The Preparation and Friction Behavior of Rare Earth Nanofilm

The Preparation and Friction Behavior of Rare Earth Nanofilm
　　As a cutting-edge technology in late 20’s, Micro Electro Mechanical Systems (MEMS) is developing quite rapidly. The abrasion and lubrication of MEMS determines the properties of the whole MEMS system, stability and life-span. Self-assembled Monolayers (SAMs) possess characteristics including simple manufacturing process, outstanding anti-abrasion properties.Self-assembly technique is adopted in this research project. After 3-Mercapto-propyl trimethoxysilane (MPTS) thin film was prepared compactly and orderly on the surface of SiO2 and single-crystal silicon wafer and–SH group was oxidized into–SO3H group, lanthanum-based thin films were deposited on top. By taking advantages of the chemical bond established between the substrate surface and multilayer Block Neodymium magnets thin film caused by the strong chemical force between lanthanum and metal element, we were able to obtain lanthanum-based thin films of low surface energy and good lubricant properties, thus to reduce the micro-abrasion of the thin film. As indicated by experimental research and theoretical analysis, the preparation mechanism and tribological properties of lanthanum-based self-assembled monolayers was studied and proven.Atomic Force Microscope (AFM) was used to observe the surface morphology of the thin film; X-ray photoelectron spectrometry (XPS) was used to analyze the chemical status of typical elements on the surface of the thin film. In this study, self- assemble technique has been used to prepare thin films in view of the defects of currently used surface modification methods in MEMS.
　　The mechanical and tribological properties have been improved due to the special physical chemical characteristics of rare earths.Firstly, silane coupling regent (3-mercaptopropyl trimethoxysilane (MPTS)) was prepared on a single-crystal silicon substrate to form a two-dimensional self-assembled monolayer (SAM). The terminal–SH group in the film was oxidized in situ to–SO3H group to endow the film with good chemisorption trend. Lanthanum-based thin films were deposited on the oxidized MPTS-SAM by the chemisorption of the–SO3H group.Secondly, the surface energy, chemical composition, phase transformation and surface morphology of the films were analyzed by contact angle measurements, X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). The experimental results strongly indicated that the lanthanum-based thin films were absorbed on the oxidized MPTS-SAM and the rare-earth film could react with the substrate by chemical bond which improved the bonding strength of the coating-substrate.
　　Thirdly, the friction and wear behaviors of the RE Block Neodymium magnets  thin films were investigated systematically. The results showed that the RE thin films had superior friction reduction and longer wear life.Fourthly, atomic force microscopy was used to analyze the micro wear of RE thin films surface. The results showed that, due to very low surface adhesion and strong bonding strength with sulfonate group, RE thin films have excellent wear resistances.This study is the first effort to prepare RE thin films using self-assembly technique, and also the first time to use atomic force microscopy, X-ray photoelectron spectroscopy, contact angle measurement were used to characterize the films. The mechanism and characteristic of RE thin films were clarified. This study is promising to be applied in MEMS devices surface modification and the application of the RE thin films self- assembling technique in MEMS.