# Quasi-3D Plasmonic Metamaterials with Highly Stretch-Tunable Optical Responses

## TL;DR

This paper introduces stretchable plasmonic materials made of liquid gallium nanoparticles in a polymer, which can change their optical properties when stretched.

## Contribution

A new method for creating quasi-3D plasmonic metamaterials with highly tunable optical responses through mechanical stretching.

## Key findings

- The nanocomposites exhibit a reversible strain-induced spectral shift exceeding 300 nm.
- FDTD simulations confirm that resonance shifts result from changes in interparticle spacing.
- A refined mechanism for nanoparticle growth and embedment in the polymer matrix is proposed.

## Abstract

Three-dimensional (3D) assemblies of metal nanoparticles
(NPs)
exhibiting strong plasmonic responses have garnered significant interest
owing to their potential in optoelectronic and sensing applications.
However, the realization of active plasmonic metamaterials based on
such architectures remains nontrivial, particularly in achieving uniform
and sub-10 nm interparticle spacing within dynamically tunable media.
Here, we present mechanically reconfigurable plasmonic nanocomposites
composed of 3D stacked liquid gallium nanoparticles (GaNPs) embedded
in a polydimethylsiloxane (PDMS) matrix, fabricated through a single-step
Ga evaporation process. The resulting GaNPs/PDMS nanocomposites exhibit
multilayered NP architectures with narrow interparticle spacing that
can act as quasi-3D plasmonic metamaterials, where collective plasmon
resonances hybridize with cavity modes to generate plasmon–polariton
states. Under applied biaxial strain, the multilayered architecture
enables simultaneous modulation of both intralayer and interlayer
plasmonic coupling, giving rise to a reversible strain-induced spectral
shift exceeding 300 nm. Finite-difference time-domain (FDTD) simulations
confirm that the observed resonance shifts primarily originate from
variations in both intra- and interlayer interparticle spacing. Based
on structural characterization, furthermore, we propose a refined
mechanism for the growth and embedment of nanoparticles within the
polymer matrix. These findings could advance the understanding of
nanoparticle–polymer interactions and benefit the development
of mechanically tunable plasmonic metamaterials.