Reducing the loss of electric field enhancement for plasmonic core–shell nanoparticle dimers by high refractive index dielectric coating

Abstract

Plasmonic nanoparticle (NP) dimers, generating highly intense areas of electric field enhancement named hot spots, have been playing a vital role in various applications like surface enhanced Raman scattering. For stabilization and functionalization, such metallic NPs are often coated with dielectric shells, yet suffer from a rapid degeneration of the hot spot with the increase of the shell thickness. Herein, it is demonstrated that the use of appropriately high refractive dielectric coatings can greatly reduce the loss of local electric field enhancement, maintaining usable hot spots. Two mechianisms work synergistically. Firstly, the high refractive index dielectric coating enables a great leap of the local electric fields reaching the gap, which follows the boundary conditions at the interface within electrodynamics. Secondly, owing to its strong Mie resonances that can participate in the plasmon hybridization, the high refractive index dielectric coating contributes to a strong light coupling effect in terms of improving the light absorption. Taking advantage of the proposed physical process decomposition, both the resonance shift and local electric field enhancement can be elaborated. These findings should be of significant importance in extended applications of surface enhanced spectroscopies and related plasmonic devices based on hot spots.

Plasmon-Enhanced Resonant Photoemission Using Atomically Thick Dielectric Coatings

“…30 In fact, metal−dielectric core−shell nanoparticles have been a staple in the plasmonics community 35 and have driven progress in diverse research lines including surface-enhanced Raman spectroscopy, 36 surface-enhanced fluorescence, 37 nanocomposite-assisted imaging, 38 catalysis, 39 and photovoltaics. 40 In recent years, the concept of enhancing fields via ultrathin high-refractive-index coatings that "trap" the enhanced fields has also been explored, e.g., in core−shell nanoparticle dimers, 41 where a different plasmon modethe bonding dipole plasmon (BDP) modewas excited. Different from the antenna mode, the BDP mode has the maximally enhanced field located in the dimer gap (see Supporting Information S3).…”

“…Different from the antenna mode, the BDP mode has the maximally enhanced field located in the dimer gap (see Supporting Information S3). Nevertheless, the underlying enhancing mechanisms are similar: 41 (i) plasmonic field confinement following the boundary conditions at the dielectric−vacuum interface; (ii) high-refractive-index dielectric coating contributing to a strong light coupling effect in terms of improving the light absorption efficiency (see Figure 1a and Supporting Information S3).…”

Mie‐Resonance‐Enhanced Visible Light Absorption in Dielectric‐Supported Small Pt Nanoparticles for Photocatalysis

“…[33,[40][41][42] In analogy with the literature report, dozens of small ϕ = 5 nm Pt NPs are loaded onto the surface of a R = 150 nm spherical dielectric support, forming the core-satellite nanostructure, as shown schematically in Their refractive indexes are set to be N ≈ 2.5, 2.0, and 1.47 over the visible spectrum, representing the dielectric with a high, moderate, and low refractive index, respectively. [43][44][45] The light absorption by TiO 2 and ZnO semiconductors below ≈ 350 nm is deliberately ignored for theoretical study and weak interactions between adjacent hybrid NPs are ignored in our modeling. [33] The ambient environment is set to be water (N 0 ≈ 1.33) to simulate the aqueous solution in common photocatalytic reactions.…”

“…This is governed by the boundary conditions at the dielectric-Pt interface within electrodynamics. [44,45] Compared with SiO 2 , the high refractive index of TiO 2 leads to high electric field intensities inside the Pt NPs near the interface. Note that the AEF max for individual Pt NPs is nearly 15, which is much larger than that using the pure SiO 2 support.…”

“…Figure 2a.For comparison, different transparent supports including TiO 2 , ZnO, and SiO 2 are considered. Their refractive indexes are set to be N ≈ 2.5, 2.0, and 1.47 over the visible spectrum, representing the dielectric with a high, moderate, and low refractive index, respectively [43][44][45]. The light absorption by TiO 2 and ZnO semiconductors below ≈ 350 nm is deliberately ignored for theoretical study and weak interactions between adjacent hybrid NPs are ignored in our modeling [33].…”