2023-05-21

The Origin of Moiré-Level Stick-Slip Behavior on Graphene/h-BN Heterostructures

Frictional behavior of a nanoscale tip sliding on superlattice of aligned graphene/(hexagonal boron nitride) h-BN heterostructure is found to be strongly regulated by the moiré superlattices, resulting in long-range stick-slip modulation in experimental measurements. Through molecular dynamics simulations, it is shown that the origin of moiré-level stick-slip comes from the strong coupling between in-plane deformation and out-of-plane distortion of the moiré superlattice. The periodicity of long-range modulation decreases as the interfacial twist angle increases, once the periodicity of moiré becomes smaller than the contact region between the tip and graphene, the long-range modulation becomes smooth and the stick-slip behavior disappears. It is found that the contact trajectory of the tip during sliding is the key to reveal the underlying mechanism, based on which a modified Prandtl-Tomlinson model is proposed considering deformation coupled effect to reproduce the frictional properties observed in molecular dynamics simulation. These findings emphasize the critical role of the moiré superlattice on frictional properties of van der Waals (vdW) heterostructures and open an avenue for the rational design of vdW devices with controllable tribological properties.

2023-05-07

Catalytic Growth of Ultralong Graphene Nanoribbons on Ilnsulating Substrates

Bosai Lyu, Jiajun Chen, Shuo Lou, Can Li, Lu Qiu, Wengen Ouyang, Jingxu Xie, Izaac Mitchell, Tongyao Wu, Aolin Deng, Cheng Hu, Xianliang Zhou, Peiyue Shen, Saiqun Ma, Zhenghan Wu, Kenji Watanabe, Takashi Taniguchi, Xiaoqun Wang, Qi Liang, Jinfeng Jia, Michael Urbakh, Oded Hod*, Feng Ding*, Shiyong Wang*, Zhiwen Shi*, “Catalytic Growth of Ultralong Graphene Nanoribbons on Insulating Substrates”, Adv. Mater., 2022: 2200596.

2022-11-04

Nanoserpents Graphene Nanoribbon Motion on Two-Dimensional Hexagonal Materials

Wengen Ouyang, Davide Mandelli, Michael Urbakh*, Oded Hod, “Nanoserpents: Graphene Nanoribbon Motion on Two-Dimensional Hexagonal Materials”, Nano Lett. 2018, 18, 6009−6016

2022-11-02

Load-velocity-temperature relationship in frictional response of microscopic contacts

Frictional properties of interfaces with dynamic chemical bonds have been the subject of intensive experimental investigation and modeling, as it provides important insights into the molecular origin of the empirical rate and state laws, which have been highly successful in describing friction from nano to geophysical scales. Using previously developed theoretical approaches requires time-consuming simulations that are impractical for many realistic tribological systems. To solve this problem and set a framework for understanding microscopic mechanisms of friction at interfaces including multiple microscopic contacts, we developed an analytical approach for description of friction mediated by dynamical formation and rupture of microscopic interfacial contacts, which allows to calculate frictional properties on the time and length scales that are relevant to tribological experimental conditions. The model accounts for the presence of various types of contacts at the frictional interface and predicts novel dependencies of friction on sliding velocity, temperature and normal load, which are amenable to experimental observations. Our model predicts the velocity-temperature scaling, which relies on the interplay between the effects of shear and temperature on the rupture of interfacial contacts. The proposed scaling can be used to extrapolate the simulation results to a range of very low sliding velocities used in nanoscale friction experiments, which is still unreachable by simulations. For interfaces including two types of interfacial contacts with distinct properties, our model predicts novel double-peaked dependencies of friction on temperature and velocity. Considering friction force microscopy experiments (FFM), we found that the non-uniform distribution of normal load across the interface leads to a distribution of barrier heights for contact formation. The results obtained in this case allowed to reveal a mechanism of nonlinear dependence of friction on normal load observed in recent FFM experiments and predict the effect of normal load on velocity and temperature dependencies of friction. Our work provides a promising avenue for the interpretation of the experimental data on friction at interfaces including microscopic contacts and opens new pathways for the rational control of the frictional response.

2022-10-21

Load and Velocity Dependence of Friction Mediated by Dynamics of Ilnterfacial Contacts

Ouyang Wengen, Shivaprakash N. Ramakrishna*, Antonella Rossi, Michael Urbakh, Nicholas D. Spencer, Andrea Arcifa, “Load and Velocity Dependence of Friction Mediated by Dynamics of Interfacial Contacts”, Phys. Rev. Lett, 2019, 123(11): 116102.

2022-09-29

Frictional Properties of Nanojunctions Including Atomically Thin Sheets

Wengen Ouyang, Ming Ma, Quanshui Zheng, Michael Urbakh*, “Frictional Properties of Nanojunctions Including Atomically Thin Sheets”, Nano Lett. 2016, 16, 1878−1883