Oxygen RF-Plasma Ion Source für NanoSIMS/Optical Microscope upgrade

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Lehrstuhl für Bodenkunde, TUM, Freising is running a NanoSIMS instrument, granted in 2009 by German Research Foundation and installed in 2010, registered on the German Research Foundation Database as a research infrastructure available for external use with focus on soil as also adjacent sciences (geology, microbiology, plant physiology). The development of special methods for sample preparation and the evaluation of the obtained NanoSIMS measurements, using imaging and classification techniques represents a unique opportunity for our group and other national and international users for soils, geologic and plant materials. The NanoSIMS instrument, uniquely allowing elemental and isotopic analyses at the nanometer scale, is equipped with two ion sources, Cesium and Oxygen. This configuration is mandatory to cover a wide spectrum of the measured constituents, due to the different electron affinity of different species. While, in our research field, Cesium is mostly used to detect ions specific for organic matter (carbon, nitrogen), the Oxygen source is needed, in combination, to depict the localization of mineral phases or metals (Al, Fe,Ca, K, Mg). Unfortunately, the actual Oxygen source has a poorer lateral resolution compared to Cesium (~300nm versus ~50nm), short unpredictable life time (~50h), yielding in long service time. This makes its usage and performance less productive and suboptimal. We apply for a new RF O source with improved performance including an upgrade for the existing optical system. Very similar performance between the ion source in O- mode and the microbeam Cs+ ion source is required to get insight in the interaction between the principal players in soil, organic matter and mineral phase at a useful scale. With a beam diameter of 100nm at usual working conditions of a 2pA primary beam comparable to the Cs source, long lifespans (>500h) and an improved stability better than 1% over 10 minutes, the increased usage of the O RF source will lead to a higher output with a superior performance. This affords us more flexibility in switching between the two sources to measure soil relevant species, such as Ca, Al, Fe at best yield and spatial resolution conditions.