The effects of stacking mode and thickness on the frictional behaviour of multilayer silicene

Understanding the contact behaviour of 2D materials in nanoscale is of great importance for their applications. In the present work, molecular dynamics simulation is employed to study the frictional behaviour of the AA' and AB stacked multilayer silicene for up to 4 layers placed on the weakly adhesive amorphous SiO₂ substrate with a sliding AFM tip. During the sliding process, the AFM cantilever represented by virtual atoms moves with the velocity of 2 m s^-1 along the zigzag direction under a load of 2 nN at 300 K. The stick-slip frictional behaviour shows high sensitivity to the number of layers. As the thickness increases, the friction force first increases from the monolayer to bilayer and then decreases from the bilayer to 4-layer, which shows an exotic tendency for the first time among all the reported lamellar materials to date where the friction usually decreases monotonically with thickness. For all the investigated thicknesses, the friction on AA'-stacked silicene is slightly larger than the AB stacked counterpart, and the difference diminishes with increasing thickness. The frictional behaviour of AA' bilayer presents the highest peak force with evolving weakening phenomenon induced by a phase transition to the planar structure. Herein, we analyze the frictional force distribution on the tip with kurtosis and skewness as measurement parameters for the commensurability and rigidity components, respectively. The contact area between silicene and the diamond tip is compared for different silicene morphologies. The result shows an affinity between friction and rigidity of multilayer silicene, which is closely related to the interlayer covalent bonds and limited shear between sublayers.