Abstract
In micro∕nanoelectromechanical systems (MEMS∕NEMS), surface-dominated forces, such as stiction∕adhesion and friction, play an important role because of the large surface-area-to-volume ratio. In order to control these forces and wear properties, optimal lubricant systems have been extensively investigated. Perfluoroalkyl self-assembled monolayers (SAMs) are considered to be a strong candidate since the fluorinated carbon backbones are expected to show lower adhesion and friction. In this paper, surface properties of perfluoroalkylsilane SAMs are investigated and compared with those of standard alkylsilane SAMs. The SAMs are deposited on silicon with a native oxide layer and silica substrates by a vapor deposition process. Surface properties, such as surface energy, water contact angle, roughness, adhesive and friction forces, and wear resistance, are evaluated. An atomic force microscope (AFM) is used for evaluations of the micro∕nanotribological properties. The influence of humidity, temperature, and sliding velocity is also examined. In addition, the tribological mechanisms of the SAMs on molecular scale are discussed based on the AFM observations to aid the design and selection of proper lubricants for MEMS∕NEMS.