Ligand-free synthesis of gold nanoparticles incorporated within oriented cylindrical block copolymer films: towards optical metamaterials

We report a method to incorporate non-functionalized gold nanoparticles (AuNPs) in oriented cylindrical phases of poly(styrene)-b-poly(vinylpyridine) (PS-b-PVP) block copolymers, perpendicular to a substrate. The combination of AFM, TEM, GISAXS and spectroscopy allows complete characterization of the nanocomposites. AuNPs are produced by the ultra-sound reduction of a gold salt in the copolymer solution, prior to the deposition of the films by spin-coating. The AuNPs are found to be located within the PVP cylinders exclusively. The seeded-growth of these pre-formed AuNPs by a further ultra-sound treatment produced plasmonic AuNPs (up to d =10 nm). For perpendicular cylinders, the PVP domains are swollen without any change in their orientation. Ellipsometric optical properties of these plasmonic AuNPs embeded into oriented cylinders show a definite extinction in reflectivity at a precise energy and incidence angle.