The frictional behavior of supported graphene is known to be influenced by the physical properties and surface morphologies of the underlying substrate. However, it is unclear how a surface defect on the substrate aff...The frictional behavior of supported graphene is known to be influenced by the physical properties and surface morphologies of the underlying substrate. However, it is unclear how a surface defect on the substrate affects the friction of supported graphene,and it is even unknown how to define the defect-induced friction force in this context. Here we conduct molecular dynamics(MD) simulations to investigate the friction between a square diamond slider and a graphene sheet supported by a copper substrate with a surface cavity defect. Our results demonstrate that the defect-induced friction exhibits a nonlinear increase with cavity size, while it decreases nonlinearly with slider size. We propose that the definition of defect-induced friction can be linked to the increase in friction work over the length of the slider, and is closely correlated to the defect-induced relative change in indentation depth and the ratio of the cavity area to the contact area. These findings provide a comprehensive evaluation of the impact of a substrate cavity defect on the friction of supported graphene and offer insights that may have broader implications for understanding defect-induced friction in other two-dimensional materials.展开更多
Nanoindentaion has been proposed as an efficient technique to measure mechanical single-layer two-dimensional(2D) materials via combining the membrane theory with the indentation data. However, for multilayered struct...Nanoindentaion has been proposed as an efficient technique to measure mechanical single-layer two-dimensional(2D) materials via combining the membrane theory with the indentation data. However, for multilayered structures of 2D materials, significant discrepancy exists between the Young's modulus obtained from the existing membrane model and those from other methods.Here we develop a multilayer indentation model by taking the multilayer effect into account in the previous membrane model.We show that the present model can accurately predict the Young's modulus of multilayered 2D carbon materials. For few layer graphene and twin graphene structures, the deviation of the Young's moduli obtained by the present model are both within a reasonable range, while the error caused by the direct use of the previous single-layer membrane model increases with the number of layers. The present model provides an efficient tool to extract the mechanical properties of 2D materials from the nanoindentation data of their multilayered structures.展开更多
The energy dissipation mechanism of graphene layers in commensurate contact is studied by molecular dynamics simulations.The commensurability between graphene layers is controlled by misfit angles between graphene lay...The energy dissipation mechanism of graphene layers in commensurate contact is studied by molecular dynamics simulations.The commensurability between graphene layers is controlled by misfit angles between graphene layers or an in-plane strain applied to one of the graphene layers.We find that for small size graphene,the main energy dissipation is not caused by stick-slip.We propose two potential energy dissipation channels,the lattice distortion induced by the moirésuperlattice structure and variation of entropy of the contacting landscape.Our results provide an insight into the energy dissipation mechanism of commensurate contact graphene.展开更多
基金supported by the National Natural Science Foundation of China(Grant No.12132008)the Key Research Project of Zhejiang Laboratory(Grant No.2021PE0AC02)。
文摘The frictional behavior of supported graphene is known to be influenced by the physical properties and surface morphologies of the underlying substrate. However, it is unclear how a surface defect on the substrate affects the friction of supported graphene,and it is even unknown how to define the defect-induced friction force in this context. Here we conduct molecular dynamics(MD) simulations to investigate the friction between a square diamond slider and a graphene sheet supported by a copper substrate with a surface cavity defect. Our results demonstrate that the defect-induced friction exhibits a nonlinear increase with cavity size, while it decreases nonlinearly with slider size. We propose that the definition of defect-induced friction can be linked to the increase in friction work over the length of the slider, and is closely correlated to the defect-induced relative change in indentation depth and the ratio of the cavity area to the contact area. These findings provide a comprehensive evaluation of the impact of a substrate cavity defect on the friction of supported graphene and offer insights that may have broader implications for understanding defect-induced friction in other two-dimensional materials.
基金supported by the National Natural Science Foundation of China(Grant No.11425209)the Shanghai Pujiang Program(Grant No.13PJD016)+1 种基金the Innovation Program of Shanghai Municipal Education Commission(Grant No.2017-01-07-00-09-E00019)the National Key R&D Program of China(Grant No.2017YFB701600)
文摘Nanoindentaion has been proposed as an efficient technique to measure mechanical single-layer two-dimensional(2D) materials via combining the membrane theory with the indentation data. However, for multilayered structures of 2D materials, significant discrepancy exists between the Young's modulus obtained from the existing membrane model and those from other methods.Here we develop a multilayer indentation model by taking the multilayer effect into account in the previous membrane model.We show that the present model can accurately predict the Young's modulus of multilayered 2D carbon materials. For few layer graphene and twin graphene structures, the deviation of the Young's moduli obtained by the present model are both within a reasonable range, while the error caused by the direct use of the previous single-layer membrane model increases with the number of layers. The present model provides an efficient tool to extract the mechanical properties of 2D materials from the nanoindentation data of their multilayered structures.
基金the National Natural Science Foundation of China(Grant Nos.11602132,11425209 and 11872238)the Innovation Program of Shanghai Municipal Education Commission(Grant No.2017-01-07-00-09-E00019)the Program of Shanghai Academic Research Leader(Grant No.19XD1401500)。
文摘The energy dissipation mechanism of graphene layers in commensurate contact is studied by molecular dynamics simulations.The commensurability between graphene layers is controlled by misfit angles between graphene layers or an in-plane strain applied to one of the graphene layers.We find that for small size graphene,the main energy dissipation is not caused by stick-slip.We propose two potential energy dissipation channels,the lattice distortion induced by the moirésuperlattice structure and variation of entropy of the contacting landscape.Our results provide an insight into the energy dissipation mechanism of commensurate contact graphene.
