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Effects of Contact Geometry Upon Pull-Off Force Measurements With a Colloidal Probe



Seung Ho Yang, Huan Zhang, Michael Nosonovsky, Koo-Hyun Chung


This paper examines the effects of contact geometry on the pull-off (adhesion) force between a glass sphere (colloidal probe) and a silicon substrate in an environment with controlled relative humidity. An atomic force microscope (AFM) is used to measure the pull-off force between the colloidal probe and the substrate mounted at different tilt angles. The results show that the measured pull-off force is very sensitive to the tilt angle. By using a newly developed direct scanning method, the exact contact geometry is determined for the no-tilt case (or at a zero-tilt angle). 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 substrate. The strong dependence of the adhesion on the tilt angle may result from the change of meniscus dimensions associated with the probe-substrate separation, which in turn is controlled by the highest peak above the probe sphere. Our observation emphasizes the combined role of micro surface shape around the contact and nano roughness within the contact in determining the colloidal probe pull-off force and also micro adhesion force in general.


adhesion, AFM, colloidal probe, contact geometry


, S. , Zhang, H. , Nosonovsky, M. and Chung, K. (2008), Effects of Contact Geometry Upon Pull-Off Force Measurements With a Colloidal Probe, Langmuir (Accessed April 16, 2024)
Created February 5, 2008, Updated February 19, 2017