Abstract

Nanostructuring materials at small scales enables control over their physical properties, revealing behaviors not observed at larger dimensions. This strategy is particularly effective in two-dimensional materials, where surface effects dominate, and is especially promising for energy conversion and thermal management. Here, we use multilayer graphene (4-6 nm thick) as a test platform to study the effect of nanomeshing on its thermoelectric coefficients. The nanomesh consists of a hexagonal array of holes, with a measured diameter and neck-width of ~360 nm and ~160 nm, respectively. The multilayer graphene is integrated into field-effect transistor-like devices supported by hexagonal boron nitride, allowing simultaneous electric and thermopower measurements, with nanomeshing applied to only part of the material. We use modulated thermoreflectance to investigate thermal transport in equivalent nanomeshed and pristine graphene flakes. Our results show a reduction in electrical conductivity that can be well described within the framework of the classical Maxwell–Eucken model for porous media. In contrast, the observed reduction in thermal conductivity exceeds what expected from geometrical modifications alone, highlighting the different mean free paths of phonons and electrons. Moreover, we find an increased thermopower in the nanomeshed graphene region, which can be qualitatively attributed to filtering of low-energy charge carriers. These findings demonstrate that nanomeshing can significantly decouple the thermoelectric coefficients of multilayer graphene, paving the way for novel engineering strategies to achieve similar control across a wider range of 2D materials.

Abstract

Nanostructuring materials at small scales enables control over their physical properties, revealing behaviors not observed at larger dimensions. This strategy is particularly effective in two-dimensional materials, where surface effects dominate, and is especially promising for energy conversion and thermal management. Here, we use multilayer graphene (4-6 nm thick) as a test platform to study the effect of nanomeshing on its thermoelectric coefficients. The nanomesh consists of a hexagonal array of holes, with a measured diameter and neck-width of ~360 nm and ~160 nm, respectively. The multilayer graphene is integrated into field-effect transistor-like devices supported by hexagonal boron nitride, allowing simultaneous electric and thermopower measurements, with nanomeshing applied to only part of the material. We use modulated thermoreflectance to investigate thermal transport in equivalent nanomeshed and pristine graphene flakes. Our results show a reduction in electrical conductivity that can be well described within the framework of the classical Maxwell–Eucken model for porous media. In contrast, the observed reduction in thermal conductivity exceeds what expected from geometrical modifications alone, highlighting the different mean free paths of phonons and electrons. Moreover, we find an increased thermopower in the nanomeshed graphene region, which can be qualitatively attributed to filtering of low-energy charge carriers. These findings demonstrate that nanomeshing can significantly decouple the thermoelectric coefficients of multilayer graphene, paving the way for novel engineering strategies to achieve similar control across a wider range of 2D materials.

Abstract

Nanostructuring materials at small scales enables control over their physical properties, revealing behaviors not observed at larger dimensions. This strategy is particularly effective in two-dimensional materials, where surface effects dominate, and is especially promising for energy conversion and thermal management. Here, we use multilayer graphene (4-6 nm thick) as a test platform to study the effect of nanomeshing on its thermoelectric coefficients. The nanomesh consists of a hexagonal array of holes, with a measured diameter and neck-width of ~360 nm and ~160 nm, respectively. The multilayer graphene is integrated into field-effect transistor-like devices supported by hexagonal boron nitride, allowing simultaneous electric and thermopower measurements, with nanomeshing applied to only part of the material. We use modulated thermoreflectance to investigate thermal transport in equivalent nanomeshed and pristine graphene flakes. Our results show a reduction in electrical conductivity that can be well described within the framework of the classical Maxwell–Eucken model for porous media. In contrast, the observed reduction in thermal conductivity exceeds what expected from geometrical modifications alone, highlighting the different mean free paths of phonons and electrons. Moreover, we find an increased thermopower in the nanomeshed graphene region, which can be qualitatively attributed to filtering of low-energy charge carriers. These findings demonstrate that nanomeshing can significantly decouple the thermoelectric coefficients of multilayer graphene, paving the way for novel engineering strategies to achieve similar control across a wider range of 2D materials.

Abstract

Nanostructuring materials at small scales enables control over their physical properties, revealing behaviors not observed at larger dimensions. This strategy is particularly effective in two-dimensional materials, where surface effects dominate, and is especially promising for energy conversion and thermal management. Here, we use multilayer graphene (4-6 nm thick) as a test platform to study the effect of nanomeshing on its thermoelectric coefficients. The nanomesh consists of a hexagonal array of holes, with a measured diameter and neck-width of ~360 nm and ~160 nm, respectively. The multilayer graphene is integrated into field-effect transistor-like devices supported by hexagonal boron nitride, allowing simultaneous electric and thermopower measurements, with nanomeshing applied to only part of the material. We use modulated thermoreflectance to investigate thermal transport in equivalent nanomeshed and pristine graphene flakes. Our results show a reduction in electrical conductivity that can be well described within the framework of the classical Maxwell–Eucken model for porous media. In contrast, the observed reduction in thermal conductivity exceeds what expected from geometrical modifications alone, highlighting the different mean free paths of phonons and electrons. Moreover, we find an increased thermopower in the nanomeshed graphene region, which can be qualitatively attributed to filtering of low-energy charge carriers. These findings demonstrate that nanomeshing can significantly decouple the thermoelectric coefficients of multilayer graphene, paving the way for novel engineering strategies to achieve similar control across a wider range of 2D materials.