Field emission performance of nanostructured carbon films

The field emission performance of n-type NCD films with different composition and nanostructure is investigated in detail by analyzing the different role played by composition, grain size and orientation in the attempt to identify the material better suited for cold emitters realization in terms of low voltage operation, current driving capability and stability. Different configurations of collecting electrodes are employed to verify the occurrence of nitrogen induced morphology changes and partial orientation into elongated in plane diamond domains. By increasing nitrogen content up to N₂=25% the threshold field for an electron emission current density of 1 muA/mm decreases from 25 V mum^-1 down to 11 V mum^-1. In addition, by comparing the field emission performance achieved for the sample with N₂ = 25% using planar and vertical electrode arrangements, a further reduction of threshold electric field from 11 to 7.5 V mum^-1 and much higher emission current density (up to 50 mA/cm²) are found, without showing fatigue effects after prolonged emission. Thanks to the composition and to the orientation of carbon emission sites, the N₂ = 25% UNCD film then appears the elective material for the realization of stable cold cathodes.