Diamond-like carbon coatings prepared in an asymmetric bipolar pulsed d.c.plasma

High quality diamond-like carbon (DLC) coatings can be routinely produced i n r.f. (13.56 MHz) based capacitively coupled plasma-assisted chemical vapo ur deposition processes. In practice, this process is limited to relatively small batch volumes (<1 m(3)). Bipolar pulsed d.c. processes may offer an alternative to way forward to large-scale processing. In this work, DLC coa tings were deposited from CH4 using an asymmetric bipolar pulsed d.c, power supply. The positive pulse was fixed at a low voltage of +75 V, while the negative pulse amplitude was varied between -300 V and -1100 V. The followi ng coating properties were characterized: C-H and C-C bonding structure usi ng Fourier transformed IR and Raman spectroscopy, hardness using depth sens ing indentation and internal stress using the bending beam technique. Subst rate heating during deposition was evaluated using the annealing characteri stics of hardened 100Cr6 steel pins. These properties are correlated with t he major variables of the power supply: pulse frequency (120-250 kHz) and p ulse amplitude. Under optimised plasma conditions, coating hardnesses as hi gh as 18 GPa could be obtained. (C) 1999 Elsevier Science S.A. All rights r eserved.