Friction mechanism and lubricant coverage study using laser bumps as model asperities

Realizing that the long-range molecular interactions scale effectively with number of contact spots whereas the short-range molecular interactions scale with contact area, we study friction mechanisms and lubricant coverage using three types of model surfaces with different bump densities. The kinetic friction coefficient for all three-model surfaces converged to the same value of ~0.15 for lubricant thickness thicker than 3 nm, indicating that a full lubricant coverage was reached. The dependence of the kinetic friction on lubricant thickness for various bump densities can be described by a linear equation with different slopes, resulting from the interplay of partial lubrication and long-range molecular interactions. Formulae for calculation of interaction forces are derived for spherical and crater bumps with a magnetic head. Interaction forces are experimentally derived for crater bumps