Preparation And Tribological Properties Of Rare Earth Treated Carbon Nanotubes Self-assembled Monolayers

Silicon material is widely used in Micro-electromechanical systems/Nano-electromechanical systems (MEMS/NEMS) because of its goodchemical stability, high hardness, small surface roughness, low cost, etc.However, there is a lack of effective lubrication technology in theMEMS/NEMS equipment, which is different from the traditionalmacro-scale machine and leads the silicon surface has shortcomings ofhigh static friction force and low anti-wear property. Surface modificationof silicon surface is an effective means of improving friction, reducingwear, and enhancing reliability of the equipment’s operation.Self-assembly monolayers(SAM) have compact structure, greater rigidity,and simple preparation process, thus having advantage in solving the microfriction and wear problem of MEMS/NEMS. However, currently SAM stillhave problems, such as poor chemical stability, low interfacial bondingforce and carrying capacity, poor wear resistance as well as sensitivity toenvironmental change.In view of the problem of surface modification in micro structures ofMEMS/NEMS, excellent mechanical and physical properties of carbonnanotubes(CNTs) and special physical and chemical properties of rareearth, as well as SAM technique were used to prepare rare earth modifiedcarbon nanotubes SAM with excellent tribological property on the siliconsubstrate.Firstly, rare earth modified carbon nanotubes SAM were prepared onthe basis of two pretreatment monolayers by SAM technique. The pretreatment monolayers were poly dimethyl diallyl ammoniumchloride(PDDA) SAM and3-Aminopropyltriethoxysilane(APTES) SAM.The self-assembly process and assembly mechanisms of SAM wereanalyzed. Scanning electron microscope (SEM) was used to observe thesurface morphology of SAM. X-ray photoelectron spectrometer (XPS) wasused to study the chemical state of the typical element on the surface ofSAM, and the contact Angle meter was used to evaluate the surface energyof SAM.Secondly, the tribological properties of SAM were studied. Theresults showed that: poly dimethyl diallyl ammonium chloride/carbonnanotubes SAM (abbreviation: PDDA/CNTs-SAM) and3-Aminopropyltriethoxysilane/carbon nanotubes SAM(abbreviation:APTES/CNTs-SAM) had excellent antifriction and anti-wear performance.In experimental condition, the friction coefficient of PDDA/CNTs-SAMwas0.13, the friction coefficient of APTES/CNTs-SAM was0.11; theworn out time of PDDA-SAM was700seconds, the worn out time ofAPTES-SAM was820seconds, the worn out time of PDDA/CNTs-SAMwas8000seconds, the worn out time of APTES/CNTs-SAM was greaterthan8000seconds.Thirdly, the main factors including layer numbers of SAM, rare earth,carbon nanotubes, which influenced the tribological performance of SAMwere analyzed. Among them, the outstanding physical, chemical andmechanical property of carbon nanotubes was the most important factorthat made PDDA/CNTs-SAM and APTES/CNTs-SAM and two otherpretreatment monolayers have difference in tribological performance. Therare earth modified carbon nanotubes SAM had better tribological property.The carbon nanotubes could play the role of “molecules bearing”, bothcarrying a certain pressure to improve the anti-wear property and reducingthe friction coefficient of the surface of SAM.In this paper, SAM technique was used to prepare rare earth modifiedcarbon nanotubes SAM. Modern analytical testing techniques were used to study the surface property of SAM. The self-assembly mechanism of SAMwas clarified. The friction and wear behaviors of rare earth modifiedcarbon nanotubes SAM were investigated under certain experimentalconditions. The result of this study provided an effective approach to solvethe component failure problem of MEMS/NEMS caused by too largemicro-friction and wear.