Effect of H2/Ar plasma on growth behavior of ultra-nanocrystalline diamond films: The TEM study

Incorporation of H2 species into Ar plasma was observed to markedly alter the microstructure of diamond films. TEM examinations indicate that, while the Ar/CH4 plasma produced the ultrananocrystalline diamond films with equi-axed grains (~ 5 nm), the addition of 20% H2 in Ar resulted in grains with dendrite geometry and the incorporation of 80% H2 in Ar led to micro-crystalline diamond with faceted grains (~ 800 nm). Optical emission spectroscopy suggests that small percentage of H2-species (< 20%) in the plasma leads to partially etching of hydrocarbons adhered onto the diamond clusters, such that the C2-species attach to diamond surface anisotropically, forming diamond flakes, which evolve into dendrite geometry. In contrast, high percentage of H2-species in the plasma (80%) can efficiently etch away the hydrocarbons adhered onto the diamond clusters, such that the C2-species can attach to diamond surface isotropically, resulting in large diamond grains with faceted geometry. The field needed to turn on the electron field emission for diamond films increases from E0 = 22.1 V/μm (Je = 0.48 mA/cm2 at 50 V/μm applied field) for 0% H2 samples to E0 = 78.2 V/μm (Je < 0.01 mA/cm2 at 210 V/μm applied field) for 80% H2 samples, as the grains grow, decreasing the proportion of grain boundaries.