MRI: Acquisition of a field emission electron microprobe for Caltech Division of Geological and Planetary Sciences

MRI：为加州理工学院地质与行星科学部购买场发射电子探针

• 批准号: 2117942
• 负责人: Paul Asimow
• 金额: $ 100万
• 依托单位: California Institute of Technology
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2021
• 资助国家: 美国
• 起止时间: 2021-09-01 至 2023-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2117942&HistoricalAwards=false
• 关键词: MRI; Acquisition; field; emission; electron

This Major Research Instrumentation (MRI) award will enable the purchase, installation, and commissioning of a state-of-the-art instrument for chemical analysis of natural and engineered solid materials down to the nanometer (one billionth of a meter) scale. The instrument will be available to all science and engineering programs across the Caltech campus, NASA’s Jet Propulsion Laboratory, as well as to outside users. The instrument may be operated remotely and will be made available via the Remotely Accessible Instruments in Nanotechnology (RAIN) consortium for free access by student researchers and classes at minority-serving institutions nationwide ranging from community and technical colleges to high schools and even elementary schools. The electron microprobe is a basic tool of solid Earth geology and geochemistry as well as related fields such as meteoritics and planetary sample return, environmental microbiology, material science and nanotechnology. The advanced electron source included in this instrument provides a very bright, focused beam that enables imaging at high spatial resolution and excitation of characteristic X-rays from a very small analytical volume. Each chemical element emits X-rays at particular wavelengths; the count rate of X-ray photons emitted by a sample at these characteristic wavelengths is proportional to the concentration of that element in the sample. The electron probe automates the job of separating X-rays by wavelength, counting the number of X-ray photons emitted at particular wavelengths, and comparing the count rate in an unknown material to that in standard materials. This allows the electron microprobe to detect when an element is present above a low detection limit and to determine the abundance of each element in a sample with about 1% relative precision. Initial applications will include characterization of tiny mineral grains in meteorites that date back to (or even precede) the origin of the Solar system, experimental samples that reproduce conditions in the deep Earth or during collisions in the asteroid belt, and functional materials for batteries and energy generation.The key capabilities that the new instrument will bring are the field emission electron source, the Si-drift detector energy dispersive X-ray spectrometer, and the high-resolution cathodoluminescence sensor. While nanoscale imaging resolution, essential for targeting analyses and ensuring sample homogeneity, is straightforward, optimizing the spatial resolution of quantitative analysis without sacrificing accuracy or precision, requires special care. The new instrument will support a study of new approaches to unsupported thin specimen analysis as a path to high-resolution analysis. Challenges to be overcome include holding unsupported specimens in the beam path, updated software that accounts accurately for thin samples, and an extensive campaign of verification against well-characterized standards. Turning to more of the applications of the new instrument and its improved imaging and analysis capabilities, researchers will focus on several goals. These include: (1) analysis of experimental samples to probe diffusion at short length scales, fine-grained multiphase assemblages, and synthesized starting materials whose homogeneity at the nano-scale is essential information; (2) analysis of terrestrial igneous, metamorphic, and sedimentary rocks including basaltic glasses that may contain nano-inclusions, zircons for geochronology, and redox-sensitive tracers with unknown hosting phases; (3) analysis of meteorites and new nano-minerals including refractory inclusions, high-pressure shock-induced phases, non-destructive bulk analysis, and bio-synthetic single-domain magnetic crystals; and (4) analysis of microbiological specimens from the environment and culture, with single-cell resolution of the distribution of key macro- and micro-nutrient elements. This award was co-funded by the MRI program and the Instrumentation and Facilities program in the Earth Science Division.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.

该重大研究仪器 (MRI) 奖项将支持购买、安装和调试最先进的仪器，用于对纳米（十亿分之一米）尺度的天然和工程固体材料进行化学分析。该仪器将可供加州理工学院校园、NASA 喷气推进实验室的所有科学和工程项目以及外部用户使用。该仪器可以远程操作，并将通过纳米技术远程访问仪器 (RAIN) 联盟提供。学生研究人员和全国范围内的少数民族服务机构（从社区和技术学院到高中甚至小学）的课程都可以免费使用电子探针是固体地球地质学和地球化学以及流星学和行星学等相关领域的基本工具。该仪器配备的先进电子源可提供非常明亮的聚焦光束，能够以高空间分辨率成像，并从非常小的分析体积中激发特征 X 射线。发出特定波长的 X 射线；样品在这些特征波长下发射的 X 射线光子的计数率与样品中该元素的浓度成正比。电子探针自动执行按波长分离 X 射线的工作。在特定波长下发射的 X 射线光子的数量，并将未知材料中的计数率与标准材料中的计数率进行比较，这使得电子微探针能够检测到元素何时高于检测下限，并确定该元素的丰度。样本中的每个元素大约 1% 的相对精度将包括对可追溯到（甚至早于）太阳系起源的陨石中微小矿物颗粒的表征，以及再现地球深处或小行星带碰撞期间的条件的实验样本，新仪器将带来的关键功能是场发射电子源、硅漂移探测器能量色散X射线光谱仪和高分辨率阴极发光传感器。成像分辨率对于目标分析和样品均匀性至关重要，它很简单，在不牺牲准确性或精度的情况下优化定量分析的空间分辨率，需要特别小心，新仪器将支持无支撑薄样品分析的新方法的研究，作为实现这一目标的途径。需要克服的挑战包括在光束路径中固定无支撑的样品、精确计算薄样品的更新软件以及根据充分表征的标准进行广泛的验证。它是为了提高成像和分析能力，研究人员将重点关注几个目标，其中包括：（1）分析实验样品以探测短长度尺度的扩散、细粒多相组合以及纳米尺度均匀性至关重要的合成起始材料。 (2) 陆地火成岩、变质岩和沉积岩的分析，包括可能含有纳米包裹体的玄武岩玻璃、用于地质年代学的锆石以及未知宿主的氧化还原敏感示踪剂相；（3）陨石和新型纳米矿物的分析，包括耐火包裹体、高压冲击诱导相、无损整体分析和生物合成单域磁性晶体；以及（4）微生物样本的分析；该奖项由地球科学部门的 MRI 项目和仪器和设施项目共同资助。授予 NSF 的法定使命，并通过评估反映使用基金会的智力优点和更广泛的影响审查标准，被认为值得支持。