INSTRUMENT

The CAMECA IMS 1280 (schematic diagram; pdf) is a large-radius double-focusing secondary-ion mass-spectrometer (SIMS) from CAMECA Instruments, a successor to the IMS-1270. The secondary ion optics have been optimized to work at full transmission up to a mass resolving power of 6000. Simultaneous acquisition of multiple isotopes is enabled by the multi-collection system combining 10 Faraday cup/Electron Multiplier ion counting detectors. New automated control of ion optics was developed for the IMS 1280 in order to achieve highly precise isotopic ratio analyses at the level of ~0.1‰ in various stable isotopic systems.

The WiscSIMS instrument was the first IMS 1280, installed in March 2005. Photos and tests (link).

A number of subsequent modifications to the CAMECA IMS 1280 have been developed at WiscSIMS. Modification details (link).

SIMS TECHNIQUE

SIMS analysis involves the sputtering of a sample surface by a focused beam of "primary ions" in order to detect atomic and molecular "secondary ions."At WiscSIMS the primary beam is made up of either Cs+ or O- ions, depending on the ionization efficiency of the elements of interest. The sputtered species that have been ionized, "secondary ions," are accelerated into a double-focusing mass spectrometer. The mass spectrometer allows the user to isolate singly-charged ionic species with a mass or masses of interest. The multi-collector array at WiscSIMS allows the user to measure secondary ion beams with a mass dispersion of up to 17.3%.

The image at right illustrates the sputtering process at an atomic scale. Note that at WiscSIMS the primary ion beam is typically 10 μm in diameter; this image is grossly out of scale.

  image: Evans Analytical Group

For more images and introductory explanations on SIMS techniques, see the SIMS Training Tutorials (link) from the Evans Analytical Group.

Another great introductory resource is the Introduction to SIMS (pdf) from the University of Edinburgh Ion Microprobe Facility.

WISCSIMS TECHNICAL RESOURCES

Technical tutorials for high-precision stable isotope analyses at WiscSIMS (link).