Zeiss Crossbeam 550, Инструкция по эксплуатации

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3 Product and Functional Description | 3.2 Main Components ZEISS
Operating
Principle
Gun
A Schottky field emitter serves as gun
1
. The filament is heated by applying the filament cur-
rent. Electrons are emitted from the heated filament while an electrical field, called extractor volt-
age (U
Ext
), is applied. To suppress unwanted thermionic emission from the shank of the Schottky
field emitter, a suppressor voltage (U
Sup
) is applied as well.
EHT
The emitted electrons are accelerated by the acceleration voltage (U
EHT
). The beam booster (U
B
,
booster voltage), which is always at a high potential if the acceleration voltage is 20 kV or less, is
integrated directly after the anode. This guarantees that the energy of the electrons in the entire
beam path is always much higher than the set acceleration voltage. This considerably reduces the
sensitivity of the electron beam to magnetic stray fields and minimizes the beam broadening.
Apertures
The electron beam passes through the anode aperture
3
first, afterwards through a single
hole aperture
5
.
The anode aperture defines the maximum possible probe current.
For the Gemini II column, two different column configurations are available:
§
40 nA high resolution configuration
Anode aperture diameter Probe current Typical application
55 μm* 10 pA to 40 nA High resolution
§
100 nA high current configuration
Anode aperture diameter Probe current Typical application
90 μm* 10 pA to 100 nA Combined high resolution
and analytical investigations
Condenser
A double condenser system allows the continuous regulation of the probe current. The upper
condenser
4
is used to continuously adjust the probe current. The lower condenser
6
is
used for aperture matching of the objective lens in order to guarantee optimum resolution at
each probe current and EHT setting.
Stigmator
The stigmator is located inside the condenser and compensates for astigmatism so that the elec-
tron beam becomes rotationally symmetrical.
Deflection System
The electron beam is focused by the objective lens
9
onto the specimen
11
while being de-
flected in a point-by-point scan over the specimen surface by the scanning coils.
Before the electron beam exits the objective lens, the electrostatic lens creates an opposing field
which reduces the potential of the electrons by +8 kV. The energy of the electrons reaching the
specimen surface therefore corresponds to the set acceleration voltage (EHT).
Signal Detection
When the primary electron beam hits the specimen, certain interaction products are released,
which can be recorded by specific detectors, e.g. the InLens SE detector
8
. For more informa-
tion see Principle of Signal Detection [
}
37] .
32 Instruction Manual ZEISS Crossbeam 550L, Crossbeam 550 | en-US | Rev. 3 | 349500-8122-000