The nanofriction properties of Au substrate and monolayer molecular deposition film and multilayer molecular deposition films on Au substrate and the molecular deposition films modified with alkyl-terminal molecule ha...The nanofriction properties of Au substrate and monolayer molecular deposition film and multilayer molecular deposition films on Au substrate and the molecular deposition films modified with alkyl-terminal molecule have been investigated by using an atomic force microscope. It is concluded that (i) the deposition of molecular deposition films on Au substrate and the modification of alkyl-terminal molecule to the molecular deposition films can reduce the frictional force; (ii) the molecular deposition films with the same terminal exhibit similar nanofriction properties, which has nothing to do with the molecular chain-length and the layer number; (iii) the unstable nanofriction properties of molecular deposition films are contributed to the active terminal of the molecular deposition film, which can be eliminated by decorating the active molecular deposition film with alkyl-terminal molecule, moreover, the decoration of alkyl-terminal molecule can lower the frictional force conspicuously; (iv) the relative humidity affects the frictional force; the higher the RH, the lower the frictional force.展开更多
The nanofriction properties of hexagonal boron nitride(h-BN)are vital for its application as a substrate for graphene devices and solid lubricants in micro-and nano-electromechanical devices.In this work,the nanofrict...The nanofriction properties of hexagonal boron nitride(h-BN)are vital for its application as a substrate for graphene devices and solid lubricants in micro-and nano-electromechanical devices.In this work,the nanofriction characteristics of h-BN on Si/SiO_(2) substrates with a bias voltage are explored using a conductive atomic force microscopy(AFM)tip sliding on the h-BN surface under different substrate bias voltages.The results show that the nanofriction on h-BN increases with an increase in the applied bias difference(V_(t–s))between the conductive tip and the substrate.The nanofriction under negative V_(t–s) is larger than that under positive V_(t–s).The variation in nanofriction is relevant to the electrostatic interaction caused by the charging effect.The electrostatic force between opposite charges localized on the conductive tip and at the SiO2/Si interface increases with an increase in V_(t–s).Owing to the characteristics of p-type silicon,a positive V_(t–s) will first cause depletion of majority carriers,which results in a difference of nanofriction under positive and negative V_(t–s).Our findings provide an approach for manipulating the nanofriction of 2D insulating material surfaces through an applied electric field,and are helpful for designing a substrate for graphene devices.展开更多
The nanofrictional behavior of non-halogentated phosphonium-based ionic liquids(ILs)mixed with diethylene glycol dibutyl ether in the molar ratios of 1:10 and 1:70 was investigated on the titanium(Ti)substrate using a...The nanofrictional behavior of non-halogentated phosphonium-based ionic liquids(ILs)mixed with diethylene glycol dibutyl ether in the molar ratios of 1:10 and 1:70 was investigated on the titanium(Ti)substrate using atomic force microscopy(AFM).A significant reduction is observed in the friction coefficientμfor the IL-oil mixtures with a higher IL concentration(1:10,μ~0.05),compared to that for the lower concentration 1:70(μ~0.1).AFM approaching force–distance curves and number density profiles for IL-oil mixtures with a higher concentration revealed that the IL preferred to accumulate at the surface forming IL-rich layered structures.The ordered IL-rich layers formed on the titanium surface facilitated the reduction of the nanoscale friction by preventing direct surface-to-surface contact.However,the ordered IL layers disappeared in the case of lower concentration,resulting in an incomplete boundary layers,because the ions were displaced by molecules of the oil during sliding and revealed to be less efficient in friction reduction.展开更多
We report the friction behavior of graphene edges within a carbon film,which encompasses structures ranging from amorphous carbon(a-C)to graphene nanocrystalline carbon(GNC).Structural characterization revealed that v...We report the friction behavior of graphene edges within a carbon film,which encompasses structures ranging from amorphous carbon(a-C)to graphene nanocrystalline carbon(GNC).Structural characterization revealed that vertically growing graphene nanocrystallites were implanted into the a-C structure,exposing high-density layer edges on the film surface.Atomic force microscopy(AFM)nanofriction tests highlighted the nature of graphene edge friction.Firstly,the edge friction of GNC films was tested in a critical-contact state,and the results showed that graphene edges exhibited lower friction forces than did a-C edges.Secondly,the surface friction of GNC films was investigated in a full-contact state,revealing that the edge friction of graphene nanocrystallites regulated the surface friction of GNC films.As the edge density of graphene nanocrystallites increased,the nanofriction force of GNC films decreased.Finally,the mechanism of the regulated friction behavior was attributed to the number of edges of the graphene nanocrystallites,which provided plentiful sp2 C dangling bonds with weak bonding interactions and edge quantum wells with low surface potentials for lowering friction.These findings shed light on the importance of graphene-related materials and their high-density edges in the structural design and nanofriction application of carbon films.展开更多
Driven by the potential applications of ionic liquid(IL)flow for charging graphene-based surfaces in many emerging technologies,recent research efforts have focused on understanding ion dynamics and structuring at IL...Driven by the potential applications of ionic liquid(IL)flow for charging graphene-based surfaces in many emerging technologies,recent research efforts have focused on understanding ion dynamics and structuring at IL–graphene interfaces.Here,graphene colloid probe(GrP)atomic force microscopy(AFM)was used to probe the dynamics and ion structuring of 1-butyl-3-methylimidazolium tetrafluoroborate at graphene surfaces under various bias voltages.In particular,the AFM-measured nanofriction provides a good measure of the dynamic properties of the ILs at graphene surfaces.Compared with the IL at the unbiased graphene surface(0 V),the charged graphene surfaces with either negative(-1,-2 V)or positive(+1,+2 V)voltages favor a reduction in the friction coefficient by the IL.A higher magnitude of the bias voltage applied on the graphene surface with either sign(-2 or+2 V)results in a smaller friction coefficient than that at -1 and+1 V.In combination with the AFM-probed contact stiffness,adhesion forces,and ion structuring force curves with an ion orientational distribution according to molecular dynamics(MD)simulations,we discovered that the unbiased graphene surface(0 V)possesses randomly structured IL ions and that the graphene colloid probe is more likely to become stuck,resulting in more energy dissipation to contribute to a larger friction coefficient.Biasing of the graphene surface under either negative or positive voltages resulted in uniformly arranged ions,which produced a more ordered ion structure and,thus,a smoother sliding plane to reduce the friction coefficient.Electrochemical impedance spectroscopy(EIS)for the IL with graphene as an electrode demonstrated a greater ionic conductivity in the IL paired with the biased graphene than in the unbiased one,implying faster ion movement at the charged graphene,which is beneficial for reducing the friction coefficient.展开更多
基金This work was supported by the National Natural Science Foundation of China(Grant No.59735110).The authors thank Associate Profs.Wang Deguo for his helpful discussions and Lin Li for his help in the experiment.
文摘The nanofriction properties of Au substrate and monolayer molecular deposition film and multilayer molecular deposition films on Au substrate and the molecular deposition films modified with alkyl-terminal molecule have been investigated by using an atomic force microscope. It is concluded that (i) the deposition of molecular deposition films on Au substrate and the modification of alkyl-terminal molecule to the molecular deposition films can reduce the frictional force; (ii) the molecular deposition films with the same terminal exhibit similar nanofriction properties, which has nothing to do with the molecular chain-length and the layer number; (iii) the unstable nanofriction properties of molecular deposition films are contributed to the active terminal of the molecular deposition film, which can be eliminated by decorating the active molecular deposition film with alkyl-terminal molecule, moreover, the decoration of alkyl-terminal molecule can lower the frictional force conspicuously; (iv) the relative humidity affects the frictional force; the higher the RH, the lower the frictional force.
基金This work was supported by the National Natural Science Foundation of China(51675097,U1632128,and 51775105)the Natural Science Foundation of Shanghai(17ZR1400700)the Fundamental Research Funds for the Central Universities ad DHU Distinguished Young Professor Program.
文摘The nanofriction properties of hexagonal boron nitride(h-BN)are vital for its application as a substrate for graphene devices and solid lubricants in micro-and nano-electromechanical devices.In this work,the nanofriction characteristics of h-BN on Si/SiO_(2) substrates with a bias voltage are explored using a conductive atomic force microscopy(AFM)tip sliding on the h-BN surface under different substrate bias voltages.The results show that the nanofriction on h-BN increases with an increase in the applied bias difference(V_(t–s))between the conductive tip and the substrate.The nanofriction under negative V_(t–s) is larger than that under positive V_(t–s).The variation in nanofriction is relevant to the electrostatic interaction caused by the charging effect.The electrostatic force between opposite charges localized on the conductive tip and at the SiO2/Si interface increases with an increase in V_(t–s).Owing to the characteristics of p-type silicon,a positive V_(t–s) will first cause depletion of majority carriers,which results in a difference of nanofriction under positive and negative V_(t–s).Our findings provide an approach for manipulating the nanofriction of 2D insulating material surfaces through an applied electric field,and are helpful for designing a substrate for graphene devices.
基金We are grateful to the support from Natural Science Foundation of Jiangsu Province(Grant No.BK20191289)the National Natural Science Foundation of China(Grant Nos.21838004,21606131,and 21676137)and the financial support from Instrument&EquipmentOpen Funding of Nanjing University of Science and Technology.The Swedish Foundation for Strategic Research(Grant No.EM16-0013)is also gratefully acknowledged for the financial support.
文摘The nanofrictional behavior of non-halogentated phosphonium-based ionic liquids(ILs)mixed with diethylene glycol dibutyl ether in the molar ratios of 1:10 and 1:70 was investigated on the titanium(Ti)substrate using atomic force microscopy(AFM).A significant reduction is observed in the friction coefficientμfor the IL-oil mixtures with a higher IL concentration(1:10,μ~0.05),compared to that for the lower concentration 1:70(μ~0.1).AFM approaching force–distance curves and number density profiles for IL-oil mixtures with a higher concentration revealed that the IL preferred to accumulate at the surface forming IL-rich layered structures.The ordered IL-rich layers formed on the titanium surface facilitated the reduction of the nanoscale friction by preventing direct surface-to-surface contact.However,the ordered IL layers disappeared in the case of lower concentration,resulting in an incomplete boundary layers,because the ions were displaced by molecules of the oil during sliding and revealed to be less efficient in friction reduction.
基金the National Natural Science Foundation of China(Nos.52105169 and 52105170)for their financial supportthe Beijing Natural Science Foundation(No.2222048)for financial support。
文摘We report the friction behavior of graphene edges within a carbon film,which encompasses structures ranging from amorphous carbon(a-C)to graphene nanocrystalline carbon(GNC).Structural characterization revealed that vertically growing graphene nanocrystallites were implanted into the a-C structure,exposing high-density layer edges on the film surface.Atomic force microscopy(AFM)nanofriction tests highlighted the nature of graphene edge friction.Firstly,the edge friction of GNC films was tested in a critical-contact state,and the results showed that graphene edges exhibited lower friction forces than did a-C edges.Secondly,the surface friction of GNC films was investigated in a full-contact state,revealing that the edge friction of graphene nanocrystallites regulated the surface friction of GNC films.As the edge density of graphene nanocrystallites increased,the nanofriction force of GNC films decreased.Finally,the mechanism of the regulated friction behavior was attributed to the number of edges of the graphene nanocrystallites,which provided plentiful sp2 C dangling bonds with weak bonding interactions and edge quantum wells with low surface potentials for lowering friction.These findings shed light on the importance of graphene-related materials and their high-density edges in the structural design and nanofriction application of carbon films.
基金the Science Fund of Shandong Laboratory of Advanced Materials and Green Manufacturing at Yantai(No.AMGM2024F18)funding from the China Postdoctoral Science Foundation and the National Natural Science Foundation of China(No.21838004)+2 种基金the Center of Analytical Facilities,Nanjing University of Science and Technology,for supporting the AFM measurementssupport from the Postgraduate Research&Practice Innovation Program of Jiangsu Provincethe financial support from the Swedish Research Council(No.2018-04133).
文摘Driven by the potential applications of ionic liquid(IL)flow for charging graphene-based surfaces in many emerging technologies,recent research efforts have focused on understanding ion dynamics and structuring at IL–graphene interfaces.Here,graphene colloid probe(GrP)atomic force microscopy(AFM)was used to probe the dynamics and ion structuring of 1-butyl-3-methylimidazolium tetrafluoroborate at graphene surfaces under various bias voltages.In particular,the AFM-measured nanofriction provides a good measure of the dynamic properties of the ILs at graphene surfaces.Compared with the IL at the unbiased graphene surface(0 V),the charged graphene surfaces with either negative(-1,-2 V)or positive(+1,+2 V)voltages favor a reduction in the friction coefficient by the IL.A higher magnitude of the bias voltage applied on the graphene surface with either sign(-2 or+2 V)results in a smaller friction coefficient than that at -1 and+1 V.In combination with the AFM-probed contact stiffness,adhesion forces,and ion structuring force curves with an ion orientational distribution according to molecular dynamics(MD)simulations,we discovered that the unbiased graphene surface(0 V)possesses randomly structured IL ions and that the graphene colloid probe is more likely to become stuck,resulting in more energy dissipation to contribute to a larger friction coefficient.Biasing of the graphene surface under either negative or positive voltages resulted in uniformly arranged ions,which produced a more ordered ion structure and,thus,a smoother sliding plane to reduce the friction coefficient.Electrochemical impedance spectroscopy(EIS)for the IL with graphene as an electrode demonstrated a greater ionic conductivity in the IL paired with the biased graphene than in the unbiased one,implying faster ion movement at the charged graphene,which is beneficial for reducing the friction coefficient.
