标题： 通过周期波形分析扩展时域热反射的低频极限 显示英文标题

标题： Extending the Low-Frequency Limit of Time-Domain Thermoreflectance via Periodic Waveform Analysis

摘要： 时域热反射法（TDTR）是一种表征层状材料热性能的强大技术。然而，在低于 0.1 MHz 的调制频率下，脉冲累积效应限制了其有效性，使其难以准确测量低于 6 W/(m K) 的面内热导率。在这里，我们提出了一种基于周期波形分析的 TDTR（PWA-TDTR）方法，该方法通过最小程度修改常规设置，将可测量的频率范围扩展至 50 Hz。这一改进极大地提高了测量灵敏度，使得能够准确测量低至 0.2 W/(m K) 的面内热导率。我们通过使用 PWA-TDTR 测量聚甲基丙烯酸甲酯（PMMA）和石英玻璃，验证了该技术，同时利用常规 TDTR 测量垂直方向上的热导率。结合这些方法，可以提取出热导率和体积热容，并且结果与文献值高度一致。此外，我们进一步展示了 PWA-TDTR 的多功能性，包括（1）薄液膜的热导率和热容量测量；以及（2）铌酸锂晶体中的深度分辨热导率剖面分析，揭示了深度达 100 微米的点缺陷引起的不均匀性。通过克服频率和灵敏度的限制，PWA-TDTR 显著扩展了 TDTR 的适用范围，使研究以前难以探究的材料和条件下的热传输特性成为可能。 显示英文摘要

摘要： Time-domain thermoreflectance (TDTR) is a powerful technique for characterizing the thermal properties of layered materials. However, its effectiveness at modulation frequencies below 0.1 MHz is hindered by pulse accumulation effects, limiting its ability to accurately measure in-plane thermal conductivities below 6 W/(m K). Here, we present a periodic waveform analysis-based TDTR (PWA-TDTR) method that extends the measurable frequency range down to 50 Hz with minimal modifications to the conventional setup. This advancement greatly enhances measurement sensitivity, enabling accurate measurements of in-plane thermal conductivities as low as 0.2 W/(m K). We validate the technique by measuring polymethyl methacrylate (PMMA) and fused silica, using PWA-TDTR to obtain in-plane thermal diffusivity and conventional TDTR to measure cross-plane thermal effusivity. Together, these allow the extraction of both thermal conductivity and volumetric heat capacity, with results in excellent agreement with literature values. We further demonstrate the versatility of PWA-TDTR through (1) thermal conductivity and heat capacity measurements of thin liquid films and (2) depth-resolved thermal conductivity profiling in lithium niobate crystals, revealing point defect-induced inhomogeneities at depths up to 100 um. By overcoming frequency and sensitivity constraints, PWA-TDTR significantly expands the applicability of TDTR, enabling detailed investigations of thermal transport in materials and conditions that were previously challenging to study.