Yang Seungho, Zhang Huan, Nosonovsky Michael, Chung Koo-Hyun
National Institute of Standards and Technology, 100 Bureau Drive, Gaithersburg, Maryland 20899, USA.
Langmuir. 2008 Feb 5;24(3):743-8. doi: 10.1021/la701900f. Epub 2008 Jan 3.
This paper examines the effects of contact geometry on the pull-off (adhesion) force between a glass sphere (colloidal probe) and a silicon wafer in an environment with controlled relative humidity. An atomic force microscope is used to measure the pull-off force between the colloidal probe and the sample mounted at different tilt angles. The results show that the measured pull-off force is very sensitive to the tilt angle. Through the use of a newly developed direct scanning method, the exact contact geometry is determined for the zero-tilt angle case. The obtained digital image is then rotated to determine the contact geometry for the cases with other tilt angles. A detailed examination of the contact geometry, along with a magnitude analysis of the capillary force, suggests that the adhesion is most likely dominated by the capillary force from the meniscus formed between the probe and the sample. The strong dependence of the adhesion on the tilt angle may result from the change of meniscus dimensions associated with the probe-sample separation, which in turn is controlled by the highest peak on the probe sphere. Our observation emphasizes the combined role of microsurface shape near the contact and nanoroughness within the contact in determining the colloidal probe pull-off force and also microadhesion force in general.
本文研究了在相对湿度可控的环境中，接触几何形状对玻璃球体（胶体探针）与硅片之间的拉脱（粘附）力的影响。使用原子力显微镜测量胶体探针与以不同倾斜角度安装的样品之间的拉脱力。结果表明，测量得到的拉脱力对倾斜角度非常敏感。通过使用新开发的直接扫描方法，确定了零倾斜角度情况下的精确接触几何形状。然后旋转获得的数字图像，以确定其他倾斜角度情况下的接触几何形状。对接触几何形状的详细研究以及对毛细力的大小分析表明，粘附力很可能主要由探针与样品之间形成的弯月面产生的毛细力主导。粘附力对倾斜角度的强烈依赖性可能是由于与探针 - 样品分离相关的弯月面尺寸变化导致的，而这种变化又由探针球体上的最高峰控制。我们的观察强调了接触附近微观表面形状和接触内部纳米粗糙度在决定胶体探针拉脱力以及一般微粘附力方面的综合作用。
