Graphene nanoribbons on gold: Understanding superlubricity and edge effects

TL;DR

This study uses simulations to reveal that graphene nanoribbons on gold exhibit superlubricity internally, with static friction mainly due to edge effects, and that friction oscillates with GNR length due to lattice mismatch.

Contribution

It provides a detailed atomistic understanding of edge effects and superlubricity in GNRs on gold, linking friction behavior to lattice mismatch and GNR length.

Findings

Interior of GNR is superlubric, reducing overall static friction.

Static friction oscillates with GNR length due to lattice mismatch.

Edge pinning causes friction to remain constant despite GNR length.

Abstract

We address the atomistic nature of the longitudinal static friction against sliding of graphene nanoribbons (GNRs) deposited on gold, a system whose structural and mechanical properties have been recently the subject of intense experimental investigation. By means of numerical simulations and modeling we show that the GNR interior is structurally lubric ("superlubric") so that the static friction is dominated by the front/tail regions of the GNR, where the residual uncompensated lateral forces arising from the interaction with the underneath gold surface opposes the free sliding. As a result of this edge pinning the static friction does not grow with the GNR length, but oscillates around a fairly constant mean value. These friction oscillations are explained in terms of the GNR-Au(111) lattice mismatch: at certain GNR lengths close to an integer number of the beat (or moire') length there is good force compensation and superlubric sliding; whereas close to half odd-integer periods there is significant pinning of the edge with larger friction. These results make qualitative contact with recent state-of-the-art atomic force microscopy experiment, as well as with the sliding of other different incommensurate systems.