Significantly reduced thermal conductivity and enhanced thermoelectric properties of single- and bi-layer graphene nanomeshes with sub-10 nm neck-width

When graphene is shrunk into ~10 nm scale graphene nanoribbons or nanomesh structures, it is expected that not only electrical properties but also thermal conductivity and thermoelectric property are significantly altered due to the quantum confinement effect and extrinsic phonon-edge scattering. Here, we fabricate large-area, sub-10 nm single- and bilayer graphene nanomeshes from block copolymer self-assembly and measure the thermal conductivity, thermoelectric and electrical transport properties to experimentally verify the effect of sub-10 nm quantum confinement, phonon-edge scattering and cross-plane coupling. Among the large variety of the samples, bilayer graphene nanomesh having 8 nm-neck width showed significantly low thermal conductivity down to ~78 W m⁻¹ K⁻¹, which is the lowest thermal conductivity for suspended graphene nanostructures, and a high thermopower value of −520 μV K⁻¹, while it still shows the comparably high carrier mobility. Classical and quantum mechanical calculations successfully supported our nanomesh approach, which can achieve high thermoelectric properties based on the significantly reduced thermal conductivity and higher thermopower due to the confined geometry.