The field emission（FE） characteristics of nano-structured carbon films（NSCFs） are investigated.The saturation behaviour of the field emission current density found at high electric field E cannot be reasonably explained by the traditional Fowler-Nordheim（F-N） theory.A three-region E model and the curve-fitting method are utilized for discussing the FE characteristics of NSCFs.In the low,high,and middle E regions,the FE mechanism is reasonably explained by a modified F-N model,a corrected space-charge-limited-current（SCLC） model and the joint model of F-N and SCLC mechanism,respectively.Moreover,the measured FE data accord well with the results from our corrected theoretical model.

Nano-sheet carbon films(NSCFs) were fabricated on Si wafer chips by means of quartz-tube-type microwave plasma chemical vapour deposition(MWPCVD).In order to further improve the field emission(FE) current density,a 2-nm Ti film was prepared on the samples by using electron beam(EB) evaporation.The FE characteristics of the Ti-coated NSCF were measured in an ultrahigh vacuum system.The FE properties of the NSCF are obviously improved due to its surface modified by titanium carbide after deposition of a thin layer of Ti film.The threshold field is decreased from 2.6 V/μm to 2.0 V/μm and the FE current density at a macroscopic electric field of 9 V/μm is increased from 12.4 mA/cm2 to 20.2 mA/cm2 for Ti-coated nano-sheet carbon films.