Visualizing Ultrafast Structural Deformations in Nanocrystals Under Nonequilibrium Conditions

In the last decades nanocrystals have become ubiquitous systems for optoelectronic and energy technologies with applications in solar cells, light-emitting diodes and artificial photosynthesis. Pushing performance limits in these applications beyond the state of the art requires discovering new insights on the processes causing nonradiative losses such as trapping and hot carrier relaxation. In this talk, I will present utilization of ultrafast electron diffraction probes to unravel nonradiative relaxation pathways and associated dynamics in nanocrystals from a lattice point of view. By resolving diffraction peak intensities and positions in a stroboscopic manner on picosecond timescales following a pulsed laser excitation, we visualize the dynamic evolution of both thermal and non-thermal transient disordering arising from hot-carrier cooling, electron-lattice coupling and polaron formation. Using this approach, we recently uncovered hot carrier trapping in nanocrystals which occurs through formation of small polarons on nanocrystal surfaces leading to localized lattice deformations [1]. Also, we demonstrated hot-carrier relaxation pathways in plasmonic nanocrystals with different size and surface chemistry unraveling new structure – property relationships [2].<br/>[1] B. Guzelturk, B. Cotts. D. Jasrasaria, J. Philbin, et al., Nature Communication 12, 1860 (2021)<br/>[2] B. Guzelturk, et al., ACS Nano 14, 4792 (2020)