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The plasmonic properties of a concentric nanoshell, or “nanomatryushka”, are investigated. The plasmon resonant modes are analyzed in terms of the plasmon hybridization model, where new resonances occur due to a hybridization of the plasmon modes of the inner metallic shell with those of the outer metallic shell. The plasmon resonant spectra of experimentally realized concentric nanoshells are analyzed in terms of dipolar and higher order multipolar hybridized plasmon modes. A size-dependent asymmetry in the splitting of the hybridized plasmon states is observed, which is related to phase retardation effects due to the nanostructure's finite size.

We report on the dramatic chemical reshaping of metallodielectric nanoparticles upon exposure to cetyltrimethylammonium bromide (CTAB) in aqueous solutions. Metal nanoshells possessing a silica core with a gold shell were observed to undergo a morphological change from their initial shell structure to that of large, elongated gold nanoparticles or toroids. This reaction is dependent on the chemical species available in solution and on the metal shell thickness on the nanostructure. Surprisingly, dissolution of the silica core due to the presence of CTAB was also observed during the reshaping of the nanoshells.

We present a simple and intuitive picture, an electromagnetic analog of molecular orbital theory, that describes the plasmon response of complex nanostructures of arbitrary shape. Our model can be understood as the interaction or “hybridization” of elementary plasmons supported by nanostructures of elementary geometries. As an example, the approach is applied to the important case of a four-layer concentric nanoshell, where the hybridization of the plasmons of the inner and outer nanoshells determines the resonant frequencies of the multilayer nanostructure.

We report a general chemical strategy for producing reduced-symmetry metallodielectric nanoparticles, nanocups, and nanocaps that combines nanoscale masking techniques and nanoparticle-seeded electroless plating. Using this approach, silica nanoparticles with a gold cup-shaped shell and, alternatively, a gold cap, are obtained. The plasmon response of both nanostructures is a sensitive function of orientation of the nanostructure with respect to the direction and polarization of incident light. This orientation dependence is examined experimentally by studying the extinction spectra of oriented nanocups and nanocaps on transparent substrates, and is also evaluated theoretically using a three-dimensional finite difference time domain (FDTD) method.

Understanding the chemistry of carbon nanotubes is a crucial step towards their ultimate practical use. Here we report the first nanoscale images of single wall nanotubes (SWNTs) whose sidewalls have been chemically derivatized. Scanning tunneling microscopy (STM) images of fluorinated SWNTs reveal a dramatic banded structure which indicates broad continuous regions of fluorination terminating abruptly in bands orthogonal to the tube axis. This pattern is consistent with an energetically favored addition mechanism where fluorine atoms add around the circumference of the tube. STM images of sparsely butylated SWNTs, for which fluorinated SWNTs served as precursor, are also reported.

A silica-encapsulating layer of a 60–70 nm thickness is fabricated around composite nanoparticles consisting of a silica core and a gold shell (metal nanoshells). The outer silica layer provides greatly enhanced thermal stability to the nanoparticle, effectively raising its melting temperature by 300° relative to uncoated nanoshells. Both spectroscopic and microscopic structural evaluations are used to assess changes in the nanostructure when subjected to potentially destructive heating cycles. This encapsulation method may prove valuable in enhancing the thermal stability of other types of assembled nanostructures and nanoscale photonic materials.

Summary form only given. Gold nanoshells are colloidal particles with a dielectric core covered by a gold shell. The plasmon resonance of the nanoshells can be tuned by varying the ratio of the core/shell radii. An enhancement in the electromagnetic energy can be found, at resonance, in the region close to the nanoshell known as the near field. It has been shown theoretically and experimentally that if the evanescent near fields of a surface plasmon polariton and a particle plasmon overlap, an efficient exchange of energy from the freely propagating electromagnetic waves into surface plasmons can be achieved. Previous experiments used particles that lacked the extraordinary tunability of nanoshells. We give our sample geometry. After evaporating a layer of gold onto a glass slide, we deposit self-assembled monolayers (SAMs) of a polymer (PDDA) and Hectorite (a synthetic clay), to control the spacing between the gold surface and the nanoshells.

Nanoshells are mesoscopic particles consisting of a dielectric core coated with a metal shell, in particular gold or silver, of uniform nanometer scale thickness. This topology supports plasmon excitations with frequencies that are sensitively dependent on the relative radii of the nanoparticle's core and shell. The plasmon linewidth for this geometry is typically quite broad, nominally 100 nm or more in wavelength at plasmon resonance wavelengths in the near infrared. Several distinct physical mechanisms control the plasmon lineshape: phase retardation effects, including multipolar plasmon contributions; inhomogeneous broadening due to core and shell size distributions; and electron scattering at the shell interfaces. These mechanisms are examined in terms of their relative contributions to the plasmon line shape for nanoshells fabricated with diameters of 100--250 nm.

We have demonstrated a method of fabricating long-range arrays of 2D metallic microstructures on glass surfaces and measured the optical resonances of those structures. Gold and silver stripes are fabricated using microcontact printing with PDMS gratings and electroless plating techniques without the use of resist masks or etching. Changing the blaze angle and periodicity of the gratings used to make the PDMS stamps varies the line widths. The optical response of these fabricated transmission gratings was evaluated by measuring the transmission spectra while varying the angle of the incident light.

We report a surprising chemical reactivity of gold nanoshells with carbon tetrachloride. Gold nanoshells are nanoparticles constructed from a silica core encapsulated in a gold shell. An aminoalkoxysilane linker molecule is used to derivatize the silica surface, which facilitates the attachment of the gold shell. Evidence is shown for the decomposition of the gold shell due to a reaction with carbon tetrachloride. The reaction is believed to proceed through the formation of a charge transfer complex between carbon tetrachloride and the gold-amine complex. The reaction is facilitated by the presence of defects in the shell layer.

We have measured the dependence of the strength of Raman activity of polycrystalline m-WO3 on spot size at constant laser power density. These data are compared to surface area scaling measurements obtained using scanning tunneling microscopy. We argue that the spatial distribution of scattering centers is the complement of the spatial distribution of crystallographic shear (CS) structures on or near the oxide surface. Our results are consistent with there being an essentially uniform spatial distribution of scattering sites which implies the spatial distribution of defect sites is also uniform. At the laser power density involved and at the defect densities studied, we found no evidence suggesting a large amount of cooperativity in the formation of CS structures. These results suggest a qualitative description of the structure of common oxide surfaces in agreement with a basic assumption of the JMAK theory of first order phase transformations.