The assembly of plasmonic nanoparticles (NPs) into tailored complex colloids can produce desired and original optical resonators, shown to be excellent building blocks for functional metadevices in the visible [1-2-3]. Within this trend, we have produced resonators consisting of clusters of NPs, by adapting an emulsion route [2]. We have also applied this methodology to the fabrication of controlled depositions of the complex colloids on surfaces.
The synthesis technique used to obtain colloidal assemblies of NPs involved the emulsification followed by a controlled ripening of an aqueous suspension of gold or silver nanoparticles (10-20 nm radius) in an oil phase. Deposits of such colloidal particles were also obtained by slowly drying the initial emulsions as liquid films above a flat substrate, resulting in a deposition of dense NP-clusters with a regular surface density (see Fig 1).
The structure of self-assembled clusters was monitored by different techniques, such as electron microscopy (see Fig 2) and small-angle X-ray scattering (SAXS). Measurements using a spectroscopic angle- and polarization- resolved light scattering set-up were also performed. In agreement with modelling and simulations [4-5], they demonstrated that the resonators present a strong magnetic dipolar scattering mode, significantly overlapping spectrally with the electric dipolar mode. As a consequence, the colloids scatter strongly and mostly forward. These optical properties can be tuned by monitoring the clusters inner structure, changing the NPs radius and initial volume fraction, as well as the thickness of the ligands layer on the NPs surfaces.

Keywords: self-assembly, nanocolloids, emulsion, metamaterial
Session 2nd choice: Composite Materials and Nanostructures

References

[1] A. Baron, A. Aradian, V. Ponsinet, P. Barois, Comptes Rendus – Physique, 2020, 21 (4-5), 443.
[2] R. Elancheliyan, R. Dezert, S. Castano, A. Bentaleb, E. Nativ-Roth, O. Regev, P. Barois, A. Baron, O. MondainMonval, V. Ponsinet, Nanoscale, 2020, 12, 24177.
[3] L. Lermusiaux, V. Many, P. Barois, V. Ponsinet, S. Ravaine, E. Duguet, M. Tréguer-Delapierre, A. Baron, Nano Letters, 2021, 21, 2046.
[4] C. Rockstuhl, F. Lederer, C. Etrich, T. Pertsch, T. Scharf, Physical Review Letters, 2007, 99, 017401.
[5] R. Dézert, P. Richetti, A. Baron, Physical Review B, 2017, 96, 180201.