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Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
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#1
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Electron Microscope Focus Problem
The image of our Amray SEM has a horizontal band across the center
third of the image which is slightly out of focus. The top and bottom thirds are fine. This machine, while being fairly old, is new to our institution and I believe some of the maintenance practices have lapsed. I was wondering if it was possible that a weak filament or contaminated optical column or dirty apertures could cause a problem like this. Any advice would be appreciated. Thanks. Gary |
#2
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Electron Microscope Focus Problem
"Mac" writes:
The image of our Amray SEM has a horizontal band across the center third of the image which is slightly out of focus. The top and bottom thirds are fine. This machine, while being fairly old, is new to our institution and I believe some of the maintenance practices have lapsed. I was wondering if it was possible that a weak filament or contaminated optical column or dirty apertures could cause a problem like this. Is it affected by settings like magnification? Have you ruled out stupid stuff like the video monitor itself? Is the change in focus sudden (with respect to vertical location) or gradual? Have you looked at any of the signals that control focus? --- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/ Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/ +Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm | Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html Important: Anything sent to the email address in the message header above is ignored unless my full name AND either lasers or electronics is included in the subject line. Or, you can contact me via the Feedback Form in the FAQs. |
#3
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Electron Microscope Focus Problem
The problem is only evident in the 400 to 1200 magnification range. The
change in focus does seem to be sudden. We ruled out the video monitor on the basis that the image is digitized on a computer as well as being sent to the monitor of the SEM and both show the focus problem. We haven't as yet started looking focus control signals. At this point I'm trying to get a feel for whether the lack of maintenance could be the problem or an electronic failure. Thanks, Gary |
#4
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Electron Microscope Focus Problem
How about a wild guess, something needs degaussing?
Mac wrote: The problem is only evident in the 400 to 1200 magnification range. The change in focus does seem to be sudden. We ruled out the video monitor on the basis that the image is digitized on a computer as well as being sent to the monitor of the SEM and both show the focus problem. We haven't as yet started looking focus control signals. At this point I'm trying to get a feel for whether the lack of maintenance could be the problem or an electronic failure. Thanks, Gary -- Joe Leikhim K4SAT "The RFI-EMI-GUY"© "Treason doth never prosper: what's the reason? For if it prosper, none dare call it treason." "Follow The Money" ;-P |
#5
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Electron Microscope Focus Problem
Mac wrote:
The image of our Amray SEM has a horizontal band across the center third of the image which is slightly out of focus. The top and bottom thirds are fine. This machine, while being fairly old, is new to our institution and I believe some of the maintenance practices have lapsed. I was wondering if it was possible that a weak filament or contaminated optical column or dirty apertures could cause a problem like this. Any advice would be appreciated. Thanks. Gary Is this at TV-Scan rate and Slow scan too ! What is the specimen being examined, This is behaving like a Charging artifact. Try another type of specimen, Sounds more like a specimen charging problem to me. What is the Accelerating Voltage. Dirty Column and apertures usually just cause astigmatism problems Yukio YANO Retired SEM Tech. |
#6
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Electron Microscope Focus Problem
Our operator doesn't use the TV-scan, only the slow scan. Her
specimens are organic. She is familiar with what a charging artifact produces on the system. She describes it as horizontal streaks across the image at which point she deposits more gold on the specimen to correct the charging problem. This problem is a very subtle focus issue in a horizontal band across the center of the image. The band takes up acout 1/3 to 1/2 of the image in width. The accelerating voltage is 15KV. I have an image showing the problem at the following link: www.noobie.ca/tmp/blurry.jpg Thanks, Gary |
#7
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Electron Microscope Focus Problem
"Mac" writes:
Our operator doesn't use the TV-scan, only the slow scan. Her specimens are organic. She is familiar with what a charging artifact produces on the system. She describes it as horizontal streaks across the image at which point she deposits more gold on the specimen to correct the charging problem. This problem is a very subtle focus issue in a horizontal band across the center of the image. The band takes up acout 1/3 to 1/2 of the image in width. The accelerating voltage is 15KV. I have an image showing the problem at the following link: www.noobie.ca/tmp/blurry.jpg Wow, that doesn't exactly jump out at you! Is the location/severity magnification dependent? What does adjusting the focus of the microscope actually do to the image? --- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/ Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/ +Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm | Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html Important: Anything sent to the email address in the message header above is ignored unless my full name AND either lasers or electronics is included in the subject line. Or, you can contact me via the Feedback Form in the FAQs. |
#8
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Electron Microscope Focus Problem
Mac wrote:
Our operator doesn't use the TV-scan, only the slow scan. Her specimens are organic. She is familiar with what a charging artifact produces on the system. She describes it as horizontal streaks across the image at which point she deposits more gold on the specimen to correct the charging problem. This problem is a very subtle focus issue in a horizontal band across the center of the image. The band takes up acout 1/3 to 1/2 of the image in width. The accelerating voltage is 15KV. I have an image showing the problem at the following link: www.noobie.ca/tmp/blurry.jpg Thanks, Gary My Long Stare makes me wonder if I am looking at a small fibre strand in the Column! My next step would be to use a "ANOPORE Filter" as a Test object I think 0.01 micron would be best, although 0.2 micron would do. Check with the Biology Department for a sample. I think I would have recommended it for sample preparation where dehydration on a membrane filter was indicated. This is an Aluminum Oxide Filter Media that I used for a High Mag Test Object Sputter Coat a fragment bonded to a stub using Double-coated Tape. This will Give you an extremely Uniform Mesh that will allow you to see Focus/astigmatism problems over the entire Field of View. I suspect that at lower Magnification~ 400X, a small segment will show a localized area of astigmatism, (dirty side of Column) At a higher Magnification ~ 1500/2500X the majority of the field would be astigmatic as the beam would sweep across a smaller and smaller portion of the Column, or maybe asymptomatic as it sweeps across an unaffected part of the column. Anyway I don't really think it is an Electronic Problem, more likely Housekeeping, "Contaminated Liner Tube", Scrub with Aluminum Oxide. The Microtombe people use it for Polishing their Knives, and its cheaper than "Wenol". Yukio YANO |
#9
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Electron Microscope Focus Problem
Yukio YANO wrote: Mac wrote: Our operator doesn't use the TV-scan, only the slow scan. Her specimens are organic. She is familiar with what a charging artifact produces on the system. She describes it as horizontal streaks across the image at which point she deposits more gold on the specimen to correct the charging problem. This problem is a very subtle focus issue in a horizontal band across the center of the image. The band takes up acout 1/3 to 1/2 of the image in width. The accelerating voltage is 15KV. I have an image showing the problem at the following link: www.noobie.ca/tmp/blurry.jpg Thanks, Gary My Long Stare makes me wonder if I am looking at a small fibre strand in the Column! My next step would be to use a "ANOPORE Filter" as a Test object I think 0.01 micron would be best, although 0.2 micron would do. Check with the Biology Department for a sample. I think I would have recommended it for sample preparation where dehydration on a membrane filter was indicated. This is an Aluminum Oxide Filter Media that I used for a High Mag Test Object Sputter Coat a fragment bonded to a stub using Double-coated Tape. This will Give you an extremely Uniform Mesh that will allow you to see Focus/astigmatism problems over the entire Field of View. I suspect that at lower Magnification~ 400X, a small segment will show a localized area of astigmatism, (dirty side of Column) At a higher Magnification ~ 1500/2500X the majority of the field would be astigmatic as the beam would sweep across a smaller and smaller portion of the Column, or maybe asymptomatic as it sweeps across an unaffected part of the column. Anyway I don't really think it is an Electronic Problem, more likely Housekeeping, "Contaminated Liner Tube", Scrub with Aluminum Oxide. The Microtombe people use it for Polishing their Knives, and its cheaper than "Wenol". Yukio YANO |
#10
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Electron Microscope Focus Problem
I am the operator of this SEM in question, so I thought it might be
helpful if I joined in on the group. I am currently using the largest spot size to image my specimens - do you suspect any connection with this to my problem? I will plan to obtain a test object such as the one you mentioned and image it to check for focu/astigmatism problems. Thanks for your advice. Glenda |
#11
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Electron Microscope Focus Problem
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