Observation ON/OFF for sample change and use of filament standby

[KerstinGruender]

Hi fellow probe people,

we have a JEOL JXA-8230 (W filament) and existing user instructions are to turn Observation OFF every time for a sample change, plus OFF at the end of the day if it isn't running overnight (then back on next morning). I've been wondering whether that's good for the filament, and whether it'd could affect things like alignment, if you're doing that all the time? Or is it worse to have it on during sample change that results in vacuum fluctuations? In the lab where I did my undergrad we virtually never touched the Observation button (JXA-8200, also W filament). The JEOL user manual says it 'can' stay on during sample change. Nothing definitive.

I've recently taken over lab management for our JXA-8230 and would like to get to the bottom of it as to what we should be doing - i.e. ON or OFF for sample changes?

Also, what do you all do at the end of the day, or over the weekend - Observation OFF, and back ON the next day, (e.g., without first changing the probe current/or reducing the probe current down before doing it?), or would it be better to regularly use the filament standby function (i.e. set filament to 90 or 80), and then resaturate the next day? We used to do this in my undergrad-lab, noting the saturation code on a whiteboard. Different people I have spoken to here that have used EPMAs at different universities seem to all do it slightly differently (mostly different EPMA make/models too though).

I'd like to do the 'right' thing, making sure I do what's best for the filament (maybe it would last longer than what it currently does - 800-1000 hrs?)?

Any insights?

Cheers,
Kerstin

[Anette von der Handt]

Hi Kerstin,

The observation On/Off button just opens and closes the electron gun chamber isolation valve (V1). Closing it (Turning it "Off") protects the filament from a degraded vacuum during sample change. The recommendation to also leave it on "Off" at the end of the day is just further protective measure in case of sudden vacuum loss while being unattended (from some failure, power outage).

It does not change anything in terms of filament saturation or gun alignment. I would always turn observation off during sample change. On my iHP-200F it is not even an option to keep it on.

Your actions at the end of the day are ultimately your decision. I typically would turn off the observation mode if it is idle, but I would not be overly concerned if I forgot. I've noticed that the newer JEOL probes are designed to quickly close the gun valve in the event of a problem, but keeping it off routinely does provide an additional layer of protection.

For the end of a day, it is best to determine what works for your specific situation. Personally, I did not utilize the standby mode but frequently monitored the filament saturation. I felt that frequently adjusting the filament was not beneficial, and I was able to achieve up to six months of use from a single filament. However, if you do not have the time or desire to closely monitor it, or if it is impossible over an extended break, following the standby recommendation in general might be preferable. Some other may find that they achieve better results using standby mode, and JEOL is knowledgeable regarding their electron guns, so their default recommendations tend to be reliable.
In my experience, the vacuum quality is most relevant for filament lifetime followed by your choice of saturation point, how to seat the filament etc.

Good luck with your new lab!

[KerstinGruender]

Thank you, Anette! 

Makes sense that vacuum fluctuations will be worse for the filament life. I'm not really fond of changing the filament more frequently than I'd need to Six months is pretty good!
I wonder if it may also depend on how good your vacucum is to start with/how much it will fluctuate. Perhaps this is why diffeent people who have worked on different probes/labs remember different things. I'll quiz the JEOL engineer about it too, next time they come.
I'll continue to turn observation off/on for now and will see what works best for us with the saturation. Our probe is running almost 24/7 anyway, so not much time to even think about standby.

How, and how often, did you monitor the filament saturation? Run an auto saturation to see whether the code has changed - like every week, or more/less frequently?

Cheers,
Kerstin

[KerstinGruender]

Hi, replying to myself and Anette - I had a look at what happens to the valves, and if I leave observation on and vent the exchange chamber, the beam 'retreats' into the top part of the column and a valve closes, but the beam itself stays on. This valve automatically re-opens during evac after the sample change. Not sure at what stage it is triggered and why, maybe related to the vacuum. Turning observation off turns the beam totally off (no more beam in the sketch in the observatioon tab). So may be a different setup to what you're referring to, Anette, and potentially the beam is protected automatically. In any case, I'm continuously learning about the instrument. Something new every week
Kerstin

[sem-geologist]

Reading all that confusing terminology invented by JEOL, I can't help, but it reminds me knights who no more says "Ni" but "ekki ekki ekki ekki ptang zoom boing z'nourwringmm" from Monty Python's Holy Grail  .  Why not use terminology of EHT (electron High tension), Isolation Valve, Heat Current, which are as clear as it can get clear.