Limits...
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.


Close-up of frictional scattering.Variation of the speed component vx (a) and the van der Waals bonding energy EvdW (b) as flake displacement along the x-direction, before, during and after a scattering event. Numbers indicate the snapshots of the flake (c). Vertical dotted lines in (a) and (b) indicate the angular width Δθc of the coherent region where am > 2l. The instantaneous corrugation potential, Ec, felt by the flake, for relative displacement in the x-direction about the flake's actual position (indicated by a circle) is shown before (d), during (e,f) and after (g) frictional scattering.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4007076&req=5

f3: Close-up of frictional scattering.Variation of the speed component vx (a) and the van der Waals bonding energy EvdW (b) as flake displacement along the x-direction, before, during and after a scattering event. Numbers indicate the snapshots of the flake (c). Vertical dotted lines in (a) and (b) indicate the angular width Δθc of the coherent region where am > 2l. The instantaneous corrugation potential, Ec, felt by the flake, for relative displacement in the x-direction about the flake's actual position (indicated by a circle) is shown before (d), during (e,f) and after (g) frictional scattering.

Mentions: To study the effect more closely, we zoom in on a region of frictional scattering in Fig. 3. The flake speed component, vx, and van der Waals bonding energy between flake and substrate, EvdW which is the van der Waals energy between the flake and substrate during the sliding, are displayed in Figs. 3a–b, respectively, and show rapid oscillations near alignment. Fig. 3c shows eight snapshots of the moiré pattern generated by the overlap of flake and substrate lattices, at different points indicated in Figs. 3a–b. When the flake is rotationally misaligned with the substrate, the moiré pattern has a small unit cell size, am. This means the spatial phase of flake atoms relative to the substrate potential oscillates rapidly across the flake. The result is a very small net corrugation potential for the flake as a whole: this is the origin of superlubricity for incommensurate lattices.


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

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

Close-up of frictional scattering.Variation of the speed component vx (a) and the van der Waals bonding energy EvdW (b) as flake displacement along the x-direction, before, during and after a scattering event. Numbers indicate the snapshots of the flake (c). Vertical dotted lines in (a) and (b) indicate the angular width Δθc of the coherent region where am > 2l. The instantaneous corrugation potential, Ec, felt by the flake, for relative displacement in the x-direction about the flake's actual position (indicated by a circle) is shown before (d), during (e,f) and after (g) frictional scattering.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f3: Close-up of frictional scattering.Variation of the speed component vx (a) and the van der Waals bonding energy EvdW (b) as flake displacement along the x-direction, before, during and after a scattering event. Numbers indicate the snapshots of the flake (c). Vertical dotted lines in (a) and (b) indicate the angular width Δθc of the coherent region where am > 2l. The instantaneous corrugation potential, Ec, felt by the flake, for relative displacement in the x-direction about the flake's actual position (indicated by a circle) is shown before (d), during (e,f) and after (g) frictional scattering.
Mentions: To study the effect more closely, we zoom in on a region of frictional scattering in Fig. 3. The flake speed component, vx, and van der Waals bonding energy between flake and substrate, EvdW which is the van der Waals energy between the flake and substrate during the sliding, are displayed in Figs. 3a–b, respectively, and show rapid oscillations near alignment. Fig. 3c shows eight snapshots of the moiré pattern generated by the overlap of flake and substrate lattices, at different points indicated in Figs. 3a–b. When the flake is rotationally misaligned with the substrate, the moiré pattern has a small unit cell size, am. This means the spatial phase of flake atoms relative to the substrate potential oscillates rapidly across the flake. The result is a very small net corrugation potential for the flake as a whole: this is the origin of superlubricity for incommensurate lattices.

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.