7 Operation
7.1 Adjusting ion source
7.1.1 Adjusting the axial ion source
Procedure
1. Start with the last values that provided good results, the values from the test log or, if nothing bet-
ter is available, with typical values.
2. Adjust "
Focus
" to maximum peak height.
3. Adjust "
Wehnelt
" to maximum peak height (at "
Cathode
" <50 V maximum 20 V).
4. Look for the combination of "
Field Axis
" and "
Resolution
" that provides the best peak height with
a good peak shape.
5. Determine the best HF cable polarity.
7.1.2 Adjusting crossbeam ion source
Setting the crossbeam ion source without magnet
1. Start with the last values that provided good results, the values from the test log or, if nothing bet-
ter is available, with typical values.
2. Increase the value of "
Field Axis
" by 1.5 V.
3. Increase the "
Resolution
" by approx. 15%.
4. Alternately adjust "
Focus
" and "
Extraction
" to maximum peak height.
5. Decrease the "
Field Axis
" until the peak height drops approx. 10% and evaluate the peak shape
and resolution.
6. Set the "
Resolution
" to a value that is just high enough to suffice for your purposes.
– Using an unnecessarily good resolution means forfeiting sensitivity and stability.
7. If the peak shape is not good enough (spikes, tailing), try improving it by reducing the "
Field Axis
"
parameter.
8. Try new values for "
IonRef
" (in steps of 5 V) to achieve better sensitivity.
– At each step, reconfigure all other parameters anew. Proceed systematically and record the
parameters, as well as the respective peak height and shape achieved.
9. Repeat the process for the second filament. After switching, wait for thermal stability to be estab-
lished.
– A large difference in the sensitivity between the two filaments indicate a mechanical deforma-
tion.
10. Determine the best HF cable polarity.
Setting the crossbeam ion source with magnet
For analyses at different pressures, Pfeiffer Vacuum recommends removing the magnetic unit or reduc-
ing the emission to 0.1 mA. At low emission levels (up to 0.1 mA), the procedure described in the "Set-
ting without magnet" section applies. At higher emission levels, and if you want to achieve the maximum
sensitivity, look for the most favorable emission setting, as described below.
1. Set the pressure in the system to the value for which you want to optimize.
– The pressure has to stay constant during the entire process of configuring the settings.
2. Set "
Field Axis
" to 16 V and "
Emission
" to 0.5 mA.
3. Adjust the "
Extraction
" and "
Focus
" alternately and repeatedly, to the greatest peak height.
4. Make a note of the peak height and the associated values for the "
Emission
", "
Extraction
" and
"
Focus
".
5. If the emission is <1 mA, increase it by 0.1 mA and return to step 3.
6. In the noted data, look for the point with the highest peak height and set the parameters to the
associated values again.
7. Adjust the "
Field Axis
" and "
Resolution
" as described in the "
Setting without magnet
" section.
8. Determine the most favorable value for "
IonRef
" and the best cable polarity as described in the
"
Setting without magnet
" section.
9. Increase the "
Extraction
" until the sensitivity is reduced by 5%; this increases the stability.
The ion source has now been optimized for the current pressure. For other pressures, it is usually suffi-
cient to optimize "
Extraction
" and "
Focus
" again.
Operation
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