Study On Friction And Wear Behavior Of Monocrystalline Silicon Under Various Contact Size

With the rapid development of micro/nano technology, microelectromechanical systems (MEMS) become more and more attractive in automobile, correspondence, medical treatment, environmental protection, aviation and aerospace. Due to the size effect, the tribological problems that exist in the MEMS should not be neglected. Because of its excellent physical and mechanical behavior, silicon has become the typical structural material in MEMS. It is essential to investigate the effect of crystal plane orientation and sliding velocity on the friction and wear behaviors of silicon. Moreover, manufacturing speed of silicon material has significant impacts on its quality and efficiency during the ultra-smooth surface manufacturing process. Therefore, the investigation on the effect of velocity on the wear behavior of silicon under various contact size may not only help the improvement of the nanofabrication technique of silicon, but also optimize the tribological design of MEMS.The effect of crystal plane orientation and sliding velocity on the friction and wear behaviors of monocrystalline silicon under various contact size was studied by nanoscratch and the servo hydraulic dynamic test machine. The damage characteristic of silicon was analyzed by Atomic Force Microscope (AFM), Laser Confacal Scanning Microscopy (LCSM), Opitical Microscopy (OM) and Dual-mode3D morphology analyzer (AEP, NanoMap-D). The main experimental results and conclusions can be summarized as below.(1) Under single-asperity contact conditions, the surface damage of monocrystalline silicon was characterized as the formation of hillock under low load. The height of hillock on Si(100) was the highest, whereas the height of hillock on Si(111) was the lowest. With the increase in the normal load, the surface damage of silicon was identified as the generation of groove and the crystal orientation had little influence on the wear of monocrystalline silicon.(2) It was found that both the contact size and sliding velocity played significant roles in the friction-induced surface damage of silicon. When the contact size was small enough to be considered as single-asperity contact, the height of hillock was lower with the increase in the sliding velocity. As the contact pressure increased above the hardness of silicon, the higher the sliding velocity, the more difficult the plastic deformation of the material in the contact area, and the shallower the groove. As a comparison, when the contact size was large enough to be considered as multi-asperity contact, the silicon surface may be worn even though the contact pressure was much lower than the hardness of silicon. During the wear process, both plough, fatigue and oxidation wear occurred simultaneously. With the increase in the sliding velocity, more cracks were initiated, tinier wear debris was generated, and less wear volume was observed.(3) Silicon represented different characteristic of friction and wear under various contact size. Under single-asperity contact conditions, the wear of silicon represented the transition from hillock to groove with the increase in the load. Under multi-asperity contact conditions, the main surface damage of silicon is the material removal of silicon and initiation of crack.