Thermionic Emission

Even without high vacuum, amorphous diamond coated nickel electrodes of cold cathode fluorescent lamps (CCFL) used for back lighting can reduce significantly the turn-on voltage (Fig. 9.4).

Due to its exceptional ability to increase the potential energy of electrons by absorbing heat, amorphous diamond coated metal is highly thermionic (Fig. 9.5).

Based on the above thermionic effect, the effective work function, i.e. the activation energy for electron emission in vacuum, can be lower than 1 eV. This is the lowest of all materials that have effective work function higher than 2 eV. Due to this unique thermionic character, amorphous diamond can emit more current than even

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Figure 9.4. The reduction of ignition voltage of CCFL by coating nickel electrodes with amorphous diamond.

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Figure 9.4. The reduction of ignition voltage of CCFL by coating nickel electrodes with amorphous diamond.

Figure 9.5. The great enhancement of emitted current from amorphous diamond coated nickel electrode in CCFL by modest heating.

carbon nanotubes (CNT) that have a high work function, but with a nanometer radius to enhance the electrical field (Sung, Chien-Min, US Patent No. 7,352,559). Moreover, as amorphous diamond is solid in content, it can emit electrons at a much lower temperature than CNT that will concentrate electricity on the skin of the hallow structure. In fact, the skin of each CNT will burn out when the current exceeds 20 fA. As a result, CNT devices are not reliable (e.g. Samsung's CNT front panel display or Iljin's CNT backlight). In contrast, amorphous diamond field emission can be highly robust. This is particularly suited for display or backlight applications.

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