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David J. Flannigan: Multidimensional Visualization of Materials Dynamics with Ultrafast Electron Microscopy

The ultimate goal of this project is to spatially map atomic trajectories following coherent excitation and to elucidate how this energy evolves and is transported across a wide range of spatial and temporal scales. Accomplishing this will require gaining access to a large, multidimensional parameter space (i.e., length, energy, and time). For example, femtosecond optical excitation of charge carriers at atomic length scales may manifest as millisecond micromechanical motions via coupling through collective, low-energy nanoscale lattice fluctuations. Further, in order to formulate a comprehensive and quantitative understanding of time-dependent energy nucleation, propagation, and decay, the influence of individual atomic-scale lattice imperfections must be resolved. To achieve this, Flannigan will develop correlated real- and reciprocal-space methods of ultrafast electron microscopy and use them to connect atomic-to-mesoscale excitation dynamics and energy evolution in a variety of materials, including transition metal dichalcogenides (WSe2, 1T-TaS2, MoS2, etc.) and iron (oxy)pnictides (LaFeAsO).

Frequency mapping of a single-crystal silicon cantilever illustrating localized MHz nanomechanical motions excited following femtosecond optical excitation. The color corresponds to vibration amplitude, with blue indicating no observed motion and dark-red being indicative of high-amplitude oscillation.

Funded by the National Science Foundation through the University of Minnesota MRSEC under Award Number DMR-1420013