Nanotribological characterization of self-assembled monolayers deposited on silicon and aluminium substrates

Silicon and aluminium are the substrates of choice for various micro/nanoelectromechanical systems (MEMS/NEMS) including digital micromirror devices (DMD (R)). For efficient and failure-proof operation of these devices, ultrathin lubricant films of self-assembled monolayers (SAMs) are increasingly being employed. In this study, we investigate friction, adhesion and wear properties of various SAMs. Surface properties such as contact angle, adhesive force, friction force and coefficient of friction are compared for SAMs with hydrocarbon and fluorocarbon backbone chains with different chemical structures, chain lengths and end groups. The influence of relative humidity, temperature and sliding velocity on the friction and adhesion behaviour is studied for various SAMs. Failure mechanisms of SAMs are investigated by wear tests and the potential mechanisms involved are discussed. These studies are expected to aid the design and selection of proper lubricants for MEMS/NEMS.