CAREER:Atomic Structure and Growth of Helical Nanostructures Studied by Advanced Electron Microscopy

非技术性总结：这个NSF职业计划包括一个研究和教育计划，使用成像和可视化作为工具来回答关键的科学问题以及从事科学推广。该计划的研究部分使用电子显微镜来了解复杂的纳米结构是如何形成的。纳米材料的许多性质是由生长过程中出现的结构缺陷决定的，并进而影响材料的最终结构。例如，在直接的银金合金纳米线上添加金属涂层可以使纳米线转变为双螺旋形态。在这样的纳米结构能够广泛应用于技术应用之前，有必要了解螺旋结构是如何起源的。使用先进的电子显微镜，该计划将结合非常详细和高分辨率的三维研究和高通量成像，以获得关于螺旋纳米线如何生长和扭曲的完整图像。这项研究将促进对过程的基本理解，这些过程决定了如何通过化学合成复杂的纳米结构，以满足未来的技术应用。该计划的教育部分旨在为严重缺乏服务的地区的高中生提供学习课外课程的机会。奥克兰和里士满许多地区的学生面临贫困、饥饿、暴力和种族歧视。社会和经济障碍往往禁止这些学生参加传统的暑期课外活动，这可能会扩大这一人群的学业成就差距。该计划将与当地高中教师合作，为受不公平制度影响的这些学生和其他学生开发和实施灵活和适应性强的暑期研究体验。这个项目将使用成像和可视化作为工具来传达科学知识，并激发学生对科学职业的兴趣。它还旨在发展导师网络，帮助学生实现他们在大学和就业市场的目标。技术总结：该项目的研究部分将使用电子显微镜来确定核壳纳米线中手性的结构来源。纳米尺度的三维表征将被用来研究纳米线在添加壳的过程中从直结构到扭曲结构的形态。通过改变壳层厚度和原子种类，将确定晶格失配在这些线中从直线到螺旋结构转变中所起的作用。原子分辨电子断层扫描将用于测量这些材料中缺陷的位置和应变分布，以确定这些结构特征与这些材料采用的螺旋结构之间的关系。将开发一种使用机器学习方法的高通量电子显微镜工作流程，以测量直纳米线和扭曲纳米线的许多群体的结构异质性。对所研究的核壳纳米线螺旋形态发展的全面了解将把微结构特征(缺陷、应变、晶界)的存在与纳米线的整体形态联系起来。这反过来将使基于该系统的功能材料的合理设计、在光电子学、纳米机械、仿生或催化应用中的应用成为可能。该奖项反映了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。

Non-technical Summary: This NSF CAREER program encompasses a research and educational plan that uses imaging and visualization as tools to answer key scientific questions as well as engage in scientific outreach. The research component of the program uses electron microscopy to understand how complex nanostructures form. Many properties of nanoscale materials are determined by structural imperfections that appear during the growth process and go on to affect the material's final structure. For example, adding a metallic coating to straight silver-gold alloy nanowires can cause the wires to transition to a double helix morphology. Before nanostructures such as these can be widely used in technological applications, there is a need to understand how the helical structure originates. Using advanced electron microscopy, this program will combine extremely detailed and high resolution studies in three-dimensions with high-throughput imaging to obtain a complete picture as to how the helical nanowires grow and twist. This research will advance the fundamental understanding of the processes that determine how complicated nanostructures can be chemically synthesized for future technological applications. The educational component of this program aims to provide access to academic extra-curriculars for high school students in severely underserved areas. Students in many areas in Oakland and Richmond face poverty, hunger, violence and racial discrimination. Social and economic hurdles often prohibit these students' participation in traditional summer extracurricular activities, which can increase the academic achievement gap in this population. Working with local high school teachers, this program will develop and implement a flexible and adaptable summer research experience for these and other students affected by inequitable systems. This program will use imaging and visualization as tools to convey scientific knowledge and excite the students about careers in science. It also aims to develop mentorship networks to help students attain their goals in the college and job market.Technical Summary: The research portion of this program will use electron microscopy to determine the structural origin of chirality in core-shell nanowires. Nanoscale three-dimensional characterization will be used to study the morphology of the nanowires as they transition from straight to twisted structures during addition of the shell. By varying the shell thickness and atomic species, the role that lattice mismatch plays in the structural transformation from straight to helical in these wires will be determined. Atomic resolution electron tomography will be used to measure the position of defects and the strain distribution in these materials to determine how these structural features are related to the helical structure that these materials adopt. A high-throughput electron microscopy workflow using a machine learning approach will be developed to measure structural heterogeneity in many populations of the straight and twisted nanowires. The comprehensive understanding of the development of the helical morphology demonstrated by the core-shell nanowires under study will relate the presence of microstructural features (defect, strain, grain boundaries) to the overall morphology of the nanowires. This in turn will enable the rational design of functional materials based on this system, application in optoelectronic, nanomechanical, biomimetic or catalytic applications.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.