Electron emission microscopy of nano-crystal graphitic films as high current density electron sources

Electron emission can be described by thermionic and field effects or a combination of both and can be characterized by the laws of Richardson–Dushman and Fowler–Nordheim, respectively. Nano-crystal graphitic films exhibit a film morphology comprised mainly of crystalline graphite sheets which are vertically aligned with respect to the substrate surface. Field emission from these films exhibits a low threshold field of < 1 V/μm, an emission site density of ∼3 × 105/cm2 and a significant distribution in brightness. The temperature dependence of the emission is complex and may be influenced by molecular adsorbates and interface reactions. For nano-crystalline graphite films on molybdenum it was found that the emission current is significantly increased with temperature. The results suggest a field dependent barrier which may be an indication of field penetration.