Wednesday February 16, 2005
4 PM
PHO 339

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"Plasmonics: Optical Nanostructures by Rational Design (Joint ECE/CNN Colloquium) "
Prof. Naomi Halas
Rice University

In recent years, we have shown that certain topologies of metallic nanoparticles possess plasmon resonances that can be tuned by controlling the size and shape of the nanostructure during growth. The interesting observation that some nanoscale geometries support plasmons that are highly dependent on aspect ratio, such as nanoshells and nanorods, provides a starting point for the Plasmon Hybridization model recently developed (Prodan et al., Science 302, 419 (2003)). This simple and intuitive picture shows that we can interpret their plasmon response of metallic nanostructures as being due to the mixing and “hybridization” of plasmons of simpler geometries, in direct analogy with the hybridization of electron wave functions in molecular orbital theory. Plasmon hybridization provides a “design rule” that guides the development of more complex nanostructures with a plasmon response we can both predict and experimentally realize. In general, metallic nanostructures present interesting, well-defined electromagnetic nanoenvironments for studying the effect of the local fields of these structures on nearby molecules, nanostructures, materials or substrates. One recent example that has emerged from our work is a utilization of the nanoshell geometry as a nanoengineered substrate on which the Surface Enhanced Raman Scattering (SERS) response can be precisely controlled and optimized. Systematic variations of the internal geometry of the nanoparticle allow us to optimize the Raman response of molecules adsorbed onto Nanoshell substrates, an extremely useful feature for chemical and biosensing applications.

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