Strain Effects of Vertical Separation and Horizontal Sliding in Commensurate Two-Dimensional Homojunctions

Strain, as an economic yet controllable approach for structural modulation, frequently plays a vital role in the preparation and performance optimization of two-dimensional nanomaterials (TNMs). Here, utilizing first-principles simulations, the analysis of energetics shows that the biaxial stretching and compressing could facilitate the vertical separation and horizontal sliding in graphene (Gr/Gr), hexagonal boron nitride (h-BN/h-BN), and molybdenum disulfide (MoS₂/MoS₂) bilayers. The quantification of electron redistribution between layers confirmed that the shifts of interlayer charge density (ρ_inter-) and its relative values (Δρ_inter-) are responsible for the vertical separation and horizontal sliding facilitated by biaxial strain. More effortless horizontal sliding was enabled by a smoother potential energy surface because a smaller Δρ_inter- can be acquired under compression, whereas more effortless vertical separation followed a more vulnerable surface energy because a lower ρ_inter- occurs under tensile strain. The vertical and horizontal division of strain effect provides a novel idea for further understanding its pivotal roles in strain engineering of commensurate-contact TNMs, such as mechanical exfoliation and solid lubrication.