报告题目：Vibrational exciton and polaron nano-imaging: new functional nano-imaging for molecular electronic, photonic, and photovoltaic materials
报 告 人：Markus B. Raschke (Department of Physics and JILA, University of Colorado)
Properties and functions of molecular materials often emerge from intermolecular interactions and associated nanoscale structure and morphology. However, defects and disorder give rise to confinement and many-body localization of the associated wavefunction, disturbing the performance of, e.g., molecular electronic materials. Similarly, in organic-inorganic perovskites, while the soft lattice gives rise to polaron formation believed to be responsible for their extraordinary photovoltaic performance, it simultaneously facilitates a high degree of spatial heterogeneity in the optoelectronic response. However, conventional microscopy techniques lack sensitivity to the low-energy scales of intermolecular interactions, carrier-phonon coupling, and polaron formation leaving a missing link between material structure and observed heterogeneity in the electronic or photonic response.
We address this outstanding problem in several novel combinations of spatio-spectral and spatio-temporal infrared nano-imaging. Through probing vibrational exciton formation as a molecular ruler, we resolve the evolution of defects in growth of competing amorphous and crystalline phases in porphyrin model organic electronic materials . Similarly, imaging intramolecular and intermolecular vibrational coupling in polymers and molecular monolayer, we spatially resolve the molecular level origin of multiscale morphologies. In the extension to probing both electronic and lattice degrees of freedom, in organic-inorganic perovskites we image the elementary processes of heterogeneous cation-lattice coupling , and associated both vibrational and polaron dynamics in ultrafast visible/IR nano-imaging. These nm-ps resolved space-time movies provides for a direct view how the low-energy charge-phonon interactions leads to optoelectronic heterogeneity. As a perspective we show how electronic, vibrational, and polaron quantum state nano-spectroscopy in the low energy landscape of molecular matter provides for functional imaging as a new tool to guide the molecular device fabrication with improved performance.
 E. A. Muller, T. P. Gray, Z. Zhou, X. Cheng, O. Khatib, H. A. Bechtel, and M. B. Raschke, “Vibrational exciton nanoimaging of phases and domains in porphyrin nanocrystals”, PNAS 117, 7030 (2020).
 J. Nishida, A. H. Alfaifi, T. G. Gray, S. E. Shaheen, and M. B. Raschke, “Heterogeneous cation-lattice interaction and dynamics in triple-cation perovskites revealed by infrared nanoscopy”, ACS Energy Letters. 5, 1636 (2020).
Markus Raschke is professor at the Department of Physics, Department of Chemistry, and JILA at the University of Colorado at Boulder. His research is on the development and application of new nano-scale nonlinear and ultrafast spectroscopy techniques to control the light-matter interaction on the nanoscale. These techniques allow for imaging structure and dynamics of molecular and correlated matter with nanometer spatial resolution. He received his PhD in 2000 from the Max-Planck Institute of Quantum Optics and the Technical University in Munich, Germany. Following research appointments at the University of California at Berkeley, and the Max-Born-Institute in Berlin, he became faculty member at the University of Washington in 2006, before moving with his group to Boulder in 2010. He is fellow of the Optical Society of America, the American Physical Society, and the American Association for the Advancement of Science.