Field emission studies have been carried out on undoped as well as N- and B-doped graphene samples prepared by arc-discharge method in a hydrogen atmosphere. These graphene samples exhibit very low turn-on fields. N-doped graphene shows the lowest turn-on field of 0.6 V/μm, corresponding to emission current density of 10 μA/cm2. These characteristics are superior to the other types of nanomaterials reported in the literature. Furthermore, emission currents are stable over the period of more than 3 h for the graphene samples. The observed emission behavior has been explained on the basis of nanometric features of graphene and resonance tunneling phenomenon.

We report the growth of ultrathin diamond nanorods (DNRs) by a microwave plasma assisted chemical vapor deposition method using a mixture gas of nitrogen and methane. DNRs have a diameter as thin as 2.1 nm, which is not only smaller than reported one-dimensional diamond nanostructures (4-300 nm) but also smaller than the theoretical value for energetically stable DNRs. The ultrathin DNR is encapsulated in tapered carbon nanotubes (CNTs) with an orientation relation of (111)diamond//(0002)graphite. Together with diamond nanoclusters and multilayer graphene nanowires/nano-onions, DNRs are self-assembled into isolated electron-emitting spherules and exhibit a low-threshold, high current-density (flat panel display threshold: 10 mA/cm2 at 2.9 V/microm) field emission performance, better than that of all other conventional (Mo and Si tips, etc.) and popular nanostructural (ZnO nanostructure and nanodiamond, etc.) field emitters except for oriented CNTs. The forming mechanism of DNRs is suggested based on a heterogeneous self-catalytic vapor-solid process. This novel DNRs-based integrated nanostructure has not only a theoretical significance but also has a potential for use as low-power cold cathodes.

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Enhanced electron field emission (EFE) behavior was observed in ultrananocrystalline diamond (UNCD) and microcrystalline diamond (MCD) films upon irradiation with 100 MeV Ag9+-ions in a fluence of 5×1011 ions/cm2. Transmission electron microscopy indicated that while the overall crystallinity of these films remained essentially unaffected, the local microstructure of the materials was tremendously altered due to heavy ion irradiation, which implied that the melting and recrystallization process have occurred along the trajectory of the heavy ions. Such a process induced the formation of interconnected nanocluster networks, facilitating the electron conduction and enhancing the EFE properties for the materials. The enhancement in the EFE is more prominent for MCD films than that for UNCD films, reaching a low turn-on field of E0=3.2 V/μm and large EFE current density of Je=3.04 mA/cm2 for 5×1011 ions/cm2 heavy ion irradiated samples.

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The single or multienergy nitrogen ͑N͒ ion implantation ͑MENII͒ processes with a dose ͑4 ϫ 10 14 ions/ cm 2 ͒ just below the critical dose ͑1 ϫ 10 15 ions/ cm 2 ͒ for the structural transformation of ultrananocrystalline diamond ͑UNCD͒ films were observed to significantly improve the electron field emission ͑EFE͒ properties. The single energy N ion implantation at 300°C has shown better field emission properties with turn-on field ͑E 0 ͒ of 7.1 V / m, as compared to room temperature implanted sample at similar conditions ͑E 0 = 8.0 V / m͒ or the pristine UNCD film ͑E 0 = 13.9 V / m͒. On the other hand, the MENII with a specific sequence of implantation pronouncedly showed different effect on altering the EFE properties for UNCD films, and the implantation at 300°C further enhanced the EFE behavior. The best EFE characteristics achieved for the UNCD film treated with the implantation process are E 0 = 4.5 V / m and current density of ͑J e ͒ = 2.0 mA/ cm 2 ͑at 24.5 V / m͒. The prime factors for improving the EFE properties are presumed to be the grain boundary incorporation and activation of the implanted N and the healing of induced defects, which are explained based on surface charge transfer doping mechanism.