CNx coatings deposited by pulsed RF supersonic plasma jet: hardness, nitrogenation and optical properties

A low pressure pulsed RF supersonic plasma jet system (RPJ) has been used for deposition of CNx thin films. The aim of the CNx thin films deposition was an application for tribological coatings. Chemical composition, mechanical and optical properties of deposited CNx films have been measured. The obtained parameters were found to be similar to those of CNx films prepared by DC magnetron sputtering. The deposition rate for the CNx films prepared in RPJ reactor was of approximately 2 μm/h. During the deposition process, the substrate temperature did not exceed 250°C, as required for certain kinds of machine tribological coatings. A strong correlation between DC bias magnitude, nitrogen concentration and mechanical properties was found. The value of the substrate bias VDC=−100 V was found to be optimal for deposition of hard CNx films with maximum microhardness H=22 GPa. The films with the highest microhardness had the lowest atomic concentration of nitrogen. Analogous correlation has been found in ‘Diamond Relat. Mater. 7 (1998) 417’, although the deposition method and conditions were quite different. The chemically active plasma has been investigated in the RF supersonic plasma jet channel during the deposition process by means of ‘in situ’ emission spectroscopy. The mechanism of CNx formation has been studied as well.