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

Phonon energy dissipation in friction between black phosphorus layers

Herein, we employ molecular dynamics simulations to decode the friction properties and phonon energy dissipation between black phosphorus layers. The observations reveal the influence of three factors, temperature, velocity, and normal load, on the friction force of monolayer/bilayer black phosphorus. Specifically, friction is negatively correlated with layer thickness and temperature, and positively correlated with velocity and normal load. The change in friction force is further explained in terms of frictional energy dissipation, and supplemented by the height of potential barriers as well as the number of excited phonons. From the phonon spectrum analysis, the phonon number at the contact interface is found to be higher than that at the non-contact interface. This is due to the larger distance of the contact interface atoms deviate from their equilibrium positions, resulting in higher total energy generated by more intense oscillations, and therefore contributes greater to friction.

Coupling Effect of Structural Lubrication and Thermal Excitation on Phononic Friction

This work investigates the coupling effect of structural lubrication and thermal excitation on phononic friction between black phosphorus (BP) layers. As the rotation angle increases from commensurate to incommensurate states, the friction gradually decreases at any temperature. However, the role of temperature in friction depends on commensurability. For a rotation angle less than 10°, increasing temperature leads to a decrease in friction due to thermal excitation. Conversely, when the rotation angle exceeds 10°, elevated temperature results in an increase in friction due to the effect of thermal collision. At a critical rotation angle of 10°, higher temperatures lead to reduced friction through thermal lubrication at low speeds, and at large speeds, the thermal excitation duration becomes so short that the role of thermal lubrication is weakened, and instead thermal collision dominates. Further research reveals that BP's ability to withstand different maximum speeds is also determined by commensurability. Finally, a method to measure the sliding period length of a rotated tip through an unrotated substrate potential energy topography is proposed and simply verified by using the phonon spectrum.

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

Interfacial thermal conductance (ITC) between two contact surfaces is an important factor in accurately measuring energy transfer and heat dissipation at the interface; however, it is still not fully resolved how to more effectively modulate the ITC and unravel the related inner mechanisms. In this study, the contribution of commensurability and normal load to ITC at the atomic-scale silicon/silicon interface is disclosed. The results manifest that the ITC gradually reduces with the transition from commensurability to incommensurability. This is because the reduced force constant at the incommensurate interface decreases the transmittance of phonons, leading to the suppression of high-frequency phonon excitation and a red shift in the phonon spectrum, thereby weakening the ITC. We further discovered that increasing the normal loads can significantly enhance the ITC in both contact states, and the reason is that the interlayer distance decreases with increasing normal loads, which strengthens the interfacial potential and force constant, consequently resulting in greater heat transfer efficiency. This paper reveals that interfacial thermal transport can be regulated by applying normal loads and changing the interfacial contact states.