Nano/microtribology stick-slip number under an atomic force microscope and its characteristics

The atomic force microscope (AFM) has become a main instrument in observing nano/microtribological characteristics of sample surfaces. In this paper, we investigated the micro-scale adhesive contact between the AFM tip and the sample surface based on the Maugis-Dugdale contact model, and analyzed the energy conversion and dissipation process during the AFM scanning process. A dimensionless stick- slip number eta=root8U(1)h(2)/(k(theta)R(s)(2)) was defined, which can serve as a characteristic index for the appearance of nano/microtribology stick-slip behavior. If the stick- slip number is less than one, i.e., eta<1; the AFM tip slides on the sample surface and no stick- slip behavior occurs in the AFM lateral force signal. When the stick- slip number equals one, i.e., eta=1; the tip jumps on the sample surface and the AFM lateral force signal begins to exhibit a stick- slip behavior but without energy dissipation. Only in the case of eta>1 does the stick- slip behavior appear in the AFM lateral force signal accompanied by an obvious energy dissipation. The defined stick- slip number demonstrates that the nano/microtribological stick- slip behavior is due to the adhesive hysteresis as well as the instability motion of the AFM tip during the scanning process. Finally, the influence on nano/microtribology stick- slip behavior of sample surface energy, surface topography, scanning velocity, spring constant of AFM cantilever probe, etc. are investigated theoretically and experimentally. Various experimental results of nano/microtribology stick-slip behavior under AFM are successfully interpreted according to the stick- slip number.