Laboratory-scale NEXAFS spectroscopy for the investigation of Fe oxides and organic matter in soil

近边缘x射线吸收精细结构（NEXAFS）光谱探测被研究元素的氧化状态和化学环境。因此，它可以表征矿物，也可以表征短程有序固体、无定形化合物和金属配合物。到目前为止，NEXAFS光谱仅限于同步辐射。由于NEXAFS仪器严重超额预订，只有在经过漫长而竞争激烈的审查过程后才能获准使用。然而，基于激光驱动等离子体源的台式光谱仪已经在激光实验室Göttingen开发出来。在软x射线辐射的光谱范围（<1 keV），它允许C1s， N1s, O1s, Ca2p， Mn2p和Fe2p光谱不仅在真空，而且在环境条件下（水，惰性气体）。在一个联合项目中，我们提议开发、测试和应用台式NEXAFS光谱仪，用于分析地球科学样品。激光实验室Göttingen的子项目旨在提高光源的亮度，开发灵活的样品环境，提高仪器的光谱分辨率。耶拿大学的子项目将重点研究软x射线辐射NEXAFS光谱的应用。本文将探讨该方法在样品制备、检出限和不同基质中不同化合物的辐射损伤等方面的优缺点。随后，特别关注了环境样品中Fe氧化物（Fe2p, O1s）的定量和有机物质（C1s, N1s）的表征。在项目结束时，一个改进的新型台式光谱仪将在Friedrich-Schiller-Universität耶拿可用。通过该仪器，我们缩小了对低结晶矿物，金属配合物和铁氧化物相关有机物表征的分析差距。当样品在制备或取样后需要快速分析时，例如氧化还原敏感样品或易于快速老化的样品（亚稳低结晶Fe和Mn相，碳酸盐前驱物相），光谱仪将特别有价值。此外，分析成本将大大降低，与同步加速器测量相比，可以实现更高的样品吞吐量。

Near Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy probes the oxidation state and the chemical environment of the element under investigation. Thus, it may characterize minerals, but also short-range ordered solids, amorphous compounds, and metal complexes. NEXAFS spectroscopy has so far been limited to synchrotron radiation. As NEXAFS instruments are heavily overbooked, access is granted only after a lengthy, highly competitive review process. However, a table-top spectrometer based on a laser-driven plasma source has been developed at the Laser-Laboratorium Göttingen. In the spectral range of soft X-ray radiation (<1 keV) it allows for C1s, N1s, O1s, Ca2p, Mn2p, and Fe2p spectroscopy not only in vacuum, but also at ambient conditions (water, inert gases). Within a joint project we propose to develop, test and apply the table-top NEXAFS spectrometer for the analysis of geoscientific samples. The sub-project of Laser-Laboratorium Göttingen aims at increasing the brilliance of the source, developing a flexible sample environment and increasing the spectral resolution of the instrument. The sub-project of the University of Jena will focus on the application of NEXAFS spectroscopy with soft X-ray radiation. Here, the strengths and weaknesses of the method with regard to sample preparation, detection limits and radiation damage of different compounds in different matrices are to be explored. Subsequently, special attention is paid to the quantification of Fe oxides (Fe2p, O1s) and the characterization of organic material (C1s, N1s) in environmental samples of increasing complexity.At the end of the project, an improved new table-top spectrometer will be available at the Friedrich-Schiller-Universität Jena. With this instrument we close the analytical gap for the characterization of poorly crystalline minerals, metal-complexes and Fe oxide-associated organic matter. The spectrometer will be particularly valuable when samples need to be analyzed quickly after preparation or sampling, such as redox-sensitive samples or samples prone to fast aging (metastable poorly crystalline Fe and Mn phases, carbonate precursor phases). In addition, analysis costs will be greatly reduced, and a higher sample throughput can be achieved compared to synchrotron measurements.