Investigation of the tribological behavior of 3-mercaptopropyl trimethoxysilane deposited on silicon

Abstract

3-Mercapto-propyl trimethoxysilane (MPTS) thin film was prepared on hydroxylated silicon substrates by a self-assembling process and the terminal −SH group in the film was in situ oxidized to −SO 3H group. Atomic force microscope (AFM) and X-ray photoelectron spectroscopy (XPS) were used to characterize the thin films. The tribological properties of the as-prepared thin films sliding against a steel ball were evaluated on a friction and wear tester. It was found that the macroscopic friction coefficients for coating times more than 1 h ranged between 0.1 and 0.2 whereas the value for short coating time was as high as 0.7. And the friction coefficient was higher for the SAM with functional group −SO 3H compared to the SAM having −SH group. Surface energy of the substrate can be obviously increased when the terminal group (−SH) of self-assembly monolayers was oxidized into sulfonate one (−SO 3H) which can reduce the adhesion force of the moving surfaces. It was also found that the frictional behaviors of MPTS coated silicon surface sensitive to applied load and sliding velocity.