CAREER: Engineering Heat Conduction Through Alloys and Interfaces

该项目的研究目标是使用原子级建模技术来理解通过合金和界面的热传导，然后使用所获得的见解来指导具有前所未有特性的材料/系统的设计或识别。教育目标是提高围绕原子级振动/传热的科学素养，因为传热在我们的能源基础设施中起着重要作用。教育方法是创建一个新的计划，针对代表性不足的少数民族高中生，通过MD模拟数据的超声处理（例如，将原子振动转化为可听的声音），然后将其用于制作音乐。该推广计划将通过格鲁吉亚技术教育中心管理的两个推广计划，每年夏天招募非洲裔美国人和女性本科生、高中音乐教师和高中生。参与者将通过合作创建一个移动的应用程序，建立对原子运动和编码的理解。学生和公众用户将使用该移动的应用程序，将元素周期表上每个元素的声波产生的声音制作成音乐，这将为学生学习化学提供一种新的方式。该计划将促进PI和参与者之间的长期指导关系，这将加强和多样化代表性不足的少数STEM管道。通过非导电介质的热传导主要是由原子之间的能量转移，由于它们的运动。在固体中，这些运动是振动，称为声子，几乎所有关于声子热传导的知识都是通过所谓的声子气体模型（PGM）来理解的。PGM在许多情况下都能很好地工作，但是这个想法本身在无序材料中就失效了，在无序材料中人们不能严格定义声子速度。最近，PI开发了一种新的分子动力学（MD）为基础的形式主义，提出了一种替代图片的PGM，其中运输描述的正常模式相关，而不是声子准粒子散射。最重要的是，新的形式主义提供了一个更普遍的观点声子输运，使人们能够处理任何类别的材料，并利用新的功能是不可想象的从PGM的角度来看，利用这一新的视角，该提案侧重于（1）研究半导体和绝缘体合金，以了解通过非传播振动模式的热传导。这样做的目的是确定是否有可能识别或设计一种合金，其热导率高于其组成纯晶体化合物之一。这样的材料将是前所未有的，因为目前的理论表明这是不可能的，但实验数据和预测的基础上PI？的新形式主义表明，否则。(2)该提案还侧重于研究半导体和绝缘体界面，以了解不同类型的振动模式的作用，并找到可用于识别/设计高导电界面的最有用的描述符。这样做的目的是确定界面是否可能具有高于PGM极限的电导，其中简单地假设所有振动模式传输100%的能量。超过PGM极限将是前所未有的，因为目前的理论认为这是不可能的，但新的实验数据和PI新形式主义的预测表明这是不可能的。如果能够实现超过PGM极限的界面热导率和热导率高于其纯化合物的合金，则可能对涉及散热的能源应用产生重大影响，例如多结太阳能电池，LED和电力电子。

The research objective in this project is to use atomistic level modeling techniques to understand heat conduction through alloys and interfaces and then use the insights gained, to guide the design or identification of materials/systems with unprecedented properties. The educational objective is to increase scientific literacy around atomic level vibrations/heat transfer, since heat transfer plays a fundamental role in our energy infrastructure. The educational approach is to create a new program targeted at underrepresented minority high school students that stimulates a fascination with atomic level vibrations/heat transfer via sonification of MD simulation data (e.g., the conversion of atomic vibrations into audible sounds), which will then be used to make music. The outreach program will recruit African-American and women undergraduates, high school music teachers and high school students each summer, via two outreach programs administered by the Georgia Tech center for education. The participants will build an understanding of both atomic motions and coding as they work together to create a mobile app. The students and general public users will use the mobile app to make music from the sounds generated by sonification of each element on the periodic table, which will provide a new way for students to learn chemistry. The program will facilitate long term mentoring relationships between the PI and participants, which will both strengthen and diversify the underrepresented minority STEM pipeline.Heat conduction through non-electrically conductive media is dominated by the energy transferred between atoms due to their motions. In solids, these motions are vibrations, referred to as phonons, and virtually all knowledge of phonon heat conduction is understood through what is termed the phonon gas model (PGM). The PGM works well in many situations, but the idea itself breaks down in disordered materials, where one cannot rigorously define phonon velocities. Recently, the PI developed a new molecular dynamics (MD) based formalism that presents an alternative picture to the PGM, where transport is described by normal mode correlation, instead of phonon quasi-particle scattering. Most importantly, the new formalism provides a more general view of phonon transport that allows one to treat any class of materials and exploit new features that are inconceivable from the PGM perspective.Leveraging this new perspective, the proposal focuses on (1) studying semiconductor and insulator alloys to understand heat conduction through non-propagating vibrational modes. The purpose of this is to determine if it is possible to identify or engineer an alloy that has higher thermal conductivity than one of its constituent pure crystalline compounds. Such a material would be unprecedented, because the current theory suggests this is impossible, yet experimental data and predictions based on the PI?s new formalism suggest otherwise. (2) The proposal also focuses on studying semiconductor and insulator interfaces to understand the roles of different types of vibrational modes and find the most useful descriptor that can be used to identify/engineer highly conductive interfaces. The purpose of this is to determine if it is possible for an interface to have a conductance higher than the PGM limit, where one simply assumes all vibrational modes transmit 100% of their energy. Exceeding the PGM limit would be unprecedented, because the current theory says it is impossible, yet new experimental data and predictions by the PIs new formalism suggest it is. If thermal interface conductances beyond the PGM limit and alloys with thermal conductivities higher than their pure compounds can be achieved, it could have a major impact on energy applications involving heat dissipation, such as multi-junction solar cells, LEDs and power electronics.