CAREER: Understanding the Roles of Strain and Mass Disorder on Fundamental Thermal Transport Processes in Two-Dimensional Materials

基于二维（2D）材料的技术提供了目前使用传统材料无法实现的尺寸、重量、功率和成本优势。这些特性与在原子尺度上调整这些材料特性的能力相结合，使它们成为设想的柔性纳米电子和超高频应用的理想选择。该项目将产生二维材料能量传输的基础知识，这对先进的纳米电子器件技术至关重要。这些超越下一代的技术有可能促成一场计算机革命，堪比从真空管到晶体管的转变。该项目的结果可能会对热工程界产生催化作用，因为人们对材料对弹性刺激和质量紊乱的热响应的基本性质知之甚少，这些影响被预测为对内在物理化学性质提供前所未有的控制。在弹性应变存在的情况下，热传递已经预测了巨大的变化，这是应该利用（应变增强装置）还是防止（应变增强装置）是一个关键的科学问题。由于目前还没有一种公认的技术来探测纳米材料中应变对传热机制的影响，因此解决这一问题是纳米电子技术进步的一个限制挑战。此外，同位素质量紊乱开始被理解为一种工具，可用于有益地改变热传输机制，从而实现纳米电子器件的更高功率输出。然而，对低维材料中的效应的理解是有争议的，特别是考虑到最近的声子输运模型调用相干效应。本提案的研究目的是利用技术关键的二维材料确定低维材料中热输运的弹性应变和质量无序的基本性质，以使其在柔性电子技术中得到广泛采用。研究弹性应变和质量无序对低维材料热输运的影响，使用技术关键的二维材料，如重的、半导体的准二维层状过渡金属二硫化物（ltmd）、MoS2和WS2，以及轻的、金属的真正二维石墨烯，将有助于深入了解热导率发散增加和相干声子输运等有争议的现象。一种创新的方法是开发一种测量技术，使用微测温装置和原位透射电子显微镜（TEM）来探测机械刺激下的散热机制。这项工作将为机械刺激和同位素紊乱对技术关键二维材料传热的影响提供概念性的知识进展。除了解决柔性电子技术设计所需的关键问题外，这项工作的结果将使新的和广泛适用的应变和同位素工程策略的发展成为可能，以改变低维系统中的热传输过程。通过该项目，将开发一种新的基于tem的测量工具，用于量化低维材料的弹性应变对导热性的影响，并将进一步开发用于探测长波和色散声子的拉曼光谱技术。这些新技术将允许在具有不同结构特征的二维系统中识别应变和同位素无序对热输运和声子色散的影响。特别有希望的是，本研究的方法和结果将普遍适用于广泛的低维材料。此外，通过发展纳米尺度热输运的导师/教师/学生核心，将实施和评估一组独特的学生研究人员和大学预科教育工作者的最先进的活跃实验研究和教育经验。本项目将指导数名博士生和众多本科生及预科生。通过将该项目与NSF RET项目相结合而创建的动手教育模块将扩展到K-12科学课程中。拟议的活动将扩大机会并增加实验性纳米技术研究对康涅狄格州代表性不足的人口和残疾人的可及性。

Technologies based on two-dimensional (2D) materials offer size, weight, power, and cost advantages not currently achievable using traditional materials. These attributes combined with the ability to tune the properties of these materials at the atomic scale makes them ideal for envisioned flexible nanoelectronic and ultra-high frequency applications. This project will generate fundamental knowledge of energy transport in 2D materials critical for advanced nanoelectronic device technologies. These beyond next-generation technologies have the potential to foster a revolution in computing comparable to the transition from the vacuum tube to the transistor. The outcomes of this project are likely to have a catalytic effect on the thermal engineering community as very little is known regarding the fundamental nature of a material's thermal response to elastic stimulus and mass disorder, effects which have been predicted to offer unprecedented control over intrinsic physico-chemical properties. Large changes have been predicted for thermal transport in the presence of elastic strain, and whether this should be exploited (strain enhanced devices) or prevented (strain robust devices) is a key remaining scientific question. Since no accepted technique exists in which to probe strain-effects on heat transfer mechanisms in nanomaterials, resolving this issue is a limiting challenge for the progress of nanoelectronic technologies. Furthermore, isotopic mass disorder is beginning to be understood as a tool that can be used to beneficially alter thermal transport mechanisms, thereby enabling higher power output in nanoelectronic devices. Yet understanding of the effect in low-dimensional materials is controversial, especially in light of recent phonon transport models invoking coherency effects. The research objective of this proposal is to determine the fundamental nature of elastic strain and mass disorder on thermal transport in low-dimensional materials using technologically-critical 2D materials in order to enable their widespread adoption in flexible electronic technologies. Investigating the nature of elastic strain and mass disorder on thermal transport in low-dimensional materials using technologically-critical 2D materials in heavy, semiconducting quasi-2D layered transition metal dichalcogenides (LTMDs) MoS2 and WS2, as well as in light, metallic truly-2D graphene, will yield insight into controversial phenomena such as divergently increasing thermal conductivity and coherent phonon transport. An innovative approach here is to develop a metrology technique using a micro-thermometry device and in situ transmission electron microscopy (TEM) to probe heat dissipation mechanisms in the presence of mechanical stimulus. This work will provide a conceptual advance in knowledge concerning the effect of mechanical stimulus and isotopic disorder on heat transfer in technologically-critical 2D materials. The outcome of this work will enable the development of new and widely applicable strain and isotopic engineering strategies to alter thermal transport processes in low-dimensional systems, in addition to solving critical questions needed for the design of flexible electronic technologies. Through this project, a new TEM-based metrology tool to quantify the elastic strain effect on the thermal conductivity of low-dimensional materials will be developed, and a Raman spectroscopic technique to probe both long-wavelength and dispersive phonons will be further developed. These new techniques will allow the effects of strain and isotopic disorder on thermal transport and phonon dispersions in 2D systems with different structural characteristics to be identified. Especially promising, the methods and outcome of this study will be generally applicable to a wide class of low-dimensional materials.Furthermore, through the development of a mentor/teacher/student nucleus in nanoscale thermal transport, state-of-the-art active experimental research and educational experiences for a unique group of student researchers and pre-college educators will be implemented and evaluated. Several Ph.D. students and numerous undergraduate and pre-college students will be mentored through this project. Hands-on educational modules created through integration of this project with the NSF RET program will extend its impact into K-12 science curriculum. The proposed activities will broaden opportunities and increase accessibility of experimental nanotechnology research to underrepresented populations and the disabled in Connecticut.