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.


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at 292 eV attributable to the 1s-π * and the 1s-σ * electronic transitions. [1]igure S3.Strain analysis of GMS-assembled coating.a-c) original surface, and surfaces after 150 and 300 times taping.d) Raman spectra of newly formed ball surface when original ball surface being gradually glued for 300 times.The splitting of Raman G peak into two subbands G + and G − is analogous to that induced by curvature in nanotubes. [2,3]These subbands shift with increasing strain and their splitting increases. [2,3]            We investigated the sliding behaviors of eight nano-sized GMS-assembled flake and eight nano-sized CBG-assembled flake on H-DLC substrates with H: 0 at.%, 12 at.%and 25 at.%(DLC0, DLC12 and DLC25) (Figure 6).For GMS-assembled and CBG-assembled flakes, we constructed them based on incommensurate and commensurate bilayer graphene flakes, respectively (Figure 6a-c), which was consistent with the experimental data.The H-DLC substrates with different hydrogen content were obtained by annealing from 4500 K to 300 K.In the sliding model, the H-DLC substrate was composed of ~100000 atoms with a dimension of 256 Å × 256 Å along the x and y directions, which contained two segments: the constrained bottom layer with the height of ~2 Å and the free upper layer of ~8 Å.And, the GMS-assembled or CBG-assembled flake with the length of ~150 Å was driven to slide against the substrate along x direction with the constant velocity of 20 m/s.Periodic boundary condition was employed in the x and y directions.For the sliding simulations, the AIREBO and L-J potentials were used to describe the atomic bond interactions and the inter-layer van der Waals interactions, respectively.For L-J potential, σC-C = 3.4 Å, εC-C = 2.84 meV, σC-H = 3.025 Å and εC-H = 1.376 meV.In the sliding simulations under a NVT ensemble, the system temperature was maintained at 300 K using Nosé-Hoover thermostat. [6,7]The forces along the x and z directions for graphene flakes were recorded as the friction and normal forces.
Additionaly, we also investigated the effect of the different amount of bilayer graphene flakes on sliding behavior (Figures S13-14, Supporting Information).

Figure S2 .
Figure S2.Fabrication and structure analysis of GMS-assembled coating.

Figure S4 .
Figure S4.Structural characterizations of GMS-assembled coating from other coated ball position.

Figure S5 .
Figure S5.Structural characterizations of GMSs from another position in other ball.

Figure S7
Figure S7Friction behaviors for DLC samples against GMS-assembled coating.

Figure S8 .
Figure S8.Friction coefficient curves for GMS-assembled coating against DLC25 under different conditions.

Figure S11 .
Figure S11.Structural characterization of GMS-assembled coating against DLC25 before and after friction.

Figure S12
Figure S12 Sliding simulation of a polycrystalline graphene layer with different face orientations on DLC.

Figure S13 .
Figure S13.DFT calculations of bilayer graphene and H-diamond interfaces.

Figure S15 .
Figure S15.MD simulation of GMS-assembled flake sliding on DLC.

Figure S16 .ReferencesFigure S2 .
Figure S16.MD simulation of CBG-assembled flake sliding on DLC.Text S1: GMS formation on a sphere.Text S2: MD simulations of GMS-assembled flake sliding on DLC.Text S3: DFT calculations of GMS face and DLC25 interface.References

Figure S4 .
Figure S4.Structural characterizations of GMS-assembled coating from other coated ball position.a) TEM images.b) is marked in (a).c) Original and marked FFT results of (a).

Figure S5 .
Figure S5.Structural characterizations of GMSs from another position in other ball.a) TEM images.b) is marked in (a).c) Original and marked FFT results of (a).

Figure S6 .
Figure S6.Structures and properties of DLC0, DLC12 and DLC25.a, c, e) Cross-section TEM images of DLC0, DLC12 and DLC25.b, d, f) Core-loss EELS spectrum and fitting results of DLC0, DLC12 and DLC25.The C-K edges are fitted by three Gaussian peaks C=C at 285.5 eV, C-H at 287 eV, and C-C at 292.5 eV.

Figure S7
Figure S7 Friction behaviors for DLC samples against GMS-assembled coating.(a) Friction coefficient curves.(b) Average friction coefficients of (a).

Figure S8 .
Figure S8.Friction coefficient curves for GMS-assembled coating against DLC25 under different conditions.a) Sliding velocity.b) Different contact area obtained by varying the ball diameter.c) External load.

Figure S9 .
Figure S9.TEM cross-section characterization of GMS-assembled coating against DLC25 after friction.a) Wear track under the condition of 7 N, 5 cm/s and 5 mm ball.b) FIB-SEM images marked in (a).c, d) corresponding TEM results.

Figure S11 .
Figure S11.Structural characterization of GMS-assembled coating against DLC25 before and after friction.a, b) Raman measured positions before and after friction under the condition of 7 N, 5 cm/s and 5 mm ball.c, d) Raman peak intensity ratios and typical Raman spectra corresponding to (a, b), respectively.

Figure S12 .
Figure S12.Sliding simulation of a polycrystalline graphene layer with different face orientations on DLC.(a) Simulation model DLC.(b) Friction results.

Figure S15 .
Figure S15.MD simulation of GMS-assembled flake sliding on DLC.a) Friction models, b) Friction results.c) Average friction results.

Figure S16 .
Figure S16.MD simulation of CBG-assembled flake sliding on DLC.a) Friction models, b) Friction results.c) Average friction results.