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。这些属性与在原子尺度上调整这些材料的特性的能力相结合，使它们成为设想的灵活纳米电子和超高频应用的理想选择。该项目将产生对先进纳米电子器件技术至关重要的2D材料中能量传输的基础知识。这些超越下一代的技术有可能促进计算领域的革命，就像从真空管到晶体管的过渡一样。该项目的成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无序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。在弹性应变的存在下，已经预测了热传输的巨大变化，并且是否应该利用（应变增强设备）或防止（应变鲁棒设备）是一个关键的剩余科学问题。由于没有公认的技术存在，在其中探测应变对纳米材料中的传热机制的影响，解决这个问题是一个限制挑战的纳米电子技术的进步。此外，同位素质量无序开始被理解为一种工具，可以用来有益地改变热传输机制，从而使纳米电子器件的功率输出更高。然而，在低维材料的效果的理解是有争议的，特别是在最近的声子输运模型调用相干效应。该提案的研究目标是使用技术关键的2D材料来确定低维材料中弹性应变和质量无序对热传输的基本性质，以便使其能够在柔性电子技术中广泛采用。研究弹性应变和质量无序对低维材料热输运的性质，使用重的半导体准二维层状过渡金属二硫属化物（LTMD）MoS 2和WS 2中的技术关键二维材料，以及轻的金属真正的二维石墨烯，将深入了解有争议的现象，如发散增加的热导率和相干声子输运。这里的一个创新方法是开发一种计量技术，使用微型测温装置和原位透射电子显微镜（TEM）探测存在机械刺激的散热机制。这项工作将提供一个概念性的知识进步，机械刺激和同位素无序的影响，在技术关键的二维材料的热传递。这项工作的成果将使新的和广泛适用的应变和同位素工程策略的发展，以改变低维系统中的热传输过程，除了解决柔性电子技术的设计所需的关键问题。通过该项目，将开发一种新的基于TEM的计量工具，以量化弹性应变对低维材料热导率的影响，并将进一步开发探测长波长和色散声子的拉曼光谱技术。这些新技术将允许应变和同位素无序的热输运和声子色散的影响，在2D系统具有不同的结构特征被确定。特别有前途的是，这项研究的方法和结果将普遍适用于广泛的低维材料。此外，通过在纳米热传输，国家的最先进的积极的实验研究和教育经验的学生研究人员和大学预科教育工作者的独特群体的导师/教师/学生核心的发展将实施和评估。多位博士学生和许多本科生和大学预科生将通过这个项目得到指导。通过将该项目与NSF RET计划相结合而创建的实践教育模块将其影响扩展到K-12科学课程。拟议的活动将扩大机会，增加康涅狄格州代表性不足的人口和残疾人对实验性纳米技术研究的可及性。

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.