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 (N
2
-UNCD) films were coated on thus formed SiNA by using microwave plasma chemical vapor deposition (MPECVD) process. The N
2
-UNCD/SiNWs films, which were grown in CH
4
/N
2
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 CH
4
/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 (E
0
)
N2-UNCD
=7.80 V/μm achieving larger EFE current density of (J
e
)
N2-UNCD
=0.67 mA/cm
²
at an applied field of 13.0 V/μm, whereas that of the latter materials need (E
0
)
=UNCD
=18.25 V/μm to turn on, attaining only (J
e
)
UNCD
=0.024 mA/cm
²
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/cm
²
(at an applied field of 0.35 V/μm) when N
2
-UNCD/SiNWs film was used as cathode, whereas the (J
pi
)
UNCD
=3.2 mA/cm
²
when the conventional UNCD/SiNWs film was used as cathode. In summary, it is observed that the plasma illumination charateristics of the CP-devices is closely correlated with the electron field emission behavior of the cathode materials, which, in turn, was enhanced due to the improvement in conductivity of the UNCD films.