Highly conductive and thick a-C:H:N films deposited at elevated temperatures via direct current PACVD

Abstract

DLC films exhibit high hardness, low friction coefficient and chemical inertness but generally lack sufficient electrical conductivity. To achieve conductive films with substantial thickness, the combination of direct current plasma assisted chemical vapour deposition (DC PACVD) with high coating temperatures has proven to be effective. Nitrogen doping of DLC films, a common method for improving their electrical conduction properties, typically leads to enhanced graphitization and a reduction in hardness and Young's modulus in harder DLC coatings. This study examines how nitrogen doping affects the mechanical and electrical properties of already unusually conductive, soft and thick (> 25 μm) a-C:H films deposited at elevated temperatures using pulsed direct current PACVD. The a-C:H:N films were grown using C₂H₂ at 450 °C and 550 °C with an addition of 0–63 vol.-% N₂ to the gas phase and studied subsequently. Nitrogen modification of the a-C:H was highly effective at enhancing mechanical properties in conjunction with electrical conductivity. Hardness and Young's modulus increased by up to 48 % and 95 %, respectively, compared to the undoped films. Relative load bearing capacity improved by up to a factor of 3.7. Specific electrical resistance decreased by more than two orders of magnitude for films deposited at 450 °C and by a factor of four for deposition at 550 °C, approximating and even surpassing the conductivity of graphite electrodes. Conversely, film thickness and deposition rate decreased significantly due to etching effects compared to the undoped a-C:H.