Відео

Indexing a polycrystalline DP is actually much easier compared to a single crystal DP because there is no zone axis to consider. That being said, the process is very similar with measuring ring diameters and calculating ratios. Indexing polycrystalline DPs would definitely be a good addition to the channel and I hope to do this at some point soon.

@@NicholasRudawski thankyou

You're welcome.

Hi Ajay: there could be a lot of reasons why the Omniprobe is responding how you are describing, but the most obvious one is that the frame of reference is set incorrectly. You want this set on "Stage" instead of "Port". There could be other reasons, too, but it's a bit too lengthy to cover in a YT response. The jitters are most likely due to some kind of mechanical coupling/transfer. Again, a bit hard to cover in a YT response, but I would check your Omniprobe cabling to make sure it is properly isolated because that is the most obvious way to get vibration transfer.

Thank you for your support; I hope you found the video useful.

You're welcome

Thanks, Stan. About your question, I do not believe manual control of the energy range for a given element is possible with Velox; you are stuck with whatever "window" the software assigns. However, if you collect the map with TIA, I believe that you can do this. That being said, while TIA can give you more functionality in this regard, it is very limited in terms of collecting the actual EDS data because it only allows for "single pass" analysis whereas Velox allows for as many passes as you wish.

Sure thing; I hope you found it helpful.

You're welcome; thanks for your support.

You're welcome.

Both de-ionization and distillation are processes to remove dissolved solids, so either will be a much better option compared to normal tap water. As far as one being "purer" than the other, I'm not entirely sure on that. I've never encountered a problem using our in house DI-water for sample prep, so there really isn't any reason for me to try distilled instead. That being said, it would be an interesting experiment to simply put a drop of DI (or distilled, or tap) water (no particles) on a grid, let it dry, and then image the grid to see what (if anything) still remains. Regarding the tweezers, these are actually correctly described as "self-closing" tweezers (rather than "self-locking"). Here is a link from Ted Pella: www.tedpella.com/twzr-sc_html/twzr-sc.aspx

Thank you, glad to hear you found my video helpful; do let me know how your samples turn out for you.

Thank you for the information about the pipettes, this was certainly something I was obviously not paying a lot of attention to compared to everything else. Also, I tend to avoid support films with formvar; I've had too many issues with instability under the electron beam (though the manufacturers claim over and over that formvar is fine and stable) and plus having to dip grids in chloroform to dissolve the formvar (if needed) can introduce a source of hydrocarbon contamination (though some plasma cleaning may sufficiently address this). Did you ever have hydrocarbon contamination issues when using chloroform to prep grids?

@@NicholasRudawski Hi..it would be great if you introduce us about great variety of TEM grids and their specific applications(I mean when to choose which grid).

@@NicholasRudawski That question brings back a lot of painful memories! Actually, we don’t do that anymore. A chloroform wash can be helpful, but it can also end in a mess. Let me explain the story a bit more. Patterned grids (like quantifoils) are made using a technique called soft lithography. It’s like creating a pattern on a wafer, then making a negative pattern using a soft silicone resin (e.g., Sylgard). This pattern is then used to stamp a polymer solution (like formvar) dissolved in a solvent (probably chloroform) onto a substrate like glass. Afterward, they cover the patterned film with another layer of carbon film on top to make it conductive and stable. For random holey carbon grids, the method is slightly different, but the idea is the same: first, make a patterned formvar film, and then deposit the carbon. However, I’m not sure how lacey grids are made, but I speculate that they’re produced in a similar way. It would be best to consult older EM books. Anyway, the carbon grids are supposed to be pre-washed and free of formvar or polymer backing film from the supplier. But in the past, we often received grids with formvar contamination. In some cases, a chloroform wash wasn’t enough or even made the situation worse. It was like trying to clean a huge mess with a wipe. Also, chloroform sometimes introduced its own contamination, which was really problematic. The contamination could come from mishandled tools or consumables, and in most cases, the source wasn’t clear. It could be from filter papers, mishandled parafilm, tweezers, pipettes, or even contamination in the chloroform bottle. So yes, I did experience contamination after using a chloroform wash. But nowadays, I see far fewer of these issues. Grids are usually clean from the supplier. In case I receive contaminated grids, I pass them on to other EM groups with less strict cleanliness standards. 😂 Finally, back to the original topic: heating the grids helps stabilize many of these microscopic contaminants. However, overdoing it may also make the carbon film fragile. It's also worth mentioning that in cryo-EM, we glow discharge all the grids, which effectively removes loose hydrocarbons. Although in glowdischaging cleanliness is not intended; It’s done to make the grids hydrophilic.

Thank you for your support and glad to hear you found the video helpful. I've been meaning to set up an open access Dropbox folder for all of the presentations I post on YT, but have not gotten around to doing this yet. In the interim, I will gladly send you the presentation via email, so please send me an email requesting the presentation and I will take care of this.

Yes indeed, doing the gun alignment (even with the monochromator) isn't too difficult (and the provided instructions are very good, too). As far as time to stabilize the mono after excitation, leaving it overnight is indeed probably overkill (though not a bad idea if you have the time to allow it); I think the apps person from ThermoFisher said that a couple hours was sufficient for this.

Yes, you are correct about the discs not overlapping (or at least overlapping less) in uP-STEM versus nP-STEM. I actually discussed this in a video about CBED I did several years ago using our Tecnai. You are also correct that true BF-STEM is not really possible in nP because of the discs overlapping, so uP also has an advantage here, too. It would be interesting to do an image comparison of BF-STEM in nP versus uP using a material with lots of dislocations. This would definitely be another good video to do at some point.

You're welcome; yes uP-STEM is definitely advantageous when you are trying to avoid disc overlaps in the DPs and form true BF or DF STEM images to improve contrast. I am planning to do another MSA webinar in mid November specifically about STEM imaging so that would be a great opportunity to discuss this (as well as the comparison with nP-STEM mode I did here).

You're welcome, glad to hear you found my video helpful. Your question is a very interesting one indeed. Should there be any difference between nP and uP if the convergence semi-angle and probe currents are the same in both cases? Well, in principle, there should be no difference because angles are angles and current is current, right? With the Themis being a 3 condenser lens system, it has the capability to arbitrarily set the value of alpha in either mode, but I don't know if nP has the range to obtain alpha < 3 mrad. It actually may be easier to make alpha larger in uP mode to be comparable to alpha in nP mode. Even with alpha being the same, I believe there would be a discrepancy with the currents in a 3 condenser system because of the "zoom" between C2 and C3 which causes the current to decrease as alpha is decreased.

Great question! While the OL effectively acts like two lenses, these cannot be controlled independently, so you are changing the strength (focal length) of both at the same time. This is why the MC coil is present in the upper pole piece, to reduce the effect of the OL pre-field when it (the MC) is (optically) on, which corresponds to microprobe mode. Otherwise, the system would only have nanoprobe mode.

You're welcome, and thanks so much for your well wishes. We were actually quite lucky and spared anything remotely close to serious and we never lost power. The good news of the university being closed was that it gave me an opportunity to record and upload this video!

Hello! This could be a beam shift issue or a column-to-column alignment issue. Start by zeroing the beam shifts for both the SEM and FIB. Then, set eucentric height using the SEM image as you would normally. You should then be able to use the FIB beam shift to make the FIB image coincident with the SEM image for any stage tilt between 0 and 52 degrees (the amount of FIB beam shift necessary will vary somewhat with stage tilt). If you are running out of FIB beam shift, this indicates the default FIB beam shift needs to be adjusted at the supervisor level or there may be a column-to-column misalignment. The former issue is something the instrument owner should be able to adjust, but the latter issue most definitely requires a service visit from a service technician. I hope this helps.

Thank you very much for your advice!

@@quyenhiennguyentruong4854 You're welcome; I hope your are able to get you system working properly soon.

You're welcome; yes, I I do want to make a 4D-STEM video covering EMPAD use at some point. In the interim, there are quite a few good videos already on YT about 4D-STEM (not really about how to perform it and collect the data, but about the applications and analysis of the data). There is a really good one on the Gatan YT channel that should show up in a basic search.

@@NicholasRudawski Sir，Thank you again for these useful information!

@@zhedd5954 You're welcome

sorry, too much fundamental questions! though I use TEM for many years, but never get chance to understand the mechanism behind it and why we do it. your video is great resource for me to backfill these knowledge! appreciated

@@jq58 thanks for watching my video. Yes, I apologize for not addressing the equivalent situation for two condenser systems, so I will do so here. In a two condenser system, you will no longer have the ability to maintain parallelism over a range of beam diameters; instead, there will be a single diameter corresponding to a parallel beam (when the spots are focused in the DP). The process as you describe it in your first post is otherwise correct (including the part about using "diffraction focus" to focus on the objective aperture). If the instrument is properly aligned and configured, the default "eucentric focus" value in diffraction mode shouldn't need tweaking, but it never hurts to check by imaging the OA. On my system, it is a little more complicated because I find that the DP spots become quite astigmatic when I have a perfectly focused, stigmated image of the OA, so when I stigmate the spots, the OA image loses sharpness. Not sure why this happens, but it likely has something to do with the presence of the Cs probe corrector.

@@NicholasRudawski Hi Nic, thanks for clarification. In the diffraction mode, I can rotate intensity knob clockwise to make diffraction spot a small spot, but if I keep clockwise rotating intensity, the diffraction spot is still a small spot but weaker in brightness, it seems that the beam is parallel if the intensity below certain value. but as you mentioned "there will be a single diameter corresponding to a parallel beam". it confuses me that how can I determine beam intensity to find the parallel condition since the diffraction spot keep constant small if intensity below certain value by clockwise rotation?

@@jq58 was your SA aperture inserted when you were trying to focus the spots in the DP? You need to make sure to do this without the SA aperture inserted. If the SA aperture is inserted, then you will not see the proper response from the spots as you change the intensity knob. You always want to focus the spots without the SA aperture inserted, then do not adjust the intensity knob as the beam is now parallel, then insert the SA aperture.

I have a question with the illumination area. our Themis has been 6 years old. One day I found if I focus beam into a spot, the illumination area is not zero. but if it show zero, the beam is a small disk. where can I reset this zero point?

@@jq58 Thanks again for watching my videos. And yes, I've seen this issue before, too; the beam diameter is non-zero but the UI says it's zero! If you perform the full "Condenser" alignment, this should address this, but In my experience, the actual diameter never perfectly matches the expected diameter due to hysteresis and other factors. This discrepancy tends to be more pronounced in the vicinity of the crossover point (diameter = zero) and less so as the beam is spread out within the "parallel" regime.

@@NicholasRudawski thanks you so much for the useful information. The full condenser alignment works, the correlation of beam spot with zero illumination area is much better now on our machine

You're welcome; glad to hear my video helped you out.

Hey, sorry for the late reply. Thank you for the feedback and glad my videos are providing useful information for you.

Hey, sorry for late response. Your question about seeing detail beyond the limits of the OA is a great one and really deserves an entire video to properly answer it. That being said, the short answer for why detail beyond the OA limit is observed is due to non-linear effects, which is another way of saying interference between different Bragg beams rather than interference between Bragg beams and only the direct beam. If only interference between the Bragg beams included in the OA and the direct beam was transferred to the image, then we would not see any detail beyond the OA limit, but this is never the case because interference between Bragg beams does indeed happen. This is one of the advantages of HAADF-STEM over HR-TEM: the information limit in HAADF-STEM never exceeds the probe size due to the incoherent nature of the imaging, which does not rely on any contributions from Bragg scattering. Again, this question really deserves a dedicated video, and I hope to do this eventually.

@@NicholasRudawski Hey Nicholas, no worries about the late reply. Thanks for taking the time! I agree with you and now understood this effect. Indeed, we also perform mostly HAADF-STEM nowadays, so these "phase-contrast problems" never show up there in this extend. :-) I can imagine that interference between the Bragg reflections can indeed cause the higher-order reflections, e.g., +g/-g -> 2g or something along that line - even if the 2g spatial frequency would be outside of the OA radius. That's all probably also related to using very thin samples (i.e., within weak phase object approx.) for quantitative HRTEM/comparison with image simulations. I will have another look into textbooks. Nowadays, "simple" lattice fringe imaging is often good enough for my cases.

Hey, thanks. Sorry for the late reply. I certainly acknowledge the importance of the life sciences/biological side of electron microscopy, but the work I do is basically exclusively in the physical sciences, so it's doubtful there will ever be a video about biological lamella prep on my channel. I encourage you to do some searching on YT to see if any content related to biological lamella prep may already be posted. I think ThermoFisher may have posted some short videos related to this, but I'm not sure

Thank you; I actually had several other slides about HR-TEM that i wanted to include (with a bit more technical nitty gritty stuff), but I ended up cutting to keep the total time more reasonable (though now in hindsight, I suppose I could've put them in for this version of the webinar).

You're welcome; I'm glad to see people are seeing the rerecorded version. About your OA question, yes, you will always get a better HR-TEM image with an aperture than without an aperture, because this limits the effect of spherical aberration, increases mass-thickness contrast, improves depth of field, and decreases image delocalization.

@@NicholasRudawski I had some thoughts about it, but now you've really opened my eyes! I always was made HRTEM images without an OA. And only recently I began to think about why I should use multiple n-reflexes that are not responsible for any details in the image. And then I filtered HRTEM by FFT to make it better ))) Thank you for highlighting this basic aspects, which helped me identify a gap in my knowledge.

@@adrianzavodov6745 @NicholasRudawski I can add to this question for the case of an image-corrected Titan with the default OA set: I was wondering the same ("To use OA or not to use OA?") on an image-corrected system. The default OA set "only" goes up to a 100 µm size and I measured once that this corresponds to a radius of around 9.5-10 nm-1 (i.e., around 100 pm resolution). An image-corrected Titan is typically specified with an HRTEM resolution of 80 pm (under ideal conditions and a nice sample). So in this case of an image-corrected TEM, I was imaging HRTEM without an objective aperture. However, I probably would have used a potentially large OA that cut of at 80 pm (= 12.5 nm-1) if it was available due to the reasons Nicholas mentioned. For uncorrected systems, I try to use the closest OA given by Nicholas' formula in the video (typically around 40 µm for 200 keV TEMs).

​@@electronmicroscopist1986 Yea, this works great! I've tried it today with 40 mkm OA and without it. The main improvement - reduction of ghost images (delocalization) and as a sequence more uniform focus over entire field of view. Live and learn!

The conical dark field Imaging - nice method for visualisation, but in my opinion (even though no one asked me) this method is a relic of the past, when dark fields were obtained only with an objective aperture. Now, when you have HAADF, BF, DF2, DF4 and wide variation of camera lengths you can obtain the same or even better image much more easier and without any astigmatism, which is definitely present when you continuously deflect the beam in all directions.

Thanks for your comment. I realize there are some inconsistencies with some of my earlier videos. This is can obviously happen as you learn new things and get new information; the information I've received from the TF apps people over the years has also changed with time, too, so nobody is immune from this (ha ha). I am very familiar with the application note from Muller in the link you provided. I've actually asked the TF apps people about changing the MC value from the default and they have always told me not to do it, so it's a little odd that this appears to be suggested in the Muller app note. Keeping your optics settings the same and putting in a proper sized C2 aperture is probably the best approach for tuning the angle in a 2 condenser system, but this is not always the most convenient thing to do (plus you need to find and/or fabricate an appropriately sized aperture). As far as conical dark-field, I am familiar with this and have performed it but have not yet made a video about it. I do think it would be a worthwhile addition to the video library at some point.

@@adrianzavodov6745 Thanks for the answer! I agree - with the flexibility of collection angles it might be a bit of a relic and the STEM method is likely superior.

@@NicholasRudawski Thanks for you detailed answer! Regarding inconsistencies - no worries and I can fully relate that one picks up new insights into some of the inner workings of the instruments over time. Just wanted to share my view on the focusing-with-which-lens-in-STEM issue. :-) Regarding the Muller paper - I just realized they change MC lens instead of C2 - so I agree that this makes it more complicated and probably only useful for a handful of people playing with TEMspy values if they desire to change the convergence angle.

Sure thing; many people have asked about setting up an alignment file, so I wanted to document this when I had the opportunity. The "auto help" when do the alignments can also be quite helpful when you first go through doing these yourself. I definitely want to help people feel more empowered about being able to set up alignment files on their own, particularly if their facilities don't have staff members who take care of this regularly (which I hear is actually surprisingly common).

Hi Adrian: you probably noticed as I changed the spot size that the probe didn't really move. This is because I did all the other alignments previously. I've never actually touched the MF knobs when doing Intensity List [FOCUS], but I think these actually control a spot size dependent beam shift. I would be careful about adjusting these because this could create a non-zero exported element in SCORR. Again, if everything else is aligned, there shouldn't be a need to tweak these.

You're welcome.

Hi Blake: thanks for watching. The TF people recommend using ~200 pA regardless of the kV setting, so I would also do this at 300 kV. The aberration-free alpha range at 300 kV is again limited by the phase plate, but from experience I find that I can get this to very similar values that I can obtain at 200 kV. The instrument should be capable of 60 pm resolution at 300 kV, which translates to a value of alpha = 20 mrad for an aberration-free probe. In practice, I have been able to get the "green" part of the phase plate at least 5 - 7 mrad higher than this at 300 (or 200) kV.

You're very welcome.

Hi Adrian: yes, I specifically had you in mind while I was recording this! I was going to ping you and let you know, but you already found it. You are indeed correct that performing the full gun alignment is not too daunting of a task (though to be sure, it is far more involved with this configuration compared to an S-FEG with no monochromator). You're welcome and thanks as always for your support.

You're welcome.

Ha ha, yes; at 11 pm, the manager may not have even answered you anyway! Hopefully, the restart fixed everything for you.

Thank you.

Thank you for your support. So, funny thing about the C2 aperture I am using here: it was actually one of the original C2 apertures, but it was originally too small. So, I used the dual FIB/SEM in the next room and I opened it up a little bit (I think the final diameter was 30 or 50 um; I'm not entirely sure as this was 7 years ago when I did this). With the 2 condenser S/TEMs, you don't have the ability to set the convergence angle as desired, so alpha is effectively fixed by the C2 aperture size. 100 um is definitely going to be too large for performing any kind of HR-STEM, but if you measure alpha using a 100 um C2 aperture, you can then extrapolate to the necessary C2 diameter to give an appropriate value of alpha (at 200 kV with Cs = 1.2 mm, this should be ~10.0 +/- 0.5 mrad). I also have an application note from FEI about measuring alpha; if you want it, please email me and I will send it to you. Tuning your optimal value of alpha for HR-STEM would also be a good future video topic.

Yes!

You're welcome! It is a little more difficult to use the FFT to assist with zone axis alignment, though you can indeed see changes in the FFT as the zone axis alignment changes. The issue with the FFT is that opposite spots will always have the same intensity, regardless of how close the alignment is to the zone axis, so this is much less helpful compared to the DP. That being said, the spots will become more intense and you will see more spots farther away from the center of the FFT as the zone axis alignment improves, so these also indicate the precision of the alignment. If you compute the FFTs of the two HR-TEM images of Si that I showed, you will see this (actually, this would be good to post as a video).

thank you very much. it would be very nice to see such a video (simple explanations as this is and step by step procedure ) with comparison and highlights in similarities and differences between DP and FFT. also how to determine zone axis from FFT. and also not only cubic phase where the rings are relatively easy, but some other structures as well. thanks again.

Hi Crystal; glad you like my webinar. 4D-STEM has certainly been requested by quite a few people up to this point. It would need to be a 2-part series: one part discussing the collection of the data and the second part discussing the actual analysis of the data. I definitely hope to get around to this sooner rather than later (particularly the part about data collection, because I feel this is really quite lacking based on what is available here on YT). That being said, there are already some very good YT videos talking about the applications of 4D-STEM; this one from Gatan is probably my personal favorite: ua-cam.com/video/-KpxeNDoB5I/v-deo.html

How to find kikuchi pattern (TEM and STEM mode) in thin sample for good zone axis alignment ? Please help Sir.

​@@arupghoshal5814 Kikuchi diffraction will decrease as the sample becomes thinner; at some point, you may not observe any Kikuchi diffraction at all, so this definitely can make it more challenging to obtain accurate zone axis alignment in a very thin sample. It is actually easier to check the alignment in STEM mode, since CBED patterns are more sensitive to crystal tilts. After you align in STEM mode, you could then go back and perform TEM imaging on the same location. Otherwise, if you only use TEM mode, you need to evaluate the symmetry of the intensity of the spots in the diffraction pattern. Please check out this video on zone axis alignment when performing S/TEM (apologies if you already did): ua-cam.com/video/0VfJLJP6tP4/v-deo.html

Thank you!