Electron emission from a polycrystalline diamond coated silicon field emitter surface was studied using in situ exposure to various gas species during its operation. Significant enhancement of the electron emission was found after the emitting surface was exposed to hydrogen at pressures in the range 5×10−4 to 10−3 Torr. Introducing other gases such as Ne and He only suppressed the emission current. A continuous emission current was measured from such a hydrogen-exposed surface even after the electric field was reduced to below the initial threshold for electron emission. No similar result was found for pure silicon surface when identical conditions applied. This phenomenon was interpreted as the formation of a dynamically vacuum-stable layer by polarized hydrogen and the diamond surface. Such a surface layer may significantly lower the surface barrier and exhibit the negative electron affinity property.

Silicon field emitters have been modified by coating with a thin SiC film through a chemical conversion process. Silicon carbide was formed on Si emitter surfaces by reacting with ethylene gas at temperatures between 850 and 950 °C using pressures as high as 5×10−3 Torr. The thickness of the coatings ranged from 2 to 500 nm, determined by a combination of reaction time, pressure, and temperature. Stable emission currents above 10 μÅ were measured from individual SiC coated emitters.