Superlubricity of epitaxial monolayer WS2 on graphene

Abstract

We report the superlubric sliding of monolayer tungsten disulfide (WS 2) on epitaxial graphene (EG) grown on silicon carbide (SiC). Single-crystalline WS 2 flakes with lateral size of hundreds of nanometers are obtained via chemical vapor deposition (CVD) on EG. Microscopic and diffraction analyses indicate that the WS 2 /EG stack is predominantly aligned with zero azimuthal rotation. The present experiments show that, when perturbed by a scanning probe microscopy (SPM) tip, the WS 2 flakes are prone to slide over the graphene surfaces at room temperature. Atomistic force field-based molecular dynamics simulations indicate that, through local physical deformation of the WS 2 flake, the scanning tip releases enough energy to the flake to overcome the motion activation barrier and trigger an ultralow-friction rototranslational displacement, that is superlubric. Experimental observations show that, after sliding, the WS 2 flakes come to rest with a rotation of n/3 with respect to graphene. Moreover, atomically resolved measurements show that the interface is atomically sharp and the WS 2 lattice is strain-free. These results help to shed light on nanotribological phenomena in van der Waals (vdW) heterostacks, and suggest that the applicative potential of the WS 2 /graphene heterostructure can be extended by novel mechanical prospects.

Synthesis and characterization of WS2/graphene/SiC van der Waals heterostructures via WO3−x thin film sulfurization

“…A histogram of the step heights extracted from multiple images of the WS 2 /graphene/SiC surface (all measured at a sample bias of −1.5 V), shown in Fig. 3 (c), exhibits prominently recurring step heights at 0.25 nm, 0.35 nm and ~ 0.68 nm corresponding to the layer thicknesses of SiC, graphene and WS 2 , respectively 38 , 39 .

Figure 3 ( a ) STM image of monolayer WS 2 on epitaxial graphene.

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A review of recent advances in tribology

“…Researchers have also made arduous attempts, such as AFM-based nanomanipulation experiments of gold nanoparticles sliding on HOPG [34], and the superlubricity sliding of monolayer tungsten disulfide (WS 2 ) on epitaxial graphene grown on silicon carbon [35].…”

Effect of Chemical Vapor Deposition WS2 on Viability and Differentiation of SH-SY5Y Cells

“…Transition metal dichalcogenides, especially in their exfoliated flake form, have been used in bioimaging, biosensing, as antimicrobial agents, and to realize nanocomposites for tissue engineering applications to promote cell adhesion and improve mechanical properties of the scaffolds (Kalantar-zadeh et al, 2015;Agarwal and Chatterjee, 2018;Zhou et al, 2020). Tungsten disulfide (WS 2 ) is one of the most studied TMD materials, thanks to its tribological, optical and electrical properties (Ovchinnikov et al, 2014;Büch et al, 2018;Cong et al, 2018).…”