Details of Astigmatism Correction

See the Basics of SEM Alignment ( • Basic SEM Alignment (S... ) and the Alignments Handout (bit.ly/2OgnvDL)
This video provides an in-depth look at astigmatism -- how to recognize it, how to fix it, and most importantly, what underlies the stretching artifact in the first place.Failure to properly correct astigmatism accounts for the majority of users' problems getting good images, so hopefully a better physical understanding of astigmatism will make it easier to fix. Note that everything that is shown here for SEM applies also to FIB.
The main practical points to take away are:
1. If you see stretching while changing focus, that indicates that there is astigmatism.
2. The first step in fixing astigmatism is getting to the correct focal plane (if there is stretching to the left and right, settle in the middle where the edges of the features appear equally blurry).
3. If while adjusting astigmatism the image is stretching, that means you are not quite on the right focal plane; in this case, stop fixing astigmatism and try again to select the right focal plane. The image should not be stretching while adjusting astigmatism; ideally only the sharpness of the image will be changing.
This video was made on an FEI Nova 600 NanoLab Dualbeam system, using the generally-available mouse and keyboard controls. It is a continuation of the series on SEM and FIB, where the left and right conventions have been used to describe moving the focal plane above (left) and below (right) the sample. If using the multi knob user interface, these procedures correspond to turning the knobs counterclockwise (for left) or clockwise (for right). The general principles of correcting astigmatism apply to any SEM or FIB system.
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Disclaimer: This video is intended to serve as supplemental information and cannot replace in-person instrument training. Microscope operators are encouraged to consider which parameter setting is most suitable for their measurements. Caltech and KNI are not responsible for how the presented information is translated for use in other facilities.

[@rohitashva100]

Excellent explanation! Thank you so much!

[@uchenyu]

thanks a lot for the detail

[@danhallatt4954]

Is there a working link to the PDF of the file which was showed? The older comment replies to an expired link.

[@qiangli5779]

Can I have the PDF file you showed in the video? Thanks.

[@thekavlinanoscienceinstitu9490]

Yes, that PDF can be found via this link: caltech.sharepoint.com/sites/KNI/_layouts/15/guestaccess.aspx?docid=0e82f4330adb743be9b848b40d8ce8016&authkey=Aem6b1sWww36vuFC-gP0Xy8&e=0mmcRs

[@RQDK]

Is it for SEM? i'm trying to figure out the difference and degrees of astigmatism in both SEM and TEM.

[@jyyue9764]

Can I have the PDF file you showed in the video？ the link was died

[@thekavlinanoscienceinstitu9490]

Sure, you can find that graphic here: caltech.sharepoint.com/sites/KNI/_layouts/15/guestaccess.aspx?docid=0e82f4330adb743be9b848b40d8ce8016&authkey=Aem6b1sWww36vuFC-gP0Xy8&e=0mmcRs

[@dr.impactslab]

@@thekavlinanoscienceinstitu9490 It looks like this link is invalid for now.

[@alinoun330]

What is focusing to the right and left?

[@thekavlinanoscienceinstitu9490]

It just means that on our system, in order to focus, we right-click the mouse and while holding down the click, we sweep the mouse left and right in order to adjust the focus. If you have a focus knob on your system, when I say, "focus to the right and left," that's the same as saying, "spin the knob clockwise or counter-clockwise."

[@alinoun330]

@@thekavlinanoscienceinstitu9490 Thanks for the clarification.