This talk will provide an overview of recent advances in the development of theoretical methods for characterizing SERS and TERS, with emphasis on using electronic structure methods to interpret experiment. The theory work begins with electronic structure methods for describing clusters of silver atoms with 10-200 atoms as such clusters have been demonstrated to exhibit plasmon-like excited states that consist of coherent superpositions of many particle-hole excitations. These clusters are therefore useful for describing surface enhanced Raman spectroscopy (SERS), including recent two-color experiments where electrons are liberated from gold nanoparticles with 500 nm light, and we have also studied hot electron chemistry involving H2 dissociation. However self-interaction errors lead to charge transfer states that often have unphysically low energies, and this sometimes leads to unphysical features in the spectra. Recently we have developed improved INDO-based methods that generate the same spectral properties as TDDFT but the charge transfer states are physically meaningful. This has enabled us to generate a meaningful description of both the electromagnetic and chemical mechanisms of SERS and the tip-enhanced variant, TERS. In addition, this approach can be used to mimic electrochemistry experiments, and we demonstrate the utility of this by showing how this can be applied to single-molecule electrochemistry measurements that have recently been reported in the Van Duyne lab at Northwestern. In another direction, we have recently developed a method for calculating the rate of energy transfer between donor and acceptor molecules that are in the presence of a complex dispersive dielectric medium that can include plasmonic nanoparticles. This method involves full quantum electrodynamics, but the computational effort is simply that of a standard classical Maxwell equation solver, such as the finite different time-domain method. We demonstrate the application of this approach to plasmon-mediated energy transfer, where the rates can be enhanced by orders of magnitude compared to standard energy transfer dynamics in the absence of nanoparticles.

Theories of SERS, TERS, and plasmon-enhanced energy transfer

2019 Fall National Meeting

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