Enhancement of the properties of pulsed laser-deposited carbon nitride by the synchronisation of laser and N2 gas jet pulses

In surface coatings technology, especially in carbon-based materials, the deposition of energetic species is acknowledged as one of the most important factors in producing hard coatings. Pulsed laser deposition (PLD) of carbon under vacuum creates such energetic species and so carbon films with very high hardness values have been reported. However, when PLD takes place in a gas ambient, the ablated carbon species are decelerated to an extent that depends on the background pressure. As a result, during CNx deposition, although the carbon species react effectively with N-2 at the beginning of their trajectories, when they reach the substrate they usually do not have sufficient kinetic energy to form a hard coating. In this paper we describe a new technique that combines the intense environment of an expanding N-2 jet with low-pressure PLD to produce CNx species that travel almost free of collisions and reach the substrate with high kinetic energies. This new configuration is based on the synchronised pulsing of a N-2 jet with the laser pulse. The CN films produced are shown to have an increased film hardness without suppressing the nitrogen content. Furthermore, electron energy-loss spectroscopy shows the layers to have a very high proportion of pi bonding, which can be correlated to the existence of sp-hybridised carbon in the form of -C=N bonds. (C) 1998 Elsevier Science S.A. All rights reserved.