Thank you for the valuable videos. I am also an electron microscope user and currently working with FEI Tecnai G2 s twin. Your videos have helped me gaining the in depth knowledge of my field. I am very thankful to you.
Been playing with a new way to do coma free. Can be tricky getting the focus the same for both images, especially with slower cameras. I've been using direct rotation center and turning the amplitude to zero (focus step counter clockwise) then using multifunction to maximize the rings on the fft. Curious if you have any thoughts on this method.
This sounds similar to how standard coma-free alignment is performed, only in your case, you are not tilting the beam back and forth but keeping it stationary and then observing the FFT. Considering the similarities, I would probably opt to just perform the standard coma-free axis alignment method since that has a rigorous basis. That being said, I do know of at least one other coma-free alignment method that can be done with a stationary beam and was (I believe) shown to be physically identical to the standard coma-free alignment method in terms of accuracy of the result. Come to think of it, I really need to do a dedicated video on coma-free alignment because it really deserves its own video. Thanks for the inspiration and hopefully I will be able to get to this at some point in the not-to-distant future.
Really thank you for your wonderful video. Your video is really good teacher for me! I have a simple question. When you change the focus in your video, you change the Z-axis or focus knob? After you got the exact eucentric height, you don't change the Z-axis anymore after getting the zone-axis?
Hi Sumi: glad the videos help you. You need to refocus with the stage Z axis if you tilt to align to the zone axis and the sample goes grossly out of focus. Once you do that, the only other focusing would be with the actual focus knob.
Thanks for the question! HR-TEM can be performed with a thermionic emission gun TEM, too; what makes it HR-TEM is using an appropriately sized objective aperture, using sufficiently high magnification, and having an objective lens of sufficient quality to resolve the phase contrast (lattice fringes). It's far less common to perform HR-TEM with a thermionic emission gun instrument, but it can be done.
Hi Nick, very good video, help a lot! I have one quick question doing HRTEM and HRSTEM: how do I choose the optimum gun lens and spot size when doing HRTEM? Do I need a small current (like spot size 10) or a higher current (like spot size 3)? thanks
Hi Chen: glad you found the video helpful. Usually, a middle setting for the gun lens is fine for HRTEM (like 4), but something higher is better for STEM (like 7). For doing HRTEM, generally a spot size around 3 is a good starting point; something that gives 1 - 2 nA of probe current, assuming your specimen can tolerate it. Spot size 10 likely won't provide enough current to generate a usable HRTEM image with sufficient signal to noise.
Hi Bijoy: for the best image, you would want the count histogram centered around the the mid point of the camera dynamic range, so for 16 bit camera, this would be ~32000 counts. That being said, it is usually hard to get counts this high while keeping the beam current reasonable and the exposure time short enough to minimize drift effects. In practice, for a 16 bit dynamic range camera, getting the count histogram centered around at least 1500 - 3000 counts, which is ~5 - 10% of the camera dynamic range, will still produce high quality images while keeping the beam current and exposure time reasonable.
@@biijoykhomdram9658 You're welcome; I also have a video on my channel specifically discussing use of the digital camera and discussing dynamic range and other aspects. You can find it here if you are interested: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-EdBuxQQUTNg.html
Hi Tran: you're welcome; the difficulty in seeing the beam after putting the aperture in is probably due to the primitive filming setup with my phone looking at the viewing screen; I can assure it is there!
i love your videos. i am a chinese postgraduate student. my part-time job now is help people do TEM test .i am a beignning learner for operating this machine. your videos help me a lot! thanks!
You're welcome; you can indeed obtain a HR-TEM image of Si that does indeed appear to show the dumbbell structure, but you should always remember that a HR-TEM image isn't a picture of the actual material structure (that would be a good topic for another video).
Thanks for the amazing content! Really helpful! I am just curious about one thing. All of the alignments or adjustments requiring amorphous parts of the sample, how would it be done if using samples that do not have amorphous parts e.g., twin jet polished discs?
Hi Dmitri; glad my videos are helping you out; you would need amorphous regions to perform anything involving the FFT, so the coma-free axis alignment and objective astigmatism correction would be affected. Even in a jet polished disc, there is usually some residual junk/contamination/etc near the edge that is amorphous and can be used for these alignments, though it can be tricky if there is very little of it present in the image, but I've yet to come across a specimen where there is literally no amorphous material to be found!
@@NicholasRudawski Thanks for taking the time to reply! Ok, thats good to know. Will definately scan the edge more carefully next time to try and find something amorphous. Looking forward to your next video!
@@NicholasRudawski I was succeeded during my PHD thesis preparation but i used Philips CM200 microscope with FEG it was easier due to known and quite large Cs. Currently we have an aberration corrected TEM and quantitative matching between experimental and simulated defocus series of images is really tricky and fancy due to residual aberrations and small angles of the sample, sample thickness etc. it is really hard to find perfect parameters.... it would be great if you share by your experience ... if you have it ..
@@АлександрПриходько-ъ8г the simulation software I use is called muSTEM: tcmp.ph.unimelb.edu.au/mustem/muSTEM.html I've only used it for STEM/CBED simulations but it will also work for HRTEM, too.
