Vibrational exciton and polaron nano-imaging: a molecular ruler to image structure, coupling, and disorder in functional molecular materials

PC Department Online Seminar
Date: Oct 14, 2021
Time: 02:00 PM (Local Time Germany)
Speaker: Prof. Markus Raschke
University of Colorado at Boulder
Host: Melanie Müller

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 or photonic materials. Conventional microscopy and even nanoscopy lack spatio-spectral sensitivity to the low-energy and molecular length scales of intermolecular interactions, carrier-phonon coupling, and polaron formation, thus leaving a missing link between material structure and observed heterogeneity in the electronic or photonic response.We address these outstanding problems 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 organic electronic materials and nano-domains in self-assembled monolayer on molecular length scales [1,2]. 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 that control the photovoltaic response [3]. We further demonstrate through Purcell-enhanced and strongly coupled light matter interaction the emergence of new hybrid light-matter state and their control for nano-metrology and -sensing [4]. 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.[1] T. P. Gray, J. Nishida, S. C. Johnson, and M. B. Raschke, “2D Vibrational exciton nanoimaging of domain formation in self-assembled monolayers”, Nano Lett. 21, 5754 (2021).[2] 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).[3] 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).[4] B. Metzger, E. Muller, J. Nishida, B. Pollard, M. Hentschel, and M. B. Raschke, “Purcell- enhanced spontaneous emission of molecular vibrations” Phys. Rev. Lett. 123, 153001 (2019).

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