Effect of the bias voltage on the structure of nc-CrC/a-C:H coatings with high carbon content

Abstract Nanocomposite coatings consisting of a hard nanocrystalline carbide phase and a-C:H amorphous matrix are the focus of many investigations because of their mechanical and tribological properties such as high hardness, low friction coefficient and high resistance to wear. In this work, nanocomposite coatings of nanocrystalline chromium carbide embedded in an amorphous matrix (nc-CrC/a-C:H) were deposited onto silicon substrates by cathodic vacuum arc deposition using a Cr target in an Ar/C 2 H 2 gas mixture atmosphere. A linear magnetic shield was employed to reduce the macroparticle content in the films. A range of negative bias voltages from 50 to 450 V was applied to substrates during deposition. X-ray diffraction (XRD) analysis showed that amorphous or nanocrystalline thin films were formed in all cases. The hydrogen bonding in the material was studied by Fourier transform infrared spectroscopy (FTIR). X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and electron energy loss spectroscopy (EELS) were used to determine the carbon bonding and to study the presence of different forms of amorphous carbon. High resolution transmission electron microscopy (HRTEM) revealed a nanocomposite structure with chromium carbide nanocrystallites embedded in an amorphous hydrocarbon matrix. It was observed that the negative bias voltage significantly affected the carbon bonding and the hydrogen content.