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子器件在社会上得到了广泛的应用。在半导体工业面临的挑战中，消除大密度的热量产生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方法之一，原子层状材料由于其潜在的优于硅的电学、光学和热学性能，正被积极研究作为下一代电子和光电子材料。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。热可以通过这些层状材料和其他固体中的原子振动波传递。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传热能力，目前尚不清楚。此外，半导体上的光照可以激发电子到高能状态，称为激子。这些激子的载热能力及其对原子振动波的影响目前还存在知识空白。本项目旨在解决这两个控制这些层状材料热传输特性的具体基本问题。获得的知识将用于构建新的模拟工具，增强在线课程和课堂教学，并开发实践教育模块，以帮助招聘和培训下一代热工程劳动力的多样化人口。本项目的目标是促进对四声子和激子-声子相互作用在新兴层状电子和光电子材料的热输运和能量耗散中的影响的基本理解。具体而言，将解决四个对新兴层状电子和光电子材料的操作至关重要的突出问题：(1)四声子相互作用如何影响多层石墨烯和碳纳米管（CNTs）中晶格导热系数的厚度依赖性；(2)四声子相互作用是否会减小或扩大石墨材料中流体动力声子输运的温度窗；(3)激子扩散能否为层状光电和电子材料中热点的热传递提供另一种通道；(4)激子-声子耦合对新兴TMD器件晶格热输运和局部非平衡的影响。这些问题将通过新的计算模型来解决，这些计算模型结合了前沿的激子-声子和四声子耦合的第一性原理理论，以及独特的纳米级热计量工具，包括多探针热输运和光热流测量。对四声子和激子-声子相互作用的基本理解有助于为新兴层状电子和光电子器件的能量耗散和热输运建模和控制奠定基础。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值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.