Proper focusing in TEM and STEM modes

In this video tutorial (as always, recorded raw, unedited, unfiltered, and uncensored), I cover how to properly focus in both TEM and STEM modes as demonstrated using a FEI Talos F200i S/TEM. The topics covered include:
1. setting and verifying eucentric height
2. microprobe and nanoprobe modes for TEM and STEM operation
3. objective lens settings for microprobe and nanoprobe modes
4. properly setting the C2 lens for STEM mode
5. coarse focusing by adjusting stage Z
6. fine focusing by adjusting the objective lens
7. deviations from eucentric height in STEM mode
8. monitoring the deviation (defocus) from eucentric focus
Thanks for watching! Please like, subscribe, and share and let me know if you have any questions or comments. Video topic requests are always welcome and appreciated; I enjoy making these videos and wish I could make them more frequently, but the demands of my job make it tough to do so; I’m in charge of 3 S/TEMs, 2 dual FIB/SEM systems, and 1 SEM and this keeps me very busy!
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[@pabitrasahu9621]

Thanks

[@sergeiremennik7604]

Thanks for your work. Nice video, it looks like you have several grains in your sample so maybe you take grain with different ZA (it does not look like 110). The focus and stigmators looks wonderful. Thanks.

[@NicholasRudawski]

Thank you; I assure you it is [110] zone axis; I looked at this sample previously on a different instrument and I was aware of the wafer orientation when I made the lamella. I've had similar unexpected noise issues with the atomic-res STEM image on this instrument before; it's just a shame it happened while doing this demo. I could tell there was probably an issue when I was imaging the Pt grains, but then it was even more obviously when I moved on to the Si sample. It may be a time of day issue; these problems seem to pop up mostly during the late afternoon (which is when I recorded this).

[@sergeiremennik7604]

Thanks for the explanation.
Do you use field cancelation equipment? So maybe some noise in the grounding from other equipment. Hope you could solve this issue.

[@NicholasRudawski]

@@sergeiremennik7604 In the Talos room, we do not have any field cancellation equipment; at the time we did the site survey, it passed all the specs so we (justifiably) didn't think any was needed. I imagine we wouldn't have this issue if we did have active field cancellation in the room. We do have this in the Themis room, because at the time it didn't pass specs. Of course, fields in a room can change if there are modifications to the building infrastructure, and it's also possible that the issue is intermittent in nature (it seems to pop up mostly during the late afternoon). What I really should do is take HR-STEM images at different points through a whole day and see what happens. I could actually turn that into a neat video for the channel; thanks for the inspiration!

[@hcs-cw5zm]

Very nice video! Did you finally find out why you didn't get the atomic image, I had the same problem!

[@NicholasRudawski]

Hey, thanks. Regarding the atomic-res STEM issue in the video, I never "diagnosed" exactly what was causing the problem. Thankfully, the problem was transient and was gone the next day. The fact that it came and went like this along with the presentation indicates (at least to me) that this is some kind of stray electromagnetic field issue. Hopefully, it never becomes more than just a random nuisance.

[@hcs-cw5zm]

@@NicholasRudawski Thanks for your reply , I've had this problem several times, but all after cryo-cycle.

[@adrianzavodov6745]

Thank you for a workshop! Could you explain, please, the difference between two situation: 1) image in focus, when objective lens current is as it should be at eucentric height (as you do); 2) then we defocus the image by objective lens and go back to a focus but using C2 lens. Will these situation equal?
P.s. in case strong AC field, it should help, if you will do focussing at another dwell time: 31,96 mks for 512x512 frame and about (don't know exactly) 120-130 mks for 128x128 frame. Thus you will eliminate 50 Hz "saw".

[@leonli4923]

I think you need to set the focus knob function back to intensity knob when you are trying to fine tune atom images.

[@NicholasRudawski]

You could do this if you want, but it's not necessary. I've obtained good atomic-res images using both methods: fine focusing using C2 and fine focusing using the objective, but I personally no longer use the C2 method. The key in either case is to make sure that the deviation from eucentric is not very large.