Plasmon-Defined Chemical Templates for the Nanoscale Assembly of Colloidal Nanoparticles

Abstract Controlling matter with nanoscale spatial selectivity is a key hurdle for plasmonic applications such as nanophotonics, sensing, and catalysis. Plasmon-assisted nanolithography has recently emerged as a powerful strategy to address this challenge by exploiting the highly confined electromagnetic fields and hot carriers generated during plasmon excitation to confine organic or inorganic layers at the nanoscale. Among the surface chemistries compatible with this approach, aryl diazonium salts are particularly attractive because their reduction produces highly reactive aryl radicals that form robust covalent bonds with metallic surfaces under mild conditions. Under light excitation, the plasmon-induced reduction of aryl diazonium salts enables the rapid and site-selective grafting of functional organic layers confined to plasmonic hot spots. The resulting functional films provide versatile chemical handles for further modification. However, to date, the use of plasmon-mediated diazonium grafting as a spatially controlled primer layer to direct the site-selective immobilization of colloidal nanoparticles remains unexplored. We address this gap by using lithographic gold nanodisc arrays as optically programmable templates. Under plasmon excitation, these nanostructures enable the formation of positively charged nanoscale anchoring domains at plasmonic hot spots, derived from diazonium salts bearing amine groups. These localized charged domains can then guide the spatial organization of negatively charged colloidal gold nanoparticles. The geometrical parameters of the plasmonic arrays, including nanodisc diameter and interparticle spacing, were carefully tuned to access different plasmon excitation regimes around the 633 nm laser wavelength, enabling blue-shifted, near-resonant, and red-shifted conditions, and expanding the variety of achievable hybrid patterns. Complementary characterization using SEM, UV−vis spectroscopy, and FDTD simulations demonstrates that this approach provides a straightforward and versatile strategy to direct the assembly of colloidal nanoparticles on lithographic nanostructures via optical excitation.