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

• Applicants: Dr. Karin Eusterhues; Dr. Klaus R. Mann
• Subject Area: Soil Sciences ; Optics, Quantum Optics and Physics of Atoms, Molecules and Plasmas
• Term: since 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 434531747

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.

• DFG Programme: Research Grants
• Major Instrumentation: CCD-camera ; Picosecond laser system
• Instrumentation Group: 5430 Hochgeschwindigkeits-Kameras (ab 100 Bilder/Sek) ; 5700 Festkörper-Laser
• Co-Investigator: Professor Dr. Kai Uwe Totsche