CAREER: Phononic Properties of Colloidal Nanocrystal Superlattices

电、光、声、热是日常生活中常见的现象。能够对电和光的传输进行高级控制的材料分别被称为电子材料和光子材料。这些材料使许多现代技术成为可能，如笔记本电脑，手机，光纤，激光和显微镜。相比之下，对声和热的技术控制远远落后于光和电。该项目的重点是创建声子材料，可以实现对声音和热量传输的高级控制。这些声子材料将由有组织的纳米粒子-分子组装体组成，这些组装体具有天然材料中不存在的振动特性。然后，这些组件将用于制造过滤器、镜子和单向阀，以操纵声音和热量的传输。该项目还与各种教育活动相结合。它将吸引K-12学生，并通过LeRoy Eyring固态科学中心的Science is Fun计划帮助培训未来的STEM教育工作者。此外，还将为本科生开发一个关于声子晶体的实验模块。研究结果将纳入研究生课程的纳米级传热。声子晶体是具有声阻抗周期性变化的人工结构材料（即，交替的硬和软材料）。这种周期性导致声子带隙，使得能够产生许多声子器件，例如声子滤波器、波导、二极管和反射镜。该项目的目标是：（1）展示声子超晶格在声子应用方面的潜力，（2）实现三维声子晶体在100 GHz范围内的声子带隙，（3）控制声子超晶格中热传输声子的传输和反射，以及（4）创建高频声子器件，如声子滤波器，反射镜和二极管。声子带隙中心和声子带隙宽度将通过尺寸和组成以及配体组成来调节。DNA还将用于指导DNA组装，并使不同的结构可能性成为可能。为了确保超晶格的机械、化学和热稳定性，DNA接头将通过溶胶-凝胶化学转化为无机基质。声子传输和反射将使用声子光谱学进行实验研究，该光谱学使用单色声子发生器和检测器来直接测量频率分辨的声子传输。这些实验将补充计算模型，计算声子带图和模拟声子输运分别使用平面波展开法和时域有限差分法。这种超晶格也将通过电子束光刻制造的模板与衬底集成，从而为未来的芯片集成应用打开大门。

Non-Technical AbstractElectricity, light, sound, and heat are common phenomenon encountered in everyday life. Materials that enable advanced control over the transmission of electricity and light are known as electronic and photonic materials, respectively. These materials have made possible numerous modern technologies such as laptops, cellular phones, fiber optics, lasers, and microscopes. In contrast, technological control over sound and heat has lagged far behind that of light and electricity. This project focuses on the creation of phononic materials that could enable advanced control over the transmission of sound and heat. These phononic materials will consist of organized nanoparticle-molecule assemblies that possess vibrational characteristics that do not arise in naturally occurring materials. These assemblies will then be used to create filters, mirrors, and one-way valves that manipulate the transmission of sound and heat. This project is also integrated with a variety of educational activities. It will engage K-12 students and help train future STEM educators through the Science is Fun program at the LeRoy Eyring Center for Solid State Science. In addition, a laboratory module on phononic crystals will be developed for undergraduate students. Research results will be incorporated into a graduate student course on nanoscale heat transfer. Technical AbstractPhononic crystals are artificially structured materials with periodic variations in acoustic impedance (i.e., alternating hard and soft materials). This periodicity results in a phononic band gap that enables the creation of many phononic devices such as phonon filters, waveguides, diodes, and mirrors. The objectives of this project are to: (1) Demonstrate the potential of nanocrystal superlattices for phononic applications, (2) Achieve phononic band gaps in the 100 GHz regime for 3-dimensional phononic crystals, (3) Control transmission and reflection of heat transporting phonons in nanocrystal superlattices, and (4) Create high frequency phononic devices such as phonon filters, mirrors, and diodes. The phononic band gap center and phononic band gap width will be tuned via nanocrystal size and composition as well as ligand composition. DNA will also be used to direct nanocrystal assembly and enable diverse structural possibilities. To ensure mechanical, chemical, and thermal stability of the superlattices, the DNA linkers will be converted into an inorganic matrix via sol-gel chemistries. Phonon transmission and reflection will be experimentally studied using phonon spectroscopy, which uses monochromatic phonon generators and detectors to directly measure frequency-resolved phonon transport. These experiments will be complemented with computational modeling that calculates the phononic band diagram and simulates phonon transport using plane wave expansion methods and finite-difference time-domain methods, respectively. The nanocrystal superlattices will also be integrated with substrates by growing them from templates fabricated via electron beam lithography; thereby opening the door for future chip-integrated applications.