Accelerating Voltage
Notes on Settings
NOTE: The TEM is now conditioned to operate at 300 kV. The TEM accelerating voltage must be left at 315 kV at any time the scope is not being used. The scope can be operated at 100, 200, or 300 kV, but MUST BE LEFT AT 315 kV between sessions.
The Wehnelt has been adjusted so that the filament saturates at a BIAS of 7,7. The FILAMENT knob is still set to ~6.
The 200 kV dark current is still ~61.4 µA. The 300 kV dark current is 92.3 µA. REMEMBER that the scope can never be operated at a beam current above 10 µA.
Hysteresis
At 300 kV, the lenses operate at higher voltage and hysteresis becomes a problem. Even with a perfect alignment, the beam will not remain in the screen center when switching between magnification ranges. One can minimize the effect by returning the magnification to 5000X and then slowly increasing the magnification.
Anti Contamination Devices
The column ion pump has been replaced and now the ACD heaters work properly. In warm, humid weather use ACD's each time you run the scope. The last user of the day will insert the heaters and depress the ACD HEAT buttons. The heat cycle will last ~1 hr and the column ion pump will come back on. See Filling ACDs under Operating Procedures in JEOL JEM-4000FX TEM.
Setting the Accelerating Voltage
NOTE: Ensure that the CM button in the LH drawer is ON (lamp on) when you use 200 or 300 kV.
At 200 kV
Starting at 315 kV, issue the keyboard command HTSET 200 and press the return button. The accelerating voltage will immediately go to 200 kV. Saturate as usual.
At 300 kV
Starting at 315 kV
Starting at 315 kV, issue the keyboard command HTSET 300 and press the return button. The accelerating voltage will immediately go to 300 kV. Saturate as usual.
Starting Below 300 kV
Starting at accelerating voltage below 300 kV, use the HTUP program. Issue the keyboard command Load HTUP <return>, then RUN <return>. Follow the prompts that will ask you what kV you are beginning with and the final kV (less than or equal to 315 kV). USE CAUTION – DOUBLE CHECK THE VALUES YOU INPUT TO THE PROGRAM!! Use a time of no less that 30 minutes; 60 minutes is better. Note that this may not be necessary if another user is coming in after you. Check the booking calendar. In this case, the last user of the day would increase the HV to 315 kV.
Returning the Scope to 315 kV
Issue the keyboard command Load HTUP <return>, then RUN <return>. Follow the prompts that will ask you what kV you are beginning with and the final kV = 315. USE CAUTION – DOUBLE CHECK THE VALUES YOU INPUT TO THE PROGRAM!! Use a time of no less that 30 minutes; 60 minutes is better. Note that this may not be necessary if another user is coming in after you. Check the booking calendar. In this case, the last user of the day would increase the HV to 315.
NEVER use the HTSET command to INCREASE the accelerating voltage!!
