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.