The investigation of the field emission (FE) properties of carbon nanotube (CNT) films by a scanning anode FE apparatus, reveals a strong dependence on the density and morphology of the CNT deposit. Large differences between the microscopic and macroscopic current and emission site densities are observed, and explained in terms of a variation of the field enhancement factor β. As a consequence, the emitted current density can be optimized by tuning the density of CNTs. Films with medium densities (on the order of 107 emitters/cm2, according to electrostatic calculations) show the highest emitted current densities.

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Field emission measurements on chemical vapor deposition diamond and laser ablated a-C films show an activation step after reaching a certain critical electric field. At this field a vacuum arc of some hundred ns duration initiates. While high current arcing leads to the evaporation of the spot surface melting, amorphization or cracking of the film is encountered for lower currents. In any case, much higher electron emission can be observed after this activation procedure due possibly to tip formation resulting in an electric field enhancement. By using a 1 GΩ resistance the discharge current can be limited nevertheless, an activation is observed.

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