In situ Formation of Plasmonic Gold Nanoparticles in Ordered Block Copolymer Films

International audienceContext: Metamaterials are of current interest for their unique optical properties. Although they are traditionally obtained by lithography, bottom-up ways of fabrication are now investigated for a precise nanometric control of the structure, through self-assembly and nanochemistry. To this end, organized films containing gold nanoparticles are widely studied for they combine the controlled structure of a film to the plasmonic properties of these nanoparticles. We report here the $in\ situ$ formation of gold nanoparticles (AuNPs) in a polystyrene-$block$-poly(vinylpyridine) (PS-b-PVP) copolymer solution, then cast as AuNP containing ordered films. By use of an appropriate solvent, casting a block colymer solution can form films of oriented cylinders (perpendicular or parallel to the substrate). The addition of gold salt $_Au$($III$)$chloride$($AuCl_3$)-followed by ultra-sound treatment before casting the film gives birth to spherical AuNPs (2-3 nm in size) located, after deposition, inside the cylinders. For parallel cylinders, AuNPs are found to redirect them to a quasi-perpendicular orientation, while no major perturbation is found for the perpendicular cylinders. Larger spherical AuNPs (3-4 nm) exhibiting a plasmon resonance are also obtained by successive additions of gold salt to the AuNPs and locate equally inside the cylinders after casting the film. This method of $in\ situ$ insertion of AuNPs in patterned films provides nanocomposite materials with plasmonic properties and opens new ways for the preparation of metamaterials