Field emission characteristics of thin-metal-coated nano-sheet carbon films

Nano-sheet carbon films (NSCFs) coated with very thin (approximate to 5-nm-thick) metal layers were fabricated on Si wafer chips by means of quartz-tube-type microwave-plasma chemical-vapour-deposition method with hydrogen-methane gas mixture and an electron beam evaporation method. Field emission (FE) current densities obtained at a macroscopic average electric field, E, of approximate to 10V/mu m changed from 13mA/cm(2) for NSCF with no coated metal to 1.7, 0.7 and 30mA/cm(2) for Ti-, Al- and Au-coated NSCFs, respectively, while the threshold E varied from 4.4V/mu m for the former one to 5.3, 5.4 and 2.0V/mu m for the corresponding latter ones, respectively. As the FE currents of Au-coated NSCFs tended to be saturated in a higher E region, compared to those of NSCFs with no coated metal, no simple Fowler-Nordheim (F-N) model is applicable. A modified F-N model considering statistic effects of the FE tip structures and a space-charge-limited-current effect is successfully applied to an explanation for the FE data observed in the low and high E regions. (C) 2010 Elsevier B.V. All rights reserved.