About NanoSIMS
The Cameca NanoSIMS 50L instrument was installed in March 2010 at our department. The instrument provides access to an ion microprobe technique based on optimized SIMS analysis performance at high lateral resolution.
For SIMS, secondary ion mass spectrometry, the sample is continuously bombarded with energetic ions, such as cesium (Cs+) or oxygen (O−). These primary ions sputter atoms and molecules out of the near-surface area of the sample. A part of the sputtered atoms is ionized and can be detected as secondary ions with a mass spectrometer and distinguished by their mass-to-charge ratio.
By sputtering with Cs+ or oxygen O−, the ionization yield of secondary ions is enhanced considerably (by several orders of magnitude compared to non-reactive primary ions).
In July 2020, our machine was upgraded with a new radio-frequency plasma oxygen source. This O− primary ion source permits obtaining beam density and lateral resolution similar to that of the Cs+ source. This opens new research opportunities by enabling simultaneous analyses by both sources (dual primary ion source NanoSIMS) at a similar spatial resolution down to 50 nm.
The instrument uses a coaxial setup for the primary and secondary ion beams. The advantage of this setup is the high collection efficiency of secondary ions. Due to this design, only oppositely charged secondary ions can be measured.
The secondary ions are guided to a magnetic sector mass analyzer. Their trajectories get curved in the magnetic field according to their mass. The setup allows a high mass resolution, giving the possibility to differentiate between ionic species of the same mass number, such as 12C15N- and 13C14N- where the mass difference is only about 0.007 amu.
Theoretically, masses from 1 amu (1H) to 400 amu can be detected with some constraints given by the configuration of the mass spectrometer: a mass range of factor 21 and a mass separation between adjacent detectors of Mmax/58, where Mmax is the highest mass to be measured.
Up to 7 selected mass images can be recorded simultaneously by 7 detectors with sensitivity in the ppm range, originating from the same sputtered volume of the sample. This enables the comparison of images of the distribution of different measured isotopes (e.g. 12C, 13C, 14N, 15N). Dual primary ion source approaches (O− and Cs+) can be used to visualize elements commonly related to minerals (K, Si, Ca, Mg, Mn, Na, Al, Fe) together with major constituents of organic matter (C, N, P, S).