Effect of Compressive Prestrain on the Anti-Pressure and Anti-Wear Performance of Monolayer MoS2: A Molecular Dynamics Study

Abstract

The effects of in-plane prestrain on the anti-pressure and anti-wear performance of monolayer MoS₂ have been investigated by molecular dynamics simulation. The results show that monolayer MoS₂ observably improves the load bearing capacity of Pt substrate. The friction reduction effect depends on the deformation degree of monolayer MoS₂. The anti-pressure performance of monolayer MoS₂ and Pt substrate is enhanced by around 55.02% when compressive prestrain increases by 4.03% and the anti-wear performance is notably improved as well. The improved capacities for resisting the in-plane tensile and out-of-plane compressive deformation are responsible for the outstanding lubrication mechanism of monolayer MoS₂. This study provides guidelines for optimizing the anti-pressure and anti-wear performance of MoS₂ and other two-dimension materials which are subjected to the in-plane prestrain.

Keywords: anti-wear; compressive prestrain; molecular dynamics; monolayer MoS2.

Figure 1

MD simulation model of a diamond tip and MoS₂/Pt substrate.

Figure 2

After relaxation process, (a) atomic morphology of monolayer MoS₂ (color symbolizing the atomic heights of S layer on the top). (b) Surface roughness of the monolayer MoS₂ under different compressive prestrain conditions.

Figure 3

(a) The force-depth relations of the MoS₂/Pt substrate (black curve) and the bare Pt substrate (blue-violet curve) with the indentation process, the number of broken bonds in monolayer MoS₂ during the indentation process (red curve). (b) The force-depth curves (black curve) and the number of broken bonds (red curve) of the MoS₂/Pt substrate with different compressive prestrains. (c) The contact pressure curves between the diamond tip and MoS₂ before the bonds breaks. (d) The critical load forces of the MoS₂/Pt substrate with different compressive prestrains.

Figure 4

Radially averaged deformation distribution of monolayer MoS₂ (a) and Pt substrate (b) at the end of the elastic stage, obtained by averaging the atomic displacement from the center of the contact area at radial intervals of 2.0 Å. To better reflect the deformation of the Pt substrate, only the top three layers of Pt atoms are considered.

Figure 5

Evolution of D_(Mo–S) (a) D_(Mo–Mo) (b) and D_(S–S) (c) for atoms in the contact area between the diamond tip and MoS₂ during the indentation process. Radially averaged distance distribution of D_(S–S) for MoS₂ at the end of the elastic stage (d) and at the critical loading depth (e), which is obtained by averaging the D_(S–S) from the center of the contact area at radial intervals of 3.0 Å. (f) The ultimate strains of D_(Mo–S), D_(Mo–Mo), and D_(S–S) before the critical loading depth of each model, respectively.

Figure 6

Cutaway view of the model and the friction-distance curves during the sliding process, (a,b) indentation depth = 1.5 Å at elastic stage; (c,d) indentation depth = 5.4 Å, at plastic stage; (e,f) indentation depth = 8.4 Å at the critical loading depth. (g) Average friction varies with the indentation depths during the sliding process.

Figure 7

During the sliding process, the friction-distance relation curves (a) and the number of broken bonds (b) of each model at the critical loading depth with ideal monolayer MoS₂ (8.4 Å). (c) The average friction under various compressive prestrains, obtained by averaging the friction force when the friction is stable.

Figure 8

(a) The average contact area between the diamond tip and MoS₂ with different in-plane compressive prestrain, obtained by averaging the contact area during the sliding process; Evolution of D_(Mo–S) (b), D_(Mo–Mo) (c), and D_(S–S) (d) for atoms in the contact area between the diamond tip and MoS₂, when the friction is stable.