JEOL JSM-6390 LA, User Manual

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SEM manual ETHZ v1.4
15
E) Activate the electron beam
WARNING! Different procedure to activate the electron beam if a W or a LaB
6
electron
source is loaded ( Fig. 12 )! Check the note W or LaB
6
below the computer screen!!!
If you see a BLUE sign W-mode , refer to Appendix A2 for separate instructions.
E.1) Activating a LaB
6
electron source
in “LaB
6
mode”
When a lanthanum hexaboride (LaB
6
) electron source is loaded, it is left active at optimum
filament heat all the time, and only the gun bias is adjusted to control the electron emission.
LaB
6
offers a higher stability, a better image resolution, and a longer lifetime. However, it is
fragile and expensive; it can be damaged when warmed up or cooled down too quickly.
Please, strictly respect the following to activate the electron beam:
•
Ensure that the window “Sample” indicates “Ready” (= high-vacuum condition).
•
Check that VT-3 is opened and that the “Beam blank” is OFF.
•
Open the window “Gun”.
•
Click on “Set Bias” and click “Preset”.
This calls back the default bias value (~100 to 150).
•
Do NOT change anything else in the window “Gun Alignment”! NEVER change
the filament heat! The optimum is set by the lab manager or the assistant.
•
The “Filament heating” should read between 20 and 30 µA.
•
An SE image should now be visible in the JEOL SEM program.
•
Perform a beam alignment following the instructions in Section F .
E.2) Activating a W electron source
in “LaB
6
mode”
The tungsten (W) electron source is usually left in “standby” condition; the filament heat is
just enough to keep the filament warm, but not enough to emit electron. You’ll need to
perform a
filament saturation by setting the filament heat to its optimum:
•
Ensure that the window “Sample” indicates “Ready” (= high-vacuum condition).
•
Check that VT-3 is opened and that the “Beam blank” is OFF.
•
Saturate the W-filament…
o
Insert the Faraday cup by pressing the button “PCD”.
o
Press the top-left button “LOCAL / CONFIGURATION” on the ammeter. This
will activate the live beam current reading. If the wording “CONFIGURATION”
appears on the ammeter display, press another time on the same button. If
you still don’t see a live reading of the beam current, press the button “TRIG”.
o
The ammeter should indicate a varying value around zero.
o
Set the “Spotsize” around 74 to 78 (= medium to high beam current).
o
Open the window “Gun” and increase the filament heat until the emission
current and the beam current increase. Continue increasing the heat, until the
beam current decrease again (= “false peak”). Continue increasing the heat
until the beam current increases again. You will reach the saturation point
when the increase in beam current slows down or drops down slightly.
o
The emission current should read ~30 to 60 µA (or more), and the ammeter
should read ~2 to 3 nA at the beam aperture #2.
o
Note that with a W filament, you can increase the heat rapidly. This saturation
should not take you more than a minute…
o
When done, click on “PCD” to remove the Faraday cup.
•
An SE image should now be visible in the JEOL SEM program.
•
Perform a beam alignment following the instructions in Section F .