Exploiting Combinatorics to Investigate Plasmonic Properties in Heterogeneous AgAu Nanosphere Chain Assemblies

Abstract

Chains of coupled metallic nanoparticles are of special interest for plasmonic applications because they can sustain highly dispersive plasmon bands, allowing strong ballistic plasmon wave transport. Whereas early studies focused on homogeneous particle chains exhibiting only one dominant band, heterogeneous assemblies consisting of different nanoparticle species came into the spotlight recently. Their increased configuration space principally allows engineering multiple bands, bandgaps, or topological states. Simultaneously, the challenge of the precise arrangement of nanoparticles, including their distances and geometric patterns, as well as the precise characterization of the plasmonics in these systems, persists. Here, the surface plasmon resonances in heterogeneous AgAu nanoparticle chains are reported. Wrinkled templates are used for directed self‐assembly of monodisperse gold and silver nanospheres as chains, which allows assembling statistical combinations of more than 109 particles. To reveal the spatial and spectral distribution of the plasmonic response, state‐of‐the‐art scanning transmission electron microscopy coupled with electron energy loss spectroscopy accompanied by boundary element simulations is used. A variety of modes in the heterogeneous chains are found, ranging from localized surface plasmon modes occurring in single gold or silver spheres, respectively, to modes that result from the hybridization of the single particles. This approach opens a novel avenue toward combinatorial studies of plasmonic properties in heterosystems.

Tailoring Plasmonics of Au@Ag Nanoparticles by Silica Encapsulation

“…This again corroborates the high‐quality of both the silica shell and the Au@Ag NP and their stability under both the electron beam and ambient conditions (see, e.g., ref. [5] for degraded optical properties of bare Au@Ag NPs).…”

“…Localized surface plasmon (LSP) resonances of (noble) metal nanoparticles (NPs) with a size comparable or smaller than the wavelength of incident light lead to intriguing optical properties such as frequency‐dependent electromagnetic field confinement and amplification. These are exploited in a multitude of applications, such as sensors, [ 1 ] spectroscopy signal enhancement, [ 2 ] nanoantennas [ 3 ] and catalysis, [ 4 ] where the frequency of the surface plasmons on individual particles can be tuned specifically by varying compositions (e.g., use of different metals or alloys), [ 5,6 ] morphology and size of the particles, [ 7 ] and environment (e.g., different dielectric surroundings). [ 8 ] The latter offers a particular rich playground ranging from mere frequency tuning over generation of hybridized surface plasmon modes [ 9–11 ] and plasmon bands [ 5,12 ] in NP oligomers, polymers, and superlattices, to strong coherent coupling between surface plasmons and other excitations such as excitons.…”

“…These are exploited in a multitude of applications, such as sensors, [ 1 ] spectroscopy signal enhancement, [ 2 ] nanoantennas [ 3 ] and catalysis, [ 4 ] where the frequency of the surface plasmons on individual particles can be tuned specifically by varying compositions (e.g., use of different metals or alloys), [ 5,6 ] morphology and size of the particles, [ 7 ] and environment (e.g., different dielectric surroundings). [ 8 ] The latter offers a particular rich playground ranging from mere frequency tuning over generation of hybridized surface plasmon modes [ 9–11 ] and plasmon bands [ 5,12 ] in NP oligomers, polymers, and superlattices, to strong coherent coupling between surface plasmons and other excitations such as excitons. [ 8 ] Here, the NP morphology, their interparticle distance, and arrangement within the assembly define the coupling strength and hence the resonance energies of the coupled mode.…”

“…[ 8 ] In consequence, the plasmonic response of silver NPs deteriorates, shifts over time and is generally not‐well defined. [ 5 ] This is one of the reasons why silver is a relatively unpopular plasmonic material, despite its broad plasmon band and low loss in the optical regime.…”

Nanoparticle Chains for Plasmonic Band Engineering

“…Furthermore is was funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under Germany's Excellence Strategy through Würzburg-Dresden Cluster of Excellence on Complexity and Topology in Quantum Matterct.qmat (EXC 2147, project-id 390858490). [3]. The corresponding EELS maps are shown in c).…”