Surface-enhanced Raman spectroscopy (SERS): nonlocal limitations

TL;DR

This paper demonstrates that nonlocal effects in plasmonic materials impose fundamental limits on the field enhancement achievable in SERS, challenging previous assumptions based on local-response models.

Contribution

It introduces a nonlocal response framework for SERS, revealing intrinsic length scale effects that cap field enhancement even in sharp geometries.

Findings

Nonlocal effects smear out field singularities.

Maximum enhancement factor is limited to 10^10.

Local models overestimate SERS enhancement potential.

Abstract

Giant field enhancement and field singularities are a natural consequence of the commonly employed local-response framework. We show that a more general nonlocal treatment of the plasmonic response leads to new and possibly fundamental limitations on field enhancement with important consequences for our understanding of SERS. The intrinsic length scale of the electron gas serves to smear out assumed field singularities, leaving the SERS enhancement factor finite even for geometries with infinitely sharp features. For silver nano-groove structures, mimicked by periodic arrays of half-cylinders (up to 120 nm in radius), we find no enhancement factors exceeding ten orders of magnitude (10^10).