Research On Friction And Dissipation Of Low-dimensional Nanomatetials

Friction between sliding surfaces is very common and plays an important role in our everyday life and industrial processes.With the reduction in the size of nano-electromechanical devices,the frictional phenomenon becomes complicated and the friction becomes more and more important.The atomic-scale friction law is significantly different from the macro-scale friction law.At present,the interpretation for the microscopic or nano-scale friction dissipation mechanism is not perfect.The study of atomic-scale friction behavior is not only important in industrial application,but also important in science.Due to the possible ultra-low friction between the walls of multi-walled carbon nanotubes,researchers at home and abroad have attached great importance to the design and application of nanoelectromechanical motion control,and have carried out a lot of work.Due to its unique two-dimensional stable structure and excellent properties,graphene is considered to be an ideal material for studying atomic-scale friction laws.A clear understanding of the graphene friction characteristics provides theoretical guidance for the design of graphene-based M/NEMS.In this paper,we focus on van der Waals nano-oscillators based on graphite or carbon nanotubes,and study the conditions for stable oscillation under the periodical harmonic driving force.The operating characteristics of the nano-oscillators were calculated and analyzed.The results show that the sustained stable oscillation of the nano-electromechanical system can be achieved by properly choosing the driving amplitude and frequency.This method has important reference value for the further study of nano-electromechanical system design based on graphite or multi-walled carbon nanotubes,and provides a simple and feasible way to realize the application of super-lubrication in M/NEMS.The numerical calculation method was used to study the interlayer sliding behavior of two graphene disks.The influences of the mismatch angle,the translational displacement,and the interlayer distance between the upper and lower graphene discs on the potential energy,lateral force,and torque were analyzed.It was found that the torque of the upper graphene plate is small when the system is in the commensurate state,but it is difficult to achieve superlubric sliding due to the significant disturbance of the lateral force.Corresponding to the incommensurate state,when the graphene disk moves in certain directions,the torque is close to zero,and it is easy to achieve superlubric sliding.Whether for commensurate or incommensurate contact,the amplitudes of the lateral force are in qualitative agreement with experimental observations.We discussed how to properly operate the graphene disk to achieve the superlubric motion of the graphene disk.The dynamics as the tip of the friction force microscope(FFM)moves on the sample surface is analyzed by the equivalent coupled-oscillator model based on the two-mass-two-spring model.The power dissipation spectrum is calculated using the linear response theory.Resonance dissipation occurs when the relative slip velocity reaches a certain value.Based on the generalized FK model,the energy conversion in the friction process is analyzed.The conclusion that the energy dissipation is mainly caused by phonon excitation is obtained.It is found that the distance has a abnormal dependency on the initial velocity when the micro-nano-scale objects slides against the substrate.The dependence of the sliding distance of the one-dimensional atomic chain on the size of the atomic chain and the coupling strength between the atomic chain and the substrate is also discussed.The research results will provide a theoretical basis for establishing energy conversion and dissipation mechanisms.