The Anatomy of a Scanning Electron Microscope

All scanning electron microscopes are made from various primary components. The engineering behind these elements will establish the resulting quality of the image and the result of the investigation.

This article will evaluate, one by one, the key components of an SEM and will offer some intriguing insights into how they function and what their role is in the microscope.

2.1 The Electron Source

CeB6 and tungsten are both thermionic sources with a filament referred to as a cathode, from which electrons are generated.

The emission begins when the electrons are supplied with sufficient energy to cross the potential barrier, supplied by the cathode material’s work function, which can either be tungsten or CeB6.

The energy is supplied by heating the cathode, which, in turn, is performed by letting the current travel through it. A Wehnelt electrode that is negatively charged in relation to the cathode moves the undesired electrons back into the filament, successfully calculating the size of the emitting area.

Underneath Wehnelt electrode and the cathode, an anode offers a powerful electric field, or a strong lens that makes the electron beam intersect into a crossover between the anode and the Wehnelt.

The next image displays the schematics of the CeB6 source, comprising a Wehnelt electrode, an anode, and a filament.

The filament and the Wehnelt are both at high potential, but the anode is grounded. The circuitry positioned in between the anode and the filament calculates the emission current.

This is a schematic of thermionic source consisting of a CeB6 crystal (the filament), a Wehnelt electrode. and the anode. The red trajectories indicate that the electrons are pushed back in the filament, due to the Wehnelt voltage and the trajectories of the emitted electrons, forming the primary beam.

This is a schematic of thermionic source consisting of a CeB6 crystal (the filament), a Wehnelt electrode. and the anode. The red trajectories indicate that the electrons are pushed back in the filament, due to the Wehnelt voltage and the trajectories of the emitted electrons, forming the primary beam. Image Credit: Thermo Fisher Scientific Phenom-World BV

 

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This information has been sourced, reviewed and adapted from materials provided by Thermo Fisher Scientific Phenom-World BV.

For more information on this source, please visit Thermo Fisher Scientific Phenom-World BV.

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