Collaborative Research: Thermal Transport via Four-Phonon and Exciton-Phonon Interactions in Layered Electronic and Optoelectronic Materials

在过去的几十年里，半导体的研究和发展使电子和光电设备在社会上得到了广泛的使用。在半导体行业面临的挑战中，消除大密度的发热和防止硅微芯片过热变得越来越困难。作为克服这一挑战的途径之一，原子层状材料由于其潜在的优异的电学、光学和热学性能而成为下一代电子和光电子材料的研究热点。与已被广泛研究的硅的性质相比，这些新兴材料的许多性质仍有待了解。热可以通过原子振动波在这些层状材料和其他固体中传输。目前还不清楚高度非线性的原子间弹簧如何影响这些层状材料中原子振动的热传递能力。此外，半导体上的光照射可以将电子激发到高能态，这种状态被称为激子。目前，在这些激子的载热能力及其对原子振动波的影响方面存在着一个知识空白。本项目旨在解决控制这些层状材料中热传输特性的这两个特定基本原理上的悬而未决的问题。所获得的知识将用于建立新的模拟工具，加强在线课程和课堂教学，并开发实践教育模块，以帮助招募和培训不同人口的下一代热工工作人员。这个项目的目标是促进对四声子和激子-声子相互作用在新兴的层状电子和光电子材料中的热输运和能量耗散中的影响的基本理解。具体地说，对新型层状电子和光电子材料的运行至关重要的四个悬而未决的问题将被解决：(1)四声子相互作用如何影响多层石墨烯和碳纳米管(CNT)中晶格热导率的厚度相关性；(2)四声子相互作用是否减少或拓宽了石墨化材料中流体动力学声子输运的温度窗口；(3)激子扩散是否能够为层状光电材料中热点的热输运提供另一种通道；以及(4)激子-声子耦合如何影响新兴TMD器件中的晶格热输运和局域非平衡。这些问题将通过新的计算模型来解决，这些模型集成了激子-声子和四声子耦合的前沿第一原理理论，以及独特的纳米尺度热计量工具，包括多探针热传输和光热电流测量。对四声子和激子-声子相互作用的基本了解有助于为建模和控制新兴的层状电子和光电设备中的能量耗散和热传输奠定基础。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。

Semiconductor research and development over the past several decades have enabled widespread use of electronic and optoelectronic devices in society. Among the challenges that the semiconductor industry is facing, it has become increasingly difficult to remove the large density of heat generation and prevent overheating of silicon microchips. As one of the approaches to overcoming this challenge, atomic layered materials are now being actively investigated as next-generation electronic and optoelectronic materials due to their potentially superior electric, optical, and thermal properties compared to those of silicon. Compared to the silicon properties that have been extensively investigated, many properties of these emerging materials have remained to be understood. Heat can be transported by atomic vibration waves in these layered materials and other solids. It is currently unclear how the highly nonlinear interatomic springs influence the heat transfer ability of the atomic vibration in these layered materials. In addition, light illumination on semiconductors can excite electrons to high-energy states that are referred as excitons. There is currently a knowledge gap in the heat-carrying ability of these excitons and their influence on the atomic vibration waves. This project aims to address the outstanding questions on these two specific fundamentals that control the heat transport properties in these layered materials. The obtained knowledge will be used to build new simulation tools, enhance online courses and classroom instruction, and develop hands-on education modules to aid the recruitment and training of a diverse population of next-generation workforce in thermal engineering. The goal of this project is to advance the fundamental understanding of the effects of four-phonon and exciton-phonon interactions in thermal transport and energy dissipation in emerging layered electronic and optoelectronic materials. Specifically, four outstanding questions that are essential for the operation of emerging layered electronic and optoelectronic materials will be addressed: (1) How four-phonon interactions impact the thickness dependence of the lattice thermal conductivity in multi-layered graphene and carbon nanotubes (CNTs); (2) Whether four-phonon interactions reduce or broaden the temperature window of hydrodynamic phonon transport in graphitic materials; (3) Whether exciton diffusion can provide another channel for heat transport from hot spots in layered optoelectronic and electronic materials; and (4) How exciton-phonon coupling influences the lattice thermal transport and local non-equilibrium in emerging TMD devices. These questions will be addressed by new computational models that integrate frontier first-principles theory of exciton-phonon and four-phonon coupling, and unique nanoscale thermal metrology tools including the multi-probe thermal transport and photo-heat current measurements. The obtained fundamental understanding of four-phonon and exciton-phonon interactions helps to establish the foundation for modeling and controlling energy dissipation and thermal transport in emerging layered electronic and optoelectronic devices.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.