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<p>Friction at atomic step edges arises from intertwined topographic and chemical interactions, but the nature of their coupling has remained unresolved. Here, we combine atomic force microscopy with reactive molecular dynamics simulations to reveal a fundamental mechanism at graphene step edges: interfacial strain induced by step geometry regulates the strength of chemical bonding. We show that sliding direction and angle determine the local shear strain in the silica tip, which amplifies or suppresses hydrogen-bond formation with hydroxyl-terminated step edges. This strain-mediated coupling produces strong directional asymmetry—synergistic during step-up motion and antagonistic during step-down—and explains why friction decreases by nearly 80% as the sliding angle increases from 0° to 75°, despite an angle-independent chemical bonding capacity. These findings establish strain-controlled chemical interactions as a key origin of friction at 2D-material discontinuities and suggest a new strategy for ultralow-friction graphene interfaces: engineering nanoscale topography to tune interfacial strain, rather than modifying surface chemistry alone.</p>

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Strain-mediated topography-chemistry coupling in atomic-scale friction: Insights from graphene step edges

  • 期刊论文

  • 发表日期：

    2026年7月27日

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  • Chaoying Wang,
  • Dunhua Hu,
  • Bing Xu,
  • Huayong Yang,
  • Seong H. Kim,
  • Zhe Chen

摘要

Friction at atomic step edges arises from intertwined topographic and chemical interactions, but the nature of their coupling has remained unresolved. Here, we combine atomic force microscopy with reactive molecular dynamics simulations to reveal a fundamental mechanism at graphene step edges: interfacial strain induced by step geometry regulates the strength of chemical bonding. We show that sliding direction and angle determine the local shear strain in the silica tip, which amplifies or suppresses hydrogen-bond formation with hydroxyl-terminated step edges. This strain-mediated coupling produces strong directional asymmetry—synergistic during step-up motion and antagonistic during step-down—and explains why friction decreases by nearly 80% as the sliding angle increases from 0° to 75°, despite an angle-independent chemical bonding capacity. These findings establish strain-controlled chemical interactions as a key origin of friction at 2D-material discontinuities and suggest a new strategy for ultralow-friction graphene interfaces: engineering nanoscale topography to tune interfacial strain, rather than modifying surface chemistry alone.