Collaborative Research: Thermionic Transport across Single and Multiple Barrier Heterostructures Based on 2D Layered Materials

热离子输运尤其令人兴奋，因为它有潜力为废热回收（例如，在汽车中）和发电厂的热电联产提供高效的能量转换设备。此外，高效热电学可以提供有效的固态冷却，与传统的蒸汽压缩制冷系统相媲美。这些器件可用于为电子电路提供主动冷却，最终提高计算、传感和成像的性能。除了热电能量转换，热离子输运的拟议研究将影响范围广泛的其他器件系统，包括发光二极管（led），场效应晶体管（fet）和谐振隧道二极管（rtd），目前正在由其他研究小组进行研究。如果可以适当地设计热离子势垒，固态热离子能量转换可以比基于体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研究相对较少，主要是因为难以制造具有适当能量势垒的界面，表征这些界面上的热输运，以及将体热电性质与界面性质分开。二维层状异质结构使我们能够克服这些困难，并有可能在高效率热电发电机和冷却器的设计中创造一种范式转变。提出的研究旨在克服以前使用具有热离子势垒高度门调谐的层状异质结构进行热离子能量转换所面临的挑战。除了优化和测量这些新型器件的热电性能系数（ZT）外，本项目还将：1.)评估高各向异性结构和弱界面范德华键是否会导致低的平面热传导，2.)建立电子在范德华键界面上传输的条件，发生很少的散射，3.)评估各种发射极和势垒材料（例如，BN, MoS2, Bi2Te3）的性能，4.)确定热电子引起热非平衡声子居群的程度。5.)分离体效应和界面效应，6.)利用第一性原理方法建立电子和声子在这些新设备上传输的严格模型，以解决上述问题。

CBET-1402906/1403089Cronin/EsfarjaniThermionic transport is especially exciting for its potential to provide high-efficiency energy conversion devices for waste-heat recovery (e.g., in automobiles) and co-generation of electricity in power plants. In addition, highly efficient thermionics can provide efficient solid state cooling that rivals conventional vapor-compression refrigeration systems. These devices could be used to provide active cooling of electronic circuits, ultimately leading to increased performance of computing, sensing, and imaging. In addition to thermoelectric energy conversion, the proposed study of thermionic transport will impact a wide range of other device systems, including light emitting diodes (LEDs), field effect transistors (FETs), and resonant tunnel diodes (RTDs), currently being investigated by other research groups.Solid state thermionic energy conversion can 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 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. 2D Layered heterostructures enable us to overcome these difficulties, and can potentially create a paradigm shift in the design of thermoelectric power generators and coolers with high efficiency. The proposed study is designed to overcome the challenges previously facing thermionic energy conversion using layered heterostructures with gate-tuning of the thermionic barrier height. In addition to optimizing and measuring the thermoelectric figure of merit (ZT) of these novel devices, this project will: 1.) assess whether the highly anisotropic structure and the weak interface van der Waals bonding give rise to low cross-plane thermal conductance, 2.) establish the conditions under which electron transport across van der Waals bonded interfaces occurs with little scattering, 3.) evaluate the performance of various emitter and barrier materials (e.g., BN, MoS2, Bi2Te3), 4.) ascertain the extent to which hot electrons give rise to thermal non-equilibrium phonon-populations, and 5.) separate bulk and interfacial effects, and 6.) develop a rigorous model of the electron and phonon transport across these novel devices using a first-principles approach in order to address the above questions.