Plasmon-Mediated Functionalization of Gold Nanoparticles by Aryl Diazonium Salts for Controlled Surface Patterning: Impact of Annealing on Roughness and Regioselectivity

Plasmon-driven surface chemistry has recently attracted significant attention, as it enables spatially controlled functionalization of plasmonic nanostructures. Among various approaches, aryl diazonium salts have emerged as efficient and robust functionalization agents, forming site-selective covalent Au–C bonds through reductive electron transfer from plasmonic nanoparticles under plasmon excitation. However, the regioselective growth of polyaryl layers derived from diazonium salts remains poorly controlled, with radical side reactions often limiting the spatial resolution of the grafted organic patterns. While recent studies have shown that nanoparticle geometry and light parameters can modulate regioselectivity through near-field localization, the influence of surface roughness on plasmon-mediated grafting remains underexplored. In this work, we address this gap by investigating how the surface roughness of gold nanoparticle arrays, fabricated by electron beam lithography, affects the spatial extent of polyaryl layer growth. Surface roughness was modulated by applying or not a thermal annealing step, which is known to significantly reduce surface irregularities. Our results demonstrate that surface roughness plays a key role in determining the spatial resolution and regioselectivity of the organic coating. Specifically, annealing improves the confinement of the grafting to regions of intense electric field enhancement around the gold nanostructures. This regioselective localization offers promising opportunities for plasmonic-based sensing, as chemical functionalities can be preferentially positioned at plasmonic hot spots where electromagnetic fields are maximal. This study thus provides valuable insights into the role of nanoscale morphology in plasmon-driven chemical functionalization and offers a simple route to improve the precision of surface patterning for sensing applications.