nanoSIMS

NanoSIMS is a nanoscale secondary ion mass spectrometry instrument designed for high-resolution isotopic and elemental imaging. It is widely used in geology, cosmochemistry, materials science, biology, and archaeology to map isotopes and elements with nanometer-scale lateral resolution.

The instrument operates by bombarding a small, focused primary ion beam (commonly Cs+ for enhanced negative secondary ions or O- for positive ions) onto a sample surface. The impact sputters secondary ions from the surface, which are then directed into a high-sensitivity magnetic sector mass spectrometer. Multiple detectors allow near-simultaneous detection of several isotopes, enabling the creation of isotopic ratio maps across a scanned area. The typical lateral resolution can reach about 50 nanometers, with a depth resolution governed by the sputtering rate, often tens of nanometers per layer.

Applications span many fields. In geoscience and cosmochemistry, NanoSIMS is used to measure isotopic ratios in minerals and presolar grains. In biology and archaeology, it enables tracing of nutrient uptake and labeling experiments through stable isotope imaging. In materials science, it supports diffusion studies and corrosion analysis. The technique is valued for its high sensitivity to trace elements and its ability to preserve spatial context while acquiring quantitative or semi-quantitative isotopic data.

Quantification relies on calibration with standards and relative sensitivity factors (RSFs), and results can be affected by matrix effects and charging in non-conductive samples. The method is destructive and requires ultra-high vacuum and careful sample preparation, including flat, polished surfaces and, for some applications, cryo-preparation.