We demonstrate that robust superlubricity can be achieved via both biaxial and uniaxial tensile strains in a substrate using molecular dynamics simulation. Above a critical strain, the friction is no longer dependent on the relative orientation between the surfaces mainly due to the complete lattice mismatch. Importantly, the larger the size of the flake is, the smaller the critical biaxial strain is.
The
sliding friction of a graphene flake atop strained graphene
substrates is studied using molecular dynamics simulation. We demonstrate
that in this superlubric system, friction can be reduced nonmonotonically
by applying strain, which differs from previously reported results
on various 2D materials. The critical strain needed for significant
reduction in friction decreases drastically when the flake size increases.
For a 250 nm flake, a 0.1% biaxial strain could lead to a more than
2-order-of-magnitude reduction. The underlying mechanism is revealed
to be the evolution of Moiré patterns. The area of the Moiré
pattern relative to the flake size plays a central role in determining
friction in strain engineering and other scenarios of superlubricity
as well. This result suggests that strain engineering could be particularly
efficient for friction modification with large contacts.
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