Understanding the impact of lattice imperfections on nanoscale thermal transport is crucial for diverse applications ranging from thermal management to energy conversion. Grain boundaries (GBs) are ubiquitous defects in polycrystalline materials, which scatter phonons and reduce thermal conductivity (κ). Historically, their impact on heat conduction has been studied indirectly through spatially averaged measurements, that provide little information about phonon transport near a single GB. Here, using spatially resolved time-domain thermoreflectance (TDTR) measurements in combination with electron backscatter diffraction (EBSD), we make localized measurements of κ within few μm of individual GBs in boron-doped polycrystalline diamond. We observe strongly suppressed thermal transport near GBs, a reduction in κ from ∼1000 W m^–1 K^–1 at the center of large grains to ∼400 W m^–1 K^–1 in the immediate vicinity of GBs. Furthermore, we show that this reduction in κ is measured up to ∼10 μm away from a GB. A theoretical model is proposed that captures the local reduction in phonon mean-free-paths due to strongly diffuse phonon scattering at the disordered grain boundaries. Our results provide a new framework for understanding phonon–defect interactions in nanomaterials, with implications for the use of high-κ polycrystalline materials as heat sinks in electronics thermal management.

中文翻译：

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直接可视化由于单个颗粒边界附近的声子散射增强引起的导热系数抑制

理解晶格缺陷对纳米级热传输的影响对于从热管理到能量转换的各种应用至关重要。晶界（GBs）是多晶材料中普遍存在的缺陷，会散射声子并降低热导率（κ）。历史上，已经通过空间平均测量间接研究了它们对热传导的影响，这些测量几乎没有提供关于单个GB附近声子传输的信息。在这里，结合使用空间分辨时域热反射（TDTR）测量和电子背散射衍射（EBSD），我们对掺硼多晶金刚石中单个GB的几微米范围内的κ进行了局部测量。我们观察到GBs附近的热传输受到强烈抑制，κ从〜1000 W m减小^-1 ķ ^-1在大颗粒的中心到〜400脉冲W M ^-1 ķ ^-1在绿带的附近。此外，我们表明，与GB相比，这种κ的减小可测量到约10μm。提出了一个理论模型，该模型捕获了由于在无序晶界处强烈扩散的声子散射而引起的声子平均自由程的局部减小。我们的结果为理解纳米材料中的声子-缺陷相互作用提供了一个新的框架，这暗示了将高κ多晶材料用作电子热管理中的散热器。