Collaborative Research: Exploring thermionic multiple barrier heterostructures and thermoelectric energy conversion using 2D layered heterostructures

如果可以适当地设计固体电子势垒，则已经预测固态电子能量转换比基于体珀耳帖和塞贝克效应的常规热电能量转换更有效。然而，有相对较少的实验研究，固态电子能量转换，主要是因为难以制造接口与适当的能量障碍，表征热传输通过这些接口，并分离的体积热电性能的界面性能。所提出的2D层状异质结构使这些困难得以克服，并且可以潜在地在具有高效率的热电发电机和冷却器的设计中创造范式转变。该项目还将包括重要的教育活动，包括本科生研究计划和高中科学教师的推广研讨会。该研究的目标是发展对使用2D分层材料的多势垒异质结构中的电子输运和能量转换的基本理解。由于电子势垒必须很薄，每个势垒之间只能有很小的温差，因此，宏观冷却和发电需要使用多级装置。在所提出的工作中，异质结构合成的物理气相沉积（PVD），它可以用来产生异质结构与数百个周期相当容易。这些结构几乎不可能通过机械剥离来制造。与分子束外延（MBE）不同，这里提出的材料合成方法是剥离兼容的，能够使用PI实验室开发的新方法可靠地测量跨平面传输现象（电学，热学和热电）。这种新的交叉平面测量方法与可配置的纳米架构（即，层厚度和总厚度）将使得本体和界面（即，电子发射）对待分离的热电压的贡献。一个现象学模型的电子和声子的运输在这些新的设备将开发使用电子发射运输的方法。提出的异质结构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能量转换器件。这个奖项反映了NSF的法定使命，并已被认为是值得支持的评估使用基金会的智力价值和更广泛的影响审查标准。

Solid-state thermionic energy conversion has been predicted to be more efficient than conventional thermoelectric energy conversion based on bulk Peltier and Seebeck effects, if the thermionic barriers can be properly engineered. However, there have been relatively few experimental studies on solid-state thermionic energy conversion, mainly because of the difficulty of fabricating interfaces with the appropriate energy barriers, characterizing thermal transport across these interfaces, and separating the bulk thermoelectric properties from the interfacial properties. The proposed 2D Layered heterostructures enable these difficulties to be overcome and can potentially create a paradigm shift in the design of thermoelectric power generators and coolers with high efficiency. The project will also encompass significant educational activities, including an undergraduate research program and an outreach workshop for high school science teachers.The goal of the study is to develop a fundamental understanding of thermionic transport and energy conversion in multiple-barrier heterostructures using 2D-layered materials. Since the thermionic barriers must be thin, each barrier can have only a small temperature difference across it. Hence, macroscopic cooling and power generation needs to be obtained using multistage devices. In the proposed work, heterostructures are synthesized by physical vapor deposition (PVD), which can be used to produce heterostructures with hundreds of periods quite easily. These structures would be nearly impossible to fabricate by mechanical exfoliation. Unlike molecular beam epitaxy (MBE), the material synthesis approach proposed here is liftoff-compatible, enabling reliable measurements of cross-plane transport phenomena (electrical, thermal, and thermoelectric) using a new approach developed in the PIs’ labs. This new cross-plane measurement approach together with the configurable nanoarchitecture (i.e., layer thicknesses and total thickness) will enable the bulk and interfacial (i.e., thermionic emission) contributions to the thermovoltage to be separated. A phenomenological model of the electron and phonon transport across these novel devices will be developed using a thermionic emission transport approach. 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 energy conversion devices.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.