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Seminar | Nanoscience and Technology Division

Time-Resolved X-Ray Absorption Spectroscopy: Watching Intermediates Dance

NST Seminar

Abstract: The introduction of pump-probe techniques to the field of X-ray absorption spectroscopy (XAS) has allowed the monitoring of both electronic and structural evolution between intermediates of photoreaction systems with unprecedented accuracy, both in time and in space. In this talk, I will first present the time-resolved (TR-XAS) technique at Advanced Photon Source Sector 11-ID-D, which was developed in the ultrafast laser pump-synchrotron X-ray probe configuration. Then, I will present the application of our TR-XAS technique to measure two representative photoreaction sample systems. In the solution case of spin-crossover [low spin (LS) ↔ high spin (HS)] Fe monomer, we have precisely determined the light-induced Fe-N bond length change from LS to HS states in two different solvents. In the suspension example of lead-free perovskite nanocrystals, we have found that upon photoexcitation, the electron is delocalized but the hole is localized at the Br atom via likely forming Br2 dimer as Vk center. At the same time, the hole localization results in a local structural distorted state, which is long-lived (~60 µs) compared with the recombination of charge carriers (~20 ns). Additionally, I will present our recent preliminary TR-XAS results of 2-D and 3-D lead perovskite thin films from our new home-built sample platform.

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