Probing the Anisotropy of SERS Enhancement with Spatially Separated Plasmonic Modes in Strongly Coupled Silver Nanocubes on a Dielectric Substrate

Abstract

The utilization of substrate–particle interactions provides a route to tuning the optical properties of strongly coupled supported plasmonic nanoparticles. In this work fine control over interparticle and particle–substrate interactions is demonstrated using Langmuir–Blodgett monolayers of silver nanocubes deposited onto titanium oxide (TiO x ) thin films of varying thickness. By using two Raman reporters, a Rhodamine-B (RhB) and benzenethiol (BT), surface-enhanced Raman spectroscopy (SERS) independently examines electromagnetic (EM) enhancement at the substrate/nanocube interface (RhB) and at the surface of the cubes, where the label is predominately 20–40 nm away from the dielectric substrate (BT). For RhB the SERS enhancement factor (EF) drops as much as an order of magnitude on 20 nm TiO x with respect to glass. However, for BT, a maximum SERS EF of (2.5 ± 0.4) × 105 was observed on TiO x compared to (1.5 ± 0.4) × 105 on glass, an increase of 60%. Control over the organization of the nanocube monolayer reveals that maximum enhancement occurs in small, discrete clusters of nanocubes as opposed to large aggregates. Fine control over the optical properties and near-field EM distribution of coupled nanostructures can be accomplished through tuning of the dielectric properties of the substrate yielding a route to optimizing properties for field-enhanced plasmonic applications.

Controlled graphene oxide assembly on silver nanocube monolayers for SERS detection: dependence on nanocube packing procedure

“…Interestingly, conventional amphiphiles cannot be transferred successfully at low surface pressure whereas for AgNC significant transfer was obtained also at 0.5 mN/m although with low nanocube density. Such behaviour, reported also by other authors for mixed AgNC/phospholipid systems [ 40 ], is likely due to the stabilizing effect of PVP cushion capping the surface of the nanocubes.…”

“…The surface density determined for QCM measurements for LB transferred directly on the QCN sensor was 41 NC/µm 2 which resulted in an average interparticle distance over the entire sensor surface of 100 nm, we recall that direct measurement of nanocube density at the water–air interface is vitiated by the presence of capping PVP molecules which cannot be directly quantified. Local interparticle distance estimated by AFM results [ 40 ] evidenced much smaller gaps of 1–3 nm between face-to-face nanocubes nm within the AgNC clusters.…”

“…As adsorption proceeds in the following additions, the dissipation increases to values characteristic of elastic films. The structural parameters obtained at surface saturation for the AgNC layer fabricated with procedure B are reported in Table 1 together with the thickness of the adsorbed layer that was extracted by the analysis of all overtones as reported elsewhere [ 40 , 46 ].…”

Design and realization of light absorbers using plasmonic nanoparticles

“…This allows a large parameter space to fine tune the optical response [18,19]. It is essential here to carefully choose the underlying metal substrate as well as the thickness of the dielectric spacer to enhance optical couplings [20][21][22]. -or embedded within a host matrix.…”

A model of compression isotherms for analyzing particle layers

“…It was shown in the literature that partially wettable particles form cohesive films at liquid-liquid and liquid-gas interfaces [1][2][3][4][5][6][7][8][9]. The particle films have numerous applications in tion and formation of a cohesive layer on the water surface [19]; in the case of hydrophilic spheres, this contact is weakened by hydration shells.…”