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FE, or Field emission, refers to a phenomenon where high-density electrons are emitted when a strong electric field is applied to a cathode (electron emission element) with a sharpened tip.
At room temperature, FE technology provides an electron beam that is approximately 1,000 times more dense (high intensity) than conventional thermionic electron cathodes (Tungsten hairpin filament).
This FE technology has been applied to electron source development for ultra-high resolution scanning electron microscopes. The key to its practical usability is to stabilize emissions. Since the first practical implementation of cold field emission technology in a commercial SEM in 1972, Hitachi has rigorously investigated and applied ultra-high vacuum technology to house the field emitter and has thus managed to make cold field emission usable for ultra-high resolution imaging in today's most advanced SEMs, like the SU8200 series and the SU9000.
Small source size - fine beam
Small energy spread : 0.2 - 0.3 eV
Higher brightness and resolution
As a result of these efforts, in the latest generation of CFE source SEM (SU8200 and SU9000), Hitachi has further improved the ultra-high vacuum conditions of the electron gun. This slows down the coverage of the FE tip with gas molecules to such a level that the FE-SEM can now be operated in the initial, truly clean tip status for several hours.
Advantages: Higher and more stable emission current, no drift of the virtual electron source and thus no re-alignment of focus.
In addition, Hitachi has developed a patented "mild flashing" technology. This technology is executed automatically in the background to gently clean the FE source at regular intervals while maintaining the high-voltage level.
This enables stable continuous operation of the new cold FE source during working hours.
Automated mild flashing sequence executed with HV-on in the background.
To summarize the advantages of our new steady-state cold field emitter:
Today, two different FE sources have been established in the marketplace: Coherent-Beam cold field emitters, and Schottky Emitters.
Schottky emitters - operated typically at high temperatures of 1,700K - are a good choice for general applications focused on analytical work using large, very stable probe currents.
However, their effective electron source size and the large energy spread of the emitted electrons severely limit the achievable resolution. Furthermore, the need to exchange Schottky emitters after typically 1 year is also a considerable cost factor for FE-SEM operation.