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.

We herein report high dose nitrogen (N) ion implantation induced nanostructural modifications and enhanced electron field emission (EFE) properties of ultrananocrystalline diamond (UNCD) pyramid tips. Transmission electron microscopy investigations indicate nanostair type surface formation on the pyramid tips. Evidence of complex nanostructural changes due to ion implantation are found, such as, graphitic or amorphous type transition, volume expansion (about 0.56 μm³), and nanostair type surface formation. The nanostructural modifications possibly enhanced the grain boundary incorporation of N and the electron transport through a transfer doping mechanism, which in turn improved the EFE properties of the ion-implanted pyramid tips. In particular upon N ion implantation the turn-on field is found to reduce from 3.6 V/μm (for unimplanted tips) to 2.8 V/μm and the current density is increased from 0.1 mA/cm² (unimplanted tips) to 5.4 mA/cm² at an applied field of 12.5 V/μm.