Browsing by Author "Radloff, Corey J."

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    Concentric nanoshells and plasmon hybridization
    (2004) Radloff, Corey J.; Halas, Naomi J.
    The optical properties of metal nanostructures are related to their plasmon response, which is sensitively dependent on nanostructure geometry and environment. The metallodielectric, core-shell structure of nanoshells represents a unique geometry allowing for the systematic tunability of the plasmon resonance of the nanostructure. This is accomplished by varying the relative dimensions of the core and shell layers. Fabrication of a nanoshell particle with a strong plasmon resonance is dependent on shell quality, which is strongly dependent on the careful preparation of the metal shell. The resonant response of metal nanostructures can also be modified through plasmon-plasmon interactions. This work focuses on the fabrication of nanoparticles with a multilayer, concentric-shell structure consisting of a silica core, inner gold shell layer, silica spacer layer, and an outer gold shell layer. This concentric nanoshell particle is fabricated through the controlled growth of a nanometer-scale silica layer around a preformed nanoshell. The silica layer was found to increase the thermal and chemical stability of the nanoshell particles. A second gold shell could be grown on this layer to generate the concentric nanoshell particle. This layered nanoparticle geometry has a plasmon resonance dependent on the interaction between the inner and outer shell plasmons. This interaction can be explained in terms of a sphere-cavity model of plasmon hybridization derived from a semi-classical model of the plasmon resonance. Varying the dimensions of the concentric shell layers can independently and systematically control the plasmon resonance of the inner and outer shell, which effects the interaction between the two plasmons. The coupling between the inner and outer shell plasmons was investigated experimentally by varying the concentric nanoshell dimensions, specifically examining how the spectral detuning of the inner and outer shell resonances and spatial interaction between inner and outer shell plasmons determine the nanoparticle's optical properties. Calculations using Mie scattering theory to model the nanoshell plasmon response agree quantitatively with experimental measurements of the nanoshell plasmon resonance in both the single-layer and multi-layer regime.
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    Methods for producing submicron metal line and island arrays
    (2005-04-05) Moran, Cristin Erin; Radloff, Corey J.; Halas, Nancy J.; Rice University; United States Patent and Trademark Office
    This process results in directed electroless plating of the metal to form discrete metal structures over the entire surface. Because the surface is pre-patterned with passivated regions inert to metal deposition, the metal is directed only to the unstamped regions. This allows the formation of unconnected metal structures without any chemical etching steps. These metallic arrays are varied in size, separation and shape by using gratings of different periodicities and blaze angles as the stamp templates. A variety of well-defined geometric patterns have been fabricated and imaged using scanning probe, scanning electron, and optical microscopies.
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    Multi-layer nanoshells comprising a metallic or conducting shell
    (2006-12-05) Halas, Nancy J.; Radloff, Corey J.; Rice University; United States Patent and Trademark Office
    Composite particles containing metallic shell layers are provided. The particles may include a coating layer, such as of a protective or electrically non-conducting material, over an outermost metallic shell layer. The particle preferably has a plasmon resonance associated with at least one metallic shell layer. The coating layer preferably imparts improved thermal stability to the plasmon resonance. Further, the present invention relates to particles that include at least two metallic shell layers, separated by a coating layer. The addition of a second metallic shell layer preferably allows the plasmon resonance of the shell layer to be more red-shifted with respect to a colloidal particle of the metal that the plasmon resonance of a particle of the same size but with only a single metallic shell.