Radiative and ultrafast non-radiative electronic relaxation in individual and assembled noble metallic nanoparticles of different shapes

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TECHNICAL SUMMARYThe main focus of this renewal project, supported by the Solid State and Materials Chemistry program, is to elucidate the effects of plasmonic fields on the dynamics of important photochemical and photophysical systems (e.g. polymers, doped and undoped metal oxides, and the protein bacteriorhodopsin). Doped TiO2 has attracted much recent attention in the scientific community because the use of plasmonic silver and gold nanoparticles has greatly enhanced the material's photocatalytic and photoelectrochemical efficiency. Bacteriorhodopsin is one of only two naturally-occurring photosynthetic systems and, in addition to its important chemical and biological properties, has been considered for applications in solar-energy conversion and electronics. In all of these materials there is little known about the effects of strong plasmon-enhanced local electric fields on their fundamental dynamical light-induced processes. The dynamics may involve unknown excited states and intermediates and altered kinetic rates. Fundamental processes most important to applications in photocatalysis and solar-energy conversion will be identified and colloidal chemistry will be used to synthesize new noble-metal nanostructures that selectively enhance the probabilities and/or dynamics of photophysical events. This program will build upon the El-Sayed group's extensive accomplishments in the areas of plasmonics, metal and semiconductor nanostructures, spectroscopy, catalysis, photochemistry, and photobiology.NON TECHNICAL SUMMARYThe proposed work seeks to determine at a fundamental level the interactions between plasmonic nanoparticles and materials that can be applied for photocatalysis and solar-energy conversion, so that the mechanisms responsible for plasmon-enhanced performance may be elucidated. Success will provide chemists, physicists, materials scientists, and engineers with knowledge on how best to incorporate noble-metal nanoparticles into devices and catalytic systems. The knowledge obtained will inform scientists in the field of colloidal chemistry on new synthesis strategies and how to optimize nanoparticle shape, size, structure, composition, and interparticle arrangement for particular applications. Students, postdoctoral fellows, and junior scientists will gain valuable multidisciplinary experience in chemistry, spectroscopy, and nanotechnology in preparation for careers in academia or industry.The electric field enhancement caused by gold and silver nanostructures has revolutionized entire fields such as Raman spectroscopy. Although the cost of noble metals is very high, the many orders-of-magnitude enhancement in surface-enhanced Raman scattering suggests that only extremely small amounts of material may be needed in optimized systems. Taking full advantage of plasmonic effects while minimizing cost requires a detailed understanding of the static and dynamical properties of materials coupled to plasmonic fields, as well as scalable chemical syntheses that avoid expensive and time-consuming techniques such as electron beam lithography. Success in this endeavor will help to better utilize sunlight as an energy source and reduce the energy consumed to produce important industrial products such as H2. The resulting technological and economic growth, while slowing the rate of releasing pollutants and greenhouse gases into the environment, will have a significant worldwide impact.