ZEISS
3 Product and Functional Description | 3.3 Optional Components and Accessories
3.3 Optional Components and Accessories
3.3.1 Optional Detectors
3.3.1.1 VPSE Detector
Purpose
Since the InLens SE detector and the SE detector are both designed for the use in HV mode, SEs
cannot be detected in VP mode with these detectors. Therefore the Variable Pressure Secondary
Electron (VPSE) detector has been developed for SE detection in VP 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. 18: Schematics of the
VPSE
detector
1
Preamplifier
2
Photomultiplier
3
Objective lens
4
Light guide with collector electrode
5
Specimen
Operating
Principle
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 Crossbeam 350 | en-US | Rev. 3 | 349500-8111-000
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