Moderator: Ellery Frahm, [log in to unmask], Electron Microprobe Lab, University of Minnesota
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*
Hi,
I would like to know if anybody with a
microprobe, especially a
thanks
Clarissa Wisner
SEM Specialist
G6 MRC
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573-341-4393
'Life isn't about how to survive the storm,
But how to dance in the rain.'
From:
Sent: Friday, May 22, 2009 2:46 AM
To:
Subject: Re: [PROBE-USERS]
Hi Everybody,
Thankyou for your kind help. To quickly address a few
issues.
Spectrometer Odometer - we don't have them. Sorry this is an
8800 EPMA, I was answering Ritchie's question about the 733 (which some how did
not make it through) when I thought out loud about my old 8800.
Beam Position and charging in OL pole piece - good point, I
have seen this before in other machines, but I do not see any sign of it now.
Image is stable even under high beam currents, and the optical image of my spot
on a fluorescence specimen does not jump about or shift.
WDS belt linearity/tension/length - we have a very
experienced factory engineer and this is always checked with belt replacement,
plus the new probe with the same engineer is doing great. Also, I have used
unadjusted belts before and they do not give me this degree of trouble.
Backlash issues - Both probes old and new use the same
software and same backlash correction, only the old probe gives trouble, plus
the old probe worked fine with this backlash correction when new. Also, when I
did my reproducibility tests I tried starting numerous times from above the
peak and below the peak, no real difference. Having said that, maybe it would
be a good idea to increase this backlash correction on the older machine,
thanks!
I've also tried these various tests with open slits and
closed slits, again no real improvement.
Thanks again for all your help.
Best Regards,
Ron
From:
Sent: Thu 21/05/2009 23:24
To:
Subject: Re: [PROBE-USERS]
Moderator:
Ellery Frahm, [log in to unmask], Electron Microprobe Lab,
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* Ron,
First, your software should be setup so the spectrometer approaches the peak
from the same direction
to avoid backlash issues.
There is a spectrometer adjustment that has a large impact on reproducibility
called the belt linearity adjust. This usually is not a problem unless the
stainless steel belt on the spectrometer has been replaced. I know some service
guys will avoid doing it because it is a little tricky and very time consuming.
When the adjustment is out it is most difficult to reproduce at the higher L
values (>170mm).
You can do a quick check of the belt linearity by defocusing your sample and
re-peaking the spectrometer (at a high spectrometer L-value). First, defocus
the optical image (Z) at +/-20um intervals and re-peak the spectrometer. If the
count rate goes up and is considerably higher with the sample defocused vs
focused, you have a belt linearity problem. The specification is to have
maximum count rate within 40um of sample focus. If you plot this over the
range of the spectrometer it can also tell you if your baseplate and crystal
tilt are aligned correctly as well. Note: this check and/or adjustment should
be done with at least the 500um slit in place.
Bill
On Thu, May 21, 2009 at 8:19 AM, Ellery Frahm <[log in to unmask]> wrote:
Moderator: Ellery Frahm, [log in to unmask],
Electron Microprobe Lab,
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*
Hi Ron,
What about the beam position on the sample? Is that stable? If, for
example, there is charging in the objective lens pole piece or somewhere else
in the column, the beam could wonder a lot across the sample, constantly
changing the Bragg angles (and therefore L values) and affecting all the
spectrometers.
Best,
Ellery
On May 20, 2009, at 11:49 PM, Ron Rasch wrote:
Hi Ellery,
Yes all good questions. To go into more detail:
This probe has seen a lot of work, 15 years of 24 hrs a day, 7 days week,
excluding down time etc.
Doing a peak search during Qnt analysis, does not help anymore, but it use to
when it started "going off". For most of the probe's life I only did
a peak search during Standard analysis.
All four WDS spectrometers are giving bad results but to a greater or lesser
extent.
My FCS is probably the best and my H type is probably the worst.
The beam current looks very stable.
The standards are good and have been tested in my new probe. Plus they were
good at the start (15 years ago).
There seems to be no strong connection between L value and reproducibility,
some days the high values some days the low, but mostly the low L_values are
better.
I've had the factory check the base plate, align the crystal tilt and do the
SCA conditions, twice.
I do not believe it's the x-ray detectors (see below), but just in case I've
replaced one Xe detector and the window for one GPC, no great improvement.
My usual test (apart from just doing a typical analysis) is to do a peak search
on a standard, then take a 10 second count three times, then move off the peak
then repeat.
On any given peak search, the three count rates are quite consistent with each
other, just not consistent with the count rates after the next peak search. Two
very close peak positions may not yield similar count rates.
Next on my list is to try swapping a stepper motor and gear box with my new
probe, but I'm also looking for any other ideas or things to check.
Cheers,
Ron
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