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

Abstract

Noble metal nanostructures are highly efficient in harvesting light. Their strong plasmonic properties enable ultra-sensitive 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 and nanotips. The shell-isolated nanostructures produced 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 nanoparticles; this study sheds light on the deactivation of plasmonic nanostructures during operation and proposes a practical solution to mitigate that problem.

Regulating and Directionally Controlling Electron Emission from Gold Nanorods with Silica Coatings

“…A less dramatic (yet still considerable) nonexponential decay with the mesoporous silica thickness is attributed to free-space transmission of the photoelectrons through randomly aligned nanoscopic pores, as elucidated via simple geometric modeling with excellent quantitative agreement. Either mesoporous or dense silica coating strategies may be utilized to regulate or essentially block hot carrier transfer or emission to prevent unwanted chemical transformations in surface- or tip-enhanced Raman spectroscopy studies , or to distinguish between hot carrier and thermal effects in plasmonic catalysts. Furthermore, preliminary angle-resolved photoemission studies of nanorods with random defects in the mesoporous silica coatings have been used to demonstrate directional photocurrent distributions systematically aligned with the thinner coating defect regions.…”

Emerging Methods for Controlling Hot Carrier Excitation and Emission Distributions in Nanoplasmonic Systems

“…64 In many cases these synthetic techniques for anisotropic coatings take advantage of the reduced density of ligands such as cetyltrimethylammonium bromide (CTAB) in regions of high nanoparticle curvature 59 to either (i) selectively grow the desired coatings in these regions, 51,57 or (ii) bind larger ligands that prevent further growth, thereby promoting growth in other surface regions in subsequent coating steps. 19,57 Both dense and mesoporous silica coatings are commonly used to stabilize nanoparticles in solution while providing increased morphological photostability, 65,66 with mesoporous silica additionally providing channels for size-filtered molecular access to the metal surface. 67 Uniform dense or mesoporous silica coatings can be used to regulate the rate of hot carrier transfer, with few-to tens-of-nanometer thick layers leading to orders-of-magnitude attenuation (Figure 2b).…”

“…Both dense and mesoporous silica coatings are commonly used to stabilize nanoparticles in solution while providing increased morphological photostability, , with mesoporous silica additionally providing channels for size-filtered molecular access to the metal surface . Uniform dense or mesoporous silica coatings can be used to regulate the rate of hot carrier transfer, with few- to tens-of-nanometer thick layers leading to orders-of-magnitude attenuation (Figure b).…”

Plasmonic Core–Shell Nanomaterials and their Applications in Spectroscopies

“…To solve these serious problems limiting TERS, inspired by SHINERS, we applied the shell isolation strategy to traditional tips, and established the shell isolation tip-enhanced Raman spectroscopy technology (SITERS). [84][85][86][87] SITERS greatly improved the stability of TERS via effectively isolating the noble metal tip core from the adsorption of impurities on the tip surface without significantly interfering with TERS detection sensitivity. SITERS will help to expand the applications of TERS nanoscale imaging to the study of more complex systems like electrochemistry or life science.…”