| The preparation of CNAx films by iterative pulsed laser deposition (PLD) technique was firstly reported in the paper. A CNA target fabricated by PLD technique was ablated in the nitrogen gas atmosphere instead of the conventional graphite target, and a series of CNX films were deposited on the silicon substrates with different process parameters, such as laser flux, deposition pressure and target-to-substrate distance respectively. 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. The tribological behavior were investigated using a ball-on-disk tribometer in atmosphere (RH=48-54%). The effects of above process parameters on microstructure and triobological performance of the CNA films deposited by pulsed laser ablation of as-prepared CNAx target were investigated. The iterative pulsed laser deposition technique will provide a new approach to the fabrication of highly nitrogen-contained CNx film.The typical CNx films were deposited on monocrystalline silicon substrates with different laser fluxes by PLD technique. The results showed that an introduction of iterative PLD technique could improve the nitrogen content of the CNx films remarkably. With the increase of laser flux from 5 J cm-2 to 10 J cm-2, the percentage of N-sp3C bonding increased and the nitrogen content of the CNx film increased from 23.8 at.% to 29.9 at.%, a decreased percentage of N-sp3C and sp3C-C bonding of the CNA film were observed, and the wear rate of CNx film increased from 2.1×10-15 m3/Nm to 9.0×10-15 m3/Nm. The friction coefficient of the films ranged from 0.15 to 0.23. The maximum nitrogen content (29.9 at.%) and an optimal tribological performance were exhibited at a laser flux of 10 J cm-2 and 5 J cm"2, respectively.The effects of deposition pressure on the morphology, composition and microstructure of the films were observed by the same methods above. With the increase of nitrogen pressure, the nitrogen concentration of films had been improved from 18.7 at.%up to 28 at.%as a whole, and the area fraction of N-sp2C was up, but that of N-sp3C and sp3C-C had been decreased, and the increase of the wear rate of CNX films from 1.22×10-14m3/Nm down to 2.7×10-15 m3/Nm. The friction coefficient of the films ranged from 0.19 to 0.28. The maximum mtrogen content (28 at.%) and the best friction coefficient were observed at a deposition pressure of 11 Pa and 8 Pa, respectively.Similarly, the influence of target-to-substrate distance on the morphology, composition and microstructure of the films were also observed. With the increase of target-to-substrate distance, the nitrogen concentration of films was decreased from 23.9 at.%down to 15.4 at.%, and the area fraction of N-sp2C was up, but that of N-sp3C and sp3C-C had been decreased, and the increase of the wear rate of CNx films from 4.3×10-15m3/Nm up to 3.14×10-14m3/Nm. The coefficient of friction of films varied between 0.18 and 0.25. The minimum nitrogen content down to 15.4 at.%, and the best friction coefficient but the worse wear rate were observed at a target-to-substrate distance of 51 mm.When other process parameters were fixed, the nitrogen content of the films could be promoted with an increase of lase flux and deposition pressure, but the decrease of target-to-substrate distance reduced the nitrogen content. The percentage of the sp C hybrid bond was higher than that of the sp C hybrid bond in all the films, and it suggested that iterative PLD technique need to be further optimized in increasing sp hybrid bond content. Futhermore, the promotion of nitrogen content in the films was not corresponded to the improvement of tribological performance. |
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