3 Product and Functional Description | 3.2 Main Components
ZEISS
3.2.4 Electron Optical Column | Gemini 2
Purpose
The Gemini 2 column is the part of the microscope, where electrons are emitted, accelerated, de-
flected, focused, and scanned. Main characteristics of the Gemini optics are the beam booster
and an objective lens that consists of a combined electrostatic/electromagnetic lens doublet.
U
Sup
U
Ext
U
EHT
U
B
1
2
3
4
5
6
7
8
9
10
11
Fig. 15: Schematics of the electron optics
1
Gun
2
Extractor
Positive electrode that extracts elec-
trons from the filament.
3
Anode aperture
4
Upper condenser
5
Single hole aperture
6
Lower condenser
7
8
InLens SE detector
9
Objective lens
Focuses the electron beam on to the
specimen surface.
10
Scanning coils
Deflect the beam across the specimen
surface in what is usually referred to as
a raster scan.
11
Specimen
Sup
Suppressor voltage
Ext
Extractor voltage
Acceleration voltage
B
Liner tube voltage
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
) is applied as well.
EHT
The emitted electrons are accelerated by the acceleration voltage (U
EHT
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 re-
duces the sensitivity of the electron beam to magnetic stray fields and minimizes the beam broad-
ening.
36
Instruction Manual ZEISS GeminiSEM series | en-US | Rev. 2 | 349500-8138-000