Zeiss AURIGA Compact Crossbeam, Instruction Manual

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3.4.3. Electron optics (GEMINI
®
column)
The patented GEMINI
®
column is the area of the FESEM, where electrons are emitted, acceler-
ated, bundled, focused, and deflected. Main characteristics of the GEMINI
®
optics are the so-
called beam booster and an objective lens that consists of a combined electrostatic/electromag-
netic lens doublet.
Gun
A Schottky field emitter serves as gun ( 1 ). The filament is heated by applying the filament current.
Electrons are emitted from the heated filament while an electrical field, called extractor ( U
Ext
) volt-
age, is applied.
To suppress unwanted thermoionic emission from the shank of the Schottky field emitter, a
suppressor voltage (
U
Sup
) is applied as well.
Fig. 3.3: Schematics of the electron optics
1 Gun 5 In-lens/InlensDuo detector
2 Extractor 6 Objective lens
3 Anode 7 Scanning coils
4 Multihole aperture 8 Specimen
1
2
6
5
7
8
U
Sup U
Ext
U
B
U
EHT
3
4