CAREER: Investigation of thermal phonon scattering processes in solids

1254213 minnich热传导是众多不同技术的核心，从发电到电子，再到激光。在这些应用中，越来越多的热传导发生在远小于一微米的尺度上，与热载体本身的基本长度尺度相当。例如，纳米结构的热电器件可能包含小至几纳米的工程结构；这些纳米级材料将热量转化为电能的效率比它们的宏观材料高50%。然而，由于对晶格振动或声子散射过程的理解不足，进一步的进展很难实现，而晶格振动或声子散射过程在很大程度上决定了材料的性能。S导热系数。尽管经过50多年的研究，声子的平均自由程（MFPs）在大多数材料中都是未知的，声子的平均自由程描述了声子与其他声子、缺陷和纳米结构相互作用时如何散射。这项实验和计算研究将提供对热声子散射的全面理解。最近才开发的新实验方法将用于测量从纳米到毫米的长度尺度上的MFP分布。不同的散射机制对特定声子模式的影响将通过观察质量缺陷、晶界、纳米沉淀物和其他纳米结构引入材料时MFP分布的变化来获得。本文将利用玻尔兹曼输运方程的数值解与实验结果相比较，建立对该领域研究人员有很大帮助的mfp解析表达式。这个项目将推进我们对热传导的科学认识，并使许多应用成为可能，特别是在能源领域。在科学上，这项研究将提供对复杂的热声子散射过程的全面理解，这一过程几十年来一直困扰着科学家，并通过实验验证热声子散射率的基本计算预测。实际上，这项研究将使工程师能够在制造前设计出具有精确定制热导率的材料，而不是通过反复试验，这是目前能力的一大进步。这种能力将带来许多应用，例如从排气管中的废热中收集有用电力的高效汽车，不使用任何有害液体的环保冰箱，以及降低功耗的电子设备。

1254213MinnichHeat conduction is central to numerous and diverse technologies, ranging from power generation, to electronics, to lasers. Increasingly in these applications, heat conduction occurs at scales much less than a micron, comparable to the fundamental length scales of the heat carriers themselves. For example, nanostructured thermoelectrics may contain engineered structures as small as a few nanometers; these nanoscale materials are 50% more efficient at converting heat to electricity than their macroscopic counterparts. However, further advances are difficult to achieve because of a poor understanding of the lattice vibration, or phonon, scattering processes that largely determine a material?s thermal conductivity. Despite over 50 years of investigation, the mean free paths (MFPs) of phonons, which describe how phonons scatter when they interact with other phonons, defects, and nanostructures, are unknown in most materials. This experimental and computational investigation will provide a comprehensive understanding of thermal phonon scattering. Novel experimental methods that have been developed only recently will be used to measure MFP distributions across length scales ranging from nanometers to millimeters. The effect of different scattering mechanisms on specific phonon modes will be obtained by observing the changes in the MFP distribution as mass defects, grain boundaries, nanoprecipitates, and other nanostructures are systematically introduced into the material. Analytical expressions for the MFPs, which are of great utility to researchers in the field, will be created and validated against the experimental results using numerical solutions of the Boltzmann transport equation. This project will advance our scientific knowledge of heat conduction and enable many applications, particularly in the energy field. Scientifically, the investigation will provide a comprehensive understanding of the complex thermal phonon scattering process, which has eluded scientists for decades, as well as experimentally validate fundamental computational predictions of thermal phonon scattering rates. Practically, this research will enable engineers to design materials with precisely tailored thermal conductivities before fabrication rather than by trial-and-error, a major advance over present capabilities. This ability would lead to many applications, such as highly efficient cars that harvest useful electricity from wasted heat in the tailpipe, environmentally friendly refrigerators that do not use any harmful fluids, and electronic devices with reduced power consumption.