Enhanced electron field emission (EFE) properties due to hydrogen post-treatment at 600 °C have been observed for ultrananocrystalline diamond (UNCD) films. The EFE properties of H2-gas-treated UNCD films could be turned on at a low field of 5.3 V/μm, obtaining an EFE current density of 3.6 mA/cm2 at an applied field of 11.7 V/μm that is superior to those of UNCD films treated with H2 plasma. Transmission electron microscopic investigations revealed that H2 plasma treatment induced amorphous carbon (a-C) (and graphitic) phases only on the surface region of the UNCD films but the interior region of the UNCD films still contained very small amounts of a-C (and graphitic) grain boundary phases, resulting in a resistive transport path and inferior EFE properties. On the other hand, H2 gas treatment induces a-C (and graphitic) phases along the grain boundary throughout the thickness of the UNCD films, resulting in creation of conduction channels for the electrons to transport from the bottom of the films to the top and hence the superior EFE properties.
