The electron field emission (EFE) process for diamondfilms was tremendously enhanced by Fe-coating and post-annealing processes. Microstructural analysis indicates that the mechanism for the improvement in the EFE process is the formation of nanographites with good crystallinity that surround the Fe (or Fe3C) nanoclusters. Presumably the nanographites were formed via the reaction of Fe clusters with diamondfilms, viz. by the dissolution of carbons into Fe (or Fe3C) clusters and the reprecipitation of carbon species to the surface of the clusters, a process similar to the growth of carbon nanotubes via Fe clusters as catalyst. Not only is a sufficiently high post-annealing temperature (900°C) required but also a highly active reducing atmosphere (NH3) is needed to give a proper microstructure for enhancing the EFE process. The best EFE properties are obtained by post-annealing the Fe-coated diamondfilms at 900°C in an NH3 environment for 5 min. The EFE behavior of the films can be turned on at E 0 = 1.9 V/μm, attaining a large EFE current density of 315 μA/cm2 at an applied field of 8.8 V/μm (extrapolation using the Fowler–Nordheim model leads to J e = 40.7 mA/cm2 at a 20 V/μm applied field).