Impact of Static Distortion Waves on Superlubricity

Abstract

Friction is a major source of energy loss in mechanical devices. This energy loss may be minimized by creating interfaces with extremely reduced friction, i.e., superlubricity. Conventional wisdom holds that incommensurate interface structures facilitate superlubricity. Accurately describing friction necessitates the precise modeling of the interface structure. This, in turn, requires the use of accurate first-principles electronic structure methods, especially when studying organic/metal interfaces, which are highly relevant due to their tunability and propensity to form incommensurate structures. However, the system size required to calculate incommensurate structures renders such calculations intractable. As a result, studies of incommensurate interfaces have been limited to very simple model systems or strongly simplified methodology. We overcome this limitation by developing a machine-learned interatomic potential that is able to determine energies and forces for structures containing thousands to tens of thousands of atoms with an accuracy comparable to conventional firstprinciples methods but at a fraction of the cost. Using this approach, we quantify the breakdown of superlubricity in incommensurate structures due to the formation of static distortion waves. Moreover, we extract design principles to engineer incommensurate interface systems where the formation of static distortion waves is suppressed, which facilitates low friction coefficients.

Molecular motion of a nanoscopic moonlander via translations and rotations of triphenylphosphine on graphite

“…Similarly, for orientation-dependent diffusion of pentacene molecules on a pentacene layer at 300 K a much higher diffusivity was reported based on simulation results 46 . On the one hand such large diffusivities may be the consequence of an unusual low friction of PAHs on graphitic substrates 47 , 48 . On the other hand, for cobalt phthalocyanine, another planar molecule with about twice the mass compared to PPh 3 , a larger activation energy but a similar diffusivity with 9.6 × 10 −10 m 2 s −1 at 350 K was found on metal surfaces 49 .…”