FEI Quanta FEG 250, User'S Operation Manual

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System Options: Heating Stage 1000 °C / Heating Stage 1500 °C
9-39
arm is pushed away.
Adjusting the Heat Shield
If the heat shield touches the high temperature GSED or sits farther
than 2 mm from it, the arm needs to be adjusted. It must be centred in
the X / Y directions too (this may not typically need to be adjusted).
1. Loosen the Z adjustment hex screw and move the heat shield up
so that the tip of the GSED sits in the heat shield hole.
2. Use the X / Y adjustment screws to make any necessary centring
adjustments.
FIGURE 9-33 ADJUSTMENT OF THE 1500 °C HEAT SHIELD
3. Move the arm to the 2 mm distance from the GSED and re-tighten
the Z adjustment screw.
Note:
For the 150 mm stage the extender must be installed.
Heat Shield and Sample Bias (SSB) board
This board provides voltages used for the following features:
• A heat shield bias voltage (0 - 300 V) draws the electrons from the
sample through a small opening in the heat shield.
• At low temperatures, the sample bias (± 50 V) is negative (with
respect to ground) and pushes the electrons to the detector. At
higher temperatures, this bias is positive to suppress the thermal
electrons which are generated by a sample.
Note:
The safety A/C Interlock causes the bias voltages to switch off
whenever the specimen chamber is vented; however make sure the
supply is turned off before changing any connection.
Crucibles
The crucible types and its application see above (HS 1000).
MgO crucibles are coated with a conductive platinum paste and a
platinum wire runs inside it, allowing a sample bias to be applied
directly under the sample.
Crucibles have a finite lifetime, the platinum coating wears out after
some time.
Before inserting the crucible into the heater always check the sample
bias wire shape to avoid a poor electrical contact.
The Platinum (the heating element is made of) reacts with the silicon,
therefore always avoid free silicon.