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

这项MWN研究的重点是对美国/乌克兰联合团队在过去两年中开发的铁电畴壁基本性质的新见解。特别是，该团队利用他们为定量压电力显微镜（PFM）开发的综合理论，模拟和先进的实验框架。 利用这个框架，他们发现了超过几十纳米的铁电畴壁的意外加宽。 分析理论和相场建模预测，即使是几纳米的加宽也可以显著地改变宏观尺度的性质，例如壁运动的阈值场，通过许多数量级。 该团队预测了铁电体中不寻常的类磁性畴壁。这种壁可以被设计成非常宽（100纳米），并且它们在电场下的动力学性质，因此它们对宏观尺度性质的影响目前尚未被探索。使用扫描光谱压电力显微镜（SSPFM）和光学二次谐波发生近场扫描光学显微镜（SHG-NSOM），该团队正在探索这个神秘的新世界。总体而言，美国队（宾夕法尼亚州立大学和橡树岭国家实验室）专注于这种铁电壁的实验和相场模拟，而乌克兰团队（乌克兰国家科学院）正在开发理论框架。定量PFM和SHG-NSOM成像技术的发展，联合收割机理论，预计数值模拟和尖端实验技术将产生广泛得多的影响，超出铁电体，扩展到材料科学、化学和生命科学的其他领域。 这个美国/乌克兰团队是几年前在PI之间自发开始的真正国际合作的一个很好的例子，并且非常富有成效。 这项提案将提供资金，通过支持本科生和研究生在全球范围内工作和合作，支持PI和学生跨越大西洋的长期访问，以及大学之间的进一步互动，来激励和维持这种自发的努力。（宾夕法尼亚州立大学），一个国家实验室（Oak-Ridge国家实验室）和一个国家科学院（NAS-Ukraine），支持组织压电力显微镜年度国际讲习班和非线性光学显微镜夏季讲习班，为妇女和代表性不足的群体提供研究机会。该MWN奖由DMR-ESTA，DMR-OSP和OISE欧亚地区共同资助。

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.