Tribological properties of asperity arrays coated with self-assembled monolayers |
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Authors: | Yasuhisa Ando Yosuke Inoue Kazuo Kakuta Takashi Igari Shigeyuki Mori |
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Affiliation: | (1) National Institute of Advanced Industrial Science and Technology, Advanced Manufacturing Research Institute, 1-2 Namiki, Tsukuba, Ibaraki 305-8564, Japan;(2) Chuo University, Kasuga 1-13-27, Bunkyo-ku, Tokyo, Japan;(3) Iwate University, Ueda 4-3-5, Morioka, Iwate, Japan |
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Abstract: | The effects of a self-assembled monolayer (SAM) coating on the friction and pull-off forces were determined by using two-dimensional
asperity arrays on silicon wafers. The arrays were coated with SAM composed of one of five different alkylchlorsilanes. First,
two-dimensional asperity arrays were created by using a focussed ion beam (FIB) system to mill patterns on silicon plates.
Each silicon plate had different patterns of equally spaced asperities. Each pattern (5 × 5 μm2) had a different radius of curvature of the asperity peaks, ranging from about 200 to 2500 nm. Then, each silicon plate was
immersed in a solution of a different alkylchlorsilane in hexane (either hexyltrichlorosilane, octyltrichlorosilane, dodecyltrichlorosilane,
tetradecyltrichlorosilane, or octadecyltrichlorosilane), thus coating the asperity arrays with SAM. The friction and pull-off
forces on the SAM-coated arrays were measured by using an atomic force microscope (AFM) that had a square flat probe. The
pull-off force for SAM-coated silicon was roughly proportional to the radius of curvature of the asperity peaks. The magnitude
of the pull-off force corresponded approximately to the capillary force calculated by using the contact angle of water on
the surface of SAM. The friction coefficient correlated with the inverse of the alkyl-chain length of the SAM. |
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Keywords: | friction force pull-off force Laplace pressure contact angle chain length atomic force microscope focussed ion beam |
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