Nonmonotonic Effects of Atomic Vacancy Defects on Friction

Abstract

The presence of defects such as vacancies has a significant impact on the frictional properties of 2D materials that are excellent solid lubricants. In this study, we demonstrate that the nonmonotonic effect of Te vacancy defects on the friction of MoTe2 is related to the change in the maximum sliding energy barrier due to the variation in tip position. The experimental results of atomic force microscopy suggest that the friction shows an overall increasing trend with the increase in Te vacancy density, but this variation is nonmonotonic. Molecular dynamics simulations show that the increase in friction force with defect density can be attributed to the large and more sliding energy barriers that the tip has to overcome. Furthermore, the nonmonotonic variation of friction with defect density is dominated by the change of the maximum sliding potential barrier caused by the variation of tip position perpendicular to the sliding direction during the sliding process. Additionally, the uneven charge distribution due to charge transfer occurring at the defect also contributes to the increase in friction. This work shows the mechanism of the effect of Te vacancy defects on the friction of MoTe2, which provides guidance for the modulation of the frictional properties of solid lubricants.

Atomistic simulations of the frictional properties of 2D materials: a review

“…The degree of vacancy defect effect on friction enhancement follows: V Mo < V S < V S2 < V MoS3 < V MoS6 . Zhang et al [107] performed MD simulations to investigate the increase in friction force with Te vacancy defect in MoTe 2 and attribute it to the large and more sliding energy barriers that the tip overcome as shown in figures 8(g) and (h). Their simulations found that the nonmonotonic variation of friction with defect density is due to that the variation of tip in-plane position perpendicular to the sliding direction during the sliding process, which changes of the maximum sliding potential barrier as shown in figure 8(i).…”

“…force field and electronic field, is an effective avenue to manipulate the frictional properties of 2D materials, and intensive atomistic simulations have addressed on this topic. Sun et al [109] found that the interlayer sliding friction of a graphene/graphene interface can decrease Reprinted with permission from [107]. Copyright (2023) American Chemical Society.…”

“…(g)-(i) PES of the MoTe 2 with a single Te atomic vacancy and potential energy distributions for 6 fixed Y values, showing the vacancy will enlarge sliding barriers. The sliding trajectory change of the tip with different defect densities explains its nonmonotonic variation of friction with defect density [107].Reprinted with permission from[107]. Copyright (2023) American Chemical Society.…”