Open and Close‐Packed, Shape‐Engineered Polygonal Nanoparticle Metamolecules with Tailorable Fano Resonances

Abstract

A top‐down lithographic patterning and deposition process is reported for producing nanoparticles (NPs) with well‐defined sizes, shapes, and compositions that are often not accessible by wet‐chemical synthetic methods. These NPs are ligated and harvested from the substrate surface to prepare colloidal NP dispersions. Using a template‐assisted assembly technique, fabricated NPs are driven by capillary forces to assemble into size‐ and shape‐engineered templates and organize into open or close‐packed multi‐NP structures or NP metamolecules. The sizes and shapes of the NPs and of the templates control the NP number, coordination, interparticle gap size, disorder, and location of defects such as voids in the NP metamolecules. The plasmonic resonances of polygonal‐shaped Au NPs are exploited to correlate the structure and optical properties of assembled NP metamolecules. Comparing open and close‐packed architectures highlights that introduction of a center NP to form close‐packed assemblies supports collective interactions, altering magnetic optical modes and multipolar interactions in Fano resonances. Decreasing the distance between NPs strengthens the plasmonic coupling, and the structural symmetries of the NP metamolecules determine the orientation‐dependent scattering response.

Design Rules for Obtaining Narrow Luminescence from Semiconductors Made in Solution

“…Specific designs of sample environment can also help extract predetermined sizes and shapes from a polydisperse nanocrystal ensemble. Recent advances in lithographic patterning have allowed the extension of template-assisted assembly from the microscale down to the nanoscale. , Pairing nanoscale patterning with self-assembly has resulted in the trapping of specific sizes and shapes of individual nanocrystals and their clusters in the nanometric recesses of solid-state substrates (Figure I). − The design of the trap must be carefully optimized to achieve the stable trapping of nanocrystals, which can then be released to generate a monodisperse dispersion . The trapping of nanocrystals with complementary properties within neighboring or adjacent trap sites can lead to the development of interesting new optical features.…”

“…For instance, trapping a nanophosphor near a plasmonic nanocrystal results in the enhancement of the PL signal . Instead, trapping several gold nanocrystals within the same trap can result in the development of optical features from the assembled structure as a whole; this has been demonstrated for the case of equilateral triangles of gold nanorods and metamolecules of gold nanospheres and nanopolygons. ,, …”

Design rules for obtaining narrow luminescence from semiconductors made in solution

“…223 Instead, trapping several gold nanocrystals within the same trap can result in the development of optical features from the assembled structure as a whole; this has been demonstrated for the case of equilateral triangles of gold nanorods and metamolecules of gold nanospheres and nanopolygons. 223,225,227…”