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NetNotes TEM: oil diffusion pump (ODP)


I came in this morning and observed the following error message on our Philips CM 120: ODP Circuit. Primarily what is happening is that, upon start-up, the system gets hung up at the very fi rst step of the vacuum sequence. I am polling the expert audience to determine if anyone has encountered this issue and to learn what was done about it. Dave Rademacher drademacher@luc.edu Wed Apr 4 In the Manual, there is written “ODP Circuit - contact service department.” We had this problem a long time ago, and we have solved it by buying a new ODP heater. We bought a new one from a company in Germany. Unfortunately, I do not have the details at hand now. T e heater can be replaced by the user. It is not a diffi cult task. P.S. Just now I have found the old broken heater ring from our Philips CM100. Its specifi cation is “Chromalox Cat No. KB15 Volts 210 JB Watts 450.” T e heater can be found on the Edwards Webshop: https://shop. edwardsvacuum.com/products/H01700186/view.aspx . Please, look at your diff usion pump type if this specifi cation is also valid form your pump. Oldřich Benada benada@biomed.cas.cz T u Apr 5 It sounds like a Water Chiller problem. Your chiller is probably making hot water, maybe good for tea but not for your microscope. Greg Hendricks gregory. hendricks@umassmed.edu Wed Apr 4 I used to look aſt er two CMs until very recently. I think 'ODP circuit' means the heater's electric circuit is open (i.e., likely the heater element has failed, as someone else mentioned); 'ODP Water' is when the water temperature just aſt er the ODP reaches 60 degrees C, i.e., water fl ow or chiller issue; 'ODP Oil' is triggered when the heater has been running for a while, but the oil hasn't reached target temperature- I've had this with a working heater but with a colder thank usual water supply at higher than normal fl ow rates; but it could also be an issue with the heater. Ben Micklem ben. micklem@pharm.ox.ac.uk T u Apr 5


Common problems in order of probability: 1) open ODP heater 2) poor connection at ODP heater terminal (ceramic block located near the bottom of ODP) 3) sticky ODP relay in MS unit (power cabinet, right side, one of large relays). Watch vacuum screen on data monitor during vacuum system startup. You must hear relay clicking simulta- neously with ODP symbol highlighting shortly aſt er vac. system start, as soon as P2 reading drops below 38. (assuming room is quiet) 4) defective water safety thermostat switch on water line coil (middle of ODP) or poor connection of it. Look at connecting wires; they can be burnt if touching the bottom of ODP. Other causes are possible but unlikely. Vitaly Feingold vitalylazar@att.net Fri Apr 6


SEM:


imaging asphalt (bitumen) without cryostage A researcher would like to image asphalt/aggregate interfaces, but we have no cryostage, only a low T stage for the ESEM. Has anyone attempted this at ambient T or just below? Any advice on how to proceed? Jerry Anzalone gcanzalo@mtu.edu Fri Mar 23 We have looked at asphalt before in variable-pressure mode. We tried looking in hi-vac mode, but the chamber took hours to pump down. I think the outgassing may have been as much due to porosity as to volatility of the asphalt. However, I would want to use VP mode to keep the chamber fl ushed out. I would not want any volatile goo depositing within the chamber. We have a Quanta FEG-SEM with environmental mode. Our Peltier stage is not at all large enough to handle a slab of asphalt concrete. We simply looked at the slabs at ambient temperatures. You may fi nd that the binder smears/migrates over the aggregate. It will probably be a problem during polishing, but even if you get a good polish, you will still fi nd the oils migrating in the SEM. (A cool stage would help.) You may fi nd it necessary to keep moving to fresh areas. It would not be too noticeable at low


64


magnifi cations, but it will probably be inescapable at higher mags (several hundred times). Warren Straszheim wesaia@iastate.edu Fri Mar 23


Have you considered using an X-ray microscope? You can run scans at room temperature in air. Aya Takase aya. takase@rigaku.com Sun Mar 25


SEM: fi lament problems


We were recently examining a box of Amray SEM W fi laments and found what we think is an odd feature on some of them. T e fi lament is your basic loop or hairpin fi lament, but some have a small needle extending from one side of the wire at the apex of the point. T e needle would point down the column and has the look of purposeful manufac- turing. It's been suggested these are fi eld emission fi laments. Our Amray is NOT set up for fi eld emission. We are having trouble with fi lament driſt in use and short lifetimes, but we are reluctant to use these. I'm open to thoughts. Frank Karl frank_karl@ardl.com Wed Mar 14 A lot of years ago, Siemens manufactured for the ELMISKOP TEMs cathodes with this kind of "tip". In German, it’s called "Spitzenkathode." T eoretically, it should have some extra luminosity and may deliver—since the beam comes from a very small origin— more coherent electrons. It is known that these tips need a very good vacuum at the cathode. Otherwise, you will round the tip through ion bombardment or burn the fi lament very easily. I suppose it is kind of unstable during heating up and will shiſt a lot. In my opinion, it should be centered and mounted like a LaB 6 cathode to bring all the advantages. Lifetime had been only part of what is known from a "normal" W fi lament, maybe 10 hours or so. Stefan Diller diller@ stefan-diller.com Wed Mar 14


It sounds like those are pointed tungsten fi laments. In the days of prehistory (aka pre-FEG) to get a high brightness/coherence source people used pointed W cathodes. To get the tip of the needle hot enough to have reasonable emission, the hairpin ran very hotly with the corresponding reduction in lifetime. If I remember, cathode lifetimes of ~10 hours were common. T ey would have been used for high-resolution SEM or high-coherence TEM imaging. Henk Colijn colijn.1@osu.edu Wed Mar 14 T ere is extensive discussion of pointed fi laments in John Spence’s classic textbook: “Experimental High-resolution Electron Microscopy”, Oxford University Press, 1981 pp. 258-261. John Mardinly john.mardinly@asu.edu Wed Mar 14


EDS and XRF:


method induced differences T e story goes, there once was a fella who ran EDS on a rubber sample and found less 1% (semi quant mode). But another lab under the corporate umbrella used XRF as well as ICP and found 5%. I got my theories and hand waving, but I can't help my co-worker out. I'm open to theories. What does the collective wisdom of the microscopy community say? Frank Karl frank_karl@ardl.com Tue Mar 27 You didn't say, but I am guessing you meant they were analyzing for sulfur. I will presume so for this discussion. If you were measuring S in rubber, that would mean a lot of C in the matrix. I would really doubt the C number from semi-quant mode. C may have been dreadfully infl ated and thus would have diluted the S content. Some systems may be better than others, but I am always surprised when the C comes out even halfway close to the right amount in semi-quant mode. I would rather try to measure C(+H) by diff erence. T at would mean going somewhat beyond semi-quant mode. You would have to turn off normalization and calibrate your beam intensity to that used to collect the standards. Specify C as the element to be determined


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