Creating and Probing Optical and Material Nonlinearities in Single Nanoparticles, Dimers, Clusters and Arrays

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Norbert Scherer of the University of Chicago is supported by the Experimental Physical Chemistry Program to carry out a comprehensive plan of definitive structure-function (i.e. nonlinear optical response) measurements of individual metal nanoparticle-based materials. These materials are single silver and gold nanospheres and nanorods and spontaneously formed dimers and clusters thereof on inert surfaces that allow TEM and optical measurement. Extended one and two-dimensional materials will be created and studied. Research aims are the following: (1) to improve the spatial resolution of the optical-spatial correlation method that has been developed to ~10 nm to allow determination of the origin of the nonlinear signals from nanoparticle dimers, clusters, and arrays, (2) to implement a range of nonlinear optical measurements (e.g. SHG and 2-photon fluorescence interferometry, third-order nonlinear scattering interferometry, and SERS) for comparison with linear scattering from single nanoparticle features to quantify the local field enhancements and dynamics of the multi-particle resonances created, (3) to explore the multi-body (or multi-point) interactions among photons and one or two nanoparticles and an optical trap, to establish the force between the particles resulting from the trapping field as well as the multi-point interaction of single photons with multiple particles observed as a nonlinear enhancement ,and (4) to extend the first three projects to the study of plasmon coupling and delocalization in self-assembled close-packed monolayer arrays of nanocrystals and in ordered nanorod arrays created by standing wave optical trapping. The overall goal of this research is to improve understanding of and ultimately allow control of plasmon-based optical and material nonlinearities.The longer-range motivations of this project are stimulated by the vision of nanoscale optical devices. The fundamental science that will be achieved could ultimately lead to the development of better optical sensors and reflective mirrors that are tunable. This research could lead as well to the development of probes for investigating biological structures and local chemical composition on the nano-scale.