Threshold contact pressure for the material removal on monocrystalline silicon by SiO2 microsphere

By using an atomic force microscope, the nanowear tests of Si(100) surface against SiO2 microsphere were performed both in humid air and in water. The experimental results indicated that mechanical interaction could significantly enhance the tribochemical wear of Si/SiO2 pair. There existed a threshold pressure (~1.1 GPa) for tribochemical wear under one sliding cycle at 50% RH, which was much less than the mechanical threshold pressure (~10.9 GPa) for the initial yield of Si(100). When the wear tests were performed in water, such threshold pressure can be further reduced to less than 0.28 GPa. The reason can be explained to the facilitative tribochemical reaction in water, which was induced by the formation of more Si-O-Si bonding bridges and rupture of more Si-Si networks. Meanwhile, when the number of sliding cycles increased to 70, the threshold pressure of Si/SiO2 pair at 50% RH can also be reduced to 0.28 GPa, which may be attributed to the accumulation of residual energy within the contact area. The results may help us optimize the tribological design of dynamic MEMS and realize the high-precision polishing process under ultralow pressure.