Prediction of a threshold density of atomic hydrogen for nanocrystalline diamond growth at low pressures

A lower-threshold density of atomic hydrogen (H) for nanocrystalline diamond growth in inductively coupled plasma has been examined. Vacuum-ultraviolet absorption spectroscopy was employed to measure the absolute H density in low-pressure conditions below 10.6 Pa, where nanocrystalline diamond films with grain sizes of ∼20 nm showing a distinct diamond peak in the Raman spectra were deposited. A mechanistic explanation for the growth limitation was made by comparing kinetic rates of incorporation and desorption of adsorbed methyl radicals as principal growth precursors. The results predict a threshold H density for net diamond growth of the order of 10¹² cm^-3.