Phonon Transport Near and Across Seminductor Interfaces

该奖项支持与纳米结构材料中声子通过界面传递热能相关的理论和计算研究以及教育活动。原子建模工具包括晶格动力学计算、玻尔兹曼输运方程、分子动力学模拟和密度泛函理论计算，以及理论发展，将应用于解决有关声子传播和散射的基本问题，这些问题与体相中存在的情况非常不同。具体来说，pi的目标是：(1)推导声子界面散射率的表达式。(2)通过预测界面附近存在的非块状声子分布，解决了不同热边界阻力模型之间的差异。(3)证明密度泛函理论计算可以为基于格子动力学的热边界阻力模型提供输入。这些预测结果将用于评估电子在金属-半导体界面热传递中的作用。(4)确定布洛赫声子模式在从孤立界面到多界面再到周期超晶格的转变过程中是如何发展的，包括界面物质混合的影响。这项研究与包含多层组件的技术重要系统的丰富直接相关，例如场效应晶体管中的二氧化硅层，热电能量转换应用的硅锗和碲基超晶格，以及由GaAs， AlGaAs和GaN层构建的量子级联激光器和发光二极管。与Jon Malen教授（卡内基梅隆大学）的互动将允许将理论和计算预测与实验测量进行直接比较。该项目将促进热传递物理学新兴领域的教育：研究载流子水平的热传输，即通过声子，光子，电子和流体粒子。开设本科生选修课。NanoHUB和thermalHUB这两个在线资源将用于传播一般信息和研究成果。以发现为基础的讲座将在本科课程和匹兹堡的外展项目中开发和呈现。该奖项支持与固体-固体界面传热相关的理论和计算研究以及教育活动。当这样的界面被人类头发大小的千分之一到百万分之一的距离分开时，就像在计算机芯片和发光二极管中一样，它们可以控制热阻。高热阻使其难以去除热量，从而导致不希望的高工作温度。此外，距离较近的界面的行为不同于距离较远的界面，这是大多数先前研究的主题。PI将进行计算机模拟和理论计算，以考虑原子水平上的界面。将研究单个原子的运动，以确定能量如何流过界面。计算将以不同的精度水平进行，其中一些基于量子力学，以便与实验结果进行比较。这项工作与包含多层组件的技术上重要的系统有关，例如场效应晶体管，用于热电能量转换应用的由不同成分的周期性交替区域制成的材料，激光器和发光二极管。这个项目将促进在原子水平上研究传热的教育。开设本科生选修课。NanoHUB和thermalHUB这两个在线资源将用于传播一般信息和研究成果。以发现为基础的讲座将在本科课程和匹兹堡的外展项目中开发和呈现。

Technical SummaryThis award supports theoretical and computational research and educational activities related to the transport of thermal energy by phonons across interfaces in nanostructured materials. Atomistic modeling tools including lattice dynamics calculations, the Boltzmann transport equation, molecular dynamics simulations, and density functional theory calculations, as well as theoretical development will be applied to address fundamental questions regarding phonon propagation and scattering under conditions very different from what exists in the bulk phase. Specifically, the PIs aim to:(1) Derive an expression for the phonon-interface scattering rate.(2) Resolve the discrepancies between different thermal boundary resistance models by predicting the non-bulk-like phonon distributions that exist near an interface.(3) Demonstrate that density functional theory calculations can be used to provide the input for lattice-dynamics based thermal boundary resistance models. The predictions will then be used to assess the role of electrons in thermal transport across metal-semiconductor interfaces.(4) Identify how Bloch phonon modes develop in the transition from an isolated interface to multiple interfaces to a periodic superlattice, including the effect of interfacial species mixing.This research is immediately relevant to the wealth of technologically important systems that contain multi-layer components, such as the silica layer in a field-effect transistor, silicon-germanium and tellurium-based superlattices for thermoelectric energy conversion applications, and quantum cascade lasers and light emitting diodes built from layers of GaAs, AlGaAs, and GaN. Interactions with Professor Jon Malen (Carnegie Mellon University) will allow for direct comparison of the theoretical and computational predictions to experimental measurements.This project will promote education in the emerging field of heat transfer physics: the study of thermal transport at the carrier-level, i.e. via phonons, photons, electrons, and fluid particles. An undergraduate elective course will be developed. NanoHUB and thermalHUB, two online resources, will be used to disseminate general information and research findings. Discovery-based lectures will be developed and presented in undergraduate classes and through Pittsburgh-based outreach programs.Nontechnical SummaryThis award supports theoretical and computational research and educational activities related to heat transfer across solid-solid interfaces. When such interfaces are separated by distances of the order of one thousandth to one millionth the size of the human hair, as they are in computer chips and light-emitting diodes, they can dominate thermal resistance. High thermal resistance makes it difficult to remove heat, leading to undesirably high operating temperatures. Furthermore, closely spaced interfaces behave differently than interfaces that are far apart, the topic of most previous studies. The PI will perform computer simulations and theoretical calculations to consider interfaces at the atomic level. The motions of individual atoms will be studied so as to determine how energy flows across an interface. Calculations will be performed at different levels of accuracy, with some based on quantum mechanics, allowing for comparison to experimental results.The work is relevant to the wealth of technologically important systems that contain multi-layer components, such as field-effect transistors, materials made of periodically alternating regions of different compositions for thermoelectric energy conversion applications, lasers, and light emitting diodes. This project will promote education in the study of heat transfer at the atomic-level. An undergraduate elective course will be developed. NanoHUB and thermalHUB, two online resources, will be used to disseminate general information and research findings. Discovery-based lectures will be developed and presented in undergraduate classes and through Pittsburgh-based outreach programs.