Procedure for Coma-Free Alignment

Procedure for coma-free alignment

If you have any questions, please contact Professor L. D. Marks:

1.  Preliminary alignment must be done (gun, tilt and shift balance, eccentric height, voltage center, OBJ astigmatism etc., refer to the manual for JEOL 2100 F)

2.  Find and center an amorphous area in the GIF mode, under Process menu click Live and then Reduced FFT; You should be able to see something like below:

3.  Select Maintenance on the TEN Controller main menu and click the Alignment

4.  Click and change the frequency to 3 or lower for the tilt/shift; amplitude to 4 for the tilt/shift.

5.  Click TiltX in the alignment panel for maintenance, the beam tilt now is wobbling in x direction. Depress on the BRIGHT TILT switch, manipulate DEF/STIG X knob, to make the change in the live fft minimum. Turn off the wobbler by click TILT X again. Click TiltY in the alignment panel for maintenance, the beam tilt now is wobbling in y direction. Manipulate DEF/STIG Y knob, to make the change in the live fft minimum. Turn off the wobbler by click TILT Y again. Repeat this step for x and y directions for several times. In the end, there should be no change in the live fft when the beam tilt is wobbling in both directions. (Note that the FFT should not be circular when you the beam is wobbling, but the elliptic rings are not changing. It is acceptable what there is only a small change)

6.  To obtain the best result, correct the OBJ astigmatism after step 5; then repeat step 5 again. Do it for several times until after step 5, the rings in live fft are circular.

This is the end of coma-free alignment. Since the incoherent aberrations in the TEM, you may need to do the coma-free alignment again when you changed to another sample area or changed the magnifications.