Why edge effects are important on the intrinsic loss mechanisms of graphene nanoresonators?

TL;DR

This study uses molecular dynamics simulations to explore how free edges in graphene nanoresonators significantly reduce their quality factors due to imaginary edge vibrations and artificial effects, explaining experimental observations.

Contribution

It reveals the impact of free edges on the intrinsic loss mechanisms of graphene nanoresonators and distinguishes between natural and artificial vibration effects.

Findings

Free edges cause imaginary edge vibrations that flip between degenerate states.

Artificial vibrations slightly reduce the quality factor.

Natural vibration actuation eliminates artificial effects.

Abstract

Molecular dynamics simulations are performed to investigate edge effects on the quality factor of graphene nanoresonators with different edge configurations and of various sizes. If the periodic boundary condition is applied, very high quality factors ($3\times10^{5}$) are obtained for all kinds of graphene nanoresonators. However, if the free boundary condition is applied, quality factors will be greatly reduced by two effects resulting from free edges: the imaginary edge vibration effect and the artificial effect. Imaginary edge vibrations will flip between a pair of doubly degenerate warping states during the mechanical oscillation of nanoresonators. The flipping process breaks the coherence of the mechanical oscillation of the nanoresonator, which is the dominant mechanism for extremely low quality factors. There is an artificial effect if the mechanical oscillation of the graphene nanoresonator is actuated according to an artificial vibration (non-natural vibration of the system), which slightly reduce the quality factor. The artificial effect can be eliminated by actuating the mechanical oscillation according to a natural vibration of the nanoresonator. Our simulations provide an explanation for the recent experiment, where the measured quality factor is low and varies between identical samples with free edges.