Pushing the limits of transmission electron microscopy of polymers

第一部分：非技术总结原子和分子尺度的微观可视化正在改变人们对有机和无机材料如何组织和功能的理解。电子显微镜仪器的巨大进步继续推动着可能的极限，即使是在生物和有机化合物方面也是如此，这些化合物本身就容易因暴露于电子束而降解。然而，最近的许多进展并不是为聚合物的显微镜量身定做的。该项目将开发电子显微镜工具，以新的方式表征导电聚合物的结构，并推动分子或原子尺度的成像极限。这些技术不仅将促进有关聚合物的化学结构如何影响微观结构的基础科学，而且还将促进化学如何影响宏观性质。对共轭聚合物的重视将加速柔性电子和生物电子的发展，从而通过影响能源收集和健康而造福社会。此外，综合教育和研究活动将向一年级本科生传递一个精心设计的信息，告诉他们工程学如何能够帮助社会，以努力加强招收和留住来自代表性不足群体的学生。参与该项目的研究人员和研究生将通过为本科生提供指导和研究经验，进一步支持工程学的多样性。第二部分：技术总结计划中的研究集中在突破聚合物电子显微镜的极限。最近的工作证明了次级事件对辐射敏感性的重要性，这些新的概念提出了新的方法来减轻损害，从而提高分辨率极限。拟议工作的重点是展示检测器的进步对聚合物显微镜的影响，包括像素化扫描电子显微镜(STEM)检测器和直接电子检测器。用聚焦探头解析衍射点允许4D STEM，因此以其他方式不可能的方式映射pi-pi堆叠。与自动采样器相结合，4D STEM将允许绘制长距离的导电路径图。直接电子探测器的增强的信噪比提高了能量过滤的透射电子显微镜对元素组成差异的敏感性，或者当用于低损耗区域时，对价电子结构的差异的敏感性。结合能量过滤的透射电子显微镜和电子断层扫描将依赖于这种探测器的进步，以最大限度地减少采集所需的剂量。此外，自动采集数以千计的图像，然后对这些图像进行平均，以提高晶格面的信噪比，甚至重建单元晶格，将使聚合物电子显微镜的分辨率极限超出辐射损伤的Glaeser方程。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

PART 1: NON-TECHNICAL SUMMARYMicroscopic visualization at the atomic and molecular scale is transforming the understanding of how organic and inorganic materials organize and function. The tremendous advances in electron microscopy instrumentation continue to push the limits of what is possible, even with biological and organic compounds that are inherently susceptible to degradation from exposure to electron beams. Nevertheless, many of the recent advances are not tailored for microscopy of polymers. This project will develop electron microscopy tools to characterize the structure of conducting polymers in new ways and push the limits of imaging at the molecular or atomic scale. These techniques will not only advance the fundamental science of how the chemical structure of polymers impacts the microstructure but also how chemistry affects macroscopic properties. The emphasis on conjugated polymers will accelerate the development of flexible electronics and bioelectronics and thereby benefit society by impacting energy harvesting and health. Furthermore, integrated educational and research activities will deliver a carefully tailored message to first year undergraduate students of how engineering can help society, as an effort to enhance recruitment and retention of students from underrepresented groups. The investigator and graduate students involved in this project will further support diversity in engineering by offering mentorship and research experiences to undergraduate students. PART 2: TECHNICAL SUMMARYThe planned research is centered on pushing the limits of polymer electron microscopy. Recent work has demonstrated the importance of secondary events on radiation sensitivity, and these new concepts suggest new approaches to mitigate damage and thereby push the resolution limit. An emphasis of the proposed work is on demonstrating the consequences of advances of detectors on polymer microscopy, including pixelated scanning transmission electron microscopy (STEM) detectors and direct electron detectors. Resolving diffraction spots with a focused probe allows for 4D STEM, and therefore mapping of pi-pi stacking in a manner not otherwise possible. In combination with auto-samplers, 4D STEM will allow of mapping of conductive pathways over large distances. The enhanced signal-to-noise ratio of direct electron detectors enhances the sensitivity of energy-filtered TEM to differences in elemental composition, or when used in the low-loss regime, to differences in valence electronic structure. Combining energy-filtered TEM with electron tomography will rely on such detector advances, to minimize the dose required for acquisition. Furthermore, the automatic acquisition of thousands of images that can then be averaged to enhance the signal-to-noise of lattice planes, or even reconstruct the unit lattice, would push the resolution limit of polymer electron microscopy beyond the Glaeser equation for radiation damage. .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.