Radiofrequency plasma ion source for SIMS

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Since 2014 a high resolution ion microprobe has been operating at the Institute of Earth Sciences at Heidelberg University. Unique within the German university system, this instrument allows high-precision quantification of isotopic and elemental distributions in solids at the micro- to nanoscale. To further enable transformative research based on isotope-sensitive microanalysis in the Earth and environmental sciences, a new high-brightness radiofrequency (RF) plasma ion source is required. This type of ion source has been commercially available since only a few years, and it offers multiple advantages compared to the conventionally used duoplasmatron as the primary ion source for positive secondary ion analysis: high stability, low maintenance during routine operation, and enhanced primary ion density. Stable primary ion emission improves analytical precision, whereas the higher primary ion density directly enhances secondary ion production at a given beam diameter, or vice versa enables use of a smaller beam at the same primary ion intensity. This allows optimization of lateral spot dimensions as required to resolve material-specific structures against primary beam intensity, which controls sensitivity, precision, and analysis duration. Moreover, fine structures presently out of reach for isotopic microanalysis will become accessible for the first time. Novel fields of research are the quantification of geological and cosmological timescales that can be reconstructed from analysis of long- and short-lived isotope decay systems in minerals, which are frequently zoned. Important applications include the investigation of early solar system processes (meteorite studies), subduction initiation and orogenesis (in-situ U-Th-Pb petrochronology), and duration of magma evolution at active volcanoes (disequilibrium dating of accessory minerals and diffusion modelling of trace elements in major mineral phases). In addition, trace element distributions can be mapped at unprecedented spatial resolution in geological records to reconstruct paleoenvironmental conditions at the highest possible temporal resolution (e.g., nannofossils, speleothems). The ion microprobe facility at Heidelberg is a cornerstone lab within a pool of state-of-the-art microanalytical instrumentation targeting geomaterials (scanning electron microscopy with correlative micro-Raman, electron microprobe, backscattered electron diffraction, stylus profilometry, conventional and confocal optical microscopy). Advanced isotopic microanalysis, which is a unique domain of SIMS, will complement this instrument pool and continue to be accessible to a broad user base from the geosciences and adjacent disciplines.