Simple Theoretical Considerations for Block-Copolymer-Based Plasmonic Metamaterials

Block-copolymers (BCPs) self-assembling provides a unique tool for realizing large-area ordered metamaterials with desired optical properties due to the rich range of tunable nano-morphologies and to the chemical properties of the block polymers that can lead to the selective inclusion of functionalized nanoparticles (NPs) in specific nanodomains, generating periodic arrays of NPs according to the geometry of the BCP acting as template. In this work, we investigate nanostructured thin films of polystyrene-block-poly(methylmethacrylate) BCP (PS-PMMA) filled by functionalized metallic (Au) nanoparticles. The BCP is characterized by an hexagonal array of PS cylinders in the PMMA matrix and the Au NPs are selectively included in the PS cylindrical domains. The optical properties of such nano-structures are strongly affected by localized surface plasmons (LSPs) in the NPs. We theoretically demonstrate that the optical properties of such nano-structures can be tuned by varying the NPs loading concentration and the NPs radius. Then, we investigate the effects of the hexagonal geometry on the collective plasmonic oscillations. We fabricated the PS-PMMA/Au NPs composite and we experimentally demonstrate the existence of collective plasmonic resonances of gold nanoparticles after an electromagnetic stimulation, arising from the ordered arrangement of AuNPs in the periodic array of hexagonally packed cylinders created by the self-assembly of the BCP. This approach allows finely modulating the optical properties of NPs and can be used as an intriguing and versatile tool to build useful devices for Optics & Photonics applications, with significant benefits for both fundamental and applied investigations.