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Electron Microprobe Lab, University of Minnesota
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*
Hi Eric.
I agree, and with wavelength dispersive spectrometers there is rarely any
need for more than 15kV. On the energy dispersive systems, in contrast,
there are always the elusive questions that are most easily answered by
excitation of the K-spectrum by higher acceleration voltages. Is it P or is
it Zr? Is it Mo, Pb or S?
Jens.
----- Original Message -----
From: "Eric J Essene 1" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Tuesday, August 29, 2006 12:41 PM
Subject: Re: [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
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>
>
> *
>
> 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]
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>>> Personal http://www.geology.wisc.edu/~johnf/
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>>>
>>> "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
>>
>>
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