Dave Mitchell's DigitalMicrograph™ Scripting Website

Tutorial: Tuning the CEOS (probe) Corrector

by

Dave Mitchell and Gilberto Casillas-Garcia

This tutorial has nothing to do with DigitalMicrograph scripting. However, I have included it here as it may be of use to anyone interested in learning to use a probe corrected STEM fitted with a CEOS corrector. When I was learning I got instruction on which buttons to push in the CEOS software, but optimising the tuning cycle to rapidly converge to a good and stable result, took a lot of personal trial and error. Using the approach described here I can generally tune the corrector to obtain better than specification STEM resolution in around 1.5hrs.

The critical element to achieving success is microscope/specimen stability. If you do not have that, then you are wasting your time tuning the corrector. You will struggle to get the tune to converge, and even if you do achieve some good numbers, the tune will not be stable and drift will occur. All my corrected probe experience has been on JEOL ARMs. However, the general principles described here should be a fairly similar experience on other platforms - which use CEOS probe correctors. The latest JEOL Delta correctors use very different physics to CEOS systems and this approach is not relevant.

This tutorial assumes you are already familiar with the basics of corrector software and you are looking to optimise your tuning procedures. On my ARM I do not routinely tune the corrector. It is stable over months. The only time I tune it is if I switch voltages or after maintenance, like column bakes. I always switch voltage on a Friday evening, allow the system to re-equilibrate over the weekend, then tune on the Monday morning. When switching to 200kV I only need to tune once and the tune is stable thereafter. Lower voltage (80kV) is more challenging. I will tune on Monday morning, but the tune will drift by the end of the day. So I reserve all my low resolution, low voltage work such as mapping for Monday and Tuesday, then I retune on Wednesday morning and thereafter, the tune is stable and I can then do all the high resolution work. Given the time overhead in voltage switching (two low voltage tunes - Mon and Wed) and another tune when switching back to 200kV on the following Mon, I generally save up low voltage work until I can book out the microscope for a full week.

The tutorial can be downloaded as a PDF.