Preserving Plasmonic Nanostructures from Laser-Induced Deactivation by a Protective Dielectric Shell

Noble metal nanostructures are highly efficient in harvesting light. Their strong plasmonic properties enable ultrasensitive spectroscopy, catalysis of chemical reactions with sunlight, photothermal treatment of cancer, and much more. Ironically, they frequently lose their excellent optical properties upon irradiation with intense laser light. Here, we show that the photostability of Ag nanostructures can be dramatically improved by a protective 4 nm thick SiO₂ coating. Enhanced Raman and far-field scattering spectra were compared for bare and shell-isolated Ag nanoparticles (NPs) and nanotips. The shell-isolated nanostructures produced a stable spectroscopic signal, even at high laser fluences, contrary to their bare Ag counterparts. This result suggests that the dielectric coating immobilizes the surface Ag atoms and preserves the shape of the nanostructure and its plasmon resonance. The results presented are important for virtually any application of plasmonic NPs; this study sheds light on the deactivation of plasmonic nanostructures during operation and proposes a practical solution to mitigate that problem.