The Effect of Intrinsic Crumpling on the Mechanics of Free-Standing Graphene

TL;DR

This study investigates how intrinsic crumpling, caused by static wrinkling and flexural phonons, affects the mechanical stiffness of free-standing graphene, revealing that static wrinkling significantly softens graphene at room temperature.

Contribution

The paper introduces a sensitive experimental method to measure graphene's mechanical properties and demonstrates that static wrinkling, rather than flexural phonons, primarily causes softening.

Findings

In-plane stiffness of graphene is 20-100 N/m at room temperature.

Stiffness approaches 300 N/m when aspect ratio increases or at low temperatures.

Static wrinkling significantly contributes to graphene softening at temperatures below 400 K.

Abstract

Free-standing graphene is inherently crumpled in the out-of-plane direction due to dynamic flexural phonons and static wrinkling. We explore the consequences of this crumpling on the effective mechanical constants of graphene. We develop a sensitive experimental approach to probe stretching of graphene membranes under low applied stress at cryogenic to room temperatures. We find that the in-plane stiffness of graphene is between 20 and 100 N/m at room temperature, much smaller than 340 N/m (the value expected for flat graphene). Moreover, while the in-plane stiffness only increases moderately when the devices are cooled down to 10 K, it approaches 300 N/m when the aspect ratio of graphene membranes is increased. These results indicate that softening of graphene at temperatures less than 400 K is caused by static wrinkling, with only a small contribution due to flexural phonons. Together, these results explain the large variation in reported mechanical constants of graphene devices and paves the way towards controlling their mechanical properties.