Carbon coating objects for SEM/EDS

Suzanne Davis <davissl [at] umich__edu> writes

>The geologists usually coat their samples for SEM with carbon. As I
>understand it, this helps prevent stray X-rays from nearby areas
>from interfering with analysis of the particular spot you wish to
>analyze. We are placing the entire seal (they are quite small) in
>the SEM chamber and our analyses would be more reliable if we could
>coat the seals themselves with the carbon. Does anyone have
>experience doing this?
>...
>... We coated a glass slide this way, and I find that the
>graphite is very easy to remove with ethanol:de-ionized water in a
>1:1 ratio. I feel fairly confident that the coating can be applied
>and removed without difficulty, but I would be interested to hear
>from the conservation-science community any opinions/experiences in
>using a coating on small objects for SEM.

There is another option. There are Environmental Scanning Electron
Microscopes (ESEM) and Variable Pressure Scanning Electron
Microscopes (VPSEM) which do not require the conductive surface as
conventional SEM does, so you don't have to carbon coat. You could
contact an electron microscopy unit of a nearby university for
advice. An interesting part of your post is this comment "this helps
prevent stray X-rays from nearby areas from interfering with
analysis of the particular spot you wish to analyze". As far as I am
aware stray x-rays are not an issue for conventional SEM (the
coating is purely for conduction of surface charge), although it is
an issue in ESEM and VPSEM but it can be minimised.

Rachel White
PhD student
University of Technology, Sydney


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                  Conservation DistList Instance 17:54
               Distributed: Wednesday, February 18, 2004
                       Message Id: cdl-17-54-005
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