Thin-film friction and adhesion studies using atomic force microscopy

An atomic force microscope is used to study the effect of tip radius and hu midity on the adhesive force and coefficient of friction. Samples studied a re Si (100), 2 nm thick bonded perfluoropolyether lubricant (Z-DOL) coated Si (100), 20 nm thick diamond-like carbon (DLC) coated Si (100) and plasma etched DLC coated Si (100). Tip diameters ranged from 100 nm to 14.5 mu m. It is observed that both adhesive force and coefficient of friction are str ongly dependent on the tip radius and humidity. The change is caused by the formation of meniscus bridges from capillary condensation of water vapor. DLC coated surface is rather insensitive to the changes in the radius and h umidity because of its passivated surface. Etching of DLC activates the sur face and makes it sensitive to the environment. In addition, a technique is developed to get adhesive force maps of surfaces, which can be used to obt ain an estimate of film thickness only a couple of monolayers thick. Exampl es and applications of this technique are presented. (C) 2000 American Inst itute of Physics. [S0021-8979(00)05503-1].