Tailoring the thermal expansion of graphene via controlled defect creation

TL;DR

This study demonstrates that introducing controlled defects into suspended graphene can significantly reduce its negative thermal expansion coefficient by suppressing out-of-plane vibrations, offering new avenues for defect engineering in graphene applications.

Contribution

The paper provides systematic experimental and simulation evidence that defect creation in graphene can tailor its thermal expansion properties, a novel approach in graphene engineering.

Findings

Mono-vacancies reduce graphene's TEC by up to tenfold.

Defect-induced strain fields suppress out-of-plane fluctuations.

Simulations confirm the experimental trend and mechanism.

Abstract

Contrary to most materials, graphene exhibits a negative thermal expansion coefficient (TEC), i.e it contracts when heated. This contraction is due to the thermal excitation of low energy out-of-plane vibration modes. These flexural modes have been reported to govern the electronic transport and the mechanical response of suspended graphene. In this work, we systematically investigate the influence of defects in the TEC of suspended graphene membranes. Controlled introduction of low densities of mono-vacancies reduces the graphene TEC, up to one order of magnitude for a defect density of $5\times10^{12}$~cm$^{-2}$ . Our molecular dynamics simulations reproduce the observed trend and show that TEC reduction is due to the suppression of out-of-plane fluctuations caused by the strain fields created by mono-vacancies in their surrounding areas. These results highlight the key role of defects in the properties of "real-life" graphene, and pave the way for future proposals of electronic and mechanical defect engineering.