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
I thought the beam is parallel if I fully spread beam, and never have the idea that beam parallel is a range. Does this rule also apply to the a normal two condenser lens TEM such as JEOL? If the UI dos not show up these parallel range, how can I find the beam parallel condition? when I collect EDP, I insert the objective aperture in diff mode, and use diff focus to focus the beam at back focal plane by finding the point where the objective aperture has sharpest edge? then fully spread the beam (intensity/brightness). when the beam focused at back focal plane, is beam parallel in imaging mode?
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.
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great video ! all your videos worth watching three times :)
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
I thought the beam is parallel if I fully spread beam, and never have the idea that beam parallel is a range. Does this rule also apply to the a normal two condenser lens TEM such as JEOL? If the UI dos not show up these parallel range, how can I find the beam parallel condition? when I collect EDP, I insert the objective aperture in diff mode, and use diff focus to focus the beam at back focal plane by finding the point where the objective aperture has sharpest edge? then fully spread the beam (intensity/brightness). when the beam focused at back focal plane, is beam parallel in imaging mode?
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.