Fieldemission-Scanning electronmicroscope (FE-SEM)

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In this proposal, a scanning electron microscope with field emission cathode (FEG-SEM) is requested. The device allows the characterization of textures and surfaces with a spatial resolution in the sub-nanometer range. The high spatial resolution allows the quantification of small-scale structural parameters (e.g. crystal orientation, crystal defects) using a powerful electron backscatter diffraction detector (EBSD) as well as their chemical composition using an energy dispersive X-ray spectroscopy detector (EDS). Furthermore, the FEG-SEM will be equipped with a spectrally resolving cathodoluminescence detector (WAR-CL) to visualize element zoning and distributions of trace elements such as rare earth elements (REE) and allows to evaluate them semi-quantitatively. For samples without a conductive surface and/or with topography, the FEG-SEM is also equipped with a low-vacuum mode, which allows the analysis of e.g. organic samples.The proposed FEG-SEM will be integrated into the existing structure of GoeLEM (Goettingen Laboratory for correlative Light and Electron Microscopy) and complements the existing chemical analysis of the main and trace elements with a focus on textural and spectral analyses.Complementary detection systems are planned in addition to the standard detectors for backscatter and secondary electrons. The additional detectors are project-specific and, in particular, chosen to serve the wide range of needs across the participating working groups for which no comparable systems are available in the Geosciences Center Göttingen (GZG). The high lateral resolution and high sensitivity of the backscattered electron detector is generally relevant for all applications at the FEG-SEM, but are particularly important for research projects in mineralogy (investigation of unmixing and segregation structures) and petrology (reaction textures & diffusion chronometry). The coupling of EBSD and EDS signals significantly improves phase identification, e.g., of very fine-grained material, and also provides in-depth information on geological processes and microstructures that are difficult to visualize using serial acquisition of orientation data and element distribution. The spectrally resolving CL detector will be used to quantitatively determine trace elements and their value and lattice position in addition to the qualitative representation of the trace element zoning patterns. The use of the spectrally resolving CL detector thus allows determination of the origin (provenance analysis) and provides information on reactive processes (e.g. hydrothermal dissolution and precipitation, metamorphism and deformation) and is an essential tool for preparation of the samples used for geochronology.