Interfacial Friction Of Van Der Waals Layered Materials

MEMS/NEMS devices serve as the core components of Internet of things and artificial interlligence.Due to the large specific surface area,friction and wear induced failure becomes the main challenge of MEMS/NEMS.The structural superlubricity technologies,proposed by Professor Zheng Quanshui of Tsinghua University,are expected to solve the challenge.However,only a few superlubric systems have been found and limited to the micro/nano scale.It is costly and inefficient to discover superlubric systems from two-dimensional material gene library through experiments.Therefore,it is of great significance to develop theories and algorithms that can quickly screen out superlubric systems.In addition,experimental and theoretical studies have found that many factors(such as interface deformation,physical environment and edge effect)can lead to the failure of structural superlubricity.Therefore,understanding and controlling the friction behavior of superlubric systems has beome an important frontier topic.Under these backgrounds,this dissertation focuses on homogeneous and heterogeneous van der Waals layered materials,and systematically studies the interlayer friction behavior through theoretical modeling and numerical simultations.The main research contents and innovations are as follows:1.In view of the challenge of discovering new superlubric systems in experiments,based on the Frenchel-Kontorova model of one-dimensional atomic chain,combined with molecular dynamics simulaitons,three criteria for screening potential superlubric systems are proposed,and a dimensionless parameter with clear physical meaning is presented to quickly predict superlubric systems from the two-dimensional van der Waals layered materials.Based on the screening criteria and prediction model,combined with the first principle calculations and data mining,61 potential superlubric systems were screened from more than 200 van der Waals heterostructures,and some of the predicted systems were verified by experiments.The proposed prediction physical model also provides a basis for the regulation of interfacial friction from the perspective of material genes.2.The charge distribution and evolution in van der Waals layered materials during interlayer sliding is revealed by the first-principles calculations,and a new method to accurately control the interface friction by charge injection is proposed.It is found that the charge ingection will lead to the accumulation of interface charge and the interface friction changes accordingly.Further analysis shows that the friction change is due to the dynamic evolution of the interface charge displacement during sliding,based on which the concept of interface charge displacement roughness is proposed to predict the regulation of interlayer friction by charge injection.Finally,the charge injection method through element doping is proposed.3.It is found that the optimal configuration,interface friction and mechanical properties of quasi one-dimensional van der Waals heterostructures can be significantly regulated by the moiré superlattice.Taking graphene/h-BN heteronanotubes as an example,it is found that the optimal configuration and the moiré superlattice show the significant size and interfacial twist angle dependence,and the interface friction shows a double period modulation phenomenon.The long-range modulation has significant influence on the interface friction,which results in two friction states: structural superlubricity and high friction state(stick-slip).By analyzing the dynamic evolution of moiré patterns,it is revealed that the strong coupling between the configuration and the interface moiré superlattice during sliding is the microscopic mechanism that leads to the moiré superlattice related long-period regulation of interfacial friction.