Preparation And Tribological Properties Of Silicon-based Surface Modified Carbon Nanotube Composite Film

As a device with a size of micron or even nanometer,micro electro-mechanical systems has been widely used in aerospace,communication technology,biomedicine,national defense and military fields.However,the development and application of micro-electro-mechanical systems are severely restricted,because its parts will experience severe friction and wear due to size effects and surface effects during movement.Moreover,its main material,monocrystalline silicon,has poor tribological properties.Therefore,it is imperative to perform anti-friction and wear-resistant treatment on monocrystalline silicon,and self-assembled molecular membrane technology is an effective means to solve this problem.Based on the superior physical and chemical properties of carbon nanotubes and silane coupling agent,a modified carbon nanotube composite lubricating film system was designed and prepared by self-assembled molecular film technology in this paper.The films were prepared on Si substrates,with a connection layer of N-[3-（trimethoxymethylsiloxyl）propyl]ethylenediamine molecules,and a lubricating layer of modified carbon nanotubes.The problems of poor interfacial bonding strength between self-assembled molecular film layers were effectively solved,and the tribological properties of silicon-based surface were improved.The results of this paper are as follows.The molecular dynamics simulation method was used to explore the film forming mechanism and structural characteristics of the composite film from a molecular perspective.The optimal molecular configuration of modified carbon nanotubes was determined,and based on this,an optimization model of the silicon-based surface composite film system was established.The results show that the optimal coverage rate of the modified carbon nanotubes on the silicon substrate is 25%,and the optimal grafting position is set as the shortest distance between two adjacent silicon atoms as a,and the distance between two adjacent KH560 molecules as 2a^1/2.The dispersion behavior of carbon nanotubes was further analyzed,and the ratio of the number of molecules that makes it have a better dispersion effect in the solution is obtained.Based on the simulation results,a self-assembled molecular film method was used to prepare a carbon nanotube composite lubricating film on a silicon-based surface.The chemical composition and surface morphology of the composite film were characterized by Fourier infrared spectrometer,X-ray photoelectron spectrometer,contact angle measuring instrument,ultra-depth-of-field microscope,scanning electron microscope and other analytical devices.The influence of the assembly time and the concentration of the modified carbon nanotube solution on the film formation effect of the lubricating film was further analyzed.Therefore,the optimal preparation method of the silicon-based surface composite film was obtained.The micro/nano tribological properties of the composite film were measured and analyzed using an atomic force microscope and a material surface comprehensive performance tester.Comparing the adhesive force and nano friction force of the composite film of different components,it was found that the modified carbon nanotube composite lubricating film exhibits the most superior and stable nanotribological properties,and the adhesive force and nano friction force were significantly larger than those of the silicon substrate.The effects of chemical composition,load,concentration and assembly time on the macroscopic tribological properties of the composite film were further explored.Moreover,it was found that the wear-resisting time of the composite film prepared by the best preparation technology reached 145 min under the load of 0.3 N,and the average friction coefficient was only 0.08 within the grinding time of 60 min.The research results provide a theoretical and experimental basis for the use of carbon nanotubes to solve the tribological problem of the failure of the friction pair of MEMS devices.