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Returning to
HV mode
Returning from VP mode to HV mode is initialised by pressing the Go To HV key in the VP Control
window. This will switch off the acceleration voltage and close the column chamber valve. This is
done for safety reasons, as the TIV is reopened. As relatively poor vacuum is available in the
specimen chamber, opening the TIV using the bypass between turbo pump and column area
could result in a vacuum leakage in the gun area and damage the tip. To avoid this, the column
chamber valve is closed automatically.
The specimen chamber is then pumped to the lowest pressure with the pre-vacuum pump. Then
the TIV is opened and the RBV adjusted in such a way that the pre-vacuum pump is still connected
with the turbo pump. When high vacuum is reached in the total system, the column chamber valve
is automatically opened and beam booster and acceleration voltage are
activated.
IMPORTANT
A higher pressure can be set within a few seconds.
Achieving a lower pressure may require some more time, because the specimen chamber has to
be evacuated by the pre-vacuum pump.
Gun vacuum In the gun head is an ultra high vacuum, which is maintained by an ion getter pump (8). The vac-
uum in the gun head is called ’Gun vacuum’. It should be well below 1 x 10
-8
mbar.
The specimen is located in the evacuated specimen chamber (9). To open the specimen chamber
for specimen exchange, you have to break the vacuum in a controlled manner. This is done by
the Vent command on the SmartSEM
®
user interface or by pressing the Exchange push button
on the optional control panel.
Ventilating When receiving the Vent command, the column chamber valve closes and gaseous nitrogen
flows into the specimen chamber via the vent valve (12). As soon as the pressure equilibrium is
obtained, the chamber door can be opened to change the specimen.
Evacuating In order to continue operation, the Pump command makes pre-pump and turbo pump evacuate
the specimen chamber.
As soon as the vacuum in the specimen chamber is ready for operation, the column chamber
valve opens and the ’EHT Vac ready’ message appears in the SmartSEM
®
user interface. Gun
and EHT can be switched on.
Quiet Mode The automatically controlled Quiet Mode is optionally available.
This option allows switching off the pre-vacuum pump after specimen exchange when the vacuum
threshold is achieved.
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