Supplementary document for Electrically-tunable metasurface for dual-band spatial light modulation using epsilon-near-zero effect - 6025015.pdf

Supplemental Documen

Two-Dimensional Bipyramid Plasmonic Nanoparticle Liquid Crystalline Superstructure with Four Distinct Orientational Packing Orders

Anisotropic plasmonic nanoparticles have been successfully used as constituent elements for growing ordered nanoparticle arrays. However, orientational control over their spatial ordering remains challenging. Here, we report on a self-assembled two-dimensional (2D) nanoparticle liquid crystalline superstructure (NLCS) from bipyramid gold nanoparticles (BNPs), which showed four distinct orientational packing orders, corresponding to horizontal alignment (H-NLCS), circular arrangement (C-NLCS), slanted alignment (S-NLCS), and vertical alignment (V-NLCS) of constituent particle building elements. These packing orders are characteristic of the unique shape of BNPs because all four packing modes were observed for particles with various sizes. Nevertheless, only H-NLCS and V-NLCS packing orders were observed for the free-standing ordered array nanosheets formed from a drying-mediated self-assembly at the air/water interface of a sessile droplet. This is due to strong surface tension and the absence of particle–substrate interaction. In addition, we found the collective plasmonic coupling properties mainly depend on the packing type, and characteristic coupling peak locations depend on particle sizes. Interestingly, surface-enhanced Raman scattering (SERS) enhancements were heavily dependent on the orientational packing ordering. In particular, V-NLCS showed the highest Raman enhancement factor, which was about 77-fold greater than the H-NLCS and about 19-fold greater than C-NLCS. The results presented here reveal the nature and significance of orientational ordering in controlling plasmonic coupling and SERS enhancements of ordered plasmonic nanoparticle arrays

Shape Transformation of Constituent Building Blocks within Self-Assembled Nanosheets and Nano-origami

Self-assembly of nanoparticles represents a simple yet efficient route to synthesize designer materials with unusual properties. However, the previous assembled structures whether by surfactants, polymer, or DNA ligands are “static” or “frozen” building block structures. Here, we report the growth of transformable self-assembled nanosheets which could enable reversible switching between two types of nanosheets and even evolving into diverse third generation nanosheet structures without losing pristine periodicity. Such <i>in situ</i> transformation of nanoparticle building blocks can even be achieved in a free-standing two-dimensional system and three-dimensional origami. The success in such <i>in situ</i> nanocrystal transformation is attributed to robust “plant-cell-wall-like” ion-permeable reactor arrays from densely packed polymer ligands, which spatially define and confine nanoscale nucleation/growth/etching events. Our strategy enables efficient fabrication of nanocrystal nanosheets with programmable building blocks for innovative applications in adaptive tactile metamaterials, optoelectronic devices, and sensors

Large-Scale Self-Assembly and Stretch-Induced Plasmonic Properties of Core–Shell Metal Nanoparticle Superlattice Sheets

We report on a facile interfacial self-assembly approach to fabricate large-scale metal nanoparticle superlattice sheets from nonspherical core–shell nanoparticles, which exhibited reversible plasmonic responses to repeated mechanical stretching. Monodisperse Au@Ag nanocubes (NCs) and Au@Ag nanocuboids (NBs) could be induced to self-assembly at the hexane/water interface, forming uniform superlattices up to at least ∼13 cm² and giving rise to mirror-like reflection. Such large-area mirror-like superlattice sheets exhibited reversible plasmonic responses to external mechanical strains. Under stretching, the dominant plasmonic resonance peak for both NB and NC superlattice sheets shifted to blue, following a power-law function of the applied strain. Interestingly, the power-law exponent (or the decay rate) showed a strong shape dependence, where a faster rate was observed for NB superlattice sheets than that for NC superlattice sheets

Giant Plasmene Nanosheets, Nanoribbons, and Origami

We introduce <i>Plasmene</i> in analogy to grapheneas free-standing, one-particle-thick, superlattice sheets of nanoparticles (“meta-atoms”) from the “plasmonic periodic table”, which has implications in many important research disciplines. Here, we report on a general bottom-up self-assembly approach to fabricate giant plasmene nanosheets (<i>i.e.</i>, plasmene with nanoscale thickness but with macroscopic lateral dimensions) as thin as ∼40 nm and as wide as ∼3 mm, corresponding to an aspect ratio of ∼75 000. In conjunction with top–down lithography, such robust giant nanosheets could be milled into one-dimensional nanoribbons and folded into three-dimensional origami. Both experimental and theoretical studies reveal that our giant plasmene nanosheets are analogues of graphene from the plasmonic nanoparticle family, simultaneously possessing unique structural features and plasmon propagation functionalities