tag:blogger.com,1999:blog-401164737462963207.post7291548826856465838..comments2024-03-28T00:14:10.834-07:00Comments on Ben Krasnow: DIY Scanning Electron Microscope - Image Quality Improvements 1Ben Krasnowhttp://www.blogger.com/profile/04234629396863486242noreply@blogger.comBlogger31125tag:blogger.com,1999:blog-401164737462963207.post-28030184974635325892020-09-22T19:31:20.440-07:002020-09-22T19:31:20.440-07:00#arking over #arking over Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-401164737462963207.post-58096112286962672272020-09-22T19:30:49.922-07:002020-09-22T19:30:49.922-07:00Isolation filament power supply update:
So after a...Isolation filament power supply update:<br />So after arming over an old transformer I wound up using my ZVS driver that drove just a ferrite core from a burnt out flyback. On the secondary of that core, I wound 5 turns of 30kv rated cable and added a schottky and a capacitor. Output was 18Volts at 3amps. After that I added a buck converter that now drives the filament. And the best part I even took it down to -30kv (my power supply max) just to make sure that there was no negative affects and it works perfectly.Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-401164737462963207.post-42480477444088312202020-09-15T21:46:09.238-07:002020-09-15T21:46:09.238-07:00Thanks. That’s all I needed!!
This is a big proje...Thanks. That’s all I needed!! <br />This is a big project that will take me several month to complete but I do have a head start since I converted my fusor chamber which is in a glass bell jar similar to yours. It gets down to the 10-6 torr range. And should be a good platform to build this microscope. I got tired of the fusor since it wasn’t very useful other then emitting light.<br />Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-401164737462963207.post-9332238812219807462020-09-15T21:35:34.154-07:002020-09-15T21:35:34.154-07:00I think that I used a 5M or 10M pot for the biasin...I think that I used a 5M or 10M pot for the biasing resistor. If your filament is about 400V more positive, and you have a 4M biasing resistor, that indicates the gun is operating at 100uA emission current. These are good round numbers to get started. The power dissipation in this resistor will be almost nothing. https://www.youtube.com/watch?v=ZIJ1jI1xDhYBen Krasnowhttps://www.blogger.com/profile/04234629396863486242noreply@blogger.comtag:blogger.com,1999:blog-401164737462963207.post-66921759035519913022020-09-15T21:16:25.269-07:002020-09-15T21:16:25.269-07:00Thanks for such a quick and informative response. ...Thanks for such a quick and informative response. One more question if you don’t mind. What is the value of the potentiometer between the cathode (wenault) and the filament? Bias resistor? I did some math and was getting very high dissipation values so right now I have a 1M 10watt huge resistor. But wanted to see what value worked in your design.<br />Thanks<br />Anthony<br />xelectro@me.comAnonymousnoreply@blogger.comtag:blogger.com,1999:blog-401164737462963207.post-57347960149193377782020-09-15T19:37:47.540-07:002020-09-15T19:37:47.540-07:00Xelectro, an isolation transformer is usually not ...Xelectro, an isolation transformer is usually not rated for 10KV of isolation, but they will often work just fine. It helps a lot to use a transformer that has a "split bobbin" design so that the input and output windings are physically far apart. I used a variac to power the isolation transformer, then used the isolation transformer to power a step-down transformer that powers the filament. Later, I found that the AC on the filament can cause image instability problems, so I removed the variac, and added a typical LM317 adjustable voltage regulator with smooth capacitors to the output of the step-down transformer, which I controlled with a knob on a long plastic shaft (since the whole DC supply will be floating at -10KV). The condenser lens is an "Einzel" design, which has three in-line elements that are arranged so that the first and last element are at the same potential, and the middle element is at another potential. I don't believe it matters if it's (+ - +) or (- + -). In my case, the first and last element are grounded (same as anode potential), and the middle element is at cathode potential. A big improvement would be to add a 10M potentiometer or similar to adjust the condenser lens voltage.Ben Krasnowhttps://www.blogger.com/profile/04234629396863486242noreply@blogger.comtag:blogger.com,1999:blog-401164737462963207.post-81374561288696854932020-09-15T15:49:10.186-07:002020-09-15T15:49:10.186-07:00Hi Ben,
I would like to know how to isolate the fi...Hi Ben,<br />I would like to know how to isolate the filament power supply since it will be floating at -5kv to -10kv since my Anode is ground. I have a variac + isolation xformer + 6v xformer that will feed the filament. Also my second question is about the condenser lens potential, from your drawings it looked like it was same potential as the cathode.<br />And as far at the focusing lens I wasn’t able to make out the polarity of it so any help would be greatly appreciated.<br />Anthony<br />Xelectro@me.comAnonymousnoreply@blogger.comtag:blogger.com,1999:blog-401164737462963207.post-35245883411940131452020-04-30T11:25:21.932-07:002020-04-30T11:25:21.932-07:00Yeah, that sounds about right.Yeah, that sounds about right.Ben Krasnowhttps://www.blogger.com/profile/04234629396863486242noreply@blogger.comtag:blogger.com,1999:blog-401164737462963207.post-54464789461086106842020-04-30T11:11:16.207-07:002020-04-30T11:11:16.207-07:00Ben, I know this is an old post, but I hope you se...Ben, I know this is an old post, but I hope you see this comment, and have some time to respond. I was wondering what voltage and current ranges you use for filament heating. Best I could find is between around 3.2V and slightly below 3.8V, with a current of 3 to 4 amps. Does this sound correct to you?<br /><br />Thanks,<br />Mark<br />Epsilon ZRhohttps://www.blogger.com/profile/00400251597206045448noreply@blogger.comtag:blogger.com,1999:blog-401164737462963207.post-73608246869350154402016-02-02T22:08:29.000-08:002016-02-02T22:08:29.000-08:00Filip, the 10KV is connected to a ring that surrou...Filip, the 10KV is connected to a ring that surrounds the phosphor disc. This creates an electric field that causes electrons to be accelerated toward the disc -- some electrons may hit the ring, but many will hit the disc because the acceleration created by the ring directs them mostly toward the disc. I believe the phosphor is mixed with a slightly conductive material to help spread the charge.Ben Krasnowhttps://www.blogger.com/profile/04234629396863486242noreply@blogger.comtag:blogger.com,1999:blog-401164737462963207.post-11806862176718502922016-02-02T13:22:55.539-08:002016-02-02T13:22:55.539-08:00Hi Ben.
I have one question how you supply phospho...Hi Ben.<br />I have one question how you supply phosphor via 10kV supply to accelerate electrons? There is behind this phosphor any conductive glass and then connected to 10kV? <br /><br />Best regards<br />Filip Orłowskifiliporlohttps://www.blogger.com/profile/14131432612500850102noreply@blogger.comtag:blogger.com,1999:blog-401164737462963207.post-25347254349364848182013-11-24T11:05:20.959-08:002013-11-24T11:05:20.959-08:00Andre, sure that looks great! Thanks!Andre, sure that looks great! Thanks!Ben Krasnowhttps://www.blogger.com/profile/04234629396863486242noreply@blogger.comtag:blogger.com,1999:blog-401164737462963207.post-92054052635582862452013-11-24T10:21:40.861-08:002013-11-24T10:21:40.861-08:00Hello! This is a very cool project! I've taken...Hello! This is a very cool project! I've taken the liberty of referencing it in a small website I run for open/DIY projects that could make neuroscience more affordable and accessible. Let me know if the way it is referenced is ok for you! http://openeuroscience.wordpress.com/hardware-projects/microscopy-hardware/scanning-electron-microscope/<br /><br />Best regards,<br />André M ChagasAndré Maia Chagashttps://www.blogger.com/profile/11410776283281564452noreply@blogger.comtag:blogger.com,1999:blog-401164737462963207.post-63633831679315402172011-07-27T04:39:50.827-07:002011-07-27T04:39:50.827-07:00Thanks for keep us updated. Your information is re...Thanks for keep us updated. Your information is really informative and helpful.Venetian Blindshttp://www.imageblindsdirect.com.aunoreply@blogger.comtag:blogger.com,1999:blog-401164737462963207.post-48682711706997223382011-05-06T10:34:20.002-07:002011-05-06T10:34:20.002-07:00Ravaner, no I have tried any magnetic lenses. I w...Ravaner, no I have tried any magnetic lenses. I would have to find or make the pole pieces, which is pretty difficult either way. Commercial SEMs use magnetic lenses because they can be made to have a shorter focal length than electrostatic lenses, and apparently have lower optical aberrations. However building magnetic lenses from raw materials seems much more difficult. Electrostatic lenses are very easy to build, test and rebuild.Ben Krasnowhttps://www.blogger.com/profile/04234629396863486242noreply@blogger.comtag:blogger.com,1999:blog-401164737462963207.post-79368371061460171252011-05-05T22:40:29.850-07:002011-05-05T22:40:29.850-07:00Hi, Have you ever tried to used electromagnetic le...Hi, Have you ever tried to used electromagnetic lenses in your SEM ?Ravanernoreply@blogger.comtag:blogger.com,1999:blog-401164737462963207.post-64295908643197592882011-05-04T03:34:16.452-07:002011-05-04T03:34:16.452-07:00Hello ... Congratulations ! I've good idea of ...Hello ... Congratulations ! I've good idea of the fantastic work you realized because I'm just finishing my homemade Time Of Flight Mass Spectrometer and I've acquiered experience (painfully !) in high vacuum, electromultiplier ... May be SEM will be my next project ... One more time : BRAVO !Ravanernoreply@blogger.comtag:blogger.com,1999:blog-401164737462963207.post-89532008610508737492011-04-25T12:18:32.502-07:002011-04-25T12:18:32.502-07:00kraftphysics, I'd be happy to pay for your tim...kraftphysics, I'd be happy to pay for your time and shipping costs if you would like to send me some old SEM parts. Please email me at ben at magconcept dot com.Ben Krasnowhttps://www.blogger.com/profile/04234629396863486242noreply@blogger.comtag:blogger.com,1999:blog-401164737462963207.post-101637314900186182011-04-21T23:36:48.223-07:002011-04-21T23:36:48.223-07:00Hey- excellent work here! I don't know if you ...Hey- excellent work here! I don't know if you would feel that it's going against the spirit of this project, but I happen to literally have a storage unit full of old SEM parts and such that I not only don't need, but want to get rid of. <br /><br />You might not want most of it, but I do have some scan generators, etc. Most are parts from JSM-35 systems, which are nice in that almost everything is in small self-contained units.<br /><br />One thing I have which is small that you might want to use is a small molybdenum aperture. I have several that are of no use to me (They came from an instrument I no longer have) and I'd be happy to donate them to the cause. These are typically used for column apertures and final apertures in a commercial SEM, but are also used for other purposes, so they are not strictly SEM parts...<br /><br />--Justin.kraftphysicshttps://www.blogger.com/profile/03015250004518550329noreply@blogger.comtag:blogger.com,1999:blog-401164737462963207.post-80141121173530343752011-04-15T10:43:08.604-07:002011-04-15T10:43:08.604-07:00bricodada, thanks for the info!bricodada, thanks for the info!Ben Krasnowhttps://www.blogger.com/profile/04234629396863486242noreply@blogger.comtag:blogger.com,1999:blog-401164737462963207.post-36949302457089065792011-04-15T10:40:07.159-07:002011-04-15T10:40:07.159-07:00Anon, electron guns in CRTs are designed to emit l...Anon, electron guns in CRTs are designed to emit lots of electrons from a relatively large area (eg 2mm dia). In contrast, SEM electron guns attempt to make the electron source as small as possible, ideally just a point source. Tungsten filaments are OK, but LaB6 emitters are better, and most high-quality modern SEMs use field emission, which is even better to generate the electron source.<br /><br />Many commercial SEMs use dry nitrogen to vent the specimen chamber. This lowers the amount of atmospheric water that gets into the chamber and improves the pump-down speed. It probably would not be good enough to prevent oxygen poisoning of metal-oxide cathodes though. If you are interested in building a SEM, I would definitely recommend plain tungsten cathodes. They are durable, cheap and easier to use than anything else.Ben Krasnowhttps://www.blogger.com/profile/04234629396863486242noreply@blogger.comtag:blogger.com,1999:blog-401164737462963207.post-11441118454358659572011-04-15T10:18:47.820-07:002011-04-15T10:18:47.820-07:00sorry for double post, and double sorry if this is...sorry for double post, and double sorry if this is a stupid question, but regarding Ben's comment about not exposing CRT's to air, what if you built a chamber of another cheap gas with no O2 inside, such as CO2, N2, or He ? If it worked, the drawback would be anything you viewed would have to be "gassed" in a sealed box to flush the air out, but how much $ would it save to use a CRT ? Thanks for any replies.Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-401164737462963207.post-70171873661050455512011-04-15T10:12:54.276-07:002011-04-15T10:12:54.276-07:00Restorative to my sentiment on humanity to see peo...Restorative to my sentiment on humanity to see people doing projects advanced as this. Way to go!Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-401164737462963207.post-52333823340137089912011-04-14T02:57:03.079-07:002011-04-14T02:57:03.079-07:00Hello Ben!
You could make a convenient diaphragm w...Hello Ben!<br />You could make a convenient diaphragm with a very thin gold leaf (available on ebay for decoration), glued with silver/epoxy conductive glue on a supporting small disk with a medium sized hole (0.5 mm or so). The gold leaf is pierced with a electro-etched tungsten tip that you can make this way : http://www.phys.unt.edu/stm/tips.htm<br />http://www.ttakami.com/DCtipEtching/DCtipEtching.html<br />http://www.scielo.unal.edu.co/scielo.php?pid=S0121-49932008000100005&script=sci_arttext<br />For this application, the process can be simplified : the etching KOH solution is just a drop inside a stainless steel ring, traversed by the tungsten wire. When the etching is complete, your tip fall in a rinsing water solution.<br /><br />The piercing itself is done by electro-erosion between the gold leaf and the tungsten tip(few volts inside a droplet of distillated water).<br /><br />Holes are very clean, and, with the help of an optical microscope, you could control holes up to 10 microns.bricodadahttps://www.blogger.com/profile/07069536235850262960noreply@blogger.comtag:blogger.com,1999:blog-401164737462963207.post-50283084482348278752011-04-07T03:02:13.534-07:002011-04-07T03:02:13.534-07:00In the second image, I think the insulating region...In the second image, I think the insulating regions of the die are showing signs of charging - this creates scan-direction streaking as the secondary electron signal does not decay sufficiently rapidly. You'll need to build yourself a sample coater one day - the good news is that you already have the vacuum system :)Anonymousnoreply@blogger.com