Zeiss EVO Скачать руководство пользователя страница 23

Страница: 23 / 180

ZEISS

3 Product and Functional Description | 3.1 Vacuum System

Gun Vacuum

In the gun head, a high vacuum is maintained by an ion getter pump. The vacuum in the gun
head is displayed as

Gun vacuum

in the SmartSEM user interface. It should be below

5 × 10⁻⁷ 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, gaseous nitrogen flows into the specimen chamber via the

vent valve

. As soon as the pressure equilibrium is obtained, the chamber door can be

opened to change the specimen.

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

and EHT can be switched on.

Vacuum Modes

The microscope can be operated in different vacuum modes:

High vacuum (HV) mode

Variable pressure (VP) mode (optional)

EasyVP mode (optional)

Extended pressure (EP) mode (optional)

System Vacuum in

HV Mode

In HV mode, both gun and chamber are at high vacuum. The 20 μm or 30 μm mid-column aper-
tures are used for the beam profile control. No pressure limiting aperture is mounted under the
objective lens.

HV mode provides the means to obtain higher resolution and enables using the SE detector.

HV mode is the regular operation mode for standard applications and is recommended for imag-
ing conductive specimens.

System Vacuum in

Variable Pressure

Modes

The configuration of the microscope needs to be changed to enable variable pressure modes (VP,
EasyVP and EP Mode), refer to

Variable Pressure Modes [

}

23]

3.1.1 Variable Pressure Modes

Variable pressure (VP) modes enable imaging specimens that are non-conducting, strongly
gassing, or hydrated, without the need for vapor deposition or other preparation procedures.

This is made possible by using a differential pumping system. A pressure-limiting aperture (differ-
ential pumping aperture DPA) is mounted under the objective lens, which allows partial pressures
above 10 Pa to be set in the specimen chamber while maintaining high vacuum in the gun area.

Three different pressure-limiting aperture configurations are available:

VP mode with 100 μm VP aperture

EasyVP mode with 400 μm EasyVP aperture

EP mode with 100 μm EP aperture and 500 μm or 1000 μm beamsleeve aperture.

The following table summarizes the hardware, applications and pressure ranges of the different
vacuum modes:

Mode

Application

Pressure-lim-

iting aper-

ture

Mid-col-
umn aper-
ture

Filament