Growth and characterization of low stress amorphous carbon films by pulsed laser deposition process

Low stress amorphous carbon films have been studied for various protective coating applications. A graphite target of 99.99% purity was ablated by a KrF excimer laser of 248 nm wavelength to provide the carbon source. For the deposition of diamond-like carbon films, a multi-cycle process (10 cycle repetition of 30 sec deposition followed by 30 sec relaxation period) was used to relieve the high internal stress, which is known to develop during the coating condensation. High purity (99.999%) nitrogen gas was used to produce amorphous carbon nitride films. The microstructure changes of the amorphous carbon films were closely observed with Raman spectroscopy, X-ray photoelectron spectroscopy, and atomic force microscopy. It has been revealed that films deposited at higher laser densities exhibited more sp3 bonding contents with lower root mean square roughness values. However, no sign of coating failure due to high stress was observed from the multi-cycle deposited diamond-like carbon films and the single-cycle deposited amorphous carbon nitride films. Residual stress values of these films were measured at only ∼3 GPa. Nanoindentation measurements confirmed that the microstructures and the mechanical properties of these amorphous carbon films were effectively controlled by various process parameters for specific coating applications. Thermal degradation has been observed from amorphous carbon nitride film deposited at 450°C.