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性能的能力相结合，使它们成为设想的灵活的纳米电子和超高频应用的理想选择。这个项目将产生2D材料中能量传输的基础知识，这对先进的纳米电子设备技术至关重要。这些超越下一代技术的技术有可能推动计算革命，可以与真空管到晶体管的转变相媲美。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无序的热响应的基本性质知之甚少，这些效应被预测为对内在物理化学性质提供了前所未有的控制。已经预测到在弹性应变存在的情况下热传输将发生巨大变化，这是一个关键的剩余科学问题，是应该利用(应变增强装置)还是应该防止(应变稳健装置)。由于还没有公认的技术来探测纳米材料中的应变效应对热传递机制的影响，解决这个问题对纳米电子技术的进步是一个有限的挑战。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，从而在纳米电子器件中实现更高的功率输出。然而，对低维材料中的这种效应的理解是有争议的，特别是考虑到最近的声子传输模型引用了相干效应。这项建议的研究目标是确定使用技术关键的2D材料的低维材料中热传输的弹性应变和质量无序的基本性质，以便使其能够在灵活的电子技术中得到广泛采用。使用技术关键的2D材料在重的、半导体的准2D层状过渡金属二卤化物(LTMD)MoS2和WS2以及轻的金属真2D石墨烯中研究低维材料中热传输的弹性应变和质量无序的性质，将有助于深入了解有争议的现象，如不同程度地增加热导率和相干声子传输。这里的一种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)来探测机械刺激存在时的散热机制。这项工作将提供关于机械刺激和同位素无序对技术关键的2D材料中的热传递的影响的概念性进展。这项工作的成果将有助于开发新的、广泛适用的应变和同位素工程战略，以改变低维系统中的热传输过程，并解决设计灵活电子技术所需的关键问题。通过这一项目，将开发一种新的基于电子显微镜的测量工具，用于量化弹性应变对低维材料导热系数的影响，并将进一步发展用于探测长波和色散声子的拉曼光谱技术。这些新技术将使人们能够确定应变和同位素无序对具有不同结构特征的2D系统中的热输运和声子色散的影响。特别有希望的是，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，通过发展纳米尺度热传输的导师/教师/学生核，将实施和评估一组独特的学生研究人员和大学前教育工作者的最先进的积极实验研究和教育经验。几名博士生和许多本科生和预科学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动手教育模块将扩大其对K-12科学课程的影响。拟议的活动将扩大机会，并增加康涅狄格州代表性不足的人口和残疾人获得实验性纳米技术研究的机会。

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.