[3dem] Current measurement with viewing screen

[Bob Grassucci]

Hi Fred,
We have been using a BS factor of 0.85at 200 kV and 0.75 for 300 kV.  It 
can be set so that it is used in low dose  if you are comfortable 
editing the registry.by the following settings.
regedt32
Hkeylocalmachine
     software
         FEI
             Lowdose
                 BS factor    200 0.85
                                     300 0.75
After you do this the low dose options tab should have the correct dose 
readings,  I am told that this is routinely done with the newer scopes 
but was not early on.  Of course a faraday cup is the most accurate way 
to go but not everyone has access to one.  I hope this helps.
Bob


On 11/9/2010 12:01 PM, Fred Sigworth wrote:
> To calibrate our CCD camera we have been using the viewing screen to measure the beam current in our Tecnai F20.  Of course this measurement is in error due to backscattering, secondary electrons, etc. and the right way is to use a Faraday cup.  But, has anyone compared the value from a Faraday cup with the screen current?  If the conversion factor is known, even approximately, that would help us a lot.
>
> Fred Sigworth
>
> Fred J. Sigworth
> Department of Cellular and Molecular Physiology
> Department of Biomedical Engineering
> Yale University
> New Haven, CT  06520
> tel.  203 785 5773
> fax 203 785 4951
> fred.sigworth at yale.edu
>
>
>
> _______________________________________________
> 3dem mailing list
> 3dem at ncmir.ucsd.edu
> https://mail.ncmir.ucsd.edu/mailman/listinfo/3dem
>
>


-- 
*********************************
Howard Hughes Medical Institute
Columbia University Medical Center
Black Building Room 2-221
650 West 168th Street
New York, NY 10032-3702
rg2502 at columbia.edu
Phone: 212-305-9520
Fax: 212-305-9500