JEOL Probe Users Listserver
Moderator: Ellery Frahm, [log in to unmask],
Electron Microprobe Lab, University of Minnesota
Post a message: send your message to [log in to unmask]
Unsubscribe: send "SIGNOFF PROBEUSERS" to [log in to unmask]
On-line help and FAQ: http://probelab.geo.umn.edu/listserver.html
*
Hello Ellery,
We have the LaB6 option. Yes, it needs an ion pump at the top of the
column. The required electronics are already buiilt into the 8200; I
don't know about the 8900. Our 8200 came with the LaB6 option and
diffusion pumps, so I assume that is the default configuration. We
replaced the DPs by a turbo in the field; it's what JEOL does when you
order turbo.
We have tested both LaB6 and W, and "amazing" isn't the word I
would use. The main improvement comes at low voltages, which would be a
bonus for us, since we are often analyzing boron, but see
below...
I would say at 15 or 20kV the difference is only noticeable if you really
push the resolution way beyond what a microprobe needs. You get a few
100nm with W as it is, which lets you see a heck of a lot more than you
can analyze. At 10kV and >30nA there is a distinct advantage to
LaB6.
At 9/27/2007 12:42 PM, you wrote:
I am also curious if anyone is
currently running or has recently run
a LaB6-outfitted machine. Are the concerns about beam
stability
valid, or is the issue overblown?
I have a plot (if I can find it) that illustrates the point. We saw
current excursions in the percent-range at a time scale shorter than
between the cup measurement and the analysis, which would kill any effort
at serious analysis. I think these can probably be got rid of (at least
to some extent) with conditioning and careful pampering of the filament.
You can switch back to W, but then the LaB6 goes into a desiccator, and
according to people who have lots of experience with this (we also have a
LaB6-based TEM) it becomes useless pretty quickly if is not under
vacuum.
Alignment and saturation are also more finicky with a LaB6. A while ago I
circulated a question to other users and got two replies from people with
LaB6 options on microprobes. Neither one is using it. I will dig their
e-mails out for you.
In summary, I would say that the improvement isn't worth the pain unless
you are (a) very often running samples that need high spatial resolution
AND low accelerating voltage, and (b) you are prepared to put up with
LaB6 operation permanently.
Let me know off-list if you want to exchange more thoughts,
Alfred
Alfred Kracher
Ames Laboratory (USDOE)
Iowa State University
227 Wilhelm Hall
Ames, IA 50011-3020
Tel.: 515 294 7097