Interfacial adhesion and friction are important factors in determining the performance and reliability of microelectro- mechanical systems. We demonstrate that the adhesion of micromachined surfaces is in a regime not considered by standard rough surface adhesion models. At small roughness values, our experiments and models show unambiguously that the adhesion is mainly due to van der Waals dispersion forces acting across extensive non-contacting areas and that it is related to 1/Dave2, where Dave is the average surface separation. These contributions must be considered because of the close proximity of the surfaces, which is a result of the planar deposition technology. At large roughness values, van der Waals forces at contacting asperities become the dominating contributor to the adhesion. In this regime our model calculations converge with standard models in which the real contact area determines the adhesion. We further suggest that topographic correlations between the upper and lower surfaces must be considered to understand adhesion completely.
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Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the US Department of Energy’s National Nuclear Security Administration under contract DE AC04-94AL85000. The authors would like to thank A. Corwin for help in collecting experimental data and B. McKenzie for the SEM images.
The authors declare no competing financial interests.
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DelRio, F., de Boer, M., Knapp, J. et al. The role of van der Waals forces in adhesion of micromachined surfaces. Nature Mater 4, 629–634 (2005). https://doi.org/10.1038/nmat1431
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