Monitoring Nanoscale Optical Excitation and Energy Transfer with Optically Coupled Electron Microscopy

Transmission electron microscopes (TEM) have evolved beyond tools for atomic-scale imaging and diffraction. Modern TEMs are now integrated instruments capable of witnessing the dynamic material behavior at the nanoscale. One notable advance is the combination of the TEM with ultrafast lasers for the development of ultrafast electron microscopy (UEM) to investigate the light-matter interactions with a time resolution of hundreds of femtoseconds and a spatial resolution at the nanometer scale. Recent work will be presented on on understanding the optical excitation on earth-abundant plasmonic aluminum nanocrystals based on photon-induced near-field electron microscopy (PINEM) results on UEM. Using a visible pump pulse and a time-gated electron wave-packet probe the dynamics of photon-induced near-fields can be measured in space and time. This presentation will detail recent experimental results and theoretical insights into the behaviors observed on aluminum nanocrystals with an intrinsic aluminum oxide layer and nanocrystals modified with insulating silicon dioxide and semiconducting titanium dioxide shells. Oxide modification of plasmonic aluminum nanoparticles is hypothesized to influence energy transfer mechanisms associated with carrier excitations and extraction during plasmon excitation and decay. The results presented in this talk are expected to yield insight into other applications of modified plasmonic nanomaterials, namely photocatalysis.