Enhancement Factors: A Central Concept during 50 Years of Surface-Enhanced Raman Spectroscopy

Abstract

In this Perspective, we provide an overview of the core concepts around surface-enhanced Raman spectroscopy (SERS) enhancement factors (EFs), including both theoretical and experimental considerations: EF definitions, the distinction between maximum and average EFs, EF distribution and hot-spot localization, EF measurement and its order of magnitude. We then highlight some of the current challenges in this field, focusing on a selection of topics that we feel are both topical and important: analyte-capture onto a SERS substrate, surface-enhanced resonant Raman scattering, orientation/tensorial effects, and nonradiative effects. We hope this Perspective can provide a platform to reflect on the past 50 years of SERS and its future.

Surface-Enhanced Raman Spectroscopy: Current Understanding, Challenges, and Opportunities

“…pointed out that accurate determination of N SERS and N Raman in experiments is still challenging and fluorescence may overwhelm the Raman signal in the case of resonant molecules. On the other hand, AEF is analyte-dependent, contributing underestimated results owing to substrate orientation averaging, molecule orientation averaging, and polydispersity in the substrates …”

Surface-Enhanced Raman Scattering Coupled with In Situ Raman Spectroscopy for the Detection of the OER Mechanism: A Mini-Review

“…SERS leverages the unique optical properties of metallic nanostructures to amplify the inherently weak Raman scattering signals from molecules adsorbed onto their surfaces. − When molecules interact with the oscillating electromagnetic fields generated by the excitation of localized surface plasmons in these nanostructures, their Raman scattering cross sections can be enhanced by many orders of magnitude, enabling ultrasensitive detection and structural characterization of even single molecules. , …”

Toward Modeling the Complexity of the Chemical Mechanism in SERS

“…The SERS enhancement mechanisms increase the Raman scattering by 6 to 12 orders of magnitude. − A majority of the enhancement is due to the EM from the strong near field generated by the plasmon excitation. ,− Compared to normal Raman scattering (NRS), the near field enhances both the incident and scattered light ,,,− as illustrated in Figure (a) and (b). As a consequence, the EM enhancement in terms of the near-field enhancement factor F is usually approximated as italicF ( ω 0 ) 2 · italicF ( ω s ) 2 , which can be simplified as italicF ( ω 0 ) 4 if the difference in incident and scattered light is small. ,, The description of the EM enhancement in terms of the near field assumes that the field is homogeneous over the dimensions of the molecule.…”