Secondary ion mass spectrometry

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Secondary ion mass spectrometry (SIMS) is a surface physics / surface chemistry method that can be used to analyze the composition of a sample; it is therefore a special form of mass spectrometry .

Like secondary neutral particle mass spectrometry (SNMS) , Rutherford backscattering spectrometry (RBS) and low-energy ion scattering spectroscopy (LEIS), SIMS is one of the ion beam technologies . With SIMS, the sample is bombarded with primary ions , which then release the secondary ions to be analyzed .

functionality

The sample is made up of primary ions , which are atomic or molecular (O 2 + , Cs + , Ga + , Ar + , Bi + ) or cluster ions (SF 5 + , Au 3 + , Bi 3 + , Bi 2 3+ ) can be bombarded with an energy of 0.2–30 keV. This creates neutral particles as well as positively or negatively charged particles, the secondary ions. The neutral particles, which represent over 90% of the emitted material, are lost in the SIMS for analysis. The charged particles are separated using mass analyzers (mass filters). The most common are the quadrupole mass analyzer , the time-of-flight mass analyzer , and the sector field mass analyzer . The last two achieve mass resolutions of . With this, for example, Al + , BO + and C 2 H 3 + ions can be separated, although all three have the nominal mass 27 amu . After flying through the analyzer, the ions reach a detector or a detector group. The signal intensity as a measure of the amount of particles is used to evaluate the composition. The microchannel plates or electron multipliers usually used are able to detect individual ions.

construction

Dynamic SIMS scheme

A SIMS device consists of:

1: an ion cannon,
2: a unit that accelerates the ions and focuses them on the sample (and possibly also pulses the ion beam),
3: a high vacuum chamber with the sample and a lens for the secondary ions,
4: the sample,
5: an energy filter,
6: a mass spectrometer
and a detection unit: how
  • 7: an electron multiplier
  • or 8: a channel plate with fluorescent screen.

commitment

Despite the loss of material described above, SIMS is a very sensitive analytical method (detection limit in the ppm range for all elements), but also a material-destroying method, since during the measurement, in addition to the removal of material, primary ions are introduced into the sample, their composition and morphology is changed.

SIMS can be operated in different modes. In the depth profile mode, the composition of the sample, starting from the sample surface, is examined in depth, with a depth resolution of a few nanometers being achieved at a sampled depth of up to a few micrometers. In the imaging mode, SIMS provides information about the lateral distribution of chemical elements or compounds on the sample surface and works in the form of an ion microscope . The lateral resolution in the imaging mode is device-dependent, but ranges from 50 nm to 1 µm. By combining these two operating modes, distributions can be clearly shown using 3D images and facilitate the interpretation of processes on the surface and inside the sample down to a depth of a few µm. One of the main areas of application of SIMS today is the analysis of semiconductors and thin layers, as well as the investigation of organic contamination on surfaces.

NanoSIMS

The so-called NanoSIMS represents a further development of the method . In addition to the high depth resolution inherent in SIMS, the lateral expansion of the ion beam on the sample can be further reduced using suitable ion sources. In addition, a magnetic mass spectrometer is used, which allows high transmission and high mass resolution at the same time. As a result, a spatial resolution of up to 30 nm can be achieved while maintaining the high sensitivity and isotope identification. The parallel quantitative analysis of several mass numbers (i.e. several isotopes) from the same volume is also possible. In energy research , NanoSIMS helps to characterize nanostructured materials with complex compositions, which are increasingly important candidates for energy generation and storage. In biological samples, the isotope combinations 12 C 15 N and 13 C 14 N can be distinguished, which allows, for example, the study of food intake or biological activity and the determination of the place of installation in the cell. Further applications of the NanoSIMS can also be found in materials research, cosmology and geology, including for high-resolution measurement of trace elements, for age determination and for proof of origin based on the isotopic composition.

history

fresh liquid metal ion source

The technology goes back to JJ Thomson , who observed the emission of positively charged secondary ions when a surface was bombarded with ions in 1910. In 1949 Franz Viehböck and Richard Herzog (RFK Herzog, University of Vienna) built the first prototype of a SIMS with spectrometric analysis of the secondary ions. Further improvements in the ion optics were made by RFK Herzog and Helmut Liebl and in the USA another prototype was created at RCA Laboratories. A SIMS was developed in Paris by Georges Slodzian and Raimond Castaing in 1960 (University of Paris-South). In 1968 this led to a commercially available device from Cameca (IMS-300), which is now one of the most important international commercial manufacturers of SIMS. At GCA Corporation, Liebl and Herzog independently developed a device for NASA to analyze lunar rocks. This resulted in the Ion Microprobe Mass Analyzer (IMMA) at Applied Research Laboratories (ARL), which was launched in 1967. Both devices used argon ions and a magnetic sector mass spectrometer. In the 1970s, K. Wittmaack and C. Magee developed SIMS with quadrupole mass spectrometers. A device developed at the University of Chicago by Riccardo Levi-Setti in the 1970s (UC-HRL SIMS) was also based on this. Levi-Setti was also one of the first to use field emission techniques for ion generation ( Focused Ion Beam ) (also J. Orloff, L. Swanson). At the beginning of the 1980s, liquid metal ion sources (LMIS) with gallium brought about a considerably improved resolution of the SIMS (point sources through field ionization of the metals from sharp tips). The first devices with a liquid metal ion source were made by R. Seliger u. a. Built in 1978.

Static SIMS were developed from 1969 at the University of Münster by Alfred Benninghoven a . a. that examined only thin surface layers of the sample with minimal destruction of the sample.

literature

  • Heinz Düsterhöft , Miklos Riedel, Bettina-Kirsten Düsterhöft: Introduction to secondary ion mass spectrometry (SIMS). Teubner Study Books, 2001
  • A. Benninghoven, FG Rüdenauer, HW Werner Secondary Ion Mass Spectrometry: Basic Concepts, Instrumental Aspects, Applications, and Trends , Wiley, New York, 1987

Individual evidence

  1. ↑ The newly developed nanosims ion microprobe opens a new window into space Press release from the Max Planck Institute for Chemistry ( Memento from January 5, 2011 in the Internet Archive )
  2. ↑ [1] , Sebastian Behrens et al. Linking Microbial Phylogeny to Metabolic Activity at the Single-Cell Level by Using Enhanced Element Labeling-Catalyzed Reporter Deposition Fluorescence In Situ Hybridization (EL-FISH) and NanoSIMS
  3. ↑ Thomson Rays of positive electricity , Philosophical Magazine, 20, 1910, 252
  4. ↑ Herzog, Viehböck Ion source for mass spectrometry , Physical Review, Volume 76, 1949, 855L. Viehböck was Herzog's doctoral student.
  5. ↑ RE Honey Sputtering of surfaces by positive ion beams of low energy , J. Appl. Phys. 29, 1958, 549-555
  6. ↑ Castaing, Slodzian Optique corpusculaire - premiers essais de micro analysis par emission ionique secondaire , J. Microscopie 1, 1962, 395-399, the same: Compte Rendus Acad. Sci., 255, 1962, 1893. Slodzian was Castaing's graduate student.
  7. ↑ Liebl Ion microprobe mass analyzer , J. Appl. Phys., 38, 1967, 5277-5280
  8. ↑ HRL stands for Hughes Research Laboratories in Malibu (California), UC for University of Chicago
  9. ↑ WH Escovitz, TR Fox, R. Levi-Setti Scanning Transmission Ion Microscope with a Field Ion Source , Proceedings of the National Academy of Sciences (USA), 72 (5), 1975, 1826
  10. ↑ R. Seliger, JW Ward, V. Wang, RL Kubena A high-intensity scanning ion probe with submicrometer spot size , Appl. Phys. Lett. 34 (5), 1979, 310

See also