Title: Structure Inference from X-ray Absorption Spectroscopy: Pilot Projects for Operando Experimentation
host: Phil Allen
abstract: X-ray Absorption Near Edge Structure (XANES) is well-adapted for in situ and operando experiments. It is both atomically specific and it encodes local structure of the surrounding atoms. Due to multiple scattering effects, inferring that structure from the spectra can be complex. In the Center for Functional Nanomaterials, we are pursuing several prototype projects with collaborating groups to explore approaches to solve this inverse problem and pursue nanomaterials research enabled by these methods. We seek to go beyond the empirical fingerprint method, particularly to broaden applicability to structural motifs that emerge in studies of new or nanostructured materials. Our over-arching approach is two-fold: exploit theory for direct computation of XANES spectra for a pertinent database of material structures to support and train data analysis techniques; develop and validate these techniques through comparison to experiments. Following a brief introduction of operando experimental techniques and the role of X-ray absorption spectroscopy, I will describe a series of pilot projects [1-3] that illustrate different aspects of structure inference, including the training of artificial neural network models.
Work performed in part at the Center for Functional Nanomaterials, which is a U.S. DOE Office of Science Facility, at Brookhaven National Laboratory under Contract No. DE-SC0012704.
 J. Timoshenko, et al., J. Phys. Chem. Lett. 8, 5091 (2017).
 M. R. Carbone, et al., Phys. Rev. Mater. 3, 033604 (2019).
 D. Yan, et al., Nano Lett. 19, 3457, (2019).
Brief Biography: Mark S. Hybertsen holds a BA in Physics from Reed College in Portland, OR (1980) and a PhD in Physics from The University of California, Berkeley (1986) where his thesis research was directed to many-body perturbation theory and the GW approach. Dr. Hybertsen joined Bell Laboratories in 1986, pursuing a variety of research projects in the theory of the electronic properties of materials. He supervised the Device and Materials Physics Group in the Semiconductor Photonics Research Department for four years. From 2003 to 2006, Dr. Hybertsen was a Senior Research Scientist in the Department of Applied Physics and Applied Mathematics at Columbia University in New York, where he has also been an Adjunct Professor in the Department of Electrical Engineering. In 2006, Dr. Hybertsen joined the new Center for Functional Nanomaterials at Brookhaven National Laboratory. He is a Senior Scientist, leading the Theory and Computation Group. He has also had adjunct research appointments at Columbia University. Dr. Hybertsen is a fellow of the American Physical Society and a member of the IEEE and the American Chemical Society.