Electron Gun

A schematic diagram of an electron gun similar to that used for AES/SEM/SAM in Axis 165 is shown below. The electron source is mounted in a triode configuration which produces an accelerated electron beam from the small diameter, high brightness LaB6 emitter. The electron beam passes through an electrostatic alignment stage which compensates for any slight misalignment of the electron source with respect to the electron optical axis of the system. A coarse mechanical alignment stage is also provided. The alignment stage is followed by two demagnifying lenses and an objective lens which focuses the beam onto the specimen.

An electrostatic 8-pole stigmator is placed just before the objective lens to correct any astigmatism due to lack of symmetry in the electron optics. Four electrostatic deflector plates are mounted just after the objective lens to scan the electron beam across the sample in a rectangular raster, as in a TV display. The electron beam energy can be as high as 15 keV and can provide spatial resolution of 100 nm.