Transient X-ray spectroscopy of photocatalysts can measure element-specific electron and hole energies, structural distortions like phonons and polarons, and charge transfer in molecules and materials. The advent of high-resolution electron energy loss spectroscopy (EELS) alongside advancements in TEM (e.g., monochromation, aberration correction, direct electron detection) enables atomic resolution vibrational, valence, and core-level EELS. Because core-level EELS is the analog of X-ray absorption spectroscopy, a material’s element-specific oxidation state, valence states, and coordination can often be deduced using theory. Ultrafast core-level EELS could hypothetically image fundamental material’s photodynamics in the first few picoseconds after photoexcitation by combining the TEM’s spatial resolution with information acquired by ultrafast X-ray absorption spectroscopy. In this talk, we translate developments of transient X-ray spectroscopies to atomic-scale TEM EELS for the measurement and imaging of photoexcited dynamics. We will also briefly describe our ab-initio excited-state X-ray theory, minor modifications needed to simulate EEL spectra, and the spectral interpretation needed to understand select photoexcited dynamics.

Translating ultrafast X-ray spectroscopy and theory to ultrafast, atomic-scale electron energy loss spectroscopy and imaging in the TEM

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