How do emerging light harvesting materials form, transform, and transport energy at the nanoscale?

We are interested in the optoelectronic properties and the spatiotemporal nature of photogenerated energy carrier transport of emerging semiconducting materials, broadly defined. These materials include not only semiconductors who basic building blocks are atoms but also those made of small particles or molecules, including the aggregates of molecular pigments involved in photosynthesis. Those of greatest interest to us are ones that spontaneously assemble into organized and/or densely packed solid structures starting from the solution phase or whose structures can be thermodynamically or kinetically transformed. What are the multiscale relationships between the dynamics and products of material formation and transformation and the emergent electronic properties of these materials? How does disorder, as an inherent byproduct of the assembly process, affect these properties both locally and macroscopically?

To answer these questions I will provide examples of our work to elucidate the mechanisms for ultrafast photoinduced energy transport and for the slower dynamics of material transformations in a wide range of emerging, heterogeneous electronic materials. This work has often required the development of spectroscopic nano-imaging modalities with new, more appropriate combinations of spatial sensitivity and temporal resolution. As examples, I will take you first on a journey with transient optical elastic scattering to reveal the nature of energy flow - structure correlations for various photogenerated species in virtually any semiconductor. In related materials, we will then explore the nature of structural phase transitions both at and away from equilibrium using cathodoluminescence microscopy - the mapping of light emitted from a sample in a scanning electron microscopy - and in situ X-ray scattering.

Speaker: Naomi Ginsberg, UC Berkeley