Negative Friction Coefficients in Superlubric Graphite-Hexagonal Boron Nitride Heterojunctions

Observation of normal-force-independent superlubricity in mesoscopic graphite contacts

We investigate the dependence of friction forces on normal load in incommensurate micrometer size contacts between atomically smooth single-crystal graphite surfaces under ambient conditions. Our experimental results show that these contacts exhibit superlubricity (super-low friction), which is robust against the application of normal load. The measured friction coefficients are essentially zero and independent of the external normal load up to a pressure of 1.67 MPa. The observation of load-independent superlubricity in micro-scale contacts is a promising result for numerous practical applica…

Superlubric to stick-slip sliding of incommensurate graphene flakes on graphite

We calculate the friction of fully mobile graphene flakes sliding on graphite. For incommensurately stacked flakes, we find a sudden and reversible increase in friction with load, in agreement with experimental observations. The transition from smooth sliding to stick-slip and the corresponding increase in friction is neither due to rotations to commensurate contact nor to dislocations but to a pinning caused by vertical distortions of edge atoms also when they are saturated by Hydrogen. This behavior should apply to all layered materials with strong in-plane bonding.

Stability of superlubric sliding on graphite

Recent AFM experiments have shown that the low-friction sliding of incommensurate graphite flakes on graphite can be destroyed by torque-induced rotations. Here we theoretically investigate the stability of superlubric sliding against rotations of the flake. We find that the occurrence of superlubric motion critically depends on the physical parameters and on the experimental conditions: particular scan lines, thermal fluctuations and high loading forces can destroy the stability of superlubric orbits. We find that the optimal conditions to achieve superlubric sliding are given by large flakes…

石墨烯超润滑性由摩擦诱导纳米接触实现

Graphite superlubricity enabled by triboinduced nanocontacts

本研究通过胶体探针原子力显微镜揭示石墨超润滑性源于摩擦转移纳米微凸体的双重作用，其减小真实接触面积并控制耗散，且滑动状态受负载调控，符合Prandtl-Tomlinson模型。

临界压力以上零摩擦系数的观测

Observation of zero coefficient of friction above a critical pressure

该研究首次实验观测到微尺度单晶石墨与纳米粗糙度金基底在临界压力以上的自超润滑现象，建立了临界压力无量纲判据并验证，为低功耗长寿命微系统提供变革性原理。

由摩擦诱导石墨转移层包覆的胶体AFM探针的滑动摩擦与超润滑

Sliding friction and superlubricity of colloidal AFM probes coated by tribo-induced graphitic transfer layers

本研究利用胶体探针AFM探索石墨表面的滑动摩擦与超润滑现象，发现摩擦诱导的转移层使系统转变为低摩擦状态，其载荷驱动的粘滑到超润滑转变可由Prandtl-Tomlinson模型描述，且耗散随基底原子起伏增加而增大。