Information: Schottky Field Emission Sources

A single crystal tungsten wire with a sharp end etched to a small radius (red in the sketch) is mounted on a tungsten hairpin (also red). A current through the filament is used to maintain the tip at a temperature of 1750 - 1850 K. The tip just penetrates a hole in a cylindrical suppressor electrode mounted around the assembly. Electrons are emitted from the tip due to both thermal excitation and the electric field at the tip due to the potential difference between it and an extractor electrode (not shown). Electrons from the filament are repelled by the potential on the suppressor. Electrons from the tip are used by the subsequent column to form a focussed beam.

Details are given in:
Swanson and Martin. Journal of Applied Physics, 44, 2029-2050, 1975.
Wolfe. Journal of Vacuum Science and Technology, 16, 1704-1708, 1979

YPS Schottky Tip

SEM image of a YPS Schottky tip. Emission occurs from the crystalline facet (vertical at the right-hand end) that is about 0.3 μm across.

Other Schottky source dimensions can be fabricated to suit customer's requirements

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WHY USE SCHOTTKY SOURCES?

Very small source size (20 nm).

Highly intense axially confined beam.

Small energy spread (0.6 - 0.8 eV)

High current stability (better than 1% per hour).

Long emitter lifetime (> 5000 hrs).

May be no need for microscope "condenser" lenses.

Large currents into a conventional spot size.

Excellent for depth profiling and Auger imaging.

Minimal down-time