PROBEUSERS Archives

August 2006

PROBEUSERS@LISTS.UMN.EDU

Options: Use Monospaced Font
Show HTML 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:
Eric J Essene 1 <[log in to unmask]>
Reply To:
JEOL-Focused Probe Users List <[log in to unmask]>
Date:
Tue, 29 Aug 2006 07:41:10 -0400
Content-Type:
text/plain
Parts/Attachments:
text/plain (162 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



*

Jens,
     15 kV suffices to excite characteristic X-rays for all 92  
elements (and beyond) by using L and M lines, of course.  The only  
problem is that the intensity of these lines is not as good as they  
should be without using higher current and/or voltage.
eric


On Aug 29, 2006, at 4:32 AM, Jens C. Andersen 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 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