MRI: Acquisition of a Monochromated, Magnetic-Field-Free, Atomic-Resolution Scanning Transmission Electron Microscope Enabling Multidisciplinary Research and Education

非技术描述：纳米级材料代表至少一个维度接近单个原子大小的一类物质。这些材料表现出与更大长度尺度的物质截然不同的特性，对于推进从磁性数据存储系统到超导量子计算机到生物材料应用的广泛技术至关重要。为了研究和改进这些材料，需要工具在原子水平上对它们进行检查，同时将对其结构的任何干扰降至最低。电子显微镜是研究这种纳米材料结构的基本手段之一，它使用电子来“看到”原子。目前设计的高分辨率透射式电子显微镜需要透镜将电子束聚焦在样品表面。这种设计的副作用是样品材料不经意间暴露在强磁场中。然而，在研究磁性或超导材料时，关闭透镜以消除磁场，将使原子分辨率分析变得不可能。通过这一重大研究仪器赠款获得的仪器有一个新的透镜设计，提供了一个没有磁场的样品区域，当与一个几乎单能的电子源结合在一起时，可以对这些关键材料进行原子分辨率成像和化学分析。此外，现在还可以在加热或冷却实验期间或在施加受控磁场时实现原子分辨率和无磁场分析。为了接触到更广泛的用户群体和交流仪器的能力，首席研究人员每年举办讲习班，在国家和国际会议上组织会议，并与当地显微镜学会接触。此外，该仪器还为伊利诺伊大学芝加哥分校(UIC)的不同本科生和研究生群体提供了机会，让他们有机会在尖端量子、超导或生物材料科学方面进行实践研究和学习经验。开发了新的课堂课程模块和在线教学资源，并使用来自无场透射电子显微镜的数据免费在线分发。技术说明：虽然像差校正器、单色电子源和先进探测器的发展推动了当前的分辨率革命，但几乎所有高分辨率透射电子显微镜(TEM)实验仍然是在样品暴露在高磁场下进行的，因为物镜(OL)极件需要大约3特斯拉的磁场。这种磁场限制了可以研究的样品，阻止了磁性、磁光、磁电、超导或拓扑材料在相关条件下进行表征。传统的磁性成像方法关闭了OL，将空间分辨率限制在纳米级，不允许进行原子分辨率的化学分析。该仪器具有新颖的透镜设计，在200千伏时，空间分辨率优于100 PM，剩余磁场小于0.3 mT，能量分辨率为40 meV，探头尺寸为110 nm。原子分辨化学分析以及新的图像模式，如4D-STEM和差分相位对比度成像，可以与现场加热或冷却实验相结合，以研究磁性、超导或其他电子相变。这台新仪器使UIC的研究项目包括研究镍基钙钛矿氧化物中的新型磁相、二维材料中的激子、常规和近室温超导体、作为拓扑绝缘体的纳米颗粒/量子点、抗空洞生物膜和细胞的机械操纵。外部用户，从美国各地的大学、国家实验室和公司到国际合作机构，可以利用该仪器提供的能力，在受控磁场条件下和原子分辨率下研究新的量子材料、新的磁结构、光伏材料、储能设备和生物系统。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 Description:Nanometer scale materials represent a class of substances with at least one dimension that approaches the size of individual atoms. These materials exhibit properties that are dramatically different from substances at larger length scales and are essential to advance a wide array of technologies, ranging from magnetic data-storage systems to superconducting quantum computers to biomaterials applications. To study and improve upon these materials, tools are required to examine them at the atomic level while minimizing any disturbance to their structure. Electron microscopy, which uses electrons to "see" atoms, is one of the fundamental means by which the structures of such nanoscale materials can be studied. Current designs of high-resolution transmission electron microscopes require a lens to focus the electron beam on the sample surface. A side effect of this design is that the sample material is inadvertently exposed to a high magnetic field. Yet, turning the lens off to eliminate the magnetic field when studying magnetic or superconducting materials makes atomic-resolution analysis impossible. The instrument acquired through this major research instrumentation grant has a new lens design, providing a magnetic-field-free sample region and, when combined with a nearly mono-energetic electron source, allows for atomic-resolution imaging as well as chemical analysis of these critical materials. In addition, atomic resolution, magnetic-field-free analysis can now also be achieved during heating or cooling experiments or when a controlled magnetic field is applied. To reach a broader user community and for communicating the capabilities of the instrument, the principal investigators hold annual workshops, organize sessions at national and international conferences, and engage with local microscopy societies. The instrument, moreover, provides the diverse undergraduate and graduate student body at University of Illinois - Chicago (UIC), a Research-1 Hispanic-serving institution with opportunities for hands-on research and learning experiences in cutting-edge quantum, superconducting or biomaterials science. New in-class course modules and online teaching resources are developed and freely distributed online using data from the field-free transmission electron microscope.Technical Description:While the development of aberration-correctors, monochromated electron sources, and advanced detectors has fueled the current revolution in resolution, nearly all high-resolution transmission electron microscopy (TEM) experiments are still performed with the sample being exposed to a high magnetic field, since the objective lens (OL) pole-pieces require a magnetic field of about 3 tesla. Such a magnetic field limits the samples that can be studied, preventing magnetic, magneto-optical, magneto-electric, superconductive or topological materials from being characterized under relevant conditions. Traditional magnetic imaging methods, where the OL is turned off, limit the spatial resolution to nanometer length-scales and do not allow for atomic-resolution chemical analysis. This instrument has a novel lens design that allows for better than 100 pm spatial resolution at 200 kV with a residual magnetic field of less than 0.3 mT and 40 meV energy resolution with a probe size of 110 nm. Atomic-resolution chemical analysis, as well as novel image modes, such as 4D-STEM and differential phase contrast imaging, can be combined with in-situ heating or cooling experiments to study magnetic, superconducting or other electronic phase transitions. Research projects at UIC enabled by the new instrument include the study of novel magnetic phases in Ni-based perovskite oxides, excitons in 2-dimensional materials, conventional and near-room temperature superconductors, nanoparticles/quantum dots as topological insulators, and anti-cavity biofilms and the mechanical manipulation of cells. External users, ranging from universities, national laboratories and companies across the United States to international partner institutions, can take advantage of the capabilities provided by the instrument to study novel quantum materials, new magnetic structures, photovoltaic materials, energy-storage devices, and biological systems under controlled magnetic-field conditions and with atomic resolution.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.