
Description of the Microscope
7
MIRA3 FEG-SEM
located right in front of the filament tip and it has a positive voltage potential
of several kilovolts (extracting voltage).
The MIRA3 cross-section and schematic representation of its optical elements:
The electron flow from the gun is specified by the
emission current
, which depends
on the extracting voltage. Electron emission from the side of the filament is
suppressed by the suppressor, which is located right behind the filament tip. The
suppressor potential is several hundreds of volts lower than the filament tip
potential. The
accelerating voltage
between the cathode and the anode determines
the overall energy of the electrons.
The whole system behaves as an electron virtual source located in the region of the
end of the tip with a characteristic size of approximately 20 nm, energy of the
electrons in the range from 200 eV to 30 keV and emission current up to 300 µA.
An important parameter of the gun is the angular intensity of the electron emission
which depends mainly on the extractor voltage. The value of this parameter is
important for electron emitter lifetime, therefore the angular intensity must be
calibrated if necessary (see chapter 4.1.3). The angular intensity is also used for
Содержание MIRA3
Страница 1: ......