Plasmonic Polycrystals within Microbowl Arrays

Abstract Plasmonic polycrystals composed of loosely packed plasmonic nanoparticles formed microscale plasmonic grains with random orientations may exhibit interesting optical properties. Their fabrication includes placing nanoparticles in order to form plasmonic grains and forming the random orientation of the plasmonic grains. The seemingly mutually exclusive nanoparticle ordering and random grain orientation processes challenge existing technologies. Here a self‐assembled bowl‐in‐bowl template‐confined dewetting process to prepare plasmonic polycrystals is developed. The size and composition of the plasmonic nanoparticles can be conveniently designed before experiments, which are inaccessible to conventional fabrication methods. Complex plasmonic coupling between the Au nanoparticles and the plasmonic grains within the plasmonic polycrystals is observed. The microbowls further endow plasmonic nanostructures with more interesting optical properties arising from multiple scattering processes within the concave bowl surfaces. The broadband response of the plasmonic polycrystals makes them active under 532, 633, and 785 nm laser excitation for surface‐enhanced Raman scattering (SERS) sensing applications. Finite‐difference time‐domain simulations are performed to explain the optical properties of the plasmonic polycrystals and the SERS enhancement. The simple template‐confined dewetting process provides a powerful approach to design plasmonic polycrystals with application potentials in plasmonic, sensing, and photonic fields.