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

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.