Load dependence of two-dimensional atomic-scale friction

Experimental and Theoretical Investigations on the Nanoscale Kinetic Friction in Ambient Environmental Conditions

The liquid lubrication, thermolubricity and dynamic lubricity due to mechanical oscillations are investigated with an atomic force microscope in ambient environmental conditions with different relative humidity (RH) levels. Experimental results demonstrate that high humidity at low-temperature regime enhances the liquid lubricity while at high-temperature regime it hinders the effect of the thermolubricity due to the formation of liquid bridges. Friction response to the dynamic lubricity in both high- and low-temperature regimes keeps the same trends, namely the friction force decreases with increasing the amplitude of the applied vibration on the tip regardless of the RH levels. An interesting finding is that for the dynamic lubricity at high temperature, high-humidity condition leads to the friction forces higher than that at low-humidity condition while at low temperature the opposite trend is observed. An extended two-dimensional dynamic model accounting for the RH is proposed to interpret the frictional mechanism in ambient conditions.

Theoretical study of electronic and tribological properties of h-BNC2/graphene, h-BNC2/h-BN and h-BNC2/h-BNC2bilayers

Density functional theory methods are used to investigate the interlayer sliding energy landscape, binding energy and interlayer spacing between h-BNC₂/graphene (I), h-BNC₂/h-BN (II) and h-BNC₂/h-BNC₂(III) bilayer structures.

The diversity of friction behavior between bi-layer graphenes

For relative sliding between two rigid graphene sheets that are interacted on by a van der Waals force, we show that the friction behavior is significantly dependent on the interlayer separation distance h. Around the equilibrium interlayer distance he, the friction behavior exactly obeys a linear law. When h is far smaller than he, the linear friction behavior transforms to overlinear behavior. On the other hand, when h is larger than he, there is another critical value of the interlayer distance, hc; when h is larger than he and smaller than hc, the friction behavior transforms from linear to sublinear behavior; however, when h is larger than hc, the coefficient of friction becomes negative. Further, the different friction behaviors are found to be well described by a universal power law, τ = μ*(σ + σ0)(n).

Transition from stick-slip to continuous sliding in atomic friction: entering a new regime of ultralow friction

A transition from stick-slip to continuous sliding is observed for atomically modulated friction by means of a friction force microscope. When the stick-slip instabilities cease to exist, a new regime of ultralow friction is encountered. The transition is described in the framework of the Tomlinson model using a parameter eta which relates the strength of the lateral atomic surface potential and the stiffness of the contact under study. Experimentally, this parameter can be tuned by varying the normal load on the contact. We compare our results to a recently discussed concept called superlubricity.