Atomistic mechanisms of frictional energy dissipation have attracted significant attention.However,the dynamics of phonon excitation and dissipation remain elusive for many friction processes.Through systematic fast F...Atomistic mechanisms of frictional energy dissipation have attracted significant attention.However,the dynamics of phonon excitation and dissipation remain elusive for many friction processes.Through systematic fast Fourier transform(FFT)analyses of the frictional signals as a silicon tip sliding over a graphite surface at different angles and velocities,we experimentally demonstrate that friction mainly excites non-equilibrium phonons at the washboard frequency and its harmonics.Using molecular dynamics(MD)simulations,we further disclose the phononic origin of structural lubrication,i.e.,the drastic reduction of friction force as the contact angle between two commensurate surfaces changes.In commensurate contacting states,friction excites a large amount of phonons at the washboard frequency and many orders of its harmonics that perfectly match each other in the sliding tip and substrate,while for incommensurate cases,only limited phonons are generated at mismatched washboard frequencies and few low order harmonics in the tip and substrate.展开更多
The transition from atomic stick-slip to continuous sliding has been observed in a number of ways.If extended contacts are moved in different directions,so-called structural lubricity is observed when the two surface ...The transition from atomic stick-slip to continuous sliding has been observed in a number of ways.If extended contacts are moved in different directions,so-called structural lubricity is observed when the two surface lattices are non-matching.Alternatively,a“superlubric”state of motion can be achieved if the normal force is reduced below a certain threshold,the temperature is increased,or the contact is actuated mechanically.These processes have been partially demonstrated using atomic force microscopy,and they can be theoretically understood by proper modifications of the Prandtl−Tomlinson model.展开更多
The term“structural lubricity”denotes a fundamental concept where the friction between two atomically flat surfaces is reduced due to lattice mismatch at the interface.Under favorable circumstances,its effect may ca...The term“structural lubricity”denotes a fundamental concept where the friction between two atomically flat surfaces is reduced due to lattice mismatch at the interface.Under favorable circumstances,its effect may cause a contact to experience ultra-low friction,which is why it is also referred to as“superlubricity”.While the basic principle is intriguingly simple,the experimental analysis of structural lubricity has been challenging.One of the main reasons for this predicament is that the tool most frequently used in nanotribology,the friction force microscope,is not well suited to analyse the friction of extended nanocontacts.To overcome this deficiency,substantial efforts have been directed in recent years towards establishing nanoparticle manipulation techniques,where the friction of nanoparticles sliding on a substrate is measured,as an alternative approach to nanotribological research.By choosing appropriate nanoparticles and substrates,interfaces exhibiting the characteristics needed for the occurrence of structural lubricity can be created.As a consequence,nanoparticle manipulation experiments such as in this review represent a unique opportunity to study the physical conditions and processes necessary to establish structural lubricity,thereby opening a path to exploit this effect in technological applications.展开更多
基金National Natural Science Foundation of China(Grant Nos.52035003,52065037,51575104,and 52175161)the China Postdoctoral Science Foundation(Grant No.2021MD703810)+1 种基金the Postdoctoral Science Foundation of Gansu Academy of Sciences(Grant No.BSH202101)the Southeast University“Zhongying Young Scholars”Project for financial support.
文摘Atomistic mechanisms of frictional energy dissipation have attracted significant attention.However,the dynamics of phonon excitation and dissipation remain elusive for many friction processes.Through systematic fast Fourier transform(FFT)analyses of the frictional signals as a silicon tip sliding over a graphite surface at different angles and velocities,we experimentally demonstrate that friction mainly excites non-equilibrium phonons at the washboard frequency and its harmonics.Using molecular dynamics(MD)simulations,we further disclose the phononic origin of structural lubrication,i.e.,the drastic reduction of friction force as the contact angle between two commensurate surfaces changes.In commensurate contacting states,friction excites a large amount of phonons at the washboard frequency and many orders of its harmonics that perfectly match each other in the sliding tip and substrate,while for incommensurate cases,only limited phonons are generated at mismatched washboard frequencies and few low order harmonics in the tip and substrate.
基金E.M.acknowledges financial support by the Swiss National Science Foundation(SNF)the Commission for Technology and Innovation(CTI),COST Action MP1303 and the Swiss Nanoscience Institute(SNI).E.G.acknowledges the Spanish Ministry of Economy and Competitiveness(MINECO)Project MAT2012-26312.
文摘The transition from atomic stick-slip to continuous sliding has been observed in a number of ways.If extended contacts are moved in different directions,so-called structural lubricity is observed when the two surface lattices are non-matching.Alternatively,a“superlubric”state of motion can be achieved if the normal force is reduced below a certain threshold,the temperature is increased,or the contact is actuated mechanically.These processes have been partially demonstrated using atomic force microscopy,and they can be theoretically understood by proper modifications of the Prandtl−Tomlinson model.
基金Financial support was provided by the DFG(Project SCHI 619/8-1)the EUROCORES program FANAS of the European Science Foundation,and the EC 6th framework program(Grant No.ERAS-CT-2003-980409)U.S.acknowledges primary financial support by the National Science Foundation through the Yale Materials Research Science and Engineering Center(Grant No.MRSEC DMR-1119826).
文摘The term“structural lubricity”denotes a fundamental concept where the friction between two atomically flat surfaces is reduced due to lattice mismatch at the interface.Under favorable circumstances,its effect may cause a contact to experience ultra-low friction,which is why it is also referred to as“superlubricity”.While the basic principle is intriguingly simple,the experimental analysis of structural lubricity has been challenging.One of the main reasons for this predicament is that the tool most frequently used in nanotribology,the friction force microscope,is not well suited to analyse the friction of extended nanocontacts.To overcome this deficiency,substantial efforts have been directed in recent years towards establishing nanoparticle manipulation techniques,where the friction of nanoparticles sliding on a substrate is measured,as an alternative approach to nanotribological research.By choosing appropriate nanoparticles and substrates,interfaces exhibiting the characteristics needed for the occurrence of structural lubricity can be created.As a consequence,nanoparticle manipulation experiments such as in this review represent a unique opportunity to study the physical conditions and processes necessary to establish structural lubricity,thereby opening a path to exploit this effect in technological applications.
