Micro- and Macro-Tribological Study on a Self-Assembled Dual-Layer Film

Abstract

A novel self-assembled dual-layer film as a potential 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 98° 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).