Microstructure And Tribological Performance Of CN_x Films Prepared By Iterative Pulsed Laser Deposition

The fabrication of CNx films of three Generations by iterative pulsed laser deposition technique at various substrate temperatures were reported in this paper. The surface morphology, chemical composition, crystallinity and chemical bonding structure of the films were characterized by scanning electron microscopy (SEM), X-ray diffractometer (XRD), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy (Raman) respectively.For the second generation films, with the increase of substrate temperature, the ratio of ID /IG in the Raman spectrum of the film increased on the whole. The position of G band shifted towards a higher frequency and its full wide at half-maximum (FWHM) decreased. An increased degree of graphitization was concluded. The tribological properties of the films in atmosphere were tested by using a ball-on-disk tribometer. It was found that the nitrogen content of the films could be obviously improved by using an iterative PLD technique. An amorphous structure of the CNx films was found, and the surface morphology of the films was independent with the substrate temperature. As increasing the substrate temperature, the nitrogen content was increased from 25.3 at.%to 26.5 at.%, and significantly decreased to 21.2 at.%thereafter. A decreased content of N—sp3C, N—sp2C and an increased degree of graphitization were observed in the films. A higher temperature was favorable to the formation of sp3C—C bonds in the temperature range from RT to 300℃, and an optimum temperature 150℃ was found to form the N—sp3C bonds. With an increase in the substrate temperatures, the friction efficient of the film decreased from 0.23 to 0.13, and the wear rate of CNx film increased from 3.0×10-6mm3/Nm to 9.3×10-6mm3/Nm.For the third generation films, an amorphous structure of the CNx films was found, and the surface morphology of the films was dependent with the substrate temperature, nearly few particles could be observed above 150℃. As increasing the substrate temperature, the area fraction of C—N bonds was decreased from 31.22% to 14.14%. The area fraction of N—sp3C and N—sp2C bonds was decreased, and the optimum temperature for the formation of sp bonds was found to be 300℃. With the increase of substrate temperature, the ratio of ID/IG in the Raman spectrum of the film increased on the whole. The position of G band shifted towards a higher frequency and its full wide at half-maximum (FWHM) decreased. The microstructure of the film was prone to change from disordered a-CNx to graphite-like film with highly structural order, and an increased degree of graphitization was concluded.For the CN* films of three generations, by comparative analysis of the mirostructure and properties of the films, several conclusions are summarized as followed:1) Iterative PLD technology could improve the nitrogen content of CNx film (at room temperature) from generation to generation.2) Compared with the conventional PLD technology (15% area fraction of sp2C—N bond as measured), progressive grade can greatly improve the area percentage of sp2C—N hybrid bond (up to 23.49% for the third generation), and the disorder degree of the microstructure of films significantly increased, produce more C sp2 clusters, but area fraction of sp3C—N hybrid bond Gradually decreased.3) In properties aspect, the adhesion of the films to subsrate had a descending trend, but surface roughness and friction coefficient of the film had been improved markedly.