Probing the limits of plasmonic enhancement using a two-dimensional atomic crystal probe

Abstract

Achieving larger electromagnetic enhancement using a nanogap between neighboring metallic nanostructures has been long pursued for boosting light–matter interactions. However, the quantitative probing of this enhancement is hindered by the lack of a reliable experimental method for measuring the local fields within a subnanometer gap. Here, we use layered MoS2 as a two-dimensional atomic crystal probe in nanoparticle-on-mirror nanoantennas to measure the plasmonic enhancement in the gap by quantitative surface-enhanced Raman scattering. Our designs ensure that the probe filled in the gap has a well-defined lattice orientation and thickness, enabling independent extraction of the anisotropic field enhancements. We find that the field enhancement can be safely described by pure classical electromagnetic theory when the gap distance is no <1.24 nm. For a 0.62 nm gap, the probable emergence of quantum mechanical effects renders an average electric field enhancement of 114-fold, 38.4% lower than classical predictions.

Integrated “Hot Spots”: Tunable Sub‐10 nm Crescent Nanogap Arrays

“…Figure S6 in the Supporting Information is straight out of the FDTD software to show the maximum electric field enhancement that the CNGAs can perform, the white dotted lines indicate the position of a crescent nanogap. This result is consistent with previous reports and supported by the Maxwell's equations . The minimum G was set to be 1 nm considering that G ≥ 1 nm correspond to the classical regime, where the gap plasmonic modes is explained by the local Maxwell's equations.…”

“…To achieve the extremely concentrated and strong electric fields, lots of efforts are contributed to fabricate kinds of plasmonic structures, revealing that sub‐10 nm nanogap and nanotip are the two key characteristics . In theory, as predicted by Maxwell's equations, the electric fields would become stronger with the decreasing distance between metal nanostructures and can be confined in the gaps; for nanotips, more electrons are distributed at the structural features with high curvature and thus lead to stronger electric fields …”

Broadband SERS detection with disordered plasmonic hybrid aggregates

“…[6][7][8][9] Among them, SERS is an extensively studied analytical tool that provides molecule-specific information on the molecular structure and chemical composition of analytes through Raman scattering. It is now generally accepted that the SERS enhancement arises from the enlarged local electromagnetic (EM) fields near a nanostructured metal system, which is resulted from localized surface plasmon resonances (LPRs), 10 known as plasmonic "hot-spots" that occur near sharp asperities and in nanometer gaps between metal nanostructures such as nanoparticles (NPs), 11,12 NP-spacer-film systems, 13,14 etc. Generally, the number and intensity of plasmonic hot-spots largely determines the SERS capability of a given substrate.…”

Self-assembly of robust gold nanoparticle monolayer architectures for quantitative protein interaction analysis by LSPR spectroscopy

“…This is even more critical for LSPR detection using clusters of noble metal nanoparticles, where coupling of electronic oscillations among the adjacent nanoparticles generates plasmonic "hotspots" [11,12]. With a more than 10 6 -fold enhancement of the electromagnetic field, plasmonic hotspots have emerged as a cornerstone of a wide range of applications for surface-enhanced spectroscopies [13][14][15]. For instance, sensitivity down to the single molecule level has been achieved by surface-enhanced Raman spectroscopy [16,17].…”