Amorphous carbon (a-C) films and cesiated a-C films were synthesized on silicon substrate by Cs ion gun sputter deposition system (Cs IGSDS). The properties of a-C film were analyzed by X-ray photoelectron spectroscopy, Raman spectroscopy, and atomic force microscopy, As the negative carbon ion energy increased, relative sp(3) ratio in the a-C film increased, and surface roughness decreased. The field emission characteristics of the a-C films as a function of negative carbon ion energy were examined by diode type I-V measurement at ultra high vacuum system. From I-V measurements, the threshold voltage increased with the increase of negative carbon ion energy, and the range from 11 to 16 V/mu m was obtained. To investigate the Cs effect, cesiated a-C films were prepared by Cs+ ion and C- ion co-deposition and field emission characteristics of the cesiated a-C films were observed, too. Compared to non-cesiated a-C films, the threshold voltage is decreased by the Cs co-deposition and the value was about 6 V/mu m. In this study, we investigate that the relation between carbon ion energy and field emission, and the effect of Cs in the a-C films were examined.