Secondary neutral particle mass spectrometry
Secondary neutral particle mass spectrometry (SNMS) is an analysis method of surface physics / surface chemistry and, like secondary ion mass spectrometry (SIMS), Rutherford Backscattering Spectrometry (RBS) and low-energy ion scattering spectroscopy (LEIS), belongs to the ion beam techniques .
functionality
With the SNMS, the sample is bombarded with primary ions of atomic type (O + , Cs + , Ga + , Ar + ) or cluster ions (SF 5 + , Au 3 + , Bi 3 + ) with an energy of 0.2 to 25 keV . Particles are released from the sample by this bombardment, cf. Sputtering . These are mostly neutral, but also positively and negatively charged particles. In contrast to SIMS , the neutral particles are examined in SNMS. In order to be able to determine their mass and number by mass spectrometry, the neutral particles are re-ionized after they have left the sample, either in a low-pressure plasma by electron impact or by intensive laser light.
Advantages and disadvantages
The method has a high detection sensitivity in the ppm range, which allows a low bombardment intensity. As a result, a very high depth resolution can also be achieved. In addition, non-conductive samples can also be examined.
Compared to SIMS, SNMS has the advantage that more than 90% of the sputtered material is used, which means that there are almost no interfering matrix effects on the yield. A negative factor for the quantification is the strong variation in the ionization probability of different atoms and clusters.
SNMS using laser ionization also allows high lateral resolution, while the low-pressure plasma variant cannot achieve this.
literature
- H. Oechsner, Secondary Neutral Mass Spectrometry with Plasma Postionization. In: Encyclopedia of Mass Spectrometry, Vol. 5. (D. Beauchemin & DE Matthews, Eds.) Elsevier 2010, p. 455-469
- R. Any, H. Peters et al., Analysis of Thin Films by Mass Spectrometry of Nebulized Neutral Particles . In: Technisches Messen tm. No. 11, 1986, pp. 407-413.