Xiao Chen, Chen Chao, Yao Yangyang, Liu Hongshen, Chen Lei, Qian Linmao, Kim Seong H
Tribology Research Institute, State Key Laboratory of Traction Power, Southwest Jiaotong University, Chengdu 610031, China.
Department of Chemical Engineering and Materials Research Institute, The Pennsylvania State University, University Park, State College, Pennsylvania 16802, United States.
Langmuir. 2020 May 26;36(20):5483-5491. doi: 10.1021/acs.langmuir.0c00205. Epub 2020 May 13.
The interfacial adhesion between silicon oxide surfaces is normally believed to be governed by the surface chemistry of the topmost surface affecting the water contact angle and hydrogen bonding interactions. In the case of a silicon wafer, the physical structure of the native oxide at the surface can vary drastically depending on the aging process; thus, not only the surface chemistry but also the history of surface treatment can also have a profound impact on nanoasperity adhesion. This study reports the effect of aging conditions (ambient air, liquid water, and liquid ethanol) on the nanoasperity adhesion behaviors of a silicon surface. When the silicon surface is kept in liquid alcohol, the surface remains hydrophobic, and adhesion in ambient air can be explained with the capillary effect of the liquid meniscus condensed around the annulus of the nanoasperity contact. When the silicon surface is oxidized in ambient air, the surface gradually becomes hydrophilic, and the strongly hydrogen-bonded water network of adsorbed water plays a dominant role in the nanoasperity interfacial adhesion force. When the silicon surface is aged in liquid water, the interfacial adhesion force measured in ambient air is significantly larger than the value predicted from the theoretical model based on the water contact angle and the hydrogen bonding interaction at the topmost surface. This is because the surface layer oxidized in liquid water is gel-like and thus can swell upon uptake of water from the humid air. To fully encompass all these behaviors, a solid-adsorbate-solid model predicting the adhesion force is developed by introducing a fitting parameter β, which can be adjusted depending on the adsorbed water structure and the swelling capacity of the oxidized surface layer.
通常认为，氧化硅表面之间的界面粘附力受最顶层表面的表面化学性质支配，这会影响水接触角和氢键相互作用。对于硅片，表面原生氧化物的物理结构会因老化过程而发生显著变化；因此，不仅表面化学性质，而且表面处理历史也会对纳米粗糙度粘附力产生深远影响。本研究报告了老化条件（环境空气、液态水和液态乙醇）对硅表面纳米粗糙度粘附行为的影响。当硅表面保持在液态醇中时，表面保持疏水状态，环境空气中的粘附力可以用纳米粗糙度接触环周围凝聚的液体弯月面的毛细管效应来解释。当硅表面在环境空气中氧化时，表面逐渐变得亲水，吸附水形成的强氢键水网络在纳米粗糙度界面粘附力中起主导作用。当硅表面在液态水中老化时，在环境空气中测量的界面粘附力明显大于基于水接触角和最顶层表面氢键相互作用的理论模型预测的值。这是因为在液态水中氧化的表面层呈凝胶状，因此在从潮湿空气中吸收水分时会膨胀。为了全面涵盖所有这些行为，通过引入一个拟合参数β建立了一个预测粘附力的固体-吸附质-固体模型，该参数可根据吸附水结构和氧化表面层的膨胀能力进行调整。
