The JEOL JXA-iHP200F Field Emission EPMA (Ultrahigh imaging and analytical resolution), and the JEOL JXA-iSP100 with LaB6 EPMA (Research grade microprobe) are effectively the only models of WDS electron microprobe available now (setting aside Shimadzu).
A question for EPMA labs with FEG instruments:
- What are the downsides to having a FEG? Purchase cost? Maintenance/replacement cost? Ease of switching current or voltage? Room requirements? What else?
Thanks in advance!
Andrew
First of all I would not set aside Shimadzu. Shimadzu (I got impression from its marketing material) looks are the only one, which understood and use fully the real strengths of FEG on EPMA. Shimadzu is not just "another EMPA with SEM-designed FEG tip mounted", they use larger diameter tips which addresses main issues of FEG when used on EPMA: long term and short term stability, and long life. The small and irrelevant (for EPMA) sacrifice with that is loosing FESEM-like spatial resolution, but it is still much better than CeB6, and who would need for microanalysis resolution of few nm while interaction is anyway few hundred of nm at low Kv, and much more at high acceleration voltage? Due to this absolutely inadequate (for EPMA) and bullshit marketing race toward smaller and smaller beam size and equipping EPMA with SEM-like Schottky FEG tip, that exposes the instrument to lots of vulnerabilities and instabilities. The smaller FEG tip emitting facet - the more it is sensitive to environmental temperature changes, and is more sensitive to precision and stability of power supply. Also small sized Schottky emitter is more susceptible to ring-collapse events (shortening of tip by cascade like ring-like migration of atoms from tips end to tips sides, i.e. initiated by positive temperature swing in the room just few degrees), or arching (a complete destruction of tip end by electric arc, i.e. due to malfunction of vacuum). Anyway, Shimadzu mounts specially for EPMA designed Shottky FEG tips - larger for improved stability, resilienced against unexpected bad events, and extended longevity. Probably a biggest (and crucial) downside of Shimadzu GrandEPMA for most of users here would be currently lack of ProbeSoftware support. But from technical perspective Shimadzu GrandEPMA (at least on paper) and logically looks much more properly designed machine for microanalysis than what Jeol has to offer.
I am user/operator/ and also partly a repair man of Cameca SX100 and SXFiveFE in our laboratory, so my experience could be not completely adequate to Jeol, take it with a grain of salt. As our lab is in grave financial situation, I need to do most of repairs of both machines by myself, thus have some specific view how it compares. Cameca SX100 is in lab from 1999. SXFiveFE is from 2014 (one of few first of its kind made by Cameca). IMHO SXFiveFE looks as was made to compete with Jeol FEG EPMA's and thus was probably rushed out too fast. Marketing of Cameca took the bait dropped by Jeol of this "uselessly small beam size" and lost the game. I think they lost as Cameca still cared for beam stability which is hard to achieve with FEG made for SEM. Also Cameca clearly lacked on expertise on FEG and it is not a simple drop-in replacement to W/LaB6 - the physics behind Schottky tip emission is in many cases completely counter-intuitive to someone who are familiar with how emission works on W and LaB6 (There is non-linear response between three main components of Schottky emission: temperature, electric field and ZrOx reservoir; The short-term observed direct response can reverse to opposite response in longer term, thus it is very easy to achieve very unstable emission when ignoring the big picture how the FEG works). We had complete service covered for 5 first years, and currently last three years we have no service contracts. And our FEG tip works for last 4 years within +/- 0.5% emission stability. Running FEG on very tight budget force us to identify and address risks, which we could just ignore if being on service contract.
1)
Vacuum. Should be all time operational. Big UPS is a must. The maintenance of pumps is a mixed bag. For roughing pump we moved to Edwards Dry Scroll pump (Cameca FE- EPMA has only single) and shortened the pipe from plastic DN40 12m to 4m DN25 metal vacuum pipe: Edwards pump works without any maintenance for 2 years and can be maintained at place. Every two years we need to maintain it and I find costs of that similar to 2 oil pump (also Edwards) maintanence on our SX100. Ion pumps... while it was on Cameca service contracts the 2ndary ion pump was replaced already twice. For last 4 years while run by me without service contracts it was baked only once at FEG tip installation (nearly 4 years ago) and we had evaded any issues so long. The main issue I identified for 2ndary ion pump is argon poisoning, and contamination by overheated FEG tip. I have my own procedure to deargonize every one year (takes a one day downtime). If EPMA would be equipped with noble diode Ion pump (as 2ndary) or StarCell type this would be not an issue at all. Through lengthy observations and experience I came to conclusion that software and Vendor imposed threshold values after sample exchange is extremely very lax. Thus to protect the 2ndary ion pump from premature argon poisoning we use self-imposed much stricter threshold values, when it is safe to open the column to chamber and that is 5E-5Pa. For two standard thin sections (plus 1 or 2 metal one-inch standard sets) the time for vacuum reaching that threshold is comparable to that on SX100 to reach safe vacuum there (1-3Pa?). However, mounting two DIY epoxy-sustained one-inch sample sets would need about 15 minutes pumping time, 3 - more than one hour, and 6 more than a day, in case there would be additional degassing by samples - simply that would be unachievable. Same is with large (i.e. 3x3x1cm) polished rock slabs, where porosity would slowly degas the air (and thus 1% of Ar) into chamber vacuum - in many cases reaching the safe threshold of 5e-5 Pa in chamber would need whole day or would be unachievable. So in these cases our SX100 have a clear advantage vs SXFiveFE. However, if we would be covered with a service contract, there they would replace the 2ndary ion pump and FEG tip anyway every one-two year, we would not limit our-self so strictly with what we load.
2) Room requirements. First of all stability of room temperature can impact WDS spectrometers (position and counting, PHA shifts...), thus despite the cathode type You want to have T and humidity in the room as stable as possible. However FEG can be damaged with temperature positive swing just of few degrees if its working temperature is set just at 1800K (the case for majority of vendors) and extraction field is just just covering the tips surface stability. Prolonged exposure to numerous small swings can bring the tip into progressing ring-collapses. AC failure in conjunction with hot weather (and fast rise of temperature in room by 10 or more degrees) can shorten time for such collapse to only few hours. I don't know if Jeol instruments are prevented from that. I have made such DIY monitoring and prevention for our Cameca FEG instrument.
3) We also have 2 Zeiss FESEMs. Countless times we see that tip replacement can go wrong (in the end Cameca replacement proofed to be a top notch, compared how it is replaced on Zeiss...), and there can be new issues generated during replacement. i.e. Baking can loosen up some metal o-rings. It is not something so simple as tungsten replacement. Also You can't have just spare tip on the shelf as we normally have with tungsten tip. If it fails terribly (i.e. arching) there will be downtime for manufacturing and being sent to the lab - easily two weeks, then replacement and baking another week. It is not like "oh, the W tip had burnt at the night, I am going to replace tip in a few minutes, and in few hours I am ready to continue analyses".
When repairing and troubleshooting on your own:
4) Troubleshooting and fixing hardware/spectrometer issues can be hindered by need of switching off the FEG. FEG generally should be not switched off. A) It takes time to stabilize after switching it back on; B) In case of worn out Gun-column-chamber separation valve, venting chamber will decrease the vacuum by the gun, That requires switching gun off, and if valve is badly worn - requires re-baking of ion pumps after. (the stupid situation we are currently in :/ our 1st spectrometer does not work, and our valve is worn out, and I have no way to inspect and troubleshoot the spectrometer until valve issue is not solved. C) After venting the chamber getting the beam from gun You need much better vacuum in the chamber than on SX100, can take half a day.
As for density of FEG beam, You still can defocus beam, thus I don't see that as a problem.
Generally, I don't regeret that we have FEG EPMA - it has more advantages than disadvantages.
Nearly 4 year old tip still gives us ~1000 nA beam with stability within +/-0.5% of set value without beam regulation (a few weeks ago weekend stability test for 72 hours had shown stability within +/-0.5%). It required a lot of studying of workings of Schottky emission to achieve that. Clearly W SX100 has +/-0.05% stability with regulated beam. But as Anneta told, I also don't see obvious disadvantage in stability. Contrary, the long-term stability is so good that I can without worries set automated analyses for week in advance and if FEG is stable and apertures are not contaminated there will be no beam drift more than 1µm.
Please keep your software updated for best results!