Abstract
Friction anisotropy is one of the important friction behaviors for two-dimensional (2D) van der Waals (vdW) crystals. The effects of normal pressure and thickness on the interfacial friction anisotropy in few-layer graphene, h-BN, and MoSe2 under constant normal force mode have been extensively investigated by first-principle calculations. The increase of normal pressure and layer number enhances the interfacial friction anisotropy for graphene and h-BN but weakens that for MoSe2. Such significant deviations in the interfacial friction anisotropy of few-layer graphene, h-BN and MoSe2 can be mainly attributed to the opposite contributions of electron kinetic energies and electrostatic energies to the sliding energy barriers and different interlayer charge exchanges. Our results deepen the understanding of the influence of external loading and thickness on the friction properties of 2D vdW crystals.
Highlights
Layered van der Waals materials such as graphite, boron nitride, and transition metal dichalcogenides (TMDs) which layers bind with weak interlayer vdW interactions, have been widely used as solid lubricants in engineering technology to reduce friction and wear
Lee et al [1] used atomic force microscopy (AFM) technique to characterize the microscopic friction characteristics of monolayer and multilayer graphene, MoS2, hexagonal boron nitride (h-BN), and NbSe2 that were mechanically peeled off from weakly adherent SiO2 substrates, and reveal that the friction force decreases with the increase of the number of layers
Negative friction coefficients are found at the interfaces of layered graphene-hexagonal boron nitride (h-BN) heterojunctions due to load-induced suppression of out-of-plane distortions [8], and the interfaces between graphene sheets and the tip of atomic force microscope tip [9,10]
Summary
Layered van der Waals (vdW) materials such as graphite, boron nitride, and transition metal dichalcogenides (TMDs) which layers bind with weak interlayer vdW interactions, have been widely used as solid lubricants in engineering technology to reduce friction and wear. It is necessary to use more accurate methods to investigate the interfacial friction behaviors of 2D vdW crystals in the presence of ideal constant normal force. The effects of normal pressure and thickness on the interlayer friction anisotropy of few-layer. The interfacial friction properties of few-layer graphene, h-BN, and MoSe2 under constant normal force mode have been extensively studied by using first-principles calculations. The increase of layer number increases the friction anisotropy in graphene and h-BN and decreases that in MoSe2. The significant difference in the influence of normal pressure and layer number on the friction anisotropy among these three kinds of 2D vdW crystals can be attributed to different interlayer charge exchanges and the opposite changes in electron kinetic energies and electrostatic energies. Our results deepen the understanding of the effects of normal pressure and thickness on the friction behaviors of 2D vdW crystals
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