Nano-tribological characteristics of TiO2 films on 3-mercaptopropyl trimethoxysilane sulfonated self-assembled monolayer

Abstract

Silane coupling reagent (3-mercaptopropyl trimethoxysilane (MPTS)) was used to prepare twodimensional self-assembled monolayer (SAM) on silicon substrate. The terminal -SH group was in situ oxidized to -SO 3 H group to endow the film with good chemisorption ability. Then TiO 2 thin films were deposited on the oxidized MPTS-SAM to form composite thin films, making use of the chemisorption ability of the -SO 3 H group. Atomic force microscope (AFM) and contact angle measurements were used to characterize TiO 2 films. Adhesive force and friction force of TiO 2 thin films and silicon substrate were measured under various applied normal loads and scanning speed of AFM tip. Results showed that the friction force increased with applied normal loads and scanning speed of AFM tip. In order to study the effect of capillary force, tests were performed in various relative humidities. Results showed that the adhesive force of silicon substrate increases with relative humidities and the adhesive force of TiO 2 thin films only increases slightly with relative humidity. Research showed that surfaces with more hydrophobic property revealed the lower adhesive and friction forces.

Tribological properties of nanostructured TiO2 coatings

“…It has been described that the adhesive force of TiO 2 films surface is lower than that of silicon substrate 14,15. The result implies that the wetting characteristics are also important factors which influence the adhesion.…”

“…It has been described that the adhesive force of TiO 2 films surface is lower than that of silicon substrate. 14,15 The result implies that the wetting characteristics are also important factors which influence the adhesion. The difference between the friction behaviour of TiO 2 thin films and the substrate arises due to differences in surface energy and roughness.…”