COSMO corrector (TEM)

Do not attempt to do anything you have not been trained to do by ePSIC staff.

In order to run the COSMO corrector the sample must have areas of thin amorphous material. Any lattice in the image may interfere with the aberration calculation.

If sample contaminates significantly the aberration correction may fail. If possible beam shower the sample.

  1. Ensure that the objective lens is set to standard defocus and microscope at x800k or greater.
  2. Increase the height of the sample so that the image is under focus (rings get smaller as you move sample -z) and numerous thon rings can be observed.
  3. Stop the view on Digital Micrograph and press monitor on the COSMO TEM auto-adjust software.
  4. Using COSMO software correct 2 fold astigmatism (A2) to ≤5nm.
  5. Using the z-piezo drive set defocus to about -200nm.

    When super-fine is selected on the trackball goniometer control, the "diff-focus" dial on the right hand panel controls the z-piezo drive.

  6. Set the tableaux angle to the required level (recommended to start at ~20 mrad) and run a tableaux.

  7. Correct for higher order aberrations.

  8. Iterate 4-7 as required.

 AberrationJEOL notation'Good' value


 2-fold stigA2<5nm
 3-fold stig A3 <50nm
 Spherical O4 <2um
 Star Q4 <2um
 4-fold stig A4 <2um