ZEISS
3 Product and Functional Description | 3.3 Optional Components and Accessories
3.3.1.2 VPSE Detector
Purpose
The Variable Pressure Secondary Electron (VPSE) detector is a specific type of SE detector for use
in Variable Pressure mode where a standard SE detector cannot be used. The VPSE detector is not
usable and will not operate in HV mode.
The Variable Pressure mode enables analyzing and imaging of non-conducting specimens without
charging artefacts. This is possible, because positively ionized gas molecules stabilize local charg-
ing. Variable Pressure mode can also be used for strongly gassing or moist specimens without any
need for specimen preparation.
Position
The VPSE detector is attached to the MP-Port 1.
1
2
3
4
5
Fig. 24: Schematics of the
detector
1
Preamplifier
2
Photomultiplier
3
Objective lens
4
Light guide with collector electrode
5
Specimen
Function
The collector electrode mounted on the light guide
4
is held on a positive potential forming a
collecting field for SEs. Thus, SEs move towards the detector. In VP mode gas molecules are
present in the specimen chamber. The accelerated SEs excite gas molecules, which emit a photon
when they de-excite to the ground state. Although BSEs also cause collisions, their contribution is
less than 1 % because of the lower ionizing cross section.
The emitted photons are detected by the rod-like light guide pointing at the specimen. The photo-
multiplier
2
amplifies the light signal and converts it into an electron current. The degree of
amplification is depending on the photomultiplier voltage, which regulates the contrast. The
preamplifier
1
amplifies the signal and regulates the brightness.
Instruction Manual ZEISS GeminiSEM series | en-US | Rev. 2 | 349500-8138-000
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