Chemical Raman Enhancement of Organic Adsorbates on Metal Surfaces

TL;DR

This study combines theory and experiments to quantitatively explain how chemical interactions enhance Raman signals of benzene thiol on gold surfaces, revealing mode-specific effects and enabling extraction of chemical enhancement from experimental data.

Contribution

It introduces a quantitative, mode-dependent analysis of chemical Raman enhancement using first-principles calculations and experimental validation, advancing understanding of surface-enhanced Raman spectroscopy mechanisms.

Findings

Strong mode-dependent Raman enhancement observed.

Excellent agreement between theory and experiment.

Method for extracting chemical enhancement from measurements.

Abstract

Using a combination of first-principles theory and experiments, we provide a quantitative explanation for chemical contributions to surface-enhanced Raman spectroscopy for a well-studied organic molecule, benzene thiol, chemisorbed on planar Au(111) surfaces. With density functional theory calculations of the static Raman tensor, we demonstrate and quantify a strong mode-dependent modification of benzene thiol Raman spectra by Au substrates. Raman active modes with the largest enhancements result from stronger contributions from Au to their electron-vibron coupling, as quantified through a deformation potential, a well-defined property of each vibrational mode. A straightforward and general analysis is introduced that allows extraction of chemical enhancement from experiments for specific vibrational modes; measured values are in excellent agreement with our calculations.