Transmission electron microscopy of conjugated polymers using energy-filtering and phase contrast enhancement

第1部分：非技术总结各种聚合物材料的性能取决于纳米级的结构。因此，在纳米尺度上表征聚合物的排列和有序性对于新材料的持续开发至关重要。这一领域的许多进展归功于将先进的显微技术(透射式电子显微镜)应用于复杂的聚合物体系，以便在非常高的分辨率下解析结构。电子显微镜仪器的新发展正在突破可能的极限，但这些进展并不是为聚合物的显微镜量身定做的，因为聚合物对电子束非常敏感，并遭受快速破坏。该项目将开发电子显微镜工具，以成像用于各种新兴电子应用的导电聚合物的结构，如晶体管和太阳能电池设备。通过展示以亚纳米分辨率分辨形态的新方法，这项研究将推进聚合物化学组成如何导致微观结构的基础科学，并有助于开发用于柔性电子应用的聚合物。此外，综合教育和研究活动还将包括招收和留住任职人数不足的群体的学生。参与该项目的研究人员将通过为本科生提供指导和研究经验，进一步支持工程教育的多样性。该项目将开发用于研究聚合物材料的先进的电子显微镜工具。由于共轭聚合物体系微观结构的复杂性，在电子显微镜中产生对比度的新方法是有必要的。这项拟议的工作首先使用两个观察量：衍射强度和低损耗电子能量损失谱来检查透射电子显微镜中的辐射损伤。这些测量将指导进一步的实验，并建立成像模式的限制。低损耗能量过滤的电子显微镜将在共轭聚合物中产生长程有序的高分辨率图像。相位板将在亮场和聚焦探头模式下增强对比度，使用于光伏的聚合物/富勒烯混合物、聚合物混合物和嵌段共聚物能够成像。此外，将使用低损耗光谱成像来检查电荷传输的不均一性，以查看偏置下的态密度的偏差，并通过使用相位板成像由于电荷不均一而导致的电场的局部变化。总体而言，这项提案将展示单色电子源和相位板在共轭聚合物成像中的应用。教育目标的动机是需要加强工程方面的多样性。将实施一系列具体计划，包括招聘、留住和指导代表性不足的群体。

PART 1: NON-TECHNICAL SUMMARYThe properties of various polymeric materials depend on the structure at the nanoscale. As a consequence, characterizing the arrangement and order of polymers at nanometer length scales is crucial for the continued development of new materials. Much progress in this area is due to the application of advanced microscopy techniques (transmission electron microscopy) to complex polymeric systems in order to resolve the structure at very high resolutions. New developments in electron microscopy instrumentation are pushing the limits of what is possible, but these advances have not been tailored for the microscopy of polymers, which are very sensitive to electron beams and undergo rapid damage. This project will develop electron microscopy tools to image the structure of electrically conducting polymers used in a variety of emerging electronic applications, such as transistors and solar cell devices. By demonstrating new approaches for resolving the morphology with sub-nanometer resolution, this research will advance the fundamental science of how the chemical composition of polymers leads to the microstructure and aid in the development of polymers for flexible electronics applications. Furthermore, integrated educational and research activities will also include recruitment and retention of students from underrepresented groups. The investigators involved in this project will further support diversity in engineering education by offering mentorship and research experiences to undergraduate students. PART 2: TECHNICAL SUMMARYThis project will develop advanced electron microscopy tools for the study of polymeric materials. New methods to generate contrast in the electron microscope are warranted because of the complexity of the microstructure of conjugated polymer systems. The proposed work begins by examining radiation damage in the transmission electron microscope using two observables: diffraction intensities and low-loss electron energy-loss spectroscopy. These measurements will guide further experiments and establish limits of imaging modalities. Low-loss energy-filtered transmission electron microscopy will generate high-resolution images of long-range order in conjugated polymers. Phase plates will enhance contrast in both bright-field and focused-probe modes to enable imaging of polymer/fullerene mixtures, polymer blends, and block copolymers used in photovoltaics. Furthermore, charge transport heterogeneity will be examined using low-loss spectrum imaging to see deviations in density of states under bias, and by imaging local variations in electric fields that result from charge heterogeneity using a phase plate. Overall, this proposal will demonstrate the utility of monochromated electron sources and phase plates for imaging of conjugated polymers. Educational objectives are motivated by the need to enhance diversity in engineering. A number of specific programs will be implemented encompassing recruitment, retention, and mentoring of underrepresented groups.