Materials World Network: New Insights into Ferroelectric Domain Walls: Extended Nanoscale Structure, Bloch-Like and Neel-Like Character, and Spatially Resolved Dynamics

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This MWN research focuses on new insights into the fundamental nature of ferroelectric domain walls developed by this joint US/Ukraine team over the past two years. In particular, the team leverages the comprehensive theory, simulation and advanced experimental framework they have developed for quantitative piezoelectric force microscopy (PFM). Using this framework, they have discovered unexpected broadening of ferroelectric domain walls over tens of nanometers. Analytical theory and phase field modeling, predicts that even a few nanometers of broadening can dramatically change the macroscale properties such as threshold fields for wall motion, by many orders of magnitude. The team predicts unusual magnetic-like domain walls in ferroelectrics. Such walls can be engineered to be extremely broad, (100's nm), and their dynamical properties under electric fields, and hence their impact on macroscale properties are presently unexplored. Using Scanning Spectroscopy Piezoelectric Force Microscopy (SSPFM), and optical second harmonic generation-near field scanning optical microscopy (SHG-NSOM), the team is exploring this mysterious new world of domain walls. Broadly speaking, the US team (Penn State and Oak Ridge National Labs) focuses on the experimental and phase-field simulations of such ferroelectric walls, while the Ukranian team (National Academy of Sciences, Ukraine) is developing the theoretical framework.The development of quantitative PFM and SHG-NSOM imaging techniques that combine theory, numerical simulations and cutting-edge experimental techniques are expected to have a much broader impact that extends beyond ferroelectrics, to other fields of materials science, chemistry and life sciences. This US/Ukranian team is an excellent example of a genuine international collaboration that started rather spontaneously a few years ago between the PIs, and has been very productive. This proposal will provide funds to energize and sustain this spontaneous effort by supporting undergraduate and graduate students to work and collaborate in a global context, support extended visits across the Atlantic by PIs and students alike, further interactions between a university (Penn State), a national lab (Oak-Ridge National Lab) and a national academy (NAS-Ukraine), support organization of an annual international workshop on Piezoelectric Force Microscopy and summer workshops in nonlinear optical microscopy, and provide research opportunities for women and underrepresented groups.This MWN award is co-funded by DMR-EPM, DMR-OSP, and OISE Eurasia Region.