Control over structural symmetries can offer new material properties such as chiroptical properties but has only been realized in limited systems of nanoparticle self-assembly. Here by utilizing highly uniform gold tetrahedral nanoparticles with reduced symmetry and harnessing the interparticle interactions, we demonstrate new types of largescale and extended superlattices with surprisingly low packing fractions and unconventional chiral symmetries. The presence of substrate leads to the formation of unexpected bilayer configuration of tetrahedra in contrast to the conventional close packings with high-order rotational symmetry. Tuning the van der Waals and electrostatic interactions varies the tip position and face separation of neighboring tetrahedra, resulting in chiral structures with reduced symmetry. Further increasing the interparticle attraction leads to the symmetry breaking out-of-plane and eventually form into structures with maximized face-to-face contact. These self-assembly structures demonstrate chiroptical properties and we verify their circular dichroism response using finite-difference time-domain simulations. We expect symmetry breaking as a unique strategy to fabricate self-assemblies with various symmetries for optical applications.

Self-assemblies of gold tetrahedra with unconventional symmetry breaking

ACS Spring 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.