Optical emission spectroscopy of deposition process of ultrananocrystalline diamond/hydrogenated amorphous carbon composite films by using a coaxial arc plasma gun

Deposition processes of ultrananocrystalline diamond/hydrogenated amorphous carbon composite (UNCD/a-C:H) films in a hydrogen atmosphere using a coaxial arc plasma gun were spectroscopically investigated with an intensified charge-coupled device (ICCD) camera equipped with narrow-bandpass filters. Strong emissions lasted for more than 100 μs. From the emission time and deposition rate, a supersaturated condition should be strongly realized. This might contribute to the formation of UNCD crystallites. A UNCD crystallite size was estimated to be 2.3 nm from an X-ray diffraction peak. The extremely small value implies that nuclei are repeatedly generated without the subsequent growth. A probable reason is as follows: since the number of carbon species caused using the arc plasma gun is so large as compared to that of hydrogen atoms, which generate from ambient hydrogen molecules by the collision with carbon species, the hydrogen atoms do not effectively contribute to the UNCD crystallite formation. This consideration does not contradict the fact that a coaxial arc plasma gun makes possible UNCD crystallite formation even in vacuum.