong impact of damping. The large occupation of such modes at
room temperature implies their role across many fields, from electrochemistry,
molecular electronics, and thermoelectrics to photocatalysis and sensing.