Mode- and state-selective nanoparticle dynamics from correlative light, ultrafast, and magneto-optical imaging

Seminar: Physical Chemistry | November 14 | 4-5 p.m. | 120 Latimer Hall

 Kenneth Knappenberger, Department of Chemistry, The Pennsylvania State University

 College of Chemistry

Correlative light and electron microscopy (CLEM) is a powerful approach to developing structure-function relationships for nanoscale materials. Our group has developed nonlinear optical (NLO) imaging methods that can be used to pinpoint the location of an optical point source with one-nanometer transverse and ten-nanometer axial localization accuracies. Among the suite of NLO processes, magneto-optical (MO) methods enable simultaneous spatially resolved characterization of the electronic and optical properties of these material domains. We will provide examples using variable-temperature, variable-magnetic-field optical methods to determine electronic g factors, term symbols, and zero-field energy gaps for excitonic transitions in nanoscale materials. As one example, I will describe recent advances in understanding the influence of nanoscale structure on plasmon-mediated electron dynamics. Steady-state extinction spectra of plasmonic nanoparticle networks are accurately described using hybridization models reminiscent of molecular orbitals. We have extended these molecular-based descriptions to account for nanoparticle electron dynamics by quantifying the coherence dephasing times of collective inter-particle plasmon modes of single nanostructures. In particular, we demonstrate that interference between plasmon modes of different angular momenta leads to increased coherence times. These observations are consistent with a model based on superpositions of molecular-like electronic states. These fundamental studies are important for understanding the structure-photonic-function relationship of plasmonic nanoparticles. This is because the spectroscopically determined coherence times reflect mode quality factors, which determine achievable amplification factors of optical signals.

 Light refreshments will be served at 3:50 at The Coffee Lab, 510-643-0572