UItra-low friction and edge-pinning effect in large-lattice-mismatch van der Waals heterostructures

Abstract

Two-dimensional heterostructures are excellent platforms to realize twistangle independent ultra-low friction due to their weak interlayer van der Waals interactions and natural lattice mismatch. However, for finite-size interfaces, the effect of domain edges on the friction process remains unclear. Here, we report on the superlubricity phenomenon and the edge pinning effect at MoS 2 /graphite and MoS 2 /h-BN van der Waals heterostructure interfaces. We find that friction coefficients of these heterostructures are below 10 -6 . Molecular dynamics simulations corroborate experiments highlighting the contribution of edges and interface steps to friction forces. Our experiments and simulations provide more information on the sliding mechanism of finite low-dimensional structures, which is vital to understand the friction process of laminar solid lubricants.

Intriguing electronic, optical and photocatalytic performance of BSe, M2CO2monolayers and BSe–M2CO2(M = Ti, Zr, Hf) van der Waals heterostructures

“…Lattice mismatch of BSe, with Ti 2 CO 2 of 4.9%, with Zr 2 CO 2 of 1.2% and with Hf 2 CO 2 of 0.03%, are experimentally achievable 65 and the same hexagonal symmetry realizes the fabrication of BSe–M 2 CO 2 (M = Ti, Zr, Hf) vdW heterostructures. The electronic band structure is very sensitive to layer stacking, 66 therefore we have chosen five possible stacking configurations of BSe–M 2 CO 2 (M = Ti, Zr, Hf) vdW heterostructures, see Fig.…”

“…1, shows that the rst excitonic peak at 3.851 for BSe, 0.286 for Ti 2 CO 2 , 1.79 for Zr 2 CO 2 , and 2.416 eV for the Hf 2 CO 2 monolayer, lies in the visible range of the spectrum, consistent with ref. 61-63. In the case of the photocatalytic response at pH ¼ 0, BSe and Hf 2 CO 2 cross both the 65 and the same hexagonal symmetry realizes the fabrication of BSe-M 2 CO 2 (M ¼ Ti, Zr, Hf) vdW heterostructures. The electronic band structure is very sensitive to layer stacking, 66 therefore we have chosen ve possible stacking congurations of BSe-M 2 CO 2 (M ¼ Ti, Zr, Hf) vdW heterostructures, see Fig.…”

Negative or Positive? Loading Area Dependent Correlation Between Friction and Normal Load in Structural Superlubricity

“…The out-of-plane fluctuation ΔH (Figures 2E,F) provides more information to help us understand this interplay. The out-of-plane fluctuation of the flake is recognized to be the key for energy dissipation in superlubric systems (Van Wijk et al, 2014;Song et al, 2018;Liao et al, 2021). In the case of the small loading area, there are two peaks in ΔH(r).…”

“…Recent studies show that the dissipation behavior of edge atoms contributes greatly to friction, i.e., the edge effect. The edge atoms have a larger degree of freedom (Liao et al, 2021) and contribute 2-5 orders of magnitude greater friction dissipation than that of inner atoms (Wang et al, 2019a;Qu et al, 2020). Since the edge effect directly determines the friction of superlubricity, it is necessary to carefully understand the coupling between the loading edge and the flake edge.…”

“…In MD simulations, usually a uniform normal load is applied to all atoms on the contact area (Van Wijk et al, 2013;Wang et al, 2019d;Mandelli et al, 2019). In SSL experiments, atomic force microscope (AFM) is often used to press and drive the graphite island (Song et al, 2018;Liu et al, 2020a;Liao et al, 2021). The curvature radius of the AFM tip is in the order of 10-100 nm, while the side length of the graphite island is in the order of 1 μm (Liu et al, 2012;Vu et al, 2016;Liu et al, 2018a;Song et al, 2018).…”