Raspberry-like Metamolecules Exhibiting Strong Magnetic Resonances

Abstract

We report a synthetic approach to produce raspberry-like plasmonic nanostructures with unusually strong magnetic resonances, termed raspberry-like metamolecules (raspberry-MMs). The synthesis based on the surfactant-assisted templated seed-growth method allows for the simultaneous one-step synthesis and assembly of well-insulated gold nanoparticles. The aromatic surfactant used for the syntheses forms a thin protective layer around the nanoparticles, preventing them from touching each other and making it possible to pack discrete nanoparticles at close distances in a single cluster. The resulting isotropic gold nanoparticle clusters (i.e., raspberry-MMs) exhibit unusually broad extinction spectra in the visible and near-IR region. Finite-difference time-domain (FDTD) modeling showed that the raspberry-MMs support strong magnetic resonances that contribute significantly to the broadband spectra. The strong magnetic scattering was also verified by far-field scattering measurements, which show that in the near-IR region the magnetic dipole resonance can be even stronger than the electric dipole resonance in these raspberry-MMs. Structural parameters such as the size and the number of gold nanoparticles composing raspberry-MMs can be readily tuned in our synthetic method. A series of syntheses with varying structure parameters, along with FDTD modeling and mode analyses of corresponding model structures, showed that the close packing of a large number of metal nanoparticles in raspberry-MMs is responsible for the unusually strong magnetic resonances observed here.

Core–Shell Nanoparticle Clusters Enable Synergistic Integration of Plasmonic and Catalytic Functions in a Single Platform

“…Based on these findings, we infer that the controlled assembly of core–shell NPs with plasmonic Au cores and catalytically active Pd or Pt shells could be an effective way to realize an efficient hybrid platform with integrated plasmonic and catalytic functions. For the formation of colloidal NP assemblies, a number of approaches have been developed, which are mostly based on charge, molecular, biological, and solvent–ligand interactions between NPs . However, the structural integrity of NP assemblies, which is critical to their applications in plasmonics and catalysis, is still issued, as the above interactions are very sensitive to changes in their physicochemical environments.…”

Colloidal Clusters of Plasmonic Nanoparticles with Controlled Topological Parameters

“…In this regard, numerous approaches for the assembly of NPs in colloidal states have been developed, in which specific molecular or charge interactions between passivating ligands on NP surfaces, solvent‐ligand interactions, and van der Waals (vdW) interactions between NPs have been exploited to the formation of NP assemblies . However, the extent and features of these interactions that can drive the assembly of NPs are very sensitive to their physicochemical environments, including solvent, pH, temperature, light, ionic strength, and foreign organic or inorganic species, and the balance between the repulsive and attractive forces applied among NPs is hard to be controlled . Accordingly, the generation of robust colloidal NP assemblies with fine control over their topological parameters, such as the dimension and morphology of assemblies, average number and size of constituent NPs in individual assemblies, and shape homogeneity of NPs, is still a challenging task.…”

“…[8,9] However,t he extent and features of these interactions that can drive the assembly of NPs are very sensitive to their physicochemical environments,i ncluding solvent, pH, temperature, light, ionic strength,a nd foreigno rganic or inorganic species, and the balance between the repulsivea nd attractive forces applied amongN Ps is hard to be controlled. [2,[7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22] Accordingly,t he generationo fr obust colloidal NP assemblies with fine control over their topological parameters, such as the dimension and morphologyofassemblies, average number and size of constituent NPs in individual assemblies, and shape homogeneity of NPs, is still achallenging task.…”

Self‐Organization of Gold Nanoparticle Assemblies with 3D Spatial Order and Their External Stimuli Responsiveness

“…However, the obtained morphologies are mostly driven by the self‐assembly behavior of BCPs rather than by the AuNP. Control over AuNP self‐assembly may open up new perspectives for strong plasmonic coupling properties, such as strong magnetic resonance and propagation of low‐loss magnetic plasmons …”