CAREER: Ultrafast Phonon Dynamics in Complex Nanostructures: Systematic Investigation with Ultrafast Phonon Spectroscopy and Femtosecond Thermal Reflectance Technique

研究方向：复杂纳米结构中的超快声子动力学：基于超快声子光谱学和飞秒热反射技术的系统研究声子是量子化的晶格振动，是许多晶体材料中的主要热载体。我们对声子的科学认识落后于对电子和光子的认识，主要是因为难以测量和操纵单个声子。在块状材料中，声子输运是纯粹扩散的，受傅立叶定律支配。在纳米结构中，声子可以弹道传播，在边界、界面和纳米粒子上散射，并且可以通过量子限制效应进行局域化。当不同的纳米结构集成在一起时，声子动力学变得异常复杂。本研究将利用超快声子光谱和飞秒时域热反射技术研究复杂纳米结构中单个声子的行为。不同纳米结构对特定声子模式的影响将通过系统地将边界、界面、纳米粒子和量子阱引入材料中来详细研究。利用超快声子光谱技术表征特定声子模式下的声子寿命和群速度，并利用时域热反射技术测量对宏观导热系数的影响。将提供关于晶格失配程度、超晶格周期、纳米颗粒大小、类型和浓度以及这些机制的相互作用所产生的影响的定量信息。该结果将用于验证数值和理论研究的预测，并弥合宏观热特性测量和微观声子特性之间的差距。这项研究将解决研究人员在各种学科中遇到的基本热传输问题：热电学、量子级联激光器、红外探测器和纳米电子学。从这项研究中获得的新发现将被整合到研究生和本科课程中。该项目将培养热科学、超快光学、材料科学和物理领域的下一代领导者。拓展活动将包括展示以K-12学生为重点的大学预科项目的研究成果，并为由研究生女性指导的本科女性提供研究机会。该项目还将通过积极从女性和少数族裔等代表性不足的群体中招收研究生，增强德克萨斯大学奥斯汀分校的多样性。

CBET-1351881PI: Yaguo Wang, University of Texas at AustinCAREER: Ultrafast Phonon Dynamics in Complex Nanostructures: Systematic Investigation with Ultrafast Phonon Spectroscopy and Femtosecond Thermal Reflectance TechniquePhonons are quantized lattice vibrations and the major heat carriers in many crystalline materials. Our scientific understanding of phonons lags behind that of electrons and photons, mainly because of the difficulties in measuring and manipulating individual phonon. In bulk materials, the phonon transport is purely diffusive and governed by Fourier's Law. In nanostructures, phonons can travel ballistically, scatter at boundaries, interfaces and nanoparticles, and can be localized by quantum confinement effects. When different nanostructures are integrated together, phonon dynamics becomes exceptionally complicated. This research will investigate individual phonon behavior in complex nanostructures with ultrafast phonon spectroscopy and femtosecond time domain thermal reflectance technique. The effect of different nanostructures on specific phonon modes will be examined in detail through a systematic introduction of boundaries, interfaces, nanoparticles, and quantum wells into the material. Phonon lifetime and group velocity will be characterized for specific phonon modes with the ultrafast phonon spectroscopy, and the effect on macroscopic thermal conductivity will be measured by time domain thermal reflectance technique. Quantitative information will be provided about the effects resulting from the degree of lattice-mismatch, superlattice period, nanoparticle size, type and concentration, and the interplay of these mechanisms. The results will be used to validate the predictions from numerical and theoretical studies and bridge the gap between macroscopic thermal property measurements and microscopic phonon properties.This research will address the fundamental heat transport problems encountered by researchers in a wide variety of disciplines: thermoelectrics, quantum cascade lasers, infrared detectors, and nanoelectronics. The new discoveries obtained from this study will be integrated into both graduate and undergraduate courses. This project will prepare next-generation leaders in thermal sciences, ultrafast optics, material science and physics. Outreach activities will include demonstrating research findings in pre-college programs focused on K-12 students, and providing research opportunities to undergraduate women mentored by graduate women. This project will also enhance diversity at University of Texas at Austin by actively recruiting graduate students from under-represented populations, such as women and minorities.