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

这项合作的目标是在一个重要的新的二维（2D）晶体材料的热和热电传输的理解。这类材料具有在完全致密材料中观察到的最低热导率。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。这项工作利用了克罗宁实验室最近开发的测量技术，该技术首次精确测量了极薄薄膜的交叉平面（即垂直于层的方向）热和热电传输，以及约翰逊实验室开发的独特材料合成能力，该能力使2D层的特定序列能够制备和结构表征。这些实验室将共同解决有关这种有趣的材料系统的热和热电传输特性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和跨平面传输特性之间的差异。该提案将探索非晶态和晶态之间的一类独特材料中的热和热电现象，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，研究跨平面传输的拟议方案可以应用于广泛的其他设备系统，包括LED，FET和RTD，目前正在研究的其他团体。所提出的异质结构的几何形状开辟了新的自由度，在跨平面运输与独立控制的电子和声子，这是必不可少的实现高效的热电能量转换设备。所提出的分层异质结构将使许多参数可以变化，如材料间势垒高度，带隙（跨半导体-半金属光谱），以及在宽范围的组合物上的电荷密度波跃迁，以优化热电现象。这些结构使得研究传统方法无法实现的系统结构变化成为可能，例如，晶格不匹配的原子尖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NSF的法定使命，并通过使用基金会的智力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.