CAREER: Ultrafast Imaging and Spectroscopy of Cooperative Phenomena in Photomagnetic Nanomaterials

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Improvements in digital technology rely heavily on reducing the size of electronic components. Over the past three decades, the basic building blocks of computer chips have shrunk to nanometer dimensions, or about 1000 times smaller than a human hair. In this size range, nanostructures exhibit new properties and behaviors that are not observed in their bulk counterparts. The appearance of new nanomaterials that change their shape when exposed to light have the potential to impact many different technologies. However, watching a single particle change its shape in the laboratory presents unique challenges, since the time needed to switch from one form to the other is exceedingly short and cannot be captured by the fastest camera. In this project funded by the Chemical Structure Dynamics and Mechanism (CSDM-A) program of the Chemistry Division, Professor Renske M. Van der Veen at the University of Illinois at Urbana-Champaign (UIUC) is building a microscope that uses very short bursts of electrons (less than a millionth of a millionth of a second) to watch as a single nanostructure change its shape in response to light. Professor Van der Veen and her students are using this microscope to gain fundamental insight into the cascade of switching events that occur in metal-organic nanomaterials after light excitation. The results from this work could impact technologies ranging from data storage to optical switches in telecommunication, and thus could have significant benefit to society. As part of this CARRER project, Professor Van der Veen is developing new educational activities that will train the next generation of scientists in this emerging experimental methodology.Room temperature photoswitching is highly desired for realistic applications in functional devices. This project is advancing our understanding of first-order thermal phase transitions with cooperative hysteresis phenomena that occur around room temperature. Photoexcitation inside the hysteresis region may lead to efficient, "complete" switching of magnetic, dielectric and/or structural properties at the single-nanoparticle level. The project's focus is on iron- and iron-cobalt spin-crossover coordination polymers of different dimensionality, which undergo a rearrangement of electrons in their lowest d-orbitals upon light excitation. Transient absorption spectroscopy, ultrafast X-ray spectroscopy at synchrotron facilities, and a newly developed ultrafast electron microscope are used to investigate the interplay between structural and electronic degrees of freedom after photoexcitation. The project is also studying the mechanisms, time scales and efficiencies pertinent to cooperative photoswitching. The broader impacts of this work include STEM workforce enhancement through the development of a "3-Day Synchrotron Boot Camp" for undergraduate and graduate students, as well as research-integrated lectures and demonstration modules for female and underprivileged middle-school students.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.