Nano-tribological characteristics of TiO_2 films on 3-mercaptopropyl trimethoxysilane sulfonated self-assembled monolayer

摘要

Silane coupling reagent (3-mercaptopropyl trimethoxysilane (MPTS)) was used to prepare two-dimensional self-assembled monolayer (SAM) on silicon substrate. The terminal -SH group was in situ oxidized to -SO_3H 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_3H 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.