Collaborative Research: Understanding Cross-plane and In-plane Transport in 2D Layered Heterostructures

这项合作努力的目标是在一种重要的新型二维（2D）晶体材料中发展对热电输运的理解。这类材料具有在全致密材料中观察到的最低导热率。高效热电可以提供与传统制冷系统相媲美的高效固态冷却。这项工作利用了Cronin实验室最近开发的测量技术，该技术首次能够准确测量极薄薄膜的跨平面（即垂直于层的方向）热电输移，以及Johnson实验室开发的独特材料合成能力，该技术能够制备特定的2D层序列并进行结构表征。这些实验室将共同解决有关这种有趣材料系统的热电输运性质的几个悬而未决的问题，例如层的排列和界面的密度如何影响平面内和跨平面输运性质的差异。本提案将探索在非晶态和晶态之间的一类独特材料中的热电现象，并使用新的测量技术测试潜在的器件结构。除了热电能量转换之外，所提出的研究跨平面传输的方案可以应用于广泛的其他器件系统，包括led，场效应管和rtd，目前正在由其他小组研究。所提出的异质结构几何形状在电子和声子独立控制的跨平面传输中开辟了新的自由度，这对于实现高效的热电能量转换装置至关重要。所提出的层状异质结构将使许多参数可以改变，例如材料间势垒高度，带隙（横跨半导体-半金属光谱）和电荷密度波跃迁在广泛的成分范围内，以优化热电现象。这些结构可以研究传统方法无法实现的系统结构变化，例如，不匹配晶格的原子锐界面和具有原子突变界面的金属/半导体超晶格。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。

The goal of this collaborative effort is to develop an understanding of thermal and thermoelectric transport in an important new class of two-dimensional (2D) crystalline materials. This class of materials has the lowest thermal conductivities ever observed in a fully dense material. Highly efficient thermoelectrics can provide efficient solid-state cooling that rivals conventional refrigeration systems. This effort leverages measurement techniques recently developed in the Cronin lab, which enable the cross-plane (i.e. in the direction perpendicular to the layers) thermal and thermoelectric transport of extremely thin films to be measured accurately for the first time, and the unique materials synthesis capabilities developed in the Johnson lab, which enable specific sequences of 2D layers to be prepared and structurally characterized. Together, the labs will address several open questions regarding the thermal and thermoelectric transport properties of this interesting materials system, such as how the arrangement of layers and density of interfaces impact the difference between in plane and cross plane transport properties. This proposal will explore thermal and thermoelectric phenomena in a unique class of materials poised between the amorphous and crystalline states and test potential device structures using novel measurement techniques. In addition to thermoelectric energy conversion, the proposed scheme of studying cross-plane transport can be applied to a wide range of other device systems, including LEDs, FETs, and RTDs, currently being investigated by other groups. The proposed heterostructure geometries open up new degrees of freedom in the cross-plane transport with independent control of electrons and phonons, which is essential for achieving efficient thermoelectric energy conversion devices. The proposed layered heterostructures will enable many parameters to be varied such as inter-material barrier height, band gap (across the semiconductor-semimetal spectrum), and charge density wave transitions over a wide range of compositions to optimize thermoelectric phenomena. These structures enable investigation of systematic structural changes that are not possible with traditional approaches, for example, atomically-sharp interfaces that are not lattice matched and metal/semiconductor superlattices with atomically abrupt interfaces.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.