Tribology Research Institute, National Traction Power Laboratory, Southwest Jiaotong University, Chengdu 610031, China.
ACS Appl Mater Interfaces. 2012 Mar;4(3):1585-93. doi: 10.1021/am201763z. Epub 2012 Mar 5.
The effects of counter-surface chemistry, relative humidity, and applied normal load on nanowear of single-crystalline silicon were studied with atomic force microscopy. In the absence of humidity, the silicon surface can resist mechanical wear as long as the contact pressure is lower than the hardness of silicon regardless of the counter-surface chemistry (diamond or SiO(2)) and ambient gas type (vacuum, N(2), O(2), air). In these conditions, the sliding contact region is protruded forming a hillock. However, when the relative humidity is higher than ~7%, the hillock formation is completely suppressed and, instead, tribochemical wear of the silicon surface takes place even at contact pressure much lower than the hardness. The tribochemical wear increases drastically in the relative humidity regime where the adsorbed water layer assumes the "solid-like" structure; further increase of wear is small in higher relative humidity regime where the "liquid-like" water layer is formed. It is also noted that the humidity-induced wear occurs only when the counter-surface is SiO(2); but not with the diamond counter-surface. This implies that the interfacial shear of the water-adsorbed SiO(2) surface with a chemically inert counter-surface is not sufficient to initiate the tribochemical wear; both substrate and counter-surface must be chemically reactive. A phenomenological model is proposed to explain the experimental observations.
利用原子力显微镜研究了反式表面化学、相对湿度和外加法向载荷对单晶硅纳米磨损的影响。在没有湿度的情况下，只要接触压力低于硅的硬度，无论反式表面化学（金刚石或 SiO2）和环境气体类型（真空、N2、O2、空气）如何，硅表面都可以抵抗机械磨损。在这些条件下，滑动接触区域会突出形成凸起。然而，当相对湿度高于约 7%时，凸起的形成完全被抑制，取而代之的是硅表面的摩擦化学磨损，即使在远低于硬度的接触压力下也会发生。在吸附水层呈现“固态”结构的相对湿度范围内，摩擦化学磨损急剧增加；在形成“液态”水层的较高相对湿度范围内，磨损的增加很小。还注意到，只有当反式表面是 SiO2 时，湿度才会引起磨损；而与金刚石反式表面则不会。这意味着与化学惰性反式表面吸附的水的 SiO2 表面的界面剪切不足以引发摩擦化学磨损；基底和反式表面都必须具有反应性。提出了一个唯象模型来解释实验观察结果。
