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 it 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 approximately $360$ 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 is in very good agreement with the classical Maxwell-Eucken model for porous media. In contrast, the observed reduction in thermal conductivity exceeds the value expected from geometrical modifications alone by a factor of 1.5, 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 developing engineering strategies to achieve similar control across a wider range of 2D materials.

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• Electrical conductivity
• Seebeck effect
• Thermal conductivity
• Thermal energy harvesting devices
• Thermoelectric generators
• Multilayer graphene
• Nanostructures
• Thermoelectrics