Thermo-tunneling is a term used to describe combined emission of hot electrons (thermionic emission) and tunneling of electrons through a narrow potential barrier between two surfaces (field emission). Thermo-tunneling of hot electrons across a few-nanometer gap has application to vacuum electronics and flat panel displays, and holds great potential in thermo-electric cooling and energy generation. Theoretical and experimental studies on thermo-tunneling nano-structures have shown that the heat removal efficiency of these structures could approach the theoretical limit known as Carnot efficiency. This project aims to test a new method for constructing thermo-tunneling devices by forming a very narrow (1 nanometer wide) vacuum gap across two very smooth surfaces. Unfortunately, establishment of a nanometer vacuum gap over sufficiently large areas required for practical use of thermo-tunneling devices is very challenging and so far has not been demonstrated. The goal of this proposal, therefore, is to explore and demonstrate the feasibility of creating nanometer vacuum gaps over extended areas using a dynamic equilibrium between Lorentz, Van der Waals, and electrostatic forces. The methods of modern dynamical system analysis and boundary control of distributed parameter systems will be applied to demonstrate theoretically and experimentally the feasibility of forming such gaps and to produce a new class of high-efficiency energy conversion devices.
If successful, the proposed research will result in a novel nanometer gap-forming technique that can be used in solid-state cooling devices, solid-state thermoelectric generators, and high-speed vacuum electronic devices for defense (radiation hard) applications. The energy conversion efficiency of such devices approaches the thermodynamic (Carnot) limit, therefore the project could lead to tremendous energy savings in cooling and power-generation applications by replacing mechanical compressors in cooling applications, or producing a more efficient thermo-electric generators. The research will provide invaluable training opportunities for graduate students in the Applied Mathematics Interdisciplinary Program at the University of Arizona and for graduate student exchange with the world-renowned Department of Applied Mechanics at the Budapest Technical University of Technology and Economics.
Thermo-tunneling is a term used to describe the combined emission of hot electrons (thermionic emission) and tunneling of electrons through a narrow potential barrier between two surfaces (field emission). Thermo-tunneling of hot electrons across a few-nanometer gap has application to vacuum electronics and at panel displays, and holds great potential in thermo-electric cooling and energy generation. The objective of this project is to examine the operation of thermo-tunneling systems with flexible electrodes. More specifically, the project examined whether finite area of thermo-tunneling can exist stably under the combined action of elastic, electrostatic, and electromagnetic forces. The stable operation of such systems finds application in energy conversion systems where heat or charges are transferred preferentially across the vacuum gap resulting in power generation or solid-state cooling devices with potentially much higher efficiency. Intellectual Merit: To date, work on flexible electrodes has been limited to examining their behavior under electrostatic and elastic loads. In this project, for the first time, the presence of thermo-tunneling current and associated electromagnetic and thermal forces has been accounted for. The project resulted in a non-linear mathematical model described by a set of partial differential equations. Approximate solutions of the model have shown that the active tunneling area in such systems is approximately 1% of the total electrode area. It was further established that thermo-elastic effects play dominant role in the system. The project established performance specifications criteria for the thermal and electronic properties of such electrodes that lead to stable operation. The most stringent of these, for reasonable operation conditions, is that a stable operation requires extremely low work function of the electrode material and that the near-field radiation level should not exceed the far-field (black body) radiation by more than four orders of magnitude. Broader Impact: Thermo-tunneling is considered as a promising approach to achieving a high-efficiency energy conversion device. Many government and private-sector labs are developing experimental prototypes attempting to demonstrate efficient energy conversion. The work developed under this project is likely to provide guidance in designing new electrode materials and geometries in the quest for reducing energy consumption and minimizing its impact on the environment.