Macroscale Superlubricity on Nanoscale Graphene Moiré Structure-Assembled Surface via Counterface Hydrogen Modulation

Abstract

Interlayer incommensurateness slippage is an excellent pathway to realize superlubricity of van der Waals materials; however, it is instable and heavily depends on twisted angle and super-smooth substrate which pose great challenges for the practical application of superlubricity. Here, macroscale superlubricity (0.001) is reported on countless nanoscale graphene moiré structure (GMS)-assembled surface via counterface hydrogen (H) modulation. The GMS-assembled surface is formed on grinding balls via sphere-triggered strain engineering. By the H modulation of counterface diamond-like carbon (25 at.% H), the wear of GMS-assembled surface is significantly reduced and a steadily superlubric sliding interface between them is achieved, based on assembly face charge depletion and H-induced assembly edge weakening. Furthermore, the superlubricity between GMS-assembled and DLC25 surfaces holds true in wide ranges of normal load (7-11 N), sliding velocity (0.5-27 cm ^-1s), contact area (0.4×10⁴-3.7×10⁴ µm²), and contact pressure (0.19-1.82 GPa). Atomistic simulations confirm the preferential formation of GMS on a sphere, and demonstrate the superlubricity on GMS-assembled surface via counterface H modulation. The results provide an efficient tribo-pairing strategy to achieve robust superlubricity, which is of significance for the engineering application of superlubricity.

Keywords: counterface hydrogen modulation; graphene moiré structures; strain engineering; superlubricity; van der Waals.

Figure 1

Establishment of GMS‐assembled coating. a) Preparation schematic diagram of GMS‐assembled coating. b) ZrO₂ balls before and after ball‐milling. c,d) Scanning electron microscopy (SEM) images of GMS‐assembled coating. e–g) TEM cross‐section images of GMS‐assembled coating, (f) is marked in (e), (g) is marked in (f). h) Moiré patterns of GMS‐assembled coating cut from Figure S1 (Supporting Information). i) Schematic moiré patterns of (h). j) FFT of moiré patterns of (h).

Figure 2

Characterization of GMS‐assembled coating. a) Analytical method illustration of GMS‐assembled coating. b) Evolution of edge and interior sp³‐C bonds obtained from EELS points in Figure 1f. c) Evolution of mass densities and bond fractions obtained from EELS points in Figure 1e. d) HADDF and TEM‐EDS mapping images of Zr, O and C elements. e) Typical Raman spectra of GMS‐assembled coating and original graphene.

Figure 3

Friction behaviors. a) Friction coefficients under the tribo‐pairing of DLC0, DLC12, DLC25 at 7 N, 5 cm ⁻¹s, and 3 mm ball. b) Average friction coefficients of (a). c) Superlubric ranges of GMS‐assembled coating sliding against DLC25. d) Superlubric wear scars of ball‐supported (3, 5, and 10 mm) GMS‐assembled coating sliding against DLC25 at 7 N and 5 cm ⁻¹s. e) Average friction coefficients obtained from (c). f) Friction coefficient, normal load, sliding velocity, contact area, and contact pressure ranges obtained from (e). The steady‐state apparent average contact pressure is calculated based on (d). g) Friction coefficients for GMS‐assembled coating sliding against DLC25 at 7 N, 5 cm ⁻¹ s, and 5 mm ball.

Figure 4

Wear behaviors. a–d) Laser‐interference surface images, Raman mapping images and Raman spectra of the wear scars and tracks of GMS‐assembled coating/DLC0, GMS‐assembled coating/DLC12, GMS‐assembled coating/DLC25 and ZrO₂/DLC25 tribo‐pairs. e) Average roughness. f,g) 2D morphologies of wear track inside and outside marked in (c).

Figure 5

MD simulations of GMS formation. a) Atomic snapshots (0 and 75 ps) of GMS formation on a hemisphere. b) Strain distribution maps at each snapshots of top and lower graphene. The blue and red represent upward and downward strain. c) Maximum strain results. d) Total energy changes.

Figure 6

MD simulation between GMS‐assembled and DLC surfaces. a) Friction models of eight GMS‐assembled and CBG‐assembled flake on DLC. b,c) Structure models. d) Friction results. e) Relative potential energy images between GMS‐assembled and DLC25 surfaces, and between CBG‐assembled and DLC25 surfaces. f) The energy curves as marked in (e,g). g) Relative potential energy images between GMS‐assembled and DLC0 surfaces, or GMS‐assembled and DLC12 surfaces, respectively. h) Friction results on DLC surfaces under the tribo‐pairing of GMS‐assembled and CBG‐assembled surfaces.

Figure 7

DFT calculations of interface between GMS face and DLC25. a) Schematic illustration of the surface and interlayer of bilayer graphene. b) 2D electron density difference maps for the GMS and CBG surfaces at different perpendicular heights as marked in (a). The twisted angles between bilayer graphene of GMS and CBG are 0° and 30.0°, respectively. c,d) 3D electron density difference maps (0.0005 e Å⁻³) of GMS and CBG showing an assembly face charge depletion behavior. e–g) Electron density differences (e), and PES corrugation (f) and curves (g) of CBG/H‐diamond interface. h–j) Electron density differences (h), and PES corrugation (i) and curves (j) of GMS/H‐diamond interface. The blue and red in the (c–e,h) represent electron accumulation and depletion.