Amorphous carbon nitride thin films were synthesized using an electron cyclotron resonance chemical vapor deposition system In which a direct current (dc) bias was applied to the silicon substrate and a mixture of C2H2, H-2, and Ar was used as precursors. The films prepared in this way were further treated in an argon plasma to increase their surface roughness thereby creating a more efficient electron emitter. An onset emission field as low as similar to 3.5 V mu m(-1) can be achieved (after Ar+ plasma sputtering for 3 min), significantly lower than other carbon-based electron field emitters. This low value is mainly attributed to the increase of film roughness, decrease of film thickness, and removal of hydrogen from the film, The structural and compositional modification induced by Ar+ plasma post-treatment along with the application of a negative de bias to the synthesized film were analyzed by Fourier-transformation infrared spectroscopy, Raman spectroscopy, x-ray photoelectron spectroscopy, atomic force microscopy, and field emission scanning electron microscopy.