Low-temperature Growth of Nanocrystalline Diamond Films in Surface-wave Plasma

Abstract

We have developed a low-temperature growth technique (400 °C or lower) via microwave plasma chemical vapor deposition (CVD) for nanocrystalline diamond (NCD) films using surface-wave plasmas, whereas a substrate temperature of over 400 °C is necessary for conventional diamond CVD. Using this technique, NCD films still grow at a substrate temperature below 100 °C. This enables a wide selection of substrate material, including steel and plastics, to be used. The NCD growth in the surface-wave plasma exhibits a temperature-insensitive growth rate (activation energy =0.07 eV), which indicates a different growth mechanism from that of conventional diamond growth. The analysis of the size distribution of the diamond crystals in the NCD films implies diamond nucleation in the plasma, which is invoked by a low-electron temperature (2–3 eV) of the surface-wave plasma over the growth region. This gas-phase nucleation enables the low-temperature growth of NCD. The NCD film deposited in the surface-wave plasma exhibits high transparency and high tribological performance originating from its small surface roughness and large power-law exponent. The transparency for visible light of NCD films of 500 nm thickness on glass substrates reaches 90%. NCD films deposited on stainless steel substrates exhibit good tribological properties in air at room temperature without any lubrication, particularly a low friction coefficient (<0.1) and a low aggression strength against the stainless steel counterpart (specific wear rate ∼ 109 mm3 mN−1).