Decoding the phonon transport of structural lubrication at silicon/silicon interface

Abstract

Although the friction characteristics under different contact conditions have been extensively studied, the mechanism of phonon transport at the structural lubrication interface is not extremely clear. In this paper, we firstly promulgate that there is a 90°-symmetry of friction force depending on rotation angle at Si/Si interface, which is independent of normal load and temperature. It is further found that the interfacial temperature difference under incommensurate contacts is much larger than that in commensurate cases, which can be attributed to the larger interfacial thermal resistance (ITR). The lower ITR brings greater energy dissipation in commensurate sliding, and the reason for that is more effective energy dissipation channels between the friction surfaces, making it easier for the excited phonons at the washboard frequency and its harmonics to transfer through the interface. Nevertheless, the vibrational frequencies of the interfacial atoms between the tip and substrate during the friction process do not match in incommensurate cases, and there is no effective energy transfer channel, thus presenting the higher ITR and lower friction. Eventually, the number of excited phonons on contact surfaces reveals the amount of frictional energy dissipation in different contact states.

Coupling Effect of Structural Lubrication and Thermal Excitation on Phononic Friction

“…Consequently, the phonon mean free range is reduced, resulting in a greater conversion of kinetic energy into disordered thermal motion and increased dissipation of frictional energy, and promotes more inelastic collisions between the tip and substratecontacting surfaces, thereby further increasing interlayer friction, named thermal collision effect. 52,60,61 For the critical rotation angle of 10°, the barrier height is positioned at an intermediate level between the barrier heights of below 10°and those exceeding 10°as shown in Figure 4, while they maintain an identical amplitude of atomic vibration in Figure 5. The competition between thermal lubrication and thermal collision is relatively in a state of equilibrium.…”

“…Thus, structural lubrication does not affect the vibrational strength of the interlayer atoms, which is also in line with our previous studies. 52,60 The temperature standard deviations of the tip and substrate at 300 K are significantly higher than those at 0 K, suggesting that an increase in temperature results in a corresponding elevation of the temperature standard deviation as well as heightened thermal vibrations of the interlayer atoms.…”

Regulating interfacial thermal conductance with commensurate–incommensurate transitions at atomic-scale silicon/silicon interfaces

“…Moreover, under commensurate contact, the lattice structure of the interfacial atoms is perfectly symmetric. Once the interlayer rotation occurs on the contact surfaces, that is, the interfacial contact state alters, and the atomic structure at the interface mismatches, 37,48 which will probably cause changes in the interfacial potential energy, force constant and thermal transport. Therefore, in the commensurate-incommensurate transitions, the force constant and interfacial potential gradually decrease, resulting in decreasing the ITC in the incommensurate state.…”

“…34,35 We adjust 2.6σ (∼9.9476 Å) as the cutoff distance in all LJ interactions, beyond which the atomic interactions among the atoms are ignored, and the lattice constant of silicon is fixed at the optimized value of 5.431 Å, which is consistent with previous research studies. [36][37][38] Eight atoms are selected respectively from the hot region and cold region contact surfaces to calculate the interlayer distance and phonon density of states (PDOS). All molecular dynamics simulations have been implemented using LAMMPS package.…”

Phonon energy dissipation in friction between black phosphorus layers

“…the total energy generated by the friction interface between the tip and substrate. The total energy absorbed by the thermostat can reflect the magnitude of frictional energy dissipation [55]. The dependence of total energy on normal load is shown in figure 3(d).…”