The 9th International Conference on Multiscale Materials Modeling

Presentation information

Symposium

O. Tribology and Interface: Multi-Scale, Multi-Physics, and Multi-Chemistry Phenomena in Friction, Lubrication, Wear, and Adhesion

[SY-O9] Symposium O-9

Thu. Nov 1, 2018 9:45 AM - 11:00 AM Room5

Chairs: Yusuke Ootani(Tohoku University, Japan), Shuichi Uehara(Tohoku University, Japan)

[SY-O9] Combined experimental and computational study on the superlubricity mechanism of 2D Materials at the microscale

Invited

Tianbao Ma (Tsinghua University, China)

With chemical inertness, atomically flatness and interlayer van der Waals interaction, graphene and other 2D materials could act as potential ultra-thin protective coating to reduce adhesion, friction and wear.
Firstly, we predict a stable superlubricity state with vanishing friction between graphene and MoS2 heterostructure. This is attributed to the perpetual interfacial incommensurability with the large intrinsic lattice mismatch, which leads to near-zero sliding-induced interfacial charge density fluctuation and ultrasmooth potential energy surface. Theoretical prediction has found preliminary evidence by the measurement of interlayer lateral force constant of 2D materials.
Secondly, we report a direct AFM measurement of sliding friction between graphene-coated microsphere (GMS) and graphene, and between GMS and hexagonal boron nitride (h-BN) hetero 2D layers. The exceptionally low and robust friction coefficient of 0.003 is obtained in ambient atmosphere, under high local contact pressure. This sustainable ultralow friction is attributed to the overall incommensurability of the multi-asperity contact covered with randomly oriented graphene nanograins. Furthermore, the local contact pressure fluctuations induced by the atomic roughness could be markedly suppressed by coating few-layer graphene (layer number > 3) on the contacting asperities.
Thirdly, we report the preservation of ultra-low-friction state on graphene even under harsh chemical modifications. By proper alignment of graphene on a Ge(111) substrate, friction of graphene could be well preserved at an ultra-low level even after fluorination or oxidation. This behavior is experimentally found to be closely related to the suppression of molecular-level deformation of graphene within the moiré superlattice structure. Furthermore, friction modulation with dual-scale stick-slip behavior is observed on graphene/Ru(0001) substrate. The moiré superlattice-level slip instability could be attributed to the large sliding energy barrier, which arises from the morphological corrugation of graphene on Ru(0 0 0 1) surface.