Stereo Scan 440 - DCU

If preferred the beam alignment can be carried out by observing the screen
brightness while in nonnal mode and adjusting the gun tilt and shift controls to
produce the maximum screen brightness.
Once the filament has been saturated and centred correctly, the system can be
operated as normal and when, on SEM Shutdown, the Operating Conditions are
saved. the system can be brought back to these operating conditions simply by
pressing the RUNUP icon.
~:.- It is worth noting that when SEM Standby is selected. the EHT is removed
from the filament. but filament cu"ent continues to flow through it at a
reduced level. thus keeping the filament wann and improving stability.
Sample Changing
When changing the sample. it is only necessary to close the column isolation
valve before venting the chamber (the gun isolation valve should already be
closed). The filament will remain on during this operation. but the EHT. will be
turned off. When the chamber has been pumped out again and the vacuum ready
state achieved. the column isolation valve can be re-opened. whereupon the EHT
will be switched back on and the image restored. It is advisable at this point to
check the beam alignment by adjusting the Gun tilt for maximum signal
brightness.
2.4 Scanning Transmission Detector
From an Operators' point of view, the S'lEM attachment is comprised of three
main parts:
The detector assembly. which houses the BSD diode. and should be
fitted at the rear of the stage assembly. The detector assembly has a hole
cut out of a metal plate. beneath which can be seen the detector diode.
2. The STEM sample holder which fits onto the SEM ZTR module in place
of the standard SEM carousel. This is a circular assembly. with a series
of small holes on it's perimeter which accommodate the transmission
samples which are held in special holders.
3. The SlEM detector eleCbical feed-through, which is nonnally mounted
on one of the .. ears" of the SEM chamber. The Operator must connect
the cable coming from the SlEM detector to this feedthrough before use
Stereoscan 440 Operator Manual