The Secondary Ion Mass Spectrometry (SIMS) Laboratory
Secondary Ion Mass Spectrometry
Secondary Ion Mass Spectrometry (SIMS) relies on the physical phenomenon of “sputtering” to produce analyte ions. A primary beam of ions (generally O- or Cs+) is accelerated into a solid sample at potentials of a few kV. The impact of these primary ions gradually erodes (“sputters”) a shallow crater in the sample. A portion of the material sputtered from the sample emerges as ions, and these “secondary” ions are the analyte species that are introduced into the mass spectrometer. All instruments routinely used for geochemical research today use finely focused microbeams of primary ions, and are thus commonly referred to as “Ion Microprobes”.
Ion microprobes are capable of both isotopic ratio analysis and sub-ppm elemental analysis – both with extremely high spatial resolution.
SIMS can accomplish many types of elemental and isotopic determinations with a lateral spatial resolution of better than 5-10μm, and with sputtered pit depths of less than a few μm. For glassy materials, this represents a total sample consumption of less than 10 ng for a single analysis. Further, most elements can be quantitatively analyzed with detection limits substantially below 1 ppm (often below 10 ppb). A variety of light stable isotope determinations are also practical – with overall reproducibilities commonly better than 0.5 – 1 per mil.
Capabilities and Applications
SIMS shares the advantage with other forms of microbeam analysis ( EPMA, LA –ICP– MS and PIXE) of allowing in situ analysis of low destructivity - permitting determinations directly in intact thin sections of rock. Beyond this, SIMS permits direct analysis of individual melt inclusions, or of fine growth zones within marine biomineralization, where the extremely small size of an individual object severely limits study of their elemental or isotopic composition by any other means. Coupled with the capability to obtain Scanning Ion Images (SII) and other forms of Ion Microscopy, SIMS offers a variety of unique capabilities for geochemical analysis.
Sample preparation is normally fairly simple. Sample mounts must be compatible with the ultra-high vacuum of the sample chamber (ideally, better than 10–8 torr), and present a flat polished surface of the objects of interest. For analysis of insulating samples (such as silicate melt inclusions) mounts must generally be pre-coated with a thin (300–500 Å) conductive layer of gold or carbon. Most SIMS instruments used for light stable isotope determinations limit overall sample size to a maximum 25.4 mm diameter. The general sample requirements are, therefore, quite similar to those for electron probe microanalysis (EPMA) of major or trace elements.
SIMS at MAF-IIC
The MAF-IIC houses a fully updated Cameca IMS 4f ion microprobe. This instrument has been enhanced with additional lensing in the primary column to enable extremely bright, finely focused beams of O- for analyses with high precision and spatial resolution. It has also been equipped with modernized ion detection systems that augment performance of stable isotope analysis.
For further information:
Prof. Graham Layne
"Detailed descriptions of SIMS technique and instrumentation, with specific reference to light stable isotope analysis:"
A detailed description of SIMS technique and instrumentation, with specific reference to light stable isotope analysis:
Layne, G.D., 2006, Application of secondary ion mass spectrometry to the determination of traditional and non-traditional light stable isotopes in melt inclusions, in Melt Inclusions in Plutonic Rocks (J.D. Webster, ed.), Min. Assoc. Can. Short Course 36, 27-50.
Applications of SIMS to the study of Marine Biomineralization:
Bice, K., Layne, G.D. and Dahl, K., 2005, Application of secondary ion mass spectrometry to the determination of Mg/Ca in rare, delicate or altered planktonic foraminifera: Examples from the Holocene, Paleogene and Cretaceous, Geochem. Geophys. Geosyst., 6, Q12P07, doi: 10.1029 /2005GC000974.
Cohen, A.L., Layne G.D., Hart, S.R. and Lobel, P.S., 2001, Kinetic control of skeletal Sr/Ca in a symbiotic coral; Implications for the paleotemperature proxy, Paleoceanography, 16(1), 20.
Layne, G.D., 2009, Li, B and Cl isotope determination by SIMS, in Fayek, M. ed, Secondary Ion Mass Spectrometry in the Earth Sciences: Gleaning the big picture from a small spot, Min. Assoc. Can. Short Course 41, 89-108.
A simplified explanation of the SIMS technique and instrumentation: