Laser-irradiated inclined metal nanocolumns for selective, scalable, and room-temperature synthesis of plasmonic isotropic nanospheres

Abstract

Plasmonic nanocrystals, which exhibit extraordinary optical properties, are challenging to grow in selective positions with a cost-effective and high-throughput process. We demonstrate that plasmonic isotropic gold nanospheres (AuNSs) can be selectively synthesized on wafer-scale rigid and flexible substrates at room temperature by laser irradiation. First, we prepare gold nanocolumn (AuNC) thin films on sapphire and polydimethylsiloxane substrates with glancing angle deposition (GAD). Then, a KrF excimer laser is exposed at selected positions with a 24 ns pulse duration. Finally, highly isotropic AuNSs as plasmonic nanocrystals are synthesized at the targeted positions. We suggest that the formation of such isotropic AuNSs is caused by reshaping from the top of the AuNCs; this is verified by the temperature distribution in the AuNCs during laser irradiation through finite element method simulations. We further investigate the formation of AuNSs by varying the laser energy density and the kind of substrate. By using a simple mask process, we demonstrate patterning of the letters "KIST" via selectively grown AuNSs on a flexible substrate. The simple laser irradiation process on GAD-grown metal NC thin films is expected to be a promising method for scalable synthesis of plasmonic isotropic NSs at targeted positions with a rapid process and at room temperature.