Zeiss 940 Scanning electron microscope - Page 1
Forum section: electronics / testgear

author: samofab
author_rank: Regular Contributor
timestamp: November 14, 2013, 05:12:39 pm
content: Hello,I bought a Zeiss 940 scanning electron microscope, reportedly one of the first digital SEMs. I guess it still fits into description of test equipment to warrant the post in this area :-D I had great difficulty getting it home as it weighs lot and it didn't fit into elevator. I'll be posting my experiences with it here as I go along, but for starters here is a picture of my poor man's vacuum leak detector.The seller described the unit as in need of replacement vacuum seals, so really I shouldn't be suprised when roughing pump couldn't bring the pressure down to about 1mbar required for operation of high vacuum sensor and turbopump (that means one big leak). There are a lot of seals in this unit, and just applying a lot of vacuum grease to them didn't help. I needed a more scientific way... Google searches kept on turning expensive solutions such as using mass spectrometer inside the unit and spraying the unit with Helium. I didn't have mass spectrometer, but I did have a some Helium in my scuba tanks (likely less than 10%). Since the leak was obviously large I decided to try it. Helium molecules enter the chamber faster than air and therefore remove more heat on pirani sensor, so aparent pressure should rise. I found a test point for roughing pump pressure (there is no indicator on the unit), waited for the pressure to stabilise and the used scuba second stage to spray the seals. The changes were almost unnoticable (less than 0.01% of the reading), but when I added some plastic bags (very roughly), the pressure jumped significantly (well.. 10x more than before, helps if you have 5 1/2 digit DMM).Final result: main seal of the chamber is dead. Logically it is one of the nonstandard ones, so if anybody has any ideas where to get a large Viton seal (about 70cm, I'll measure exactly), please let me know.And however unlikely: if somebody has a schematic or service manual, that would be a excelent. Zeiss doesn't reply to requests on their website.Bonus picture: has anybody seen such a large linear power supply (weights about 50kg, water cooled, obviously)?

author: JoeyP
author_rank: Frequent Contributor
timestamp: November 14, 2013, 05:38:37 pm
content: I'm very interested in your experiences with this. Please keep us posted. I've been wanting a SEM to play with for a long time. Considered building one as a hobby project, but didn't have the time to get very far with it. Have fun, and post lots of images!

author: Vgkid
author_rank: Super Contributor
timestamp: November 14, 2013, 06:32:33 pm
content: I will add another vote to keeping us updated. For the seals, is it an o-ring, or odd shaped. try thishttp://sealscience.com/default.aspx

author: KJDS
author_rank: Super Contributor
timestamp: November 14, 2013, 06:58:55 pm
content: I've repaired numerous optical microscopes but have never played with an SEM. I'm another that would like to be kept updated.

author: TerraHertz
author_rank: Super Contributor
timestamp: November 14, 2013, 10:32:56 pm
content: Ooooh! (swoon)I too am very interested to hear how you go.A SEM is at the top of my dream finds list, but sadly no luck yet.I once _almost_ got one. It was in a hospital that was being demolished. Just sitting there, forlorn, in a room by itself. I asked about it, but the idiots in charge had some idea they were going to ship it to Africa for the poor underfunded African hospitals. Which of course they never did. The last I heard it was destroyed in the building demolition. Arrrgh!I should have applied the sensible approach, and just rescued it from the idiots without permission.Of course you realize you also need a bunch of ancillary equipment like a microtome, vacuum dryer, and vacuum metal deposition setup, for sample preparation.

author: con-f-use
author_rank: Unknown
timestamp: November 14, 2013, 10:43:00 pm
content: What do you plan on doing with it?

author: lowimpedance
author_rank: Super Contributor
timestamp: November 14, 2013, 10:53:38 pm
content: Quote from: TerraHertz on November 14, 2013, 10:32:56 pmThe Microscope's at work, (cannot remember OTTOMH who the manufacturer is), require liquid Nitrogen for the cold traps, if this unit has one that may prove interesting!.

author: ixfd64
author_rank: Frequent Contributor
timestamp: November 14, 2013, 11:34:06 pm
content: You must have pretty deep pockets. Don't electron microscopes cost several dozen grand?

author: samofab
author_rank: Regular Contributor
timestamp: November 14, 2013, 11:58:00 pm
content: Lots of responses :-DI'll reply to everbody in one post.All of the seals are O-rings, the one I need is quite large at approx. 279mm inner diameter and 4mm section.For metalic samples there is no special preparation required, as long as the surface is conductive it will work. Metal deposition and other complicated preparation steps are required for biological samples, etc. If I decap an IC and ground it, it should show up on the screen nicely (when it works again).I have no special project in mind, just learning and reviving a very cool piece of old equipment. Idea of building replacement electronics was in the pipeline, but really, at the moment I would just like to see a picture on the screen. If you substract the reqular maintenance of precision equipment that spent a number of years in warehouse (new filament, vacum pump rebuild, seals), the biggest problem that I have is reassembling it. In particular, I was hard pressed for time to get away it away from rain and in haste I took too little pictures. Some cables were cut, but that is easily solvable (color coded all the way). The main electronics unit is assembled in 3U high rack caseses with 100x160 euro cards, that are interconnected by a gazzilion flat cables, and may of them are of the same pin count. Hence the need for schematic.Cold trap is not needed on this unit (I think it is usually required for the ones with vacuum diffusion pumps) and the newer units that you see with liquid nitrogen storage use it for x-ray spectroscopy sensor (don't quote me - not an expert).The cost of shipping the unit from UK was almost the biggest expense, but if I recall the number correctly, Dave's DSA power supply repair was quite a bit more expensive than my SEM :-). That being said, I can't believe how cheap and fast it is to send half a ton across half of Europe. Incidently, even pallet shipping from USA to EU can be done for 500 USD or so (port to port).About Zeiss.. it's funny, the cast metal parts look as if they were doing production run of 10.000's, it's quite beautiful on the outside. As for electronics, it looks like it was strapped together in an almost hobby or prototype fashion.Attaching some pictures of how it looked before shipping and before I attacked it with angle grinder and wire cutters.

author: RedShoeRider
author_rank: Contributor
timestamp: November 15, 2013, 01:42:07 am
content: "Cold trap is not needed on this unit (I think it is usually required for the ones with vacuum diffusion pumps) and the newer units that you see with liquid nitrogen storage use it for x-ray spectroscopy sensor (don't quote me - not an expert)."Mostly right. The ones with the vacuum diffusion pumps didn't *need* the LN2, but it did help with absolute vacuum and helping to keep any oil contamination from getting on the sample if the backing pump wasn't perfect. There's been a general trend away from the ODP's because of the potential for contaminating the column. The turbomolecular pumps are terrific, though they can't get to quite the vacuum an ODP can on its own, though. Many of the newer scopes often don't use LN2 at all; the current generation of EDS detectors use peltiers rather than nitrogen; they switched from the old lithium-drifted silicon to solid state detectors. The old sillys needed to be below -200 to work without a metric ton of noise; the new crop of SSD's only need to be in the -30 range, which the peliters do nicely. If a newer scope does use LN2, it's usually for a cold trap.As for biologics, the metal deposition is actually pretty easy, and the coaters can be had for not that much money. The largest recurring expense is the metal target, as it's typically either gold or gold/palladium, and costs a mint these days. Granted, you usually get 100+ 100-125 angstrom thick coatings out of one target, so the per-sample cost isn't awful. The prep steps are easy; the chemicals common and cheap.Yeah, IAAEM (I am an Electron Microscopist). Honestly! It says so right on my business card. I'm in core EM lab for a one of the large Pharma companies. We run FEI TEM's and SEM's now, but I've lived with a Zeiss, a Topcon, a JEOL....Your are spot-on about Zeiss making it look like they were doing production runs of 10,000's, but the electronics look like a prototype. I cut my teeth on a Zeiss 902A TEM, and it was very much the same. While it looked gorgeous on the outside, the wiring was a mess. According to what our old technician said, Zeiss wasn't very good about keeping things absolutely the same though a production run, and as they changed things....well, they just changed them. Documentation wasn't terrific, S/N splits for changes weren't always accurate, and it looked like a prototype because, in some ways, it was. That generation of scope was pretty solid, though, as Zeiss generally overbuilt the crap out of everything, both electronically and mechanically. To be fair, Zeiss wasn't the only one who had that mentality of a "production prototype". We had a JEOL SEM for about a decade, and there were hand-drawn traces in the schematic book that came with the scope. That thing was a pile of boards (and even a little breadboard) with 100 miles of wire. Worked great, though!Zeiss's customer service is a bit fiddly; their people are supremely well trained and knowledgeable, but getting in touch with them can be a trick. You might be served well by getting in touch with Zeiss Microsystems directly. If you're in the USA, they're in Thornwood, New York (1 Zeiss Drive, no less), (914) 747-1800. I can't tell you who to talk to, though. The two techs I know there are both retired.In my humble opinion, one of the hardest things is just getting the vacuum to hold. They leak like sieves as they age. One more place to look for a leak is the apeture holder/adjuster. We've had leaks on most of our instruments at one point or another right there. It's usually just a 50 cent O-ring, but it'll leak vac enough to cause a fuss.Anyway, if I can be of help, let me know....and good luck with it!-Red

author: tized
author_rank: Contributor
timestamp: November 15, 2013, 02:21:28 pm
content: Interesting project, do keep us posted.Incidentally, yesterday I was at the unveiling of a new exhibition about antique lab equipment, at the Madatech science museum. Here is photo of the great-great-great grandfather of your microscope; A Zeiss polarizing microscope from 1907.

author: KD0CAC John
author_rank: Frequent Contributor
timestamp: November 15, 2013, 02:59:20 pm
content: I need more space ;(About a yr. ago I had a chance to buy a Zeiss SEM , it had more and larger desks and all , but had no place to put it , living in an Airstream trailer in RV park .The asking price was $1,500 , from the used equip. place that bought it from a local university doggy-dewSome friends said what would you do with it , my answer in astonishment was , look at stuff

author: TerraHertz
author_rank: Super Contributor
timestamp: November 16, 2013, 12:42:12 am
content: Have you tried taking the main O-ring out, cleaning it and the groove with solvents, re-greasing both, then putting it back in other side up? You might be lucky. If it's not visibly nicked or hardened/flat, the leak may be due to residue on the seal or metal surfaces.As for replacing it, I've been led to believe that for large O-rings you can buy lengths of the seal, cut the required length and butt/lap join it. With the right glue - but I don't yet know what that is. I haven't got the stage in my vacuum project where I need to know, and won't for a long while.

author: pickle9000
author_rank: Super Contributor
timestamp: November 16, 2013, 01:23:07 am
content: You should get in touch with Ben Krasnow the youtube guy. He seems to be able to locate and rig some unusual stuff. Maybe you could work a deal.

author: SeanB
author_rank: Super Contributor
timestamp: November 16, 2013, 08:00:45 am
content: Most seal suppliers can either make or source the seals, though you will find they might be expensive. I had some special food grade silicone seals made 2 years ago for a machine, and ordered a dozen just to get the unit price down to $12 each. Pretty cheap compared to the agents price of $100 each and it uses 2 per cylinder. A good thing though is I only use one seal new per year, as the primary will move to the secondary position when it ages. Still have a 6 year supply or so, depending on usage.

author: samofab
author_rank: Regular Contributor
timestamp: November 17, 2013, 10:07:18 pm
content: Time for an update.Regarding the seals. I don't think that gluing a custom seal works for high vacuum. I already did try to use liberal amounts of grease and turning the seal around, but carefull inspection showed some serious cracks on the seal, so it is definitely useless. I'm optimistic, though: I send some inqueries I'm expecting responses. I actually found a company in Slovenia that has that exact dimensions in their catalgoues and as far as I understand their website, they have a machine to make custom one off seals cheaply. We'll see if I get replies.I also got a reply from company that was in principle willing to rebuild my filament, but they requested a picture - so I opened the filament assembly and guess what? The filament was in one piece. It was a total PITA to align and assemble it together without a Zeiss custom tool, but I think that it will be servicable at least for first tests. I have to check the cables though, because I'm almost certain that I measured the resistance on the heating part of the HV cables and it was open circuit.While waiting for the seal problem to resolve, I started to reassemble the electronics sans schematic. A lot of best guesses, checking the location of power pins, matching the lengths of cables, matching the pin counts, discovering if the circuitry on boths sides seems to have business talking to each other, etc... This was a partial success, I guess. I did manage to mangle one cable and blow a fuse (stuck a cable to location where the ground and +5V are interchanged), but I don't think that there is any permanent damage. One of the displays on the console actually lights up, I see some digital data going around on oscilloscope from the main processor, I see a 13.01 Mhz clock on the assembly where graphics processing is likely done and I see a video signal on the monitor output. And the bad news: the video signal is one big blank screen.I also took some pictures..

author: samofab
author_rank: Regular Contributor
timestamp: November 17, 2013, 10:09:25 pm
content: PS: I did have to do some plumbing, the power supply shuts down in 2 minutes without water supply. Uses about 290W at idle :-DMore pictures.

author: amyk
author_rank: Super Contributor
timestamp: November 18, 2013, 08:06:45 am
content: A Z80! I was expecting something more substantial, from the size of the operator's console.Question to ponder: for a leaky evacuated container, do you say the vacuum is leaking in, or out...?

author: samofab
author_rank: Regular Contributor
timestamp: November 18, 2013, 08:51:14 am
content: The first clock that I saw on oscilloscope was 13Mhz and I said "uauuu, this is from early 90's". But really a 4Mhz Z80 makes sense, doesn't it?

author: SeanB
author_rank: Super Contributor
timestamp: November 18, 2013, 06:01:56 pm
content: Back up all of those Eproms before you go much further. A copy will save you later on if you pop one or it gets erased.

author: Vgkid
author_rank: Super Contributor
timestamp: November 18, 2013, 08:54:31 pm
content: Thanks for the update, there are a ton of socketed chips.

author: samofab
author_rank: Regular Contributor
timestamp: November 23, 2013, 01:53:21 am
content: A short update... I managed to source a replacement O-ring from a local company, but that didn't help with the vacuum problem. I still couldn't reach the level required for turbopump to work. Some more fiddling with helium indicated that the problem is located in specific location of the main chamber door. Carefull investigation revealed a scratch on the O-ring surface. See image.Vacuum is fiddly mistress, a hairline scratch will break your day.Any ideas on how to fix it? I'm thinking using sand paper up to 2000 grit to polish it out (not that it will be easy to squeeze it in there).Progress on electronics:still no image on main monitor, but I had some fun reverse engineering different parts, the biggest overkill IMHO was a complete power amplifier with close relation to audio amplifiers that included ICL8038. What it does is outputs about 50V rms at 20kHz in order to feed a transformer that powers the heating to filament which is floating at max 30kV. I reckon that about the time that this microscope was designed, I too was dreaming about using ICL8038, just a different application :-D everybody wants to build a function generator sometime in their electronics career. Anybody knows why they needed a pure sine wave? I didn't open the high voltage can with the actual transformer, but I almost certain that it is just a power supply to heating circuit with dedicated filtering and electronics to actually drive the filament.Lots of fimiliar high power amplifiers. Including this one I think I counted about 6 channels of what looks like up to 40Vrms amplification of frequencies from DC to 40kHz.

author: SeanB
author_rank: Super Contributor
timestamp: November 23, 2013, 05:55:40 am
content: Balsa wood dowel cut to size and use fine jewellers rouge to polish it out will be better. At worst go into the garden and get a swig and strip the bark off and use it with the rouge, or if you do not have any use wet talcum powder.

author: amyk
author_rank: Super Contributor
timestamp: November 23, 2013, 06:24:36 am
content: That picture looks like there's a cobweb from the hole to the edge...

author: samofab
author_rank: Regular Contributor
timestamp: November 23, 2013, 07:30:56 pm
content: Leak No.1 fixed with some 2000 sanding paper.But as RedShoeRider anticipated, aperture holder also leaks like a sieve.

author: eV1Te
author_rank: Regular Contributor
timestamp: November 23, 2013, 08:54:22 pm
content: Very interesting to see other people with SEMs at home. I have a Jeol JSM-T200 in my living room at the moment. I made a video some time back, just showing a light bulb filament while recording the screen.Would anyone we interested in a teardown before I have to get rid of it?Some comments on your problems:-Helium is your best bet (only option) to find leaks.-Don't use to much of that special high-vacuum grease, even the best vacuum-greases evaporates in high vacuum. You should spread it almost as thin as one atomic layer, preferably no grease at all if not required to stop leaks. (but in order to just reach below 1 mbar, to start the turbo pump, you could probably seal the chamber with Vaseline)-I have a few boxes of filaments to my SEM, do you have spare ones?

author: SeanB
author_rank: Super Contributor
timestamp: November 24, 2013, 04:27:43 am
content: Quote from: eV1Te on November 23, 2013, 08:54:22 pmTeardown of course, and hopefully somebody wants it intact.

author: samofab
author_rank: Regular Contributor
timestamp: November 27, 2013, 01:07:51 pm
content: QuoteThumbs up!QuoteI have only the one that I found inside. Everybody is saying that rebuilding the filaments in cheap and easy, but living in Europe it ads up to a significant amount. Do you have a picture of the filemant with approx. dimensions?QuoteWell, after I got new seals for my aperture I still get the huge leak on the same location. I suspect that I'll have to disassemble the whole column.. running out of options here.Disassembled aperture holder image for your pleasure is in attachment.On a different note: I'm thinking of at least partially giving up on the electronics unit. I'm thinking of just building a ramp raster generator from the two DACs in STM32, plug it into existing working power amplifiers and oscilloscope and hopefully I'll get an image.In an effort to do that I decided to test the photo-multiplier supply and it doesn't work.. or to be precise: board contains two completely populated 1.5kV power supplies and the one that was wired to the photo-multiplier is dead, but the completely unused one is fine (yes, there is actually a second supply that with certainty wasn't used for anything).QuoteIt's an excellent idea, but I don't have eeprom reader.. I could hack something together, but with current plan to forget about the Z80 parts, I don't think it's worth the effort.

author: eV1Te
author_rank: Regular Contributor
timestamp: November 27, 2013, 05:27:21 pm
content: Quote from: samofab on November 27, 2013, 01:07:51 pmThanks!Quote from: samofab on November 27, 2013, 01:07:51 pmThese are filaments for my and most of Jeols tungsten filament microscopes (K-type filaments):http://www.tedpella.com/apertures-and-filaments_html/tungsten-filaments.htm#anchor1407Quote from: samofab on November 27, 2013, 01:07:51 pmBefore you disassemble to much (more old seals that can break, or misalignment of beam), just remove the aperture assembly completely and seal the hole with with some plastic or rubber if possible. I usually use just a flat piece of rubber in these cases that can cover the entire hole, which will be held in place by the vacuum.I have been thinking about modifying the electronics for my SEM to, just a ramp generator for X and Y, and then measuring/controlling the position of these with a computer, which also analyses the signal from the photo multiplier (hence a digital SEM)I will have to get rid of my SEM in the beginning of next year. I have no idea what to do with it! So if anyone wants parts from it, you are welcome to just pay the shipping. (unless I find someone who wants the entire thing, preferably in Sweden since shipping would be expensive!)