Nanostructure design for surface-enhanced Raman spectroscopy - prospects and limits

TL;DR

This paper investigates the theoretical limits of signal enhancement in surface-enhanced Raman spectroscopy (SERS) through nanostructure design, highlighting the impact of realistic surface rounding on achievable enhancement factors.

Contribution

The study demonstrates that while ideal nanostructures can achieve very high enhancement, realistic surface imperfections significantly reduce the maximum attainable enhancement and affect optimal frequency predictions.

Findings

Ideal enhancement factors can reach ~10^12 in simulations.

Realistic samples likely have enhancement factors below ~10^8.

Surface rounding suppresses enhancement and shifts optimal frequency.

Abstract

Surface-enhanced Raman spectroscopy (SERS) allows single-molecule detection due to the strong field localization occurring at sharp bends or kinks of the metal-vacuum interface. An important question concerns the limits of the signal enhancement that can be achieved via a judicious design of the surface. By using a specific example of a technologically realizable nanopatterned surface, we demonstrate that while very high enhancement factors (~10^12) can be found for an ideal surface, these are unlikely to be achieved in laboratory samples, because even a minute, inevitable rounding-off strongly suppresses the enhancement, as well as shifts the optimal frequency. Our simulations indicate that the geometric enhancement factors are unlikely to exceed ~10^8 for real samples, and that it is necessary to consider the geometric uncertainty to reliably predict the frequency for maximum enhancement.