E02- Pencil Beam Alignment (300kV)


The following are the general steps in setting up small convergence angle pencil beam on G-ARM 300F (E02):

  1. Load the standard gold cross-grating sample.

  2. Align the microscope in TEM mode (TEM-S, Spot 1), running the corrector software (COSMO) making sure that coma is corrected to around 80 nm.

  3. In TEM mode, after establishing parallel beam [e.g. by wobbling OL and changing beam spread (CL3) until beam shape is fixed at low MAG], switch to diffraction and check roundness. Try correcting by adjusting OLS deflectors [Note: OLS deflectors have separate values in TEM MAG mode and TEM Diff mode. The deflector values in Diff mode are to be changed / recorded here]. Note down the values you reached. [Note: Insert SA aperture to reduce beam current - take care on OneView]

  4. Switch to STEM mode, and press NBD Scan button on the Maintenance panel. By doing so COMO loads the correct files. At this point have the viewing screen in the lowered position and OneView retracted.

  5. Open the Free Lens Control (FLC) panel and insert hex values for the pre-sample lenses. The screenshot here shows the values for 300 kV alignment. At this point you should see the ronchigram on phosphor screen (might have to increase camera length to 100 cm). View the ronchigram on OneView and reach focus by adjusting sample height.

  6. Go to Maintenance mode [Note that in this mode pressing any of the control buttons will set the hex values to 8000 - neutral] and manually insert CLA CMPT, CLA CMPS, MADJ, CORR, ROTA values as shown in the screenshot. Also transfer the OLS values from TEM mode.

  7. Correct for 2-fold and 3-fold stig using the quadrupole and hexapole elements in the probe corrector.

  8. Insert a CL aperture, e.g. 20 um or 30 um, and apply changes in the FLC panel to view the image of the probe on screen at 10 kx MAG. For 300 kV these are the settings shown on the RHS.

  9. Centre the aperture with respect to CL2 lens by changing its strength in FLC panel and moving the aperture to have it expand / shrink symmetrically. Now we need to correct for beam shift and tilt. Use SpotA deflectors for shifting to centre, then press HT wobble and use CLA2 deflectors to correct for beam tilt.

  10. Deactivate projection lenses in FLC to have ronchigram back on camera and repeat steps 7 to 9 one more time at 50 kx MAG.

  11. Form an STEM image, e.g. at 20 cm CL, and view the direct beam on Medipix live view. Adjust the IL Focus in the maintenance panel to minimise beam motion. Switch to other CL value that you will use in experiment and repeat. Use PLA to position the beam as needed [Note: These values will be saved and recalled after you switch to User mode].

  12. Form a relatively low MAG ADF image in the JEOL STEM Viewer. Change the rotation angle in Maintenance panel to have the x-grating grids squared with respect to the frame. Use MADJ and ROTA to adjust the scan to match the known distance and geometry.

  13. Insert the scan rotation value to match the track ball motion (136 degrees for 300 kV) in maintenance panel.

  14. The alignment is complete and you can switch to User mode.

  15. Collect au-xgrating 4D-STEM data and multiple MAGs to have calibrations for real and reciprocal space for your experiment. Check diffraction roundness on the first dataset to ensure good roundness. You can also gather one 4D-STEM data with very large CL aperture and sample moved to large defocus. This can be used to measure image / diffraction planes rotation and also to calibrate step size.