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

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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.