The Preparation Of Diamond-like Carbon Films And Their Water Lubrication

Diamond-like carbon films were successfully deposited on Si substrate by plasma enhanced chemical vapor deposition, and immersed in deionized water with or without magnetic fields. Soaked surfaces of the films in deionized water with or without magnetic fields were investigated by X-ray photoelectron spectroscopy (XPS), nanoindentation and tribometer. It is found that the magnetic fields increase the number of water molecules penetrating into DLC films, resulting in the surface changes of the films. When water molecules exist, it induce the conversion of C=C bonds to C-H bonds, and H atoms enter into films thus neutralizing free radicals with the increase of hardness and friction coefficient.Fullerene-like hydrogenated carbon (FL-C:H) films were synthesized by direct current plasma chemical vapor deposition. The structures of as-prepared films are evaluated by transmission electron microscopy and Raman spectra, in which an empirical expression relating cluster diameter to ID/IG, is considered as FL-C:H films with the degree of medium range parallel graphitic sheet stacks associated with high content pentatomic rings. The resulting FL-C:H films have the advantage of the higher hardness and higher elasticity than the reported FL-C:H films, due to the formation of medium range sheet stacks dispersed in the FL network, although they show similar ultra-low friction. Fullerene-like hydrogenated carbon (FL-C:H) films that exhibit super-low friction and wear in humid conditions have been the subject of extensive researches, but the structure-performance relationship such as the evolution of FL structures under friction is not well understood. In this study, we prepared FL-C:H films with different FL content by varying flow rate of hydrogen gas, and provided a detailed investigation on the structure-performance relationship between FL structures and tribological features. Tribological behaviors of the FL-C:H films were obtained and discussed in terms of the ultimate sliding interfaces. The films with more FL structures exhibit lower friction. Especially, the films grown H2with the flow rate of5sccm have a most FL structures and a lowest friction and wear (0.011and1.48x10-8mm3/Nm) in humid air. Besides, Raman spectroscopy of corresponding wear tracks shows one additional peaks near710cm-1which can be assigned to the curvature in graphitic planes and carbon nano-onions as has been confirmed in other reports. The Raman fitting results reveal that the odd ring fraction in the wear track is relatively higher than that of the original FL-C:H films, indicating that more FL structures generated in the tribological process. We therefore claim that the ultra-low friction and wear performances of FL-C:H films stem from their own unique fullerene-like structures, and not graphitization but friction-induced promotion of FL structures causes the excellent tribological performances.