Secondary ion mass spectrometry



Secondary ion mass spectrometry

CAMECA IMS3f Magnetic SIMS Instrument
Acronym SIMS
Classification Mass spectrometry
Analytes Solid surfaces, thin films
Other Techniques
Related Microprobe

Secondary ion mass spectrometry (SIMS) is a technique used to analyze the composition of solid surfaces and mass spectrometer to determine the elemental, isotopic, or molecular composition of the surface. SIMS is the most sensitive surface analysis technique, being able to detect elements present in the parts per billion range.

History

  In 1910 British physicist J. J. Thomson observed a release of positive ions and neutral atoms from a solid surface induced by ion bombardment [1]. Improved bismuth. [8]

Instrumentation

A classical SIMS device consists of 1) primary ion gun generating the primary ion beam, 2) a primary ion column, accelerating and focusing the beam onto the sample (and in some devices an opportunity to separate the primary ion species by wien filter or to pulse the beam), 3) high vacuum sample chamber holding the sample and the secondary ion extraction lens, 4) mass analyser separating the ions according to their mass to charge ratio, 5) ion detection unit.

Vacuum

SIMS requires a high vacuum of at least 10-6 mbar to ensure secondary ions to move undisturbed to the detector (adsorption of background gas particles during measurement.

Primary ion sources

There are three basic types of ion guns. In one, ions of gaseous elements are usually generated with melting points. The LMIG provides a fine focused ion beam (<50nm) with moderate intensity and is additionally able to generate short pulsed ion beams. It is therefore commonly used in static SIMS devices.

The choice of the ion species and ion gun respectively depends on the required current (pulsed or continuous), the required beam dimensions of the primary ion beam and on the sample which is to investigate. Oxygen primary ions are often used to investigate electropositive elements due to an increase of the generation probability of positive secondary ions - while cesium primary ions often are used when electronegative elements are to investigate. For short pulsed ion beams used in static SIMS, only LMIGs are deployable, but often combined with either an oxygen gun or a cesium gun for sample depletion.

Mass analyzers

Dependent on the SIMS type, there are three basic analyzers available: sector, quadrupole and time-of-flight. A time of flight mass analyzer separates the ions at a field free drift path according to their kinetic energy. It needs a pulsed secondary ion generation generated with a pulsed primary ion gun or a pulsed secondary ion extraction. It is the only analyzer type able to detect all generated secondary ions together and is standard analyzer for static SIMS devices.

Detectors

A fluorescent screen and signals are recorded either with a CCD-camera or with a fluorescent detector.

Detection limits

Detection limits for most trace elements are between 1012 and 1016 atoms per cubic centimeter,[9] although this is dependent on the type of instrumentation used, the primary ion beam used and the analytical area, and other factors. Samples as small as individual pollen grains and microfossils can yield results by this technique.[10] The amount of surface cratering created by the process depends on the current (pulsed or continuous) and dimensions of the primary ion beam (often Cs+, O2-, Ga+ or Bi clusters like Bi32-).

Static and dynamic modes

In the field of Surface Analysis, it is usual to distinguish sputtering process, using a DC primary ion beam and a magnetic sector or quadrupole mass spectrometer.

Applications

The COSIMA instrument on board the Rosetta was the first instrument to determine the composition of cometary’s dust with secondary ion mass spectrometry.[11]

See also

  • SHRIMP


References

  1. ^ Thomson, J. J. "Rays of positive electricity". Phil. Mag. 20(1910), 752–767..
  2. ^ Herzog, R. F. K., Viehboeck, F. "Ion source for mass spectrography". Phys. Rev. 76(1949), 855–856.
  3. ^ Liebl, H. J. "Ion microprobe mass analyzer". J. Appl. Phys. 38(1967), 5277–5280.
  4. ^ Castaing, R. & Slodzian, G. J. "Optique corpusculaire—premiers essais de microanalyse par emission ionique secondaire". Microscopie 1(1962), 395–399..
  5. ^ Wittmaack, K.. "Pre-equilibrium variation of secondary ion yield.". Int. J. Mass Spectrom. Ion Phys. 17(1975), 39–50.
  6. ^ Magee, C. W. et. al. "Secondary ion quadrupole mass spectrometer for depth profiling design and performance evaluation.". Rev. Scient. Instrum. 49(1978), 477–485.
  7. ^ Benninghoven, A. "Analysis of sub-monolayers on silver by secondary ion emission". Physica Status Solidi 34(1969), K169–171.
  8. ^ S.Hofmann. "Sputter-depth profiling for thin-film analysis". Phil. Trans. R. Soc. Lond. A (2004) 362, 55–75.
  9. ^ SIMS Detection Limits of Selected Elements in Si and SIO2 Under Normal Depth Profiling Conditions. Evans Analytical Group (May 4, 2007). Retrieved on 2007-11-22.
  10. ^ Kaufman, A.J.; Xiao, S. (2003). "High CO 2 levels in the Proterozoic atmosphere estimated from analyses of individual microfossils". Nature 425: 279-282. doi:10.1038/nature01902.
  11. ^ C. Engrand, J. Kissel, F. R. Krueger, P. Martin, J. Silén, L. Thirkell, R. Thomas, K. Varmuza. "Chemometric evaluation of time-of-flight secondary ion mass spectrometry data of minerals in the frame of future in situ analyses of cometary’s material by COSIMA onboard ROSETTA". Rapid Communications in Mass Spectrometry 20: 1361-1368. doi:10.1002/rcm.2448.

Bibliography

  • Benninghoven, A., et al., "Secondary Ion Mass Spectrometry: Basic Concepts, Instrumental Aspects, Applications, and Trends", Wiley, New York, 1987 ISBN: 0471519456
  • Bubert, H., Jenett, H., "Surface and Thin Film Analysis; A compenium of Principles, Instrumentation, and Applications", p. 86-121, Wiley-VCH, Weinheim, Germany 2002 ISBN: 3-527-30458-4
 
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