NanoSIMS The Technique

NanoSIMS is nanoscale secondary ion mass spectrometry technique that allows precise, spatially explicit, elemental and isotopic analysis down to 50 nm resolution [155]. When working in dynamic conditions, NanoSIMS analysis is a destructive process that involves the continuous bombardment of a sample with an energetic ( 16 keV) ion beam (either a Cs or O primary beam to enhance negative or positive ion formation, respectively), which results in sputtering of the upper sample surface and the consequent liberation of secondary ions. 

The use of a reactive primary ion such as Cs in positive mode (when only negatively charged secondary ions can be detected) or O in negative mode (when only positively charged secondary ions can be detected) is required to increase the secondary ion yield of negative and positive ions, respectively. 

The secondary ions are sorted on the basis of their energy in the instrument s electrostatic sector, before being dispersed in a mass spectrometer according to their m/z ratios. By acquiring a series of spatially referenced spectra, via a rasterscanning process, a map can be produced for almost any selected atomic mass, and information of isotopic ratios in the form of ROIs, line scans and depth profiles can be obtained. The system is maintained permanently under ultrahigh vacuum in order to prevent any atmospheric interference with the primary and secondary ions (typically 10 Torr in the analysis chamber) [155]. 

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