Secondary Ion Mass Spectrometry (SIMS)
Mass spectrometry describes a wide range of methods for the qualitative and quantitative analysis of chemical substances. Secondary ion mass spectrometry (SIMS) is a special technique and is used to record surface-sensitive mass spectra. Lateral resolution is obtained by sputtering the sample surface with an ion beam in a grid.
How does it work?
The sample surface is sputtered with high-energy ions. These particles, known as primary ions, penetrate the sample surface and, after releasing their kinetic energy, they trigger a collision cascade. Atoms close to the surface can be ionized that way and are knocked out of the sample. Through the detection of these so-called secondary ions, it allows to determine the composition of the sample. Before the detection, an analyzer can also be used to separate different masses. This can, for example, be a flight tube as used in TOF MS (time-of-flight mass spectrometer). Or a quadrupole filter, as in quadrupole mass spectrometers. The secondary ions generated, can be both positively and negatively charged particles. It doesn’t require an additional ion source.
The secondary ions must pass through the analyzer, i.e., the mass filter, without releasing their energy through impact with other particles or being discriminated against by parts of the equipment. As a result, it requires mean free path lengths, which are achieved at pressures p < 10-4 hPa and are therefore also necessary for the operation of quadrupole mass spectrometers. This is achieved through a suitable pumping station with pressure monitoring. A total pressure gauge protects the mass spectrometer from being switched on if the pressure is too high.
Pfeiffer Vacuum offers various dry or oil-lubricated backing pumps and turbopumps to achieve the necessary working pressure. It is often advisable to integrate ready-made pumping stations. Pfeiffer Vacuum also offers a large selection of vacuum chambers and components as well as pressure gauges that can be used in your system and your fore-vacuum line.