Hey, thanks! Yes, I actually did a previous video on performing CBED using the Tecnai, using both microprobe and nanoprobe condenser modes. You can find it here: ua-cam.com/video/DofabqzZcG8/v-deo.htmlsi=4KTlOLrF4NNVenoe
You're welcome, Praveen. At typical voltages where S/TEM is performed, a specimen would need to be extremely thick before any backscattering occurs. Just doing some quick CASINO simulations using sapphire as the target with 200 kV electrons, less than 1% of incident electrons are backscattered for a 10 um-thick sample! Needless to say, you aren't going to be getting much S/TEM work done with a 10 um-thick sample (of any material).
Great video, this was a debated topic in our center a few months ago. We sometimes observed something resembling charging in STEM mode on our Talos when imaging microtome sections: the more the beam scanned over an area, we'd see a bright vignette (in HAADF) gradually grow on the image which would dissipate after changing magnification/moving away. Very annoying. I'm still puzzled about it, for all the reasons you mentioned... but coating the grids with 2 nm carbon completely fixed the issue. 🤷♀
Hi Jillian: that's very interesting what you are describing! How thick were the microtome sections and what beam voltage were you using? If you were preparing samples via microtome, then these were most likely biological or life sciences specimens? It's possible that what you observed may be due to heating, rather than charging, but that's just a wild guess on my part. Plus, I'm not even sure of the thermal conductivity of evaporated C. I guess if the sections were sufficiently thick and the voltage sufficiently low, there may be enough suppressed transmission to possibly generate a charge. If so, it would be interesting to see if the problem goes away without C coating if the sections become sufficiently thin.
@@NicholasRudawski These were ~80 nm sections of tissue imaged at 200 kV, so pretty thin but we could try thinner. I've looked into this more and there are papers that describe TEM charging effects for biological samples but mostly for cryoTEM, with a few mentions of thin sections. I'm not sure if it's the same thing I was seeing. The two solutions mentioned (amorphous carbon coating, or including an area of the copper grid in the image) match up with what works for me. This paper describes some of the effects seen before carbon coating (and after): Specimen charging on thin films with one conducting layer: Discussion of physical principles, 2003 (Glaeser, Robert M.;Downing, Kenneth H.)
@@jilliancramer9196 Very interesting indeed! As far as S/TEM is concerned, bio samples are definitely a very different beast compared to what we typically deal with in the physical sciences. The cryo component is also probably a contributing factor, too. I'm very glad you found a solution that allows you to collect good data from your specimens.
Great video, we are testing empad detector for 4D-STEM but there is still a lot of confusion about capture parameters, so is there an operation manual in empad software?
Hello; I have a pdf manual for the EMPAP I can share with you; please email me directly and I will send it out to you. At some point, I will do a video tutorial on use of the EMPAD, too.
👍 for this topic... Do you perform Nano Area Electron Diffraction? Will be thankful if you make a demo video on it
Hey, thanks! Yes, I actually did a previous video on performing CBED using the Tecnai, using both microprobe and nanoprobe condenser modes. You can find it here: ua-cam.com/video/DofabqzZcG8/v-deo.htmlsi=4KTlOLrF4NNVenoe
Thnx once again for the video...Can you give an typical rough estimate of thickness in case of insulator for onset of charge accumulation?
You're welcome, Praveen. At typical voltages where S/TEM is performed, a specimen would need to be extremely thick before any backscattering occurs. Just doing some quick CASINO simulations using sapphire as the target with 200 kV electrons, less than 1% of incident electrons are backscattered for a 10 um-thick sample! Needless to say, you aren't going to be getting much S/TEM work done with a 10 um-thick sample (of any material).
Great video, this was a debated topic in our center a few months ago. We sometimes observed something resembling charging in STEM mode on our Talos when imaging microtome sections: the more the beam scanned over an area, we'd see a bright vignette (in HAADF) gradually grow on the image which would dissipate after changing magnification/moving away. Very annoying. I'm still puzzled about it, for all the reasons you mentioned... but coating the grids with 2 nm carbon completely fixed the issue. 🤷♀
Hi Jillian: that's very interesting what you are describing! How thick were the microtome sections and what beam voltage were you using? If you were preparing samples via microtome, then these were most likely biological or life sciences specimens? It's possible that what you observed may be due to heating, rather than charging, but that's just a wild guess on my part. Plus, I'm not even sure of the thermal conductivity of evaporated C. I guess if the sections were sufficiently thick and the voltage sufficiently low, there may be enough suppressed transmission to possibly generate a charge. If so, it would be interesting to see if the problem goes away without C coating if the sections become sufficiently thin.
@@NicholasRudawski These were ~80 nm sections of tissue imaged at 200 kV, so pretty thin but we could try thinner. I've looked into this more and there are papers that describe TEM charging effects for biological samples but mostly for cryoTEM, with a few mentions of thin sections. I'm not sure if it's the same thing I was seeing. The two solutions mentioned (amorphous carbon coating, or including an area of the copper grid in the image) match up with what works for me.
This paper describes some of the effects seen before carbon coating (and after):
Specimen charging on thin films with one conducting layer: Discussion of physical principles, 2003 (Glaeser, Robert M.;Downing, Kenneth H.)
@@jilliancramer9196 Very interesting indeed! As far as S/TEM is concerned, bio samples are definitely a very different beast compared to what we typically deal with in the physical sciences. The cryo component is also probably a contributing factor, too. I'm very glad you found a solution that allows you to collect good data from your specimens.
Great video, we are testing empad detector for 4D-STEM but there is still a lot of confusion about capture parameters, so is there an operation manual in empad software?
Hello; I have a pdf manual for the EMPAP I can share with you; please email me directly and I will send it out to you. At some point, I will do a video tutorial on use of the EMPAD, too.