Enhancement of the properties of pulsed laser-deposited carbon nitride by the synchronisation of laser and N-2 gas jet pulses

In surface coatings technology, especially in carbon-based materials, the d eposition of energetic species is acknowledged as one of the most important factors in producing hard coatings. Pulsed laser deposition (PLD) of carbo n 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, al though the carbon species react effectively with N-2 at the beginning of th eir trajectories, when they reach the substrate they usually do not have su fficient 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 je t with low-pressure PLD to produce CNx species that travel almost free of c ollisions and reach the substrate with high kinetic energies. This new conf iguration 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 w ithout 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 fo rm of -C=N bonds. (C) 1998 Elsevier Science S.A. All rights reserved.