EFFECTS OF SURFACE-DEFECTS ON FRICTION FOR A THIN SOLID FILM SLIDING OVER A SOLID-SURFACE

Effects of the most common surface defects. namely, vacancies, substit utional impurities, steps and facet boundaries, on the force of fricti on acting on a sliding film are studied theoretically using lowest-ord er perturbation theory in the force exerted on film due to the surface on which the film is sliding. It is found that the contribution to th e force of friction due to point defects, such as vacancies and substi tutional impurities, is velocity-independent (i.e., there is ''dry fri ction''). In contrast, for straight line defects, such as steps and fa cet boundaries, for nearly all orientations of the defect-relative to the crystallographic axes, the viscous friction law generally observed in the microbalance experiment is found. Implications for the interpr etation of the experimental results are discussed. The range of parame ters for which lowest-order perturbation theory is valid is tested by calculating the mean-square atomic displacement and requiring that it be much smaller than the square of an atomic spacing. [S0163-1829(98)0 3308-6].