Surface-Enhanced Raman Scattering and Surface-Enhanced Infrared Absorption by Plasmon Polaritons in Three-Dimensional Nanoparticle Supercrystals

Abstract

Surface-enhanced vibrational spectroscopy strongly increases the cross section of Raman scattering and infrared absorption, overcoming the limited sensitivity and resolution of these two powerful analytic tools. While surface-enhanced setups with maximum enhancement have been studied widely in recent years, substrates with reproducible, uniform enhancement have received less attention although they are required in many applications. Here, we show that plasmonic supercrystals are an excellent platform for enhanced spectroscopy because they possess a high density of hotspots in the electric field. We describe the near field inside the supercrystal within the framework of plasmon polaritons that form due to strong light-matter interaction. From the polariton resonances we predict resonances in the far-field enhancement for Raman scattering and infrared absorption. We verify our predictions by measuring the vibrations of polystyrene molecules embedded in supercrystals of gold nanoparticles. The intensity of surface-enhanced Raman scattering is uniform within 10% across the crystal with a peak integrated enhancement of up to 300 and a peak hotspot enhancement of 10 5 . The supercrystal polaritons induce pairs of incoming and outgoing resonances in the enhanced cross section as we demonstrate experimentally by measuring surface-enhanced Raman scattering with multiple laser wavelengths across the polariton resonance. The infrared absorption of polystyrene is likewise enhanced inside the supercrystals with a maximum enhancement of 400%. We show with a coupled oscillator model that the increase originates from the combined effects of hotspot formation and the excitation of standing polariton waves. Our work clearly relates the structural and optical properties of plasmonic supercrystals and shows that such crystals are excellent hosts and substrates for the uniform and predictable enhancement of vibrational spectra.

Smart design of high‐performance surface‐enhanced Raman scattering substrates

“…The self‐assembly 3D Au/Ag structure could improve the SERS activity by increasing a large number of hot spots 47–51 . Tian et al 52 evaporated a droplet of citrate‐Ag sols on a fluorosilicate silicon wafer, and a large number of hot spots in 3D space were produced during the evaporation process (Figure 3E).…”

Recent Notable Approaches to Study Self‐Assembly of Nanoparticles with X‐Ray Scattering and Electron Microscopy

“…[ 154 ] As for atomic crystals, different crystal structures of the supercrystals would also lead to different plasmonic band structures. [ 4 ] So these materials provide excellent opportunities to manipulate strong light–matter interactions, which is of great interest in the field of cavity quantum electrodynamics [ 153 ] but can also be used to tailor surface‐enhanced spectroscopies [ 157 ] and maybe even hot electron generation for plasmonic photocatalysis. [ 155,158 ]…”

“…[154] As for atomic crystals, different crystal structures of the supercrystals would also lead to different plasmonic band structures. [4] So these materials provide excellent opportunities to manipulate strong light-matter interactions, which is of great interest in the field of cavity quantum electrodynamics [153] but can also be used to tailor surface-enhanced spectroscopies [157] and maybe even hot electron generation for plasmonic photocatalysis. [155,158] These examples: band-like transport, superfluorescence, and deep strong coupling, show that emerging new properties from NPs superstructures are possible and that they naturally depend strongly on the geometry and-to a different extenton the quality of the supercrystals.…”

Optimization Based on the Surface Plasmon Optical Properties of Adjustable Metal Nano-Microcavity System for Biosensing

“…By using the combination of biomolecules to obtain amplified signals, this research will provide a theoretical basis for the development of ultra-sensitive biosensors and nano-optical technologies in real-time diagnostics (Ho et al, 2005). Additionally, it is hoped that the system can be applied in the research of fluorescence sensing (Uppa et al, 2018), surface-enhanced Raman scattering (SERS) (Mueller et al, 2021) and plasmon ruler (Li et al, 2018).…”