多层石墨烯纳米网化实现热电系数解耦
Decoupling thermoelectric coefficients of multilayer graphene by nanomeshing
AI总结：
本研究通过纳米网化多层石墨烯，在保持电荷输运的同时抑制热输运，实现热电系数解耦，使功率因子提升两倍、热导率降低近三倍，为二维材料热电应用提供新策略。
摘要：
在微小尺度上对材料进行纳米结构化能够控制其物理性质，揭示在较大维度下观察不到的行为。这一策略在二维（2D）材料中尤为有效，因为表面效应占主导地位，并且已被应用于热电领域。在此，我们使用多层石墨烯（厚度4-6纳米）作为测试平台，研究纳米网化对其热电性质的影响。纳米网由六角形孔阵列组成，测得孔径和颈部宽度分别约为360纳米和160纳米。多层石墨烯被集成到由六方氮化硼（hBN）支撑的类场效应晶体管器件中，能够同时进行电学和热电测量，且纳米网化仅应用于材料的一部分。我们使用调制热反射技术研究等效纳米网化和原始石墨烯薄片中的热输运，提取影响热电性能的关键参数。纳米网几何结构抑制了热输运而不会显著影响电荷输运，突显了声子和电子不同的散射长度，同时增强了热电势响应。我们观察到在室温下器件功率因子PF = S^2 σ（其中S为塞贝克系数，σ为电导率）提高了两倍，同时热导率κ降低了近三倍。结果表明，纳米网化可以显著提高多层石墨烯的热电性能，为利用二维材料的新型能量转换策略铺平了道路。
英文摘要：
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 (2D) materials, where surface effects dominate, and has been applied in the thermoelectric field. Here, we use multilayer graphene (4-6 nm thick) as a test platform to study the effect of nanomeshing on its thermoelectric properties. 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 (hBN), allowing simultaneous electric and thermoelectric 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, extracting key parameters that affect thermoelectric performance. The nanomesh geometry suppresses thermal transport without significantly impacting charge transport, highlighting the different scattering lengths of phonons and electrons while enhancing the thermopower response. We observe a twofold improvement in the device power factor, PF = S^2 sigma (with S the Seebeck coefficient and sigma the electrical conductivity), at room temperature, along with a nearly threefold reduction in thermal conductivity k. The results show that nanomeshing can significantly improve the thermoelectric performance of multilayer graphene, paving the way for novel energy conversion strategies using 2D materials.
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