FEI Talos F200i S/TEM: alternate STEM alignment method

They say there's more than one way to skin a cat (please, don't go skinning your cat) and TEM is no different in this regard.
Using the Ronchigram is the tried and true rigorous method of performing STEM alignment. That being said, it can be difficult for users to wrap their heads around what exactly they are seeing when looking at a Ronchigram; performing rotation centering using the Ronchigram can be particularly challenging.
In this video, I cover an alternate (but equally effective) method of STEM alignment that uses an image of the probe to perform C2 aperture centering and rotation centering; the Ronchigram is only used for the purpose of coarsely correcting the astigmatism in the probe.
Additionally, I cover how to set your C2 lens so the image is in focus when the sample is at eucentric height using the "Intensity List (FOCUS)" direct alignment. If you need to tilt your sample (e.g. for zone axis alignment), this will allow you to properly re-establish eucentric height without the danger of throwing your lens settings way off.
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 beam FIB/SEM systems, and 1 SEM and this keeps me very busy!
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[@aarondodd2147]

Hi Nicholas, Just wanted to thank you for making this video. You're an absolute legend, mate. The STEM alignments on our Talos have never been better.

[@NicholasRudawski]

HI Aaron: thank you, and I'm very glad to hear my videos are helping you; best of luck to you on your electron microscopy journey!

[@TheGloomrot]

I've been working with the FEI Tecnai and Titan TEMs for 8 years now and have never had a clear explanation of the alignment process as well as you explained them. This is the first time i heard terms such as Caustic spot, blowup condition, diffuse area. As well as what the controls are doing internally rather that "just push this button for better images" Thank you for taking the time to make this video as it helps immeasurably

[@NicholasRudawski]

You're welcome; it's always great to hear when my videos are helping people; thank you.

[@aamiri9380]

Hi Nick, I find the lamella at low mag but when I go to high mag I am not at lamella, and there is a shift in position. What alignment is off? C2-Aperure?

[@NicholasRudawski]

Sorry to hear of your troubles! This is most likely an issue with the image shift being off between modes. Each TEM mode (LM, M, SA, and Mh) and magnification has an image shift setting associated with it. These are used to ensure that the image doesn't move (excessively) when the magnification is changed within a mode or the mode is changed (e.g. LM to M mode). If you are seeing a large image shift when switching between modes, this is something that must be addressed in the supervisor alignments. I will make a mental note to record myself the next time I do this so everyone can see how this works, but it's not too difficult to perform (though that somewhat depends on how badly out of whack the image shift is between modes!).

[@LenzZhang]

great videos! could you make some videos on probe corrector tuning?

[@NicholasRudawski]

Thank you; I do indeed have a video on probe corrector tuning; please see here: kzbin.info/www/bejne/raiTmYNjibJ7Z7s

[@power_overwhelming]

Thanks for your nice explanation

[@guugleli]

Thank you for the nice explanation! I use a similar approach, and it's always interesting to learn from other people's alignment procedure. 🙂 I typically do the "Intensity List [Focus]" as a final step after probe tuning in image mode (here around 17:30) by simply focusing the beam to the finest spot possible (in vacuum), which is then my plane with the optimum probe as defined by the objective-lens eucentric focus setting. Then I bring my sample (with z-height) to this plane later during scanning. Thanks again for the videos! Do you record with a capture card or with software directly on the microscope PCs (e.g. OBS)?

[@NicholasRudawski]

You're welcome. Yes indeed, there are some different approaches in terms of focusing; I've heard of focusing the probe in vacuum and then focusing by adjusting Z as you indicate. As long as you are consistent in the approach and the settings are reproducible, I imagine either way should be fine. As far as how I do the videos, I use something called an "ATEM mini pro" plus my laptop and it's fairly easy to set up; I could do a video about how I film my videos so thanks for the idea.

[@rahulagrawal6026]

Hello Nicholas. Took me about a year and half to confidently perform these.

[@NicholasRudawski]

Glad to hear you eventually got it; persistence usually pays off (it eventually did for me).

[@rahulagrawal6026]

Nicholas, I noticed one interesting thing. When rotation center is off, the wings in ppx and/or ppy will be asymmetric. And when stigmation is off, the shape of wings in ppx and ppy are dissimilar. Did you also notice something like this??

[@NicholasRudawski]

@@rahulagrawal6026 Hi Rahul: yes, I noticed this as well, the "wings" when doing the beam tilt pivot points are more symmetric when the rotation center is set properly.

[@zhidaliang25]

Hi, Nicholas, this is nice Video. I have one question. When we do beam alignment in STEM, do we need calibrate C2 aperture? On the other hand, if we need, I often meet one problem, rotation center (obj) was corrected but C2 aperture is misaligned again. How do you handle this problem usually? Thank you.

[@NicholasRudawski]

Hi Zhida: glad you like the video. In general, C2 aperture alignment and rotation centering will be different between operating modes, so when you switch into STEM mode, you should check C2 centering again as best practice. In principle (and usually in practice, too) the C2 aperture alignment is more or less independent from the rotation centering. But the order of doing the alignments also matters. You always want to center the C2 aperture first and then do the rotation centering. That being said, if you are finding the C2 aperture centering to be off after doing the rotation centering, I would simply perform another iteration of the alignment steps: 1) center the C2 aperture and 2) perform rotation centering. Then you can check again and see if the alignment is better (it should be). If needed, just keep doing iterations until nothing changes. I would think 3 or 4 iterations should be more than enough. I hope this helps and good luck with your TEM work.

[@tachometerability]

Is using the condenser stigmator to make the beam circular in imaging mode much less accurate than rough stigmating with the ronchigram? At 15:15 the beam seems astigmatic although I know the recording software maybe affects how it appears. If so you could skip the Ronchigram altogether. Thanks for the videos, always quite informative.

[@guugleli]

Personally, I do the (rough) condenser-stigmator alignment as you suggest: By making the real-space probe as round as possible at the highest SA magnification and the "High-resolution" setting of the Flucam. Then, I do the fine-tuning of the astigmatism on the actual HAADF-STEM image. In this way, yes, I normally completely skip the Ronchigram in my STEM alignment (but I should learn it :D). The reason I also do the shown real-space alignment for our scope (Titan) is that our C2-C3 zoom is quite badly aligned, and the probe moves laterally during focusing, which is a nightmare for Ronchigram alignment...

[@NicholasRudawski]

Glad you like the videos. The reason I don't correct the probe astigmatism while imaging the probe is because there is also a contribution from objective astigmatism that alters the probe image, but this doesn't actually influence the probe shape. By adjusting the condenser stigmators using the Ronchigram, this confounding effect is removed. That being said, you are correct you could skip using the Ronchigram and just go straight to the image to stigmate. The only issue with this might be if the stigmators are grossly off, then it may be hard to correct using just the image. By using the Ronchigram, you at least get in the ballpark before looking at the image.

[@NicholasRudawski]

@@guugleli There should be a supervisor alignment to fix the C2-C3 zoom; sounds like whomever is in charge of the alignment file should take a look at it; it should not be too involved to fix.

[@guugleli]

@@NicholasRudawski Hello Nicholas, thank you for the comment! The reasoning with the obj. astigmatism seems plausible; in fact, I think I already encountered this problem once or twice when I couldn't get the probe tuned in the STEM image with C2 focus/stigmators. This was probably caused by strong obj. astigmatism. Typically, before I do a similar STEM alignment you show here, I roughly adjust the (lower) objective-lens stigmators at 200-300kx (amorphous region such as FIB Pt, round Thon rings) before proceeding to the STEM-probe tuning. In this way, I hope to have an "OK" lower objective lens (although I don't know if these alignments actually transfer to the "STEM" mode in TIA), and do the rest with C2 focus/stigmators as in your video. This usually works well for my STEM sessions, but you are right: Cond. stigmator alignment on the actual probe image in SA mode will probably fail if the stigmators of the lower objective lens are way off. So thank you for pointing that out, maybe it is useful for others as well!

[@guugleli]

@@NicholasRudawski You are right, I will look into it!

[@ruikaishi477]

very good video！i am curious that what is the difference between rotation center(objective) and rotation center(intensity)?

[@NicholasRudawski]

Hi Ruikai: thank you; the only difference between the two selections is which lens get automatically wobbled: intensity wobbles the C2 lens and objective wobbles the objective lens, but as you hopefully saw in this video, I eliminated wobbling before correcting the beam tilt anyway so it doesn't matter which one you choose; the multifunction knobs control beam tilt with either selection.

[@ruikaishi477]

@@NicholasRudawski THANK YOU! And I find you recommend to use CL2 to focus, why? What the difference between CL2 and OBJ focus, making coma adjustment more accurate?

[@NicholasRudawski]

@@ruikaishi477 Sorry for the very late response. The choice to keep the objective lens constant and focus with C2 is partly a matter of personal preference, but the reason I like to use this method is because you generally don't want very large changes to your objective lens setting from the default setting, so keeping it fixed and focusing with C2 means the objective lens setting is never altered. There are some variations to this method that can involve focusing with the objective lens, but any changes made to the objective lens setting should still be minor. Whether you focus with C2 or the objective lens should not really affect the accuracy of finding the coma-free axis.