Formation of continuous nanocrystalline diamond layers on glass and silicon at low temperatures

Nanocrystalline diamond thin films are grown on silicon and glass substrates by microwave plasma (MP)CVD from a gas mixture of methane and hydrogen at low substrate temperatures. The initial stages of diamond growth, i.e., i) the growth of individual nanometer-sized crystals and clusters, and ii) coalescence into a continuous layer, are investigated by diverse analytic techniques. Atomic force microscopy (AFM) measurements reveal nearly unchanging surface roughness up to 40 min. X-ray photoelectron spectroscopy (XPS) measurements detect changing of the surface composition from the very beginning of the growth process. The rapid carbon increase is assigned to the enlarging of the grown crystals and clusters. Scanning electron microscopy (SEM) images indicate a possible lateral growth type. The found dependences indicate that a two-dimensional growth mode takes place at low substrate temperatures. Grown nanocrystalline diamond films are optically transparent in a wide spectral range, and exhibit a high refractive index of 2.34.