PROBEUSERS Archives

August 2006

PROBEUSERS@LISTS.UMN.EDU

Options: Use Proportional Font
Show Text Part by Default
Show All Mail Headers

Message: [<< First] [< Prev] [Next >] [Last >>]
Topic: [<< First] [< Prev] [Next >] [Last >>]
Author: [<< First] [< Prev] [Next >] [Last >>]

Print Reply
Subject:
From:
"Jens C. Andersen" <[log in to unmask]>
Reply To:
JEOL-Focused Probe Users List <[log in to unmask]>
Date:
Tue, 29 Aug 2006 09:32:06 +0100
Content-Type:
text/plain
Parts/Attachments:
text/plain (129 lines)
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 John.

Here we have a setup with a JEOL 8200 electron microprobe and a JEOL 5400 
low-vacuum SEM. We generally try to balance our preferred acceleration 
voltage to where we get maximum benefit of the increased x-ray intensity and 
the high energy end of the x-ray spectrum without having to correct for too 
much "overvoltage" in the matrix correction procedures.

On the microprobe we work with 15kV on most materials. On rare occations, we 
use 20 or 25 kV for special applications, where the excitation of a specific 
high energy line is essential. On the low-vacuum SEM we have too many 
variables to do fully quantitative work (notably working distance, beam 
current, air pressure, coating thickness, specimen surface roughness and 
orientation). We don't have a beam current detector and our software does 
not allow us to specify any other parameters than the kV for the matrix 
correction. To do fully quantitative work, you will need to work on a 
polished surface, and need some way of measuring the beam current, and need 
to fix the working distance, coating thickness, and air pressure.

Despite the shortcomings of our SEM, our system works pretty well in a 
semiquantitative mode at a fixed kV for a measured set of standards, 
provided that the results are normalised to 100%. We have observed no 
systematic variations with changing pressure, beam current, coating 
thickness, or working distance for elements from sodium and heavier using 
this method, and our precision on a 100s live count time is good enough for 
student work and exploratory analysis of materials that cannot be prepared 
for the electron microprobe (mineral coatings, soil grains, archaeological 
specimens, paint fragments etc.). I would be cautious with fluorine on the 
low-vacuum setting. For analysis on the SEM we work at 20kV, which excites 
the K-spectrum up until around Zr. There appears to be little benefit in a 
further increase to 25kV.

I hope this helps.

Jens

Jens C. Andersen
Camborne School of Mines
School of Geography, Archaeology, and Earth Resources
University of Exeter
Cornwall Campus
Penryn, Cornwall
TR10 9EZ
United Kingdom
Tel. +44 (0)1326 371 836
Fax. +44 (0)1326 371 859

http://www.exeter.ac.uk/cornwall/csm

Visit the virtual Skaergaard intrusion at http://www.skaergaard.org

----- Original Message ----- 
From: "John Fournelle" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Tuesday, August 22, 2006 7:53 PM
Subject: [PROBE-USERS] EBSD question: what kev is good?


> 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
>
>
>
> *
>
> We have acquired a nice new SEM (W filament, variable pressure Hitachi 
> S3400) whose function principally is quality CL imaging (Gatan PanaCL/F), 
> and EBSD (HKL) work.
>
> We have a question for labs out there with more EBSD experience under 
> their belts than we do: have you determined an optimal keV setting, for 
> any/all of your work? (we are doing geological work)
>
> It seems to me that you don't want to go to higher keV than necessary as 
> the scattering will increase (though the effective backscattered, oops 
> forescattered electron signals that are relevant may only be those from 
> the first events near the surface, suggested by Prior [1999]) and the 
> spatial resolution will decrease (though I am not convinced about this) --  
> or does going to high keV improve the signal generated on the phosphor 
> screen and thus improve the Kukchi line discrimination?  Clearly having 
> significant counts (=high enough current) is probably the most important 
> factor, but given that is not a problem, would say 30 keV yield better 
> results vs 15 keV?
>
> thanks.
>
> John
> -- 
> ========================================================
> John Fournelle, Ph.D.        office: (608) 262-7964   cell: (608) 438-7480
> Cameron Electron Microprobe Lab   lab: (608) 265-4798
> Dept of Geology & Geophysics      fax: (608) 262-0693
> University of Wisconsin          home: (608) 274-2245
> 1215 West Dayton St.            email: [log in to unmask]
> Madison, WI 53706 amateur radio: WA3BTA
>      Personal    http://www.geology.wisc.edu/~johnf/
>      Probe lab   http://www.geology.wisc.edu/~johnf/sx51.html
> Probe Sign Up Calender: 
> http://www.microscopy.wisc.edu/cgi-bin/calendar/microprobe/calendar.cgi
>
> "The first rule of all intelligent tinkering is to save every cog and 
> wheel." --  Aldo Leopold
>
> "For a successful technology, reality must take precedence over public 
> relations, for Nature cannot be fooled."    --   Richard P. Feynman 

ATOM RSS1 RSS2