MECHANISM OF LUBRICATION BY A THIN SOLID FILM ON A METAL-SURFACE

Molecular dynamics simulations of frictional sliding of a tip over a f lat substrate in the presence of a lubricating solid film of one or tw o atomic layers thickness are presented. The role of adhesion in promo ting wear is discussed by reference to earlier simulations of friction al sliding in the absence of a lubricating layer. Two conditions for l ubrication are identified. First, the shear strength of the interface between the tip and the film must be lower than the shear strength of the tip or the underlying substrate. Secondly, the film must have a su fficient strength in compression to prevent penetration of the film by the tip. The importance of lubrication in obtaining images from the f rictional force microscope is also discussed.