Optical and mechanical characterization of ultrananocrystalline diamond films prepared in dual frequency discharges

Ultrananocrystalline diamond (UNCD) films were deposited directly on polished silicon substrates in microwave discharge (2.45 GHz) combined with rf capacitive plasma (13.56 MHz) ignited at the substrate electrode. The rf discharge induced a dc self-bias accelerating ions towards the growing film during the whole deposition process. The applied microwave and rf powers were 900 W and 35 W, respectively. The gas mixture contained 9.4% of methane in hydrogen at the total pressure of 7.5 kPa. The substrate was either preheated in hydrogen discharge to the deposition temperature of 900 °C or the deposition of intermediate layer started at about 200 °C and reached 900 °C in the 5th minute. The latter procedure resulted in the deposition of coating with the hardness of 70 GPa and very good fracture toughness. The analysis of optical measurement in UV–IR range confirmed the presence of 250 nm thick intermediate layer containing diamond like carbon and SiC materials.