Nanofriction properties of molecular deposition films

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.

Nanofriction characteristics of h-BN with electric field induced electrostatic interaction

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.

Probing the nanofriction of non-halogenated phosphonium-based ionic liquid additives in glycol ether oil on titanium surface

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.