Fabrication of nitrogen-doped ultrananocrystalline diamond nanowire arrays with enhanced field emission and plasma illumination performance

Large-area silicon nanowire arrays (SiNAs) were fabricated via metal catalytic etching technique, in conjunction with the polystyrene spheres lithographic process. The nitrogen-doped ultrananocrystalline diamond (N₂-UNCD) films were coated on thus formed SiNA by using microwave plasma chemical vapor deposition (MPECVD) process. The N₂-UNCD/SiNWs films, which were grown in CH₄/N₂ plasma at 700°C, possess markedly better conductivity (σ_N2-UNCD=2-3(Ω cm)^-1) than the conventional c-UNCD/SiNWs films, which were grown in CH₄/Ar plasma at around 425°C (σ_UNCD=0.01(Ω cm)^-1). The EFE process of the former materials can be turned on at (E₀)_N2-UNCD=7.80 V/μm achieving larger EFE current density of (J_e)_N2-UNCD=0.67 mA/cm² at an applied field of 13.0 V/μm, whereas that of the latter materials need (E₀)_=UNCD=18.25 V/μm to turn on, attaining only (J_e)_UNCD=0.024 mA/cm² at same applied field. While the plasma illumination process can be triggered at around 0.21 V/μm, regardless of the characteristics of the cathod materials, plasma illumination intensity/current density is larger when the materials with better EFE properties were used as cathodes for the plasma device. The plasma illumination current density is around (J_pi)_N2-UNCD=5.0 mA/cm² (at an applied field of 0.35 V/μm) when N₂-UNCD/SiNWs film was used as cathode, whereas the (J_pi)_UNCD=3.2 mA/cm² when the conventional UNCD/SiNWs film was used as cathode. In summary, it is observed that the plasma illumination characteristics of the CP-devices is closely correlated with the electron field emission behavior of the cathode materials, which, in turn, was enhanced - ue to the improvement in conductivity of the UNCD films.