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The high-speed sliding friction of graphene and novel routes to persistent superlubricity.

Liu Y, Grey F, Zheng Q - Sci Rep (2014)

Bottom Line: We show that superlubricity is punctuated by high-friction transients as the flake rotates through successive crystallographic alignments with the substrate.We can also effectively suppress frictional scattering by biaxial stretching of the graphitic substrate.These new routes to persistent superlubricity at the nanoscale may guide the design of ultra-low dissipation nanomechanical devices.

View Article: PubMed Central - PubMed

Affiliation: 1] International Center for Applied Mechanics, SV Lab, School of Aerospace, Xi'an Jiaotong University, Xi'an 710049, China [2] Centre for Nano and Micro Mechanics, Tsinghua University, Beijing 100084, China.

ABSTRACT
Recent experiments on microscopic graphite mesas demonstrate reproducible high-speed microscale superlubricity, even under ambient conditions. Here, we explore the same phenomenon on the nanoscale, by studying a graphene flake sliding on a graphite substrate, using molecular dynamics. We show that superlubricity is punctuated by high-friction transients as the flake rotates through successive crystallographic alignments with the substrate. Further, we introduce two novel routes to suppress frictional scattering and achieve persistent superlubricity. We use graphitic nanoribbons to eliminate frictional scattering by constraining the flake rotation, an approach we call frictional waveguides. We can also effectively suppress frictional scattering by biaxial stretching of the graphitic substrate. These new routes to persistent superlubricity at the nanoscale may guide the design of ultra-low dissipation nanomechanical devices.

No MeSH data available.


Related in: MedlinePlus

Flake dynamics after launch at 400 m/s.Four snapshots (a) of the instantaneous orientation where the arrows indicate the direction and magnitude of the sliding speed and the frictional scattering at four points indicated on the flake trajectory (b). The speed components of the flake vx and vy (c), show stepwise changes at each scattering. The flake rotation θ (d) shows frictional scattering occurring primarily at high-symmetry angles (multiples of 60°). The force components acting on the flake, Fx and Fy (e) show large oscillatory variations at each scattering. The kinetic energy component Ex decays within about 1 ns to less than 10% of its initial value (f), and becomes comparable to Ey and Eω.
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f2: Flake dynamics after launch at 400 m/s.Four snapshots (a) of the instantaneous orientation where the arrows indicate the direction and magnitude of the sliding speed and the frictional scattering at four points indicated on the flake trajectory (b). The speed components of the flake vx and vy (c), show stepwise changes at each scattering. The flake rotation θ (d) shows frictional scattering occurring primarily at high-symmetry angles (multiples of 60°). The force components acting on the flake, Fx and Fy (e) show large oscillatory variations at each scattering. The kinetic energy component Ex decays within about 1 ns to less than 10% of its initial value (f), and becomes comparable to Ey and Eω.

Mentions: Results presented in Fig. 2 are for a 10 × 10 nm2 flake launched at vmax = 400 m/s along the armchair direction of the substrate by adding the same velocity 400 m/s in x direction to every atom in the sliding flake. The sliding distance corresponding to 1 time step (1fs) at vmax is less than 0.0004 nm. The initial state of the flake and substrate is an energy minimum state with A–B stacking alignment, and the initial temperature of the whole system is 0 K. The sliding speed, rotation angle, angular velocity and force are defined same as the ones in the retraction simulations. The sliding behavior in Figure 2b shows the trajectory of the flake, with sporadic changes in the direction of motion indicated by vertical dashed lines. For reasons that will become apparent shortly, we refer to these events as frictional scattering. Snapshots in Fig. 2a show each scattering event occurs when the flake is briefly crystallographically aligned with the substrate. At lower speed, this alignment would result in lock-in. But at high speed, the flake has sufficient kinetic energy to escape lock-in.


The high-speed sliding friction of graphene and novel routes to persistent superlubricity.

Liu Y, Grey F, Zheng Q - Sci Rep (2014)

Flake dynamics after launch at 400 m/s.Four snapshots (a) of the instantaneous orientation where the arrows indicate the direction and magnitude of the sliding speed and the frictional scattering at four points indicated on the flake trajectory (b). The speed components of the flake vx and vy (c), show stepwise changes at each scattering. The flake rotation θ (d) shows frictional scattering occurring primarily at high-symmetry angles (multiples of 60°). The force components acting on the flake, Fx and Fy (e) show large oscillatory variations at each scattering. The kinetic energy component Ex decays within about 1 ns to less than 10% of its initial value (f), and becomes comparable to Ey and Eω.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4007076&req=5

f2: Flake dynamics after launch at 400 m/s.Four snapshots (a) of the instantaneous orientation where the arrows indicate the direction and magnitude of the sliding speed and the frictional scattering at four points indicated on the flake trajectory (b). The speed components of the flake vx and vy (c), show stepwise changes at each scattering. The flake rotation θ (d) shows frictional scattering occurring primarily at high-symmetry angles (multiples of 60°). The force components acting on the flake, Fx and Fy (e) show large oscillatory variations at each scattering. The kinetic energy component Ex decays within about 1 ns to less than 10% of its initial value (f), and becomes comparable to Ey and Eω.
Mentions: Results presented in Fig. 2 are for a 10 × 10 nm2 flake launched at vmax = 400 m/s along the armchair direction of the substrate by adding the same velocity 400 m/s in x direction to every atom in the sliding flake. The sliding distance corresponding to 1 time step (1fs) at vmax is less than 0.0004 nm. The initial state of the flake and substrate is an energy minimum state with A–B stacking alignment, and the initial temperature of the whole system is 0 K. The sliding speed, rotation angle, angular velocity and force are defined same as the ones in the retraction simulations. The sliding behavior in Figure 2b shows the trajectory of the flake, with sporadic changes in the direction of motion indicated by vertical dashed lines. For reasons that will become apparent shortly, we refer to these events as frictional scattering. Snapshots in Fig. 2a show each scattering event occurs when the flake is briefly crystallographically aligned with the substrate. At lower speed, this alignment would result in lock-in. But at high speed, the flake has sufficient kinetic energy to escape lock-in.

Bottom Line: We show that superlubricity is punctuated by high-friction transients as the flake rotates through successive crystallographic alignments with the substrate.We can also effectively suppress frictional scattering by biaxial stretching of the graphitic substrate.These new routes to persistent superlubricity at the nanoscale may guide the design of ultra-low dissipation nanomechanical devices.

View Article: PubMed Central - PubMed

Affiliation: 1] International Center for Applied Mechanics, SV Lab, School of Aerospace, Xi'an Jiaotong University, Xi'an 710049, China [2] Centre for Nano and Micro Mechanics, Tsinghua University, Beijing 100084, China.

ABSTRACT
Recent experiments on microscopic graphite mesas demonstrate reproducible high-speed microscale superlubricity, even under ambient conditions. Here, we explore the same phenomenon on the nanoscale, by studying a graphene flake sliding on a graphite substrate, using molecular dynamics. We show that superlubricity is punctuated by high-friction transients as the flake rotates through successive crystallographic alignments with the substrate. Further, we introduce two novel routes to suppress frictional scattering and achieve persistent superlubricity. We use graphitic nanoribbons to eliminate frictional scattering by constraining the flake rotation, an approach we call frictional waveguides. We can also effectively suppress frictional scattering by biaxial stretching of the graphitic substrate. These new routes to persistent superlubricity at the nanoscale may guide the design of ultra-low dissipation nanomechanical devices.

No MeSH data available.


Related in: MedlinePlus