EAGER: Developing atom probe tomography (APT) for the characterization of carbonate minerals

EAGER奖支持博士后学生协助开发方法，以使用聚焦离子束（FIB）制造适当形状的纳米级非生物和生物碳酸盐尖端，用于随后使用原子探针断层扫描（APT）进行成分分析。APT被开发用于半导体工业中的工艺控制的合成导电材料的分析和其它合成材料（例如，陶瓷）。 PI是一名矿物学家/地球化学家，专门研究生物成矿过程，旨在利用亚拉巴马大学中央分析设施（CAF）中现有的FIB-SEM和APT仪器。 APT技术使用脉冲激光蒸发极其精细的纳米级材料尖端，然后使用飞行时间质谱（TOF-MS）对样品尖端中的单个原子分布进行成像。 APT在碳酸盐岩研究中的应用尚处于起步阶段，对成功分析在原子尺度上理解矿化和成岩过程的潜在应用提出了重大挑战。 由脆性生物碳酸盐矿物制造尖端需要极其小心的离子研磨和尖端加载到APT仪器中，并且PI迄今为止仅以有限的分析精度实现了对生物碳酸盐尖端的单一成功分析。 该EAGER的目标是首先尝试改进用于后续APT分析的非生物成因碳酸盐的离子研磨尖端的方法，然后尝试将这些过程外推到天然生物成因碳酸盐矿物的离子研磨。 第二个目标是开发最佳的分析方案，以确定碳酸盐矿物的主要，次要和微量元素的相对丰度是否可以在原子尺度上成功成像。 该技术如果成功，可能会对微生物介导的碳酸盐成矿过程和古记录研究产生变革性影响，但也存在相当大的风险，因此提出了EAGER建议机制。碳酸盐岩存在于地球沉积大陆地壳的大部分地区，因此在地质研究中具有重要意义。此外，目前地球化学技术和应用的发展主要是用于古气候和古环境重建的研究，其中生物碳酸盐矿物的分析起着至关重要的作用。 原子探针的潜在应用可以提供以下方面的先进知识：1）扩散动力学（体积、晶界、微量元素等）; 2)元素划分; 3）矿物溶解和重结晶; 4）过渡非晶相向结晶相的转变。拟议的新的分析发展可以鼓励对地球化学研究和矿物分析采取新的办法，并促进跨学科研究。 如果技术开发证明是成功的，亚拉巴马大学中央分析设施（CAF）的APT和FIB仪器可以开放给社区以外的人使用。 该提案将聘请一名博士后科学家，并将通过专题研讨会、科学会议和学术出版物的讲座传播成果。

This EAGER award supports a postdoctoral student to assist in the development of methods to fabricate appropriately shaped, nanometer scale, tips of abiogenic and biogenic carbonates using a focused ion beam (FIB) for subsequent compositional analysis using atom probe tomography (APT). APT was developed for the analysis of synthesized conducting materials for process control in the semiconductor industry and sub-nanoscale/atomic scale spatially resolved analysis of elemental distributions in other synthesized materials (e.g., ceramics). The PI, a mineralogist/geochemist who specializes in studies of biogenic mineralization processes seeks to employ the extant FIB-SEM and APT instruments housed in the Central Analytical Facility (CAF) at the University of Alabama. APT technology uses pulsed laser evaporation of extremely delicate nanoscale materials tips followed by time-of-flight mass spectrometry (TOF-MS) to image individual atom distributions in sample tips. Application of APT to studies of carbonates is in its infancy and presents major challenges to successful analysis for potential application to understanding mineralization and diagenetic processes at the atomic scale. Fabrication of tips from brittle biogenic carbonates minerals requires extremely careful ion milling and tip loads into the APT instrument and the PI has thus far only achieved a single successful analysis of a biogenic carbonate tip with limited analytical precision. A goal of this EAGER is to first try to improve methods to ion mill tips of abiogenic carbonates for subsequent APT analysis and then to attempt to extrapolate those processes to ion milling of natural biogenic carbonate minerals. A second goal is develop optimal analysis protocols to determine if the relative abundances of major, minor, and trace elements of carbonate minerals can be successfully imaged at the atomic scale. The technique, should it be successful, could prove transformative for studies of microbially mediated carbonate mineralization processes and paleorecords research but it presents considerable risk, hence the EAGER proposal mechanism.Carbonate rocks are present in large parts of the sedimentary continental crust of the Earth and thus are of great significance in geological studies. Furthermore, much of the current development of geochemical techniques and applications is for studies in paleoclimate and paleoenvironmental reconstructions in which the analysis of biogenic carbonate minerals plays a crucial role. The potential use of atom probe could contribute advanced knowledge of: 1) diffusion kinetics (volume, grain-boundary, trace elements, etc.); 2) element partitioning; 3) mineral dissolution and recrystallization; and 4) transformation of transient amorphous phases into crystalline counterparts. Proposed new analytical developments could encourage new approaches to geochemistry research and mineral analysis and promote interdisciplinary research. Should the technique development prove successful, the APT and FIB instruments in the Central Analytical Facility (CAF) of The University of Alabama could be opened for outside community use. The proposal will engage a postdoctoral scientist and results will be disseminated through talks at topical workshops, scientific conferences and through scholarly publication.