Quantifying efficiency of remote excitation for surface enhanced Raman spectroscopy in molecular junctions

TL;DR

This paper demonstrates that remote excitation of surface plasmon polaritons in gold molecular junctions enables stable SERS signals and measurable photovoltage, offering a less invasive alternative to direct illumination.

Contribution

It introduces a method for remote excitation of SERS in molecular junctions, improving stability and coupling efficiency over direct excitation methods.

Findings

Remote excitation yields more stable SERS spectra.

Coupling efficiency of remote excitation is around 10%.

Remote excitation can generate both SERS emission and photovoltage.

Abstract

Surface-enhanced Raman spectroscopy (SERS) is enabled by local surface plasmon resonances (LSPRs) in metallic nanogaps. When SERS is excited by direct illumination of the nanogap, the background heating of lattice and electrons can prevent further manipulation of the molecules. To overcome this issue, we report SERS in electromigrated gold molecular junctions excited remotely: surface plasmon polaritons (SPPs) are excited at nearby gratings, propagate to the junction, and couple to the local nanogap plasmon modes. Like direct excitation, remote excitation of the nanogap can generate both SERS emission and an open-circuit photovoltage (OCPV). We compare SERS intensity and OCPV in both direct and remote illumination configurations. SERS spectra obtained by remote excitation are much more stable than those obtained through direct excitation when photon count rates are comparable. By statistical analysis of 33 devices, coupling efficiency of remote excitation is calculated to be around 10%, consistent with the simulated energy flow.