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

Georgia Tech Research Corporation, Atlanta GA

Investigators

Abstract

TECHNICAL SUMMARY: From previous studies of the El-Sayed group and other researchers in the plasmonic nanoparticle field, it is clear that the surface plasmon fields of gold and silver nanoparticles offer many new and exciting directions. A large volume of the studies in the field, especially those by the Schatz and Van Duyne groups, have shown how these fields depend on the nanoparticle size and shape. It is further known that the field between nanoparticles can be much stronger than the fields of individual nanoparticles. The dependence of the overlapping fields of pairs of gold or silver nanoparticles on their shape, size, orientation, and separation has not been given the same attention. The electron beam lithography facilities located within the Georgia Institute of Technology Microelectronics Research Center will be utilized to further these studies. Nanoprisms, nanorods, nanocubes, nanorings, and additional nanoparticle shapes will be fabricated by top down methods and studied as a function of their size, orientation, and interparticle separation. Using DDA methods, which have been previously well established in the El-Sayed group, extinction, absorption, and scattering yields as well as the surface field intensities will be calculated for all such configurations. Also, the correlation between the plasmonic field strength calculated for different configurations and the various spectroscopic properties of nanoparticle pairs (absorption and scattering) will also be studied. Plasmonic field effects associated with enhanced spectroscopic properties of nearby electronic systems (molecule and semiconductors) such as the absorption, fluorescence, non-radiative relaxation of hot electrons, and surface enhanced Raman scattering will also be investigated. From the observed dependence of the surface plasmon resonance on interparticle separation, nanoparticles of different sizes and shapes will be studied for nanoruler applications of different distance ranges for biological and macromolecular intersite separations. The observed quantitative SERS or fluorescence quenching and enhancement could also be used for sensing and diagnostic applications. NON-TECHNICAL SUMMARY: Nanostructures consisting of plasmonic nanoparticle pairs have interesting optical properties because of the very strong near-field coupling between the nanoparticles. These properties have already begun to impact a number of fields such as field-enhanced spectroscopy and plasmon resonance sensing for enhanced sensor applications, nanostructured optical probes for improved imaging devices, and nanophotonic waveguides and devices for applications in energy transport. Fundamental studies of the plasmon resonance coupling in metal nanoparticle assemblies will help characterize and optimize plasmonic nanostructures for potential applications. An important contribution during the proposed support period will be in maintaining the current cross-disciplinary relationships that have been established during the previous support period through partnerships with the Microelectronics Research Center (MiRC) at Georgia Tech. As a member of the National Nanotechnology Infrastructure Network (NNIN) the MiRC has been instrumental in catalyzing inter-disciplinary partnerships. Through collaboration with the MiRC and use of state-of-the-art equipment located therein, a versatile network of researchers has been developed that integrates scientific fundamentals and engineering optimization, which have led to several inter-discipline publications and conference presentations. There will be an educational impact of the proposed research on training of graduate and undergraduate students as well as postdoctoral researchers in the broad range of areas of nanotechnology including nanofabrication, colloidal chemistry, optical spectroscopy, and electrodynamics. In addition, the El-Sayed group has always attracted and accepted intelligent NNIN and REU summer undergraduate students to who contribute to this research while receiving exceptional experience in a research laboratory environment. The partnerships that have been established will improve upon the impressive tradition of education and training that Georgia Tech has provided to students to prepare them for careers in the field of nanotechnology, in both academia and industry.