Thermionic 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.
