Micro- and macro-tribological study on a self-assembled dual-layer film

A novel self-assembled dual-layer film as apotential excellent lubricant for micromachines was successfully prepared on single-crystal silicon substrate by chemical adsorption of stearic acid (STA) molecules on self-assembled monolayer of 3-aminopropyltriethoxysilane (APS) with terminal amino group. The structure and morphology of the film were characterized by means of contact-angle measurement, ellipsometric thickness measurement, Fourier transformation infrared spectrometric analysis, and atomic force microscopic analysis. The micro- and macro-tribological properties of the dual-layer film were investigated as well. As the results, the dual-layer STA-APS film was hydrophobic with the contact angle for water to be about 98degrees and the overall thickness about 2.2 nm. Atomic force microscopic images showed that the APS surface was characterized by defects such as small grains and holes; it became relatively smooth and homogeneous after the self-assembly of the STA film. The STA-APS film possessed good adhesive resistance and could greatly reduce the micro- and macrofriction force. Moreover, it registered better load-carrying capacity and antiwear ability than the self-assembled monolayer of octadecyltrichlorosilane (OTS) in sliding against the ceramic counterface. Thus, the dual-layer self-assembled film might find promising application in the lubrication of micro-electromechanical systems (MEMS).