The impact of inert gases on the structure, properties and growth of nanocrystalline diamond

For biomedical and electronic applications, it is highly desirable to deposit smooth diamond films with crystal sizes in the nanoscale range. We present experimental results of chemical vapour deposition diamond growth from CH₄ with incremental substitution of H₂ with He or Ar gases; the concentrations of the inert gases were varied between 0 and 98 vol%. Results show that initially the addition of either argon or helium increases the growth rate and significantly alters the film structure and crystallinity up to 60 vol%. With additions of argon or helium greater than 60 vol% in the gas phase the growth decreases and there is degradation of the crystal structure. In general, nanocrystalline diamond has been deposited at dilutions in excess of 90 vol% helium or argon.