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Selecting cathode material
► Equip the ion source with cathodes (filaments) made of the most suitable material for the respec-
3.5.2 Electron collimation magnet
Pfeiffer Vacuum recommends equipping the crossbeam ion source with a magnet unit for applications in
high mass ranges, for molecular beam detection, and in the QMA 410 for separating He and D2. The
magnet increases the real path length of the electrons and thus the ion yield. This results in higher sen-
sitivity and better injection conditions. In addition, the magnet prevents the majority of the electrons from
hitting locations of the formation area that are less critical with regard to ion optics. However, the lineari-
ty (measuring signal vs. pressure) is reduced.
Baking out analyzers with integrated magnets
► Heat analyzers with integrated magnets to max. 300 °C.
3.5.3 90° deflection
The 90° off-axis arrangement has a very low signal background because the electrostatic 90° deflection
prevents fast or excited neutrals and photons from hitting the SEM.
3.5.4 90° deflection with deflection voltage
The inner deflection plate is on potential V6 "Deflection", the outer deflection plate is directly connected
to the Faraday cup and electrometer pre-amplifier EP1 and is thus on ground potential. If no EP1 is
present, use a jump plug.
Fig. 8:
1 Deflection unit
3.5.5 Faraday cup
Faraday cup operation (QMA with Faraday or SEM types operated in Faraday mode) reduces systemat-
ic conversion errors of the SEM (e.g. mass discrimination). Faraday operation can also be used for mal-
function diagnosis. The drawback is the lower sensitivity, which requires a higher amplification and thus
limits the response speed.
3.5.6 Vacuum-annealed QMA
The QMA with the vacuum-annealed grid ion source has a very low self-outgassing and desorption rate
(<10
-10
tive application.
– Not all materials are available for all ion source types.
1
SEV
V6
Deflection
90° deflection with deflection voltage
2
hPa l/s).
2
EP1
EP2
Faraday cup
Product description
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