This grant supports acquisition of a cathodoluminescence (CL) spectrometer which will be mated to an existing variable pressure scanning electron microscope (SEM) in the Department of Geosciences at the University of Iowa. CL imaging will support studies of mineral growth history by allowing for visualization and mapping of crystal zoning and microstructural characteristics. CL scanning using an SEM will support subsequent targeted elemental analysis and/or isotopic analysis of distinct growth rims using other electron microscopy techniques, secondary ion mass spectrometery or laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). The instrument will complement a recently NSF MRI supported laser ablation ICP-MS facility in the Department of Geoscience for zircon geochronology and trace element zonation in minerals and support a range of research in igneous and metamorphic petrology, impact processes, and analysis of clastic sedimentary and carbonate phases to elucidate the environmental conditions at the time of their deposition. The CL microscope will support student research training across multiple departments on campus and the PIs seek to attract underrepresented students through an extant Alliance for Graduate Education and Professoriate (AGEP) program and a NASA Education grant targeted at encouraging undergraduate women to pursue science careers. The instrument will also support collaborative research with faculty and students from nearby Cornell College, a regional liberal arts institution.
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A Gatan ChromaCL color cathodoluminescence detector was installed on an existing Hitachi S-3400 variable pressure scanning electron microscope (SEM) in August, 2012 at the University of Iowa. The CL unit complements the back-scattered electron (BSE) and energy dispersive spectrometer (EDS) imaging capabilities already available on this SEM instrument. The SEM is housed in the Geoscience building and maintained by the University of Iowa Central Microscopy Research Facility (CMRF). Addition of a CL detector to the Geoscience SEM expands the scope of Earth Science research and education and transforms the capabilities of existing NSF-funded analytical facilities in the Department of Geoscience. The primary uses for the CL facility fall within the general categories of U-Pb geochronology, structural and metamorphic fabric analysis, igneous petrology, and paleoclimatology. The instrument has been successfully used to image zircon grains in preparation for U/Pb age dating. CL-imaging provides unique information about the internal structure of the grains that guides age analysis. Melt textures in impactites from Monturaqui crater, Chile have been imaged as well. Although the CL capacity of the SEM is primarily being used for characterization of geologic materials, there are many other applications that are expected to be explored over the next few years.
