Nanocrystalline diamond film as cathode for gas discharge sensors

Nanocrystalline diamond (NCD) film was deposited on a silicon substrate utilizing microwave plasma-enhanced chemical vapor deposition in a mixed flow of methane, hydrogen and argon. The deposited film had a cauliflower-like morphology, and was composed of NCD, carbon clusters and mixed sp2- and sp3-bonded carbon. Electron field emission (EFE) in vacuum and electrical discharges in Ar, N2 and O2 using the NCD film as the cathode were characterized. The turn-on field for EFE and the geometric enhancement factor for the NCD film were 8.5 V/μm and 668, respectively. The breakdown voltages for Ar, N2 and O2 increased with pressures from 1.33 × 104 Pa to 1.01 × 105 Pa, following the right side of the normal Paschen curve.