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

这项重大研究仪器（MRI）奖将使购买，安装和调试最先进的仪器，用于对天然和工程固体材料进行化学分析，直至纳米（十亿分之一米）尺度。该仪器将提供给加州理工学院校园，NASA喷气推进实验室以及外部用户的所有科学和工程项目。该仪器可以远程操作，并将通过纳米技术（RAIN）联盟提供，供学生研究人员和全国少数民族服务机构的学生免费使用，从社区和技术学院到高中甚至小学。电子探针是固体地球地质学和地球化学以及相关领域的基本工具，如陨石学和行星样品返回，环境微生物学，材料科学和纳米技术。该仪器中包含的先进电子源提供了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。每种化学元素都会发射特定波长的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。电子探针自动化了按波长分离X射线的工作，计算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。这使得电子探针能够检测到一种元素何时高于低检测限，并以约1%的相对精度确定样品中每种元素的丰度。最初的应用将包括对陨石中微小矿物颗粒的表征，（甚至先于）太阳系的起源、重现地球深处或小行星带碰撞过程中条件的实验样品、电池和能源发电的功能材料等，新仪器将带来的关键能力是场发射电子源、Si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。虽然纳米级成像分辨率对于靶向分析和确保样品均匀性至关重要，但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注意。新仪器将支持研究无支撑薄样品分析的新方法，作为高分辨率分析的途径。要克服的挑战包括在光束路径中保持无支撑的样品，更新软件，准确地解释薄样品，以及对表征良好的标准进行广泛的验证活动。研究人员将转向新仪器的更多应用及其改进的成像和分析能力，重点关注几个目标。其中包括：（1）分析实验样品，以探测短尺度扩散、细粒多相组合和合成起始材料，其纳米尺度的均匀性是重要信息;（2）分析陆地火成岩、变质岩和沉积岩，包括可能含有纳米包裹体的玄武玻璃、用于地质年代学的锆石和具有未知宿主相的氧化还原敏感示踪剂;（3）分析陨石和新的纳米矿物，包括耐火夹杂物、高压冲击诱导相、非破坏性整体分析和生物合成单畴磁性晶体;以及（4）分析来自环境和培养的微生物标本，对关键的宏量和微量营养元素的分布具有单细胞分辨率。 该奖项由MRI计划和地球科学部的仪器和设施计划共同资助。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

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.