Modeling of nanoshells spectra in evanescent wave field via discrete sources method

Simple, fast and flexible computer model to analyze optical spectra of individual nanoshells deposited on a prism surface has been developed. It is based on rigorous theory of discrete sources method and enables to account for complete interaction between scatterer and prism surface analytically. Model is implemented to examine local biosensor operation in a field of evanescent waves.     

Optical bistability in plasmonic nanoparticles: Effect of size,shape and embedding medium

We theoretically investigate the optical bistability, which one input signal allows two possible outputs, from single spherical/cylindrical nanoparticles and also nanoshells in the frame work of quasi-static formalism. It is shown that the bistability behavior greatly depends on several parameters such as the nanoparticle size, material and the surrounding dielectric environment. We demonstrated the width of the bistability region and also the bistable threshold depends on the geometrical parameters, and can be tuned by adjusting the size of nanoparticle, the shell thickness and the dielectric constant of the embedding medium. It is also shown that the optical bistable behavior depends strongly on the shape of plasmonic nanoparticles and nanoshells. However, these dependences of optical bistability of spherical/cylindrical nanoparticles and nanoshells on changing of their geometrical parameters can be used for realize optical switching and sensing purposes.     

Synthesis and plasmonic properties of silver and gold nanoshells on polystyrene cores of different size and of gold–silver core–shell nanostructures

Simple methods of preparing silver and gold nanoshells on the surfaces of monodispersed polystyrene microspheres of different sizes as well as of silver nanoshells on free-standing gold nanoparticles are presented. The plasmon resonance absorption spectra of these materials are presented and compared to predictions of extended Mie scattering theory. Both silver and gold nanoshells were grown on polystyrene microspheres with diameters ranging from 188 to 543 nm. The commercially available, initially carboxylate-terminated polystyrene spheres were reacted with 2-aminoethanethiol hydrochloride (AET) to yield thiol-terminated microspheres to which gold nanoparticles were then attached. Reduction of silver nitrate or gold hydroxide onto these gold-decorated microspheres resulted in increasing coverage of silver or gold on the polystyrene core. The nanoshells were characterized using transmission electron microscopy (TEM), scanning electron microscopy (SEM) and UV–vis spectroscopy. By varying the core size of the polystyrene particles and the amount of metal (silver or gold) reduced onto them, the surface plasmon resonance of the nanoshell could be tuned across the visible and the near-infrared regions of the electromagnetic spectrum. Necklace-like chain aggregate structures of gold core–silver shell nanoparticles were formed by reducing silver nitrate onto free citrate-gold nanoparticles. The plasmon resonance absorption of these nanoparticles could also be systematically tuned across the visible spectrum.     

Slowing light in diatomic nanoshelled chains

Coupled plasmon modes have been studied theoretically in periodic chains of shelled and unshelled metal nanoparticles embedded alternatively in a dielectric host, thus forming a diatomic chain. We calculate the dispersion relation of the diatomic chains and show that we can tune the shelled particle band into the unshelled particle band by varying the permittivity contrast and/or the core-shell radius ratio. This offers a precise control of the group velocity of coupled plasmon modes. The experimental realization of such diatomic chains by surface plasmon enhanced binding will be discussed.     

The optical properties in a chain waveguide of an array of silver nanoshell with dielectric holes

Plasmonic chain waveguide by employing an array of silver nanoshell with dielectric holes that interact with incident plane wave of transverse magnetic polarization are simulated by use of the finite element method. Results show that the working wavelength of the system is highly tunable by using the nanoshell instead of solid particles and by varying the dielectric constant of the core. Besides, chain waveguides that are operated on resonant multipolar modes can provide longer propagation lengths, which is beyond what is maximally achieved by conventional solid particle chains.