Shape-engineered Polygonal Nanoparticle Metamolecules with Tailorable Fano Resonances

Image of nanoparticle metamolecules by Elionix Electron Beam Lithography

Nanoparticles (NPs) exhibit interesting and useful optical, electrical, and magnetic properties which can be different than their larger bulk material state.  NP assemblies can be created from a “bottoms up” or “top down” approach.  The “bottoms up” approach uses chemical synthesis, and can be scaled to apply NPs over extensive surfaces. However, the formation of NPs into highly-defined metamolecules is difficult.  The “top down” approach using lithography and nanofabrication can often produce more arbitrary designs. However, creating ultrafine gaps and scaling to large areas can be challenging.

New research by Yi-Yu Cai, Asma Fallah, Shengsong Yang, Yun Chang Choi, Jun Xu, Aaron Stein, James M. Kikkawa, Christopher B. Murray, Nader Engheta, and Cherie R. Kagan at the University of Pennsylvania and Brookhaven National Laboratory combines a top down lithographic approach with a template assisted assembly technique to organize the formation of open- or close-packed multi-NP structures or NP metamolecules.  By changing the distance between NPs and manipulating the high order subradiant modes within the metamolecules, their Fano resonances can be tuned. Furthermore, the symmetry of the NP metamolecule determines the orientation dependent scattering response. 

This work was performed in part at the @Singh Center for Nanotechnology using an STS-Elionix ELS-7500EX electron beam lithography system.

For more information see https://doi.org/10.1002/adma.202301323

Image (Courtesy Yi-Yu Cai).

(Top) An abbreviated process flow from left to right: Nanoimprint stamp, lift off of Au NPs, distribution from NP dispersions to EBL templates.

(Bottom) SEM images of assembled polygonal Au NP metamolecules after removing the EBL template.