A short introduction to Nano-Secondary Ion Mass Spectrometry

NanoSIMS is an analytical technique that has its roots in secondary ion mass spectroscopy (SIMS). In 1910 Sir Joseph John Thomson already observed the release of positively charged ions and neutral atoms from a solid surface after ion bombardment (Thomson, 1910). With improved vacuum pump technology in the 1940s, a first prototype experiments on SIMS were performed by Herzog and Viehböck at the University of Vienna in 1949 (Herzog, 1949). Later in the 1950s, Honig constructed a SIMS instrument at RCA Laboratories in Princeton (Honig, 1958). And early in the 1960s, two SIMS instruments were developed independently of each other. One was developed by Liebel and Herzog and was sponsored by NASA, for analysing Moon samples (Liebl, 1967). The second was developed at the University of Paris-Sud in Orsay for a study on chemical and isotopic analysis methods using secondary ionic emissions (Castaing, 1962). All these first designs were based on magnetic double focusing sector field mass spectrometer and used argon as the primary ion beam.

During the 1970s, the SIMS instrument equipped with quadrupole mass analysers were developed (Wittmaack, 1975; Magee & Honig, 1978). Around the same time, static SIMS was introduced, employing pulsed primary ion sources and time-of-flight mass spectrometer (Benninghoven, 1969). The development of NanoSIMS specifically began in the 1980s and early 1990s, driven by the need for higher spatial resolution in isotopic and elemental analysis. The first NanoSIMS apparatus was introduced in 1990 by French manufacturer CAMECA (de Chambost, 2011). This first model had a spatial resolution in the order of tens of nanometers, enabling researchers to analyse samples with unprecedented detail. 
 
Over the following decades, NanoSIMS technology continued to advance rapidly. Improved ion optics, detectors, and software improvements allowed for even higher spatial resolution and sensitivity. Today, NanoSIMS is widely recognized as a powerful tool, enabling detailed analysis of isotopic compositions and elemental distributions in a wide range of materials on nanometre scale. Researchers across various fields such as geology, biology, and material science embrace NanoSIMS for its ability to provide insight into materials at very small scale. 

How it works

NanoSIMS analysis takes place under ultra-high vacuum. As mentioned before, the sample is bombarded with primary ions at a couple keV. These primary ions erode the surface, continue as a collision cascade (10-20 nm below the surface). During bombardment, secondary ions from the top ~3 atomic layers are ejected from the sample. So, the technique is destructive by nature, thus providing depth information. Only a small fraction of the released secondary atoms is ionized (either, + or – charged), and available for mass spectrometry. To maximize ionization of secondary ions, reactive primary ions are used (O^– for + ions, Cs⁺ for – ions). The secondary ions are collected and separated in a magnetic sector analyser according to their mass/charge ratio. This way, NanoSIMS reveals elemental (including H) and isotopic sample composition at the nanoscale.