Capillary Forces between Rough Surfaces Produced by the Micro/Nanotechnology Methods

Abstract

Capillary forces are one of the main sources of adhesion between the elements of microtechnological devices. This phenomenon manifests itself during the fabrication or operation of a device and plays a negative or positive role. The paper describes a method that makes it possible to estimate the capillary force between hydrophilic rough surfaces as a function of the relative humidity and the nominal contact area. The method is based on counting the number of roughness asperities, which are able to form capillary bridges spontaneously. To implement the method, detailed information about the roughness of the contacting surfaces is required, which can be obtained using an atomic force microscope (AFM). The idea of the method is illustrated, using as an example, deposited gold films of different thicknesses that come into contact with a smooth silicon surface. AFM scans of a surface with an area of 20 × 20 µm² and a resolution of 4096 pixels per line are used. The developed theory reproduces the basic patterns observed experimentally. In particular, it is shown that the relative role of capillary forces decreases with an increase in the nominal contact area, and dispersion forces begin to play a major role in adhesion. The results of the work are important for the design of microsystems and for experiments measuring dispersion forces.