Unexpected Nonmonotonic Dependence of Phononic Friction on Biaxial Strain Between MoS₂ Layers

It is generally recognized that the lattice mismatch at contact interface due to applied strain will lead to a decrease in friction; however, two aberrant phenomena of friction between strain-controlled molybdenum disulfide (MoS2) layers have been disclosed in the present work. One is that greater energy dissipation appears in the state of slight deviation from the strain-free contact, which is independent of temperature. The reason is that the lattice constant of the tip and substrate enlarges synchronously under slight strain to substrate; thus, the interfacial lattice structure does not mismatch, leading to greater friction. The other phenomenon is that the opposite effects of temperature on friction with different strain ranges are generated, and this is the result of competition between thermal lubrication and thermal collision of the interfacial atoms. Subsequently, the reason for the friction peak changing with velocity under different strains is revealed using the fast Fourier transform (FFT) of the instantaneous friction. It is indicated that the friction peak is caused by resonance, and the amplitude of FFT spectrum at the resonance peak reaches the maximum, resulting in greater energy dissipation.