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June 2011

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Subject:
From:
William J Mushock <[log in to unmask]>
Reply To:
JEOL-Focused Probe Users List <[log in to unmask]>
Date:
Tue, 14 Jun 2011 21:38:44 -0400
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*

Jim,

The good news is, it sounds like you do have a beam. Are you sure it's not
just your gun shift alignment?  If the gun shift is way out of alignment you
could get a beam at higher CL settings while losing the beam at lower CL
settings. In 20+ years of servicing JEOL Microprobes I've never seen column
charging so bad that I lost the beam as a result. Normally the protection
glass just makes the beam dance around. And, the liner tube most definitely
has to be grounded.

Do you have a beam stabilizer? Make sure you have it turned off when trying
to find the beam. Unfortunately if you fiddled with the aperture and didn't
get it back to exactly where it was, I'm afraid you just made the job of
finding the beam exponentially harder.

If the aperture is out of alignment, you may not get any current on
the Faraday cup because it is below the aperture. However, if you have a
beam stabilizer you can use your OL aperture as a faraday cup by switching
the Align/Stabilize switch on the beam stabilizer to Stabilize and
maxamizing the beam current on the beam stabilizer meter with the gun tilt
and shift controls so the current goes up on the meter with lower CL
settings. Next, you can fiddle with the aperture to get current to the cup
and ultimately to the sample. This technique also eliminates every thing
below the aperture as far as any possible charging issues.

Good Luck,
Bill


On Mon, Jun 13, 2011 at 7:19 PM, Jim Renaud
<[log in to unmask]>wrote:

> 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
>
>  *
>  Hi Everyone,
>
>     I am running a JEOL 733 and have run into some difficulties.  Last
> tuesday I did a sample exchange before closing the office up for the night.
> A couple of hours later I realized that there was no current on the cup, so
> I figured it was time for a filament change.  I inspected the old filament
> and realized it had not blown at all.  I installed a new filament and pumped
> the probe down.  The probe pumped down, 15KV was achieved.  Normally when I
> have run the probe, the coarse gain knob on the condenser lens has been on
> step 3 or 4,  but now no cup current or absorbed current are achieved at
> this setting.  I adjusted the aperature with no significant change.  I
> cycled through the coarse gain knob of the condenser lens (on the Electron
> Optical System (EOS)) from 1-7 and at step 8 (one step above 7 on the knob
> but not labelled),  I obtained picoamps of current on the cup.  At one
> point, i did achieve 12 nano-amps at the step 7 setting, but that
> disappeared.  Since I was not able to  get any current on any of the other
> steps while cycling through the condenser knob, I figured there was a
> problem with the condenser lens.  I swapped the EOS module, the ML cooling
> Box at the bottom of the console, the actual condenser lens, and the
> accelerating voltage module (thank goodness for spare parts), however, no
> change in the current, and again, I could only get picoamps of current on
> step 7 or 8.  We have checked voltages down at the ML cooling box, and at
> various other locations and they seem to coincide with the JEOL circuit
> diagrams.  We then decided to investigate the brass/copper tube liners which
> run the center of the column, cleaned them and re-installed them (are these
> column tube liners supposed to be grounded?).  Again no change in the
> current on the cup nor on the sample and only picoamps achieved at step 8 on
> the condenser lens.  I am running out of things to try.  Some other
> possibilities I am considering is the potential of charging somewhere in the
> column; perhaps the leaded OM glass has become charged?  Any thoughts,
> suggestions, or things to try would be much appreciated.
>
> Thanks,
>
> Jim.
>
>


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