Microstructure And Tribological Behavior Of CN_x Films Prepared By Glow Discharge Assisted PLD

Carbon nitride materials(CNX)has been a hot research issue due to its newly superhardness character.Nowadays,to achieve crystalline superhard CNx simply by pulsed laser deposition(PLD)technology is still hard to break through.Given nitrogen glow discharge can provide a large number of nitrogen species with the effect of bias,therefore PLD technology with the assist of DC glow discharge would benefit for improving nitrogen content.and microstructure of CNx films.The CNx films were deposited on monocrystalline silicon by DC glow discharge assisted PLD technique in this paper.The effects of deposition pressure,laser flux,discharge power density,and target distance on valence bond structure,chemical composition,nano indentation hardness,the adhesion of the films to subsrate,and tribological behavior were mainly discussed.And the optimum process parameters by DC glow discharge assisted PLD technique were concluded.The surface morphology,microstructure,and mechanical properties of the films were characterized by scanning electron microscopy(SEM),Raman spectroscopy(Raman),X-ray photoelectron spectroscopy(XPS),nano-indenter and ball-on-disk tribometer,respectively.The results show that DC glow discharge assisted PLD technique could improve the nitrogen atom percent and sp3C bond content of the CNx films remarkably.By optimizing the technologic parameters through orthogonal test,the optimal parameters are determined as followed:laser flux at 5 J/cm2,pressure at 12 Pa,target to substrate distance at 37 mm,and discharge power density at 30 mW/cm2.The nitrogen atomic content of the CNx film increases from 27.7 at.%to 34.1 at.%with the increase of laser flux from 5.1 J/cm2 to 7.5 J/cm2.An increased area percentage of sp3C—N bond,sp2C—N bond,and a decreased area percentage of sp2C—C bond are observed in the film.An increased degree of carbon sp3 hybrid and a decreased degree of graphitization of the film are found.As increasing the laser flux,the film hardness increases from 3.7 GPa to 5.3 GPa,the wear rate of the film decreases from 3.8×10-13 m3/(Nm)to 7.9×10-14 m3/(Nm),and the friction coefficient increases from 0.13 to 0.18,respectively.With the increase of deposition pressure from 8 Pa to 14 Pa,the nitrogen atomic content of the CNx film decreases from 32.85 at.%to 29.32 at.%;the area fraction of sp3C—N bond decreases from 35.5 at.%to 32.0 at.%,and the area fraction of sp2C—C bond increases from 43.35 at.%to 46.15 at.%,the decrease in the degree of carbon sp3 hybrid,surface roughness,the ratio of ID/IG decreases from 2.54 to 2.32,and friction coefficient(about 0.126)of the films and an increase in the degree of graphitization of the films are found.When pressure is 8 Pa,maximum membrane nitrogen content were reached in the film,which is the most conducive to the formation of the sp3 hybridization at this time,the film has better resistance wear,but the friction coefficient is relatively high.In addition,the phenomenon that elevated levels of nitrogen lead to higher friction coefficient could also be found.