Field emission from amorphous diamond coated Mo tip emitters by pulsed laser deposition

Previous studies have shown that carbon films deposited on needle-shaped Si emitters by filtered cathodic are are amorphous with a high sp(2) content. These results can be ascribed to the poor thermal conductivity inherent to this geometry. Our present studies overcome this difficulty by depositing amorphous diamond films on Mo tip emitters by pulsed laser deposition. Monitoring films were grown on sapphire substrates and appeared transparent with a resistivity greater than 1 X 10(6) Omega cm, showing a typical amorphous diamond nature. Electron energy loss spectroscopy showed that the sp(3) content of the film was 50% at the apex of the tip and 30% at the shank, which was lower than on planar substrates. High resolution transmission electron microscopy images revealed that the film at the apex was much denser than that at the shank, but both film showed a nano-columnar microstructure. Selected area electron diffraction confirmed that the films were amorphous in nature. Field emission from coated Mo tip emitters showed a considerable improvement in both turn-on voltage and emission current, compared with the same emitter before deposition. It has been demonstrated for the first time, that a-D films can be deposited on Mo tip emitters by pulsed laser deposition to achieve a better emission performance and the observation of this in the as-deposited structure. (C) 1997 American Vacuum Society.