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

如果热离子势垒能够被适当地设计，固态热离子能量转换被预测比基于体Peltier和Seebeck效应的传统热电能量转换更有效。然而，关于固态热离子能量转换的实验研究相对较少，这主要是因为很难制备具有合适能量势垒的界面，表征这些界面上的热传输，以及将体相热电性质与界面性质分开。所提出的2D层状异质结构能够克服这些困难，并可能在高效的热电发电机和冷却器的设计中创造一种范式转变。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外展研讨会。该研究的目标是发展对使用2D层状材料的多势垒异质结构中热离子传输和能量转换的基本理解。由于热离子势垒必须很薄，每个势垒上只能有很小的温差。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，异质结是通过物理气相沉积(PVD)来合成的，这种方法可以很容易地产生数百个周期的异质结。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与发射兼容的，能够使用PI实验室开发的一种新方法可靠地测量跨平面传输现象(电、热和热电)。这种新的跨平面测量方法与可配置的纳米结构(即层厚度和总厚度)相结合，将使体相和界面(即热电子发射)对热电压的贡献得以分离。电子和声子在这些新型器件中传输的唯象模型将使用热电子发射传输方法来开发。建议的异质结构几何结构在跨平面传输中开辟了新的自由度，可以独立控制电子和声子，这对于实现高效的能量转换设备至关重要。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

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.