前驱体对PECVD制备类金刚石涂层的结构与性能的影响OA

Diamond-like carbon(DLC)coatings have attracted significant attention in various industrial and scientific applications,including mechanical seals,biomedical implants,and microelectronic devices,owing to their exceptional combination of high hardness,superior wear resistance,and high chemical stability.These properties primarily arise from the unique hybridized carbon bonding structure(sp3/sp2 ratio)and hydrogen content within the coatings.However,the performance of DLC coatings is highly sensitive to deposition parameters,such as plasma power,substrate bias,and precursor gas composition,which influence the chemical bonding structure and microstructure of the coatings. In this study,the effects of hydrocarbon precursor hydrogen content on the structural and mechanical properties of DLC coatings deposited by direct current pulse plasma-enhanced chemical vapor deposition(DC-PECVD)were systematically investigated.Four distinct DLC coatings were synthesized with different precursor gases:pure acetylene(DLC-C2H2),hydrogen-diluted acetylene(DLC-C2H2+H2),pure methane(DLC-CH4),and hydrogen-diluted methane(DLC-CH4+H2).The influence of precursor hydrogen content on coating thickness,chemical bonding configuration(sp3/sp2 ratio),and mechanical properties(hardness and elastic modulus)was comprehensively characterized by scanning electron microscopy(SEM),Raman spectroscopy,X-ray photoelectron spectroscopy(XPS),and nanoindentation techniques. The deposition rate of DLC coatings was found to be strongly dependent on the precursor gas composition.Specifically,the DLC-C2H2 coating exhibited the highest deposition rate(0.83 μm/h),which was approximately three times greater than that of the DLC-CH4 coating(0.28 μm/h).This disparity was attributed to the higher carbon density and more efficient plasma dissociation of C2H2 compared with CH4.Interestingly,hydrogen dilution had a negligible impact(<10%)on the deposition rates of both precursor systems,suggesting that hydrogen primarily influenced the chemical bonding structure rather than the growth kinetics.Raman spectroscopy revealed a clear correlation between precursor hydrogen content and the structural evolution of DLC coatings.As the hydrogen content increased,the intensity ratio of the D peak to the G peak(ID/IG)decreased,accompanied by a redshift in the G peak position.These observations aligned with the Casiraghi model,which described the structural transition from a more graphitic(sp2-rich)to a more diamond-like(sp3-rich)configuration with increasing hydrogen incorporation.XPS analysis demonstrated that the sp3 carbon fraction in DLC coatings exhibited a positive correlation with precursor hydrogen content.The highest sp3 content(14.5%)was achieved in the DLC-CH4+H2 coating,confirming the critical role of hydrogen in stabilizing sp3-hybridized carbon bonds.In contrast,the DLC-C2H2 coating,deposited under low hydrogen conditions,exhibited the lowest sp3 content(6.1%),indicating a predominantly sp2-bonded structure.Nanoindentation measurements revealed that the DLC-C2H2 coating possessed the highest hardness(26.9 GPa)and elastic modulus(240 GPa),despite its relatively low sp3 content.This finding challenged the conventional paradigm that high hardness in DLC coatings was solely governed by a high sp3 fraction.Instead,the results suggested that a cross-linked sp2 network,formed under low hydrogen conditions,contributed significantly to mechanical reinforcement;the cognition that the sp3 fraction determined the hardness of DLC coatings originated from hydrogen-free DLC coat and was not applicable to hydrogenated DLC coatings.Furthermore,hydrogen dilution was found to generally reduce coating hardness,particularly in the CH4-based system,where a notable 18%reduction in hardness was observed. This study reveals how the hydrogen content in precursor gases and the resulting chemical bonds affect the properties of DLC coatings.Key findings show that using C2H2 instead of CH4 speeds up coating growth due to more efficient carbon delivery.While hydrogen helps form more sp3 bonds,high hardness can also come from a dense sp2 network-not just sp3 content.This means the current model linking structure to properties needs updating.Overall,tuning the gas mixture and hydrogen level allows custom-designed DLC coatings with improved mechanical and wear performance for specific applications.