The Adhesion Force in Nano-Contact During Approaching and Retrieving Processes

Atomistic simulations are used to test the continuum contact theories on the micro scale. Nominally spherical tips are pressed into a flat substrate. The force-displacement curves obtained contain information about the relationship between the adhesion force and the normal displacement. The indenter size is also taken into consideration. Snapshots of atomistic configurations are used to explain the results. Results show that the adhesion effects are different during the approaching and retrieving processes. Which means different effects of surface interaction and would give different solutions of continuum contact theories. What’s more, the maximum normal displacement (D_max) has great impact on the pull-off force, accompanied with different dislocation nucleation, movements and annihilation. Also it is found that the position where the maximum pull-off force occurred is related to the maximum normal displacement and the indenter size. It happens earlier with decreased normal displacement and indenter size.