Microstructure and mechanical properties of a-CNx films prepared by bias voltage assisted PLD with carbon nitride target

Amorphous carbon nitride (a-CNx) films were deposited on silicon substrates using pulsed laser deposition technique (PLD) with a carbon nitride target and a negative bias voltage up to - 120 V. The microstructure, chemical composition, bonding configuration and mechanical properties of the films were characterized by using scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, nanoindentation and ball-on-disc abrasion test. The results show that the negative bias voltage promotes the formation of sp(3) hybridization bonding and leads to a great improvement of nitrogen content (up to 38 at%) in the films. With an increasing bias voltage from -40 V to -120 V, the nitrogen content and the fraction of sp(3) hybridization bonding decrease, leading to an increase in graphitization of the films. A direct dependence of the hardness on the content of sp3 hybridization bonding is observed. The friction coefficient of the films ranges from 020 to 0.28. The film deposited at a bias voltage of -40 V presents the highest hardness value of 8.3 GPa. (C) 2014 Elsevier B.V. All rights reserved.