3 Product and Functional Description | 3.2 Main Components
ZEISS
Condenser
4
is used for aperture matching of the objective lens in order to guarantee op-
timum resolution at each probe current and EHT setting.
Together with the multihole aperture, the condenser allows to regulate the probe current.
Stigmator
The stigmator is located inside the condenser and compensates for astigmatism so that the elec-
tron beam becomes rotationally symmetrical.
Objective Lens and
Deflection System
The objective lens
7
focuses the electron beam onto the specimen
9
. The objective lens
consists of an electromagnetic lens and an electrostatic lens, which reduce spherical and chro-
matic aberrations, especially at low acceleration voltages. The electromagnetic lens is water
cooled.
The deflection system consists of a set of scan coils
8
that move the electron beam in a point-
to-point scan across the specimen. The scan coils deflect the beam in the X and Y directions rela-
tive to the electron-optical axis.
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
6
. For more informa-
tion refer to
Principle of Signal Detection [
3.2.4 Gun Modes
The microscope can operate in different gun modes:
§
Imaging
§
Analytic
Imaging Gun Mode
In Imaging gun mode, the temperature of the Schottky emitter and the extraction voltage are re-
duced in comparison to the Analytic gun mode. This leads to a reduction of the energy spread of
the primary electrons.
Imaging gun mode is suitable for lower probe currents. Imaging gun mode is especially useful at
low kV to reduce chromatic aberration and to achieve a better resolution.
Analytic Gun Mode
Analytic gun mode is suitable for higher probe currents. Overall, the probe current in Analytic gun
mode is about twice the probe current in Normal gun mode.
3.2.5 Detectors
This chapter describes the generation of secondary and backscattered electrons, and describes
how the detector types, that are available for use with the microscope, use these electrons to pro-
vide imaging, topographical, and other information. It also lists some characteristics of each de-
tector type.
For more information about any of the detectors, contact your local ZEISS service representative.
3.2.5.1 Principle of Signal Detection
When a primary electron (PE) beam hits a specimen, certain electron beam interaction processes
occur. The interaction products most frequently used for the generation of images in scanning
electron microscopy are secondary electrons (SEs) and backscattered electrons (BSEs).
Specific types of detectors are able to detect the SEs and BSEs. The detector signals can be used
to create images and produce information about the properties of the specimen.
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Instruction Manual ZEISS SIGMA series | en-US | Rev. 7 | 352102-9344-006