Kalpesh

The exact answer to your question depends on a few things. Some relevant
questions are:
What sort of SEM are you using (field-emission gun or thermionic)?
Are you coating your samples?
How are the samples mounted?

For low-voltage SEM of materials, I recommend this paper:
Joy, D.S. and Joy, C.S. "Low Voltage Scanning Electron Microscopy." Micron 1996
27(3-4) 247-263.

Part of the article describes the "scan square" method which one can use to
deduce the optimum accelerating voltage to use to balance out the charge added
to the sample by the beam and the charge lost to secondary and back-scattered
electrons and to conduction.

In short, you do the following:
1. Set SEM to a fast scan rate and to a magnification of about 100x.
2. Wait for 5 s for image to stabilize.
3. Raise magnification to 1000x and wait 5 s.
4. Drop back to 100x and observe scan square.

If you see a bright scan square in a dark field, the sample is charging negative
and you should lower the accelerating voltage. If you observe the reverse, the
sample is charging positive and you'll need to raise the accelerating voltage.

There are other tips in the paper as well.

Regards,

Chris Blanford

In message <20030728182654.36701.qmail@web10009.mail.yahoo.com> General MEMS
discussion  writes:
> Dear All,
>
> Can somebody tell me the optimum electron energies for
> imaging SU8 structures in SEM?
>
> Thank you in advance,
>
> Regards,
>
> Kalpesh
>

--
Christopher F. Blanford
Inorganic Chemistry Laboratory, South Parks Road, Oxford, OX1 3QR, UK
Phone: (44)/(0)-1865-282603; Fax: (44)/(0)-1865-272690
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