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

Molecular dynamics simulations of frictional sliding of a tip over a flat substrate in the presence of a lubricating solid film of one or two atomic layers thickness are presented. The role of adhesion in promoting wear is discussed by reference to earlier simulations of frictional sliding in the absence of a lubricating layer. Two conditions for lubrication 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 sufficient strength in compression to prevent penetration of the film by the tip. The importance of lubrication in obtaining images from the frictional force microscope is also discussed.