2.1 Overview
11
beam current at the specimen surface. The holder is provided with a
base to match the users SEM stub mount.
Figure 4
Universal Sample
Holder.
Figure 5
Principle of the Faraday
Cup.
e
-
Picoammeter
Electrons entering the Faraday
cup strike the internal surface.
Some are absorbed; some will
cause secondary emission. The
secondary emission electrons
will be absorbed when they do
not have sufficient energy to
cause further secondary emission
events.
The cup is sufficiently deep to
prevent lose of electrons from
the small aperture.
A Picoammeter measures the
absorbed current.
2.1.7 Picoammeter
Either a portable battery powered meter, or a high end Keithley meter
can be supplied. A BNC cable is provided to connect to the SEM
absorbed current output on the stage. If a Keithley has been supplied,
then a GPIB interface board may also be present in the PC. The GPIB
board is an option.
Sample clamp
Faraday Cup
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