Intra-particle coupling and plasmon tuning of multilayer Au/dielectric/Au nanocrescents adhered to a dielectric cylinder

Quantifying Optical Absorption of Single Plasmonic Nanoparticles and Nanoparticle Dimers Using Microstring Resonators

The wide and ever-increasing applications of thermoplasmonics demand the need for sensitive and reliable tools to probe optical absorptions of individual nanoparticles. However, most of the currently available techniques focus only on measuring the surface temperature of nanostructures in a particular medium and are either invasive or suffer from low sensitivity, lengthy calibration, or the inability to probe single structures with nanogaps. Here, we present for the first time the use of micromechanical SiN string resonators for quantifying optical absorption cross sections of individual plasmonic nanostructures. Monomers and dimers of nanospheres, nanostars, shell-isolated nanoparticles, and nanocubes are probed. A reliable data treatment method is developed to obtain the absorption cross sections as a function of responsivity across a string. The presented method exhibits an excellent sensitivity of ∼89 Hz/K. This allows quantification of optical absorption cross sections of individual plasmonic structures even when their plasmon resonance wavelengths are far from the laser excitation wavelength. The experimentally obtained optical absorption cross sections agree well with the simulations. Influencing factors including polarization, surface morphology, and nanogap size are discussed. The developed method and the obtained optical absorption profiles facilitate future development and optimization of thermoplasmonic applications.

Study on Surface-Enhanced Raman Scattering Substrate Based on Titanium Oxide Nanorods Coated with Gold Nanoparticles

A 3D surface-enhanced Raman scattering (SERS) substrate based on titanium oxide nanorods (TiOx-NRs) coated with gold nanoparticles (Au-NPs) was fabricated by a simple hydrothermal, no-template process. The nanostructure of TiOx-NRs influenced by the concentrations of hydrochloric (HCl) acid and sodium chloride (NaCl) was studied in detail. The substrate showed the strongest Raman enhancement, when the diameters of Au-NPs were around 40 nm and the gaps of Au-NPs were in the range of 5 nm to 10 nm. The surface electric field of our substrate was examined by finite-different time-domain (FDTD) solutions. Rhodamine 6G (R6G) was chosen as the probe molecule to study the SERS performance of the substrates. The Raman signal of 10−10 M R6G was detected clearly by the substrate with the enhancement factor of 2.64 × 108. All relative standard deviation (RSD) values of the major peaks for R6G were within the scope of 10.4% to 16.7%. The substrate could work efficiently even after immersed in water for one month.

Plasmon resonances of Ag capped Si nanopillars fabricated using mask-less lithography

Localized surface plasmon resonances (LSPR) and plasmon couplings in Ag capped Si Nanopillar (Ag NP) structures are studied using 3D FEM simulations and dark-field scattering microscopy. Simulations show that a standalone Ag NP supports two LSPR modes, i.e. the particle mode and the cavity mode. The LSPR peak position of the particle mode can be tuned by changing the size of the Ag cap, and can be hybridized by leaning of pillars. The resonance position of the cavity resonance mode can be tuned primarily via the diameter of the Si pillar, and cannot be tuned via leaning of Ag NPs. The presence of a substrate dramatically changes the intensity of these two LSPR modes by introducing constructive and destructive interference patterns with incident and reflected fields. Experimental scattering spectra can be interpreted using theoretical simulations. The Ag NP substrate displays a broad plasmonic resonance band due to the contribution from both the hybridized particle LSPR and the cavity LSPR modes.