Humidity Dependence of Tribochemical Wear of Monocrystalline Silicon

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• 作者：Xiaodong Wang ; Seong H. Kim ; Cheng Chen ; Lei Chen ; Hongtu He ; Linmao Qian
• 刊名：ACS Applied Materials & Interfaces
• 出版年：2015
• 出版时间：July 15, 2015
• 年：2015
• 卷：7
• 期：27
• 页码：14785-14792
• 全文大小：472K
• ISSN：1944-8252

文摘

The nanowear tests of monocrystalline silicon against a SiO₂ microsphere were performed using an atomic force microscope in air as a function of relative humidity (RH = 0%鈥?0%) and in liquid water at a contact pressure of about 1.20 GPa. The experimental results indicated that RH played an important role in the nanowear of the Si/SiO₂ interface. In dry air, a hillock-like wear scar with a height of 鈭?.4 nm was formed on the silicon surface. However, with the increase of RH, the wear depth on the silicon surface first increased to a maximum value of 鈭?4 nm at 50% RH and then decreased below the detection limit at RH above 85% or in water. The transmission electron microscopy analysis showed that the serious wear on the silicon surface at low and medium RHs occurred without subsurface damage, indicating that the wear was due to tribochemical reactions between the Si substrate and the SiO₂ counter surface, rather than mechanical damages. The RH dependence of the tribochemical wear could be explained with a model involving the formation of 鈥淪i鈥擮鈥擲i鈥?chemical bonds (bridges) between two solid surfaces. The suppression of tribochemical wear at high RHs or in liquid water might be attributed to the fact that the thickness of the interfacial water layer is thick enough to prevent the solid surfaces from making chemical bridges. The results may help us understand the nanowear mechanism of silicon that is an important material for dynamic microelectromechanical systems.