CAREER: Fundamental Investigation of the Wave Nature of Lattice Thermal Transport

热传递是纳米工程中的一个限制因素：如果微芯片或激光等微调元件过热或无法控制地传导热量，设备将无法按预期工作。因此，了解如何在纳米尺度上控制热传递在许多工程应用中是至关重要的。半导体晶体中的热传导由称为声子的集体原子振动控制。传统上，声子被视为可以通过材料传播的粒子，从而携带热量，并可以被材料缺陷或其他声子散射。然而，在由周期性或准周期性排列的元件组成的结构中，声子的波动性质可以出现甚至主导热传导，例如由交替的材料层组成的量子级联激光器和包含密集排列的纳米晶体管的集成电路。在这些结构中，声子的传播可以通过相长干涉来促进，也可以通过相消干涉来停止。这个项目旨在探索这些有趣的波动行为，并通过互补的计算和实验技术来阐明类粒子声子和类波声子之间的转变。这项研究将带来新的工程策略，使量子级联激光器和集成电路等现代设备的散热最大化，或将热电材料和热障的热传导降至最低。该项目将研究、教育和推广紧密结合在一起，包括主题科学展览、新课程开发、实践研究指导以及在线课程和研究工具共享，以对K-12、本科生和研究生的STEM教育产生广泛、长期的影响。该项目的研究目标是：1)利用互补谱声子分析和声子谱技术，严格理解周期、准周期和非周期结构中的波状声子的输运、散射和局域化；以及2)通过解耦抑制波状和粒子型声子传输，利用机器学习辅助的光谱声子分析和结构优化，最大限度地减少晶格热输运。对声子波动性质的研究可以极大地提高人们对晶体固体中热输运的认识，目前主要是基于声子的粒子性质。这些知识将使基于声子波动性质的新工程策略的开发成为可能，打破各种热传递限制技术的热设计或管理的瓶颈。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Heat transfer is a limiting factor in nanoscale engineering: if the finely tuned elements such as microchips or lasers get too hot or conduct heat uncontrollably, the devices will not function as intended. Thus, understanding how to control heat transfer at the nanoscale is critical in many engineering applications. Heat conduction in semiconductor crystals is dominated by collective atomic vibrations known as phonons. Conventionally, phonons are treated as particles that can propagate through a material, thus carrying heat, and can be scattered by material defects or other phonons. However, the wave nature of phonons can emerge or even dominate heat conduction in structures composed of periodically or quasi-periodically arranged components, e.g., quantum cascade lasers made of alternating layers of materials and integrated circuits containing densely packed nano-transistors. In those structures, the propagation of phonons can be promoted by constructive interference or halted by destructive interference. This project aims to explore these intriguing wave behaviors and elucidate the transition between particle-like and wave-like phonons through complementary computational and experimental techniques. This research will lead to novel engineering strategies to maximize heat dissipation in modern devices like quantum cascade lasers and integrated circuits or minimize heat conduction in thermoelectric materials and thermal barriers. This project will tightly integrate research, education, and outreach—including themed science exhibits, new curriculum development, hands-on research mentoring, and online course and research tool sharing—to have a broad, long-term impact on STEM education for K-12, undergraduate, and graduate students. The research objectives of this project are to: 1) rigorously understand the transport, scattering, and localization of wave-like phonons in periodic, quasi-periodic, and aperiodic structures, leveraging complementary spectral phonon analysis and phonon spectroscopy techniques; and 2) minimize lattice thermal transport through decoupled suppression of wave-like and particle-like phonon transport, leveraging machine learning-aided spectral phonon analysis and structure optimization. The proposed research on the wave nature of phonons can greatly advance the state of knowledge of thermal transport in crystalline solids, which has until now been primarily based on the particle nature of phonons. Such knowledge will enable the development of novel engineering strategies based on the wave nature of phonons, breaking the bottleneck of the thermal design or management of various heat transfer-limited technologies.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.