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

University Of Connecticut, Storrs CT

Investigators

Abstract

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.