Investigation of Tribological Behavior of Lanthanum-Based Thin Films Deposited on Sulfonated Self-Assembled Monolayer

Abstract

3-mercaptopropyl trimethoxysilane (MPTS) was prepared on glass substrate so as to form a two-dimensional self-assembled monolayer (SAM), and the terminal -SH group in the film was in situ oxidized to -SO 3H group to confer good chemisorption ability to the film. Thus, lanthanum-based thin films were deposited on oxidized MPTS-SAM, making use of the chemisorption ability of -SO 3H group. Atomic force microscopy (AFM) and X-ray photoelectron spectrometry (XPS) and contact angle measurements 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. Tribological experiment shows that the friction coefficient of glass substrate decreases from 0.8 to 0.08 after the rare earth (RE) self-assembled films (SAMs) are formed on its surface. And the RE self-assembled films have longer wear life (500 sliding passes). It is demonstrated that RE self-assembled film exhibits good wear-resistant property. The marked decrease in friction and the longer wear life of RE films are attributed to the excellent adhesion of the film to the substrate and to the special characteristics of the RE elements. The frictional behaviors of RE thin-films-coated silicon surface were sensitive to the applied load and the sliding velocity of the steel ball.