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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

The sliding behavior for different initial conditions.(a) The sliding behavior of 5 × 5 nm2 and 10 × 10 nm2 flakes launched initially at 0 K and 300 K. (b) The sliding behavior of 10 × 10 nm2 flake for different orientation (the misalignment between the flake and the substrate is from 0° to 30°).
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f5: The sliding behavior for different initial conditions.(a) The sliding behavior of 5 × 5 nm2 and 10 × 10 nm2 flakes launched initially at 0 K and 300 K. (b) The sliding behavior of 10 × 10 nm2 flake for different orientation (the misalignment between the flake and the substrate is from 0° to 30°).

Mentions: The sensitivity of the results to initial temperature and flake orientation are given in Fig. 5. The simulated system is first equilibrated at the given temperature for 50ps by Nose-Hoover thermostat. Then the initial sliding speed of 400 m/s is added to the sliding flake and the thermostat is removed in the simulation afterward. The result for 5 × 5nm2 and 10 × 10 nm2 flakes launched initially at 0 K and 300 K show similar qualitative behavior, with regions of superlubricity punctuated by frictional scattering, see Fig. 5a. Detailed inspection shows a higher degree of noise for the high-temperature simulations, which is consistent with expectations for the impact of temperature. Simulations at T = 0 K, but for different initial orientations of the flake when it is launched, show overall similar qualitative behavior, with the sliding speed of all flakes decaying within 2ns, see Fig. 5b. For the initial misalignment between the sliding flake and the substrate (such as the rotation 30° in Fig. 5b) the initial superlubricity state can last a longer time. However after the first frictional scattering it becomes the similar frictional scattering behavior as the initial alignment case. We have also tested other flake shapes and varied substrate boundary conditions. In all cases we observe a similar stepwise decay, indicating that this is a computationally robust effect.


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

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

The sliding behavior for different initial conditions.(a) The sliding behavior of 5 × 5 nm2 and 10 × 10 nm2 flakes launched initially at 0 K and 300 K. (b) The sliding behavior of 10 × 10 nm2 flake for different orientation (the misalignment between the flake and the substrate is from 0° to 30°).
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f5: The sliding behavior for different initial conditions.(a) The sliding behavior of 5 × 5 nm2 and 10 × 10 nm2 flakes launched initially at 0 K and 300 K. (b) The sliding behavior of 10 × 10 nm2 flake for different orientation (the misalignment between the flake and the substrate is from 0° to 30°).
Mentions: The sensitivity of the results to initial temperature and flake orientation are given in Fig. 5. The simulated system is first equilibrated at the given temperature for 50ps by Nose-Hoover thermostat. Then the initial sliding speed of 400 m/s is added to the sliding flake and the thermostat is removed in the simulation afterward. The result for 5 × 5nm2 and 10 × 10 nm2 flakes launched initially at 0 K and 300 K show similar qualitative behavior, with regions of superlubricity punctuated by frictional scattering, see Fig. 5a. Detailed inspection shows a higher degree of noise for the high-temperature simulations, which is consistent with expectations for the impact of temperature. Simulations at T = 0 K, but for different initial orientations of the flake when it is launched, show overall similar qualitative behavior, with the sliding speed of all flakes decaying within 2ns, see Fig. 5b. For the initial misalignment between the sliding flake and the substrate (such as the rotation 30° in Fig. 5b) the initial superlubricity state can last a longer time. However after the first frictional scattering it becomes the similar frictional scattering behavior as the initial alignment case. We have also tested other flake shapes and varied substrate boundary conditions. In all cases we observe a similar stepwise decay, indicating that this is a computationally robust effect.

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