![background image](http://html.mh-extra.com/html/zeiss/geminisem-series/geminisem-series_instruction-manual_927593029.webp)
ZEISS
3 Product and Functional Description | 3.2 Main Components
1
Gun with filament
2
Gun head
3
Aperture
4
Column chamber valve
5
Turbo pump
6
7
Specimen chamber
8
9
Vent valve
10
System Vacuum
The pre-vacuum pump
10
and the turbo pump
5
evacuate the specimen chamber
7
.
The vacuum in the specimen chamber is measured by a Penning gauge
8
. The detected vac-
uum values are displayed as
System vacuum
in the SmartSEM user interface. As long as the de-
tected pressure in the specimen chamber is not ready for operation, the column chamber valve
4
is closed in order to separate the specimen chamber from the column.
Gun Vacuum
In the gun head, an ultra high vacuum is maintained by ion getter pumps
6
. The vacuum in
the gun head is displayed as
Gun vacuum
in the SmartSEM software. It should be below
1 × 10⁻⁸ mbar.
Venting
The specimen is located in the evacuated specimen chamber. To open the specimen chamber for
specimen exchange, you have to break the vacuum in a controlled manner. This is done by the
Vent
command via the SmartSEM user interface or by pressing the
Exchange
push button on the
optional control panel.
When the
Vent
command is received, the column chamber valve closes and gaseous nitrogen
flows into the specimen chamber via the vent valve
9
. As soon as the pressure equilibrium is
obtained, the chamber door can be opened to change the specimen.
Vent is only possible when high voltage is off.
Evacuating
In order to continue operation, the
Pump
command makes the pre-vacuum pump and the turbo
pump evacuate the specimen chamber.
As soon as the vacuum in the specimen chamber is ready for operation, the column chamber
valve opens and the
EHT Vac ready
message is displayed in the SmartSEM user interface. Gun
Quiet Mode
The automatically controlled
Quiet Mode
is optionally available. This option allows switching off
the pre-vacuum pump after specimen exchange when the vacuum threshold is achieved.
3.2.2 Vacuum System Pressure Modes
Purpose
For operation of the microscope, the gun head, the column, and the specimen chamber have to
be evacuated. The vacuum is essential to operate the gun and to prevent collisions of electrons
with gas molecules.
With the variable pressure mode option, the microscope can be operated in different vacuum
modes:
§
High vacuum (HV) mode
§
Variable pressure modes: VP mode, Nano VP mode, and XVP mode
3.2.2.1 High Vacuum Mode
Purpose
HV mode is the standard mode of a microscope. It offers the possibility of analyzing and mapping
conducting specimens.
In HV mode, the pressure in the specimen chamber is less than 2 × 10⁻⁶ mbar.
Instruction Manual ZEISS GeminiSEM series | en-US | Rev. 2 | 349500-8138-000
29