Universal Scaling of Plasmon Coupling in Metal Nanostructures: Extension From Particle Pairs to Nanoshells

Laser Dynamics Laboratory, School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, Georgia 30332-0400, USA.
Nano Letters (Impact Factor: 13.59). 10/2007; 7(9):2854-8. DOI: 10.1021/nl071496m
Source: PubMed


It has been recently shown that the strength of plasmon coupling between a pair of plasmonic metal nanoparticles falls as a function of the interparticle gap scaled by the particle size with a near-exponential decay trend that is universally independent of nanoparticle size, shape, metal type, or medium dielectric constant. In this letter, we extend this universal scaling behavior to the dielectric core-metal shell nanostructure. By using extended Mie theory simulations of silica core-metal nanoshells, we show that when the shift of the nanoshell plasmon resonance wavelength scaled by the solid nanosphere resonance wavelength is plotted against the shell thickness scaled by the core radius, nanoshells with different dimensions (radii) exhibit the same near-exponential decay. Thus, the nanoshell system becomes physically analogous to the particle-pair system, i.e., the nanoshell plasmon resonance results from the coupling of the inner shell surface (cavity) and the outer shell surface (sphere) plasmons over a separation distance essentially given by the metal shell thickness, which is consistent with the plasmon hybridization model of Prodan, Halas, and Nordlander. By using the universal scaling behavior in the nanoshell system, we propose a simple expression for predicting the dipolar plasmon resonance of a silica-gold nanoshell of given dimensions.

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    ABSTRACT: In this paper, we report preparation and characterization of monodispersed hollow gold nanoparticles with the average thickness of about 25 nm through the template method. The formation of these hollow nanostructures involves three subsequent steps: preparation and functionalization of silica nanospheres, formation of a thick gold shell around the templates and following selective etching of silica particles by HF solution. In order to obtain monodispersed hollow particles, the optimum amount of trisodium citrate was used as stabilizing agent. The results show that although for both concentrated and diluted HF solution, pure gold nanoparticles were obtained, but the 10 volume percent HF solution destroys the hollow structures and just agglomerated gold particles were generated. Furthermore, by investigation the optical response of the synthesized metallic nanoparticles consisting gold nanoparticles, silica-gold nanoshells and hollow gold nanoparticles, it can be inferred that the hollow structures are capable to absorb wavelengths mainly within near infrared region. Hence, this paper introduces a new strategy to produce the metallic nanostructures with optical response within NIR range which may provide new opportunities for their applications in variety of fields such as photoelectronics, catalysis and cancer therapy.
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