Thermionic and Photo-Excited Electron Emission for Energy-Conversion Processes

Abstract

This article describes advances in thermionic and photo-emission materials and applications dating back to the work on thermionic emission by Guthrie (1873) and the photoelectric effect by Hertz (1893). Thermionic emission has been employed for electron beam generation from Edison's work with the light bulb to modern day technologies such as scanning and transmission electron microscopy. The photoelectric effect has been utilized in common devices such as cameras and photocopiers while photovoltaic cells continue to be widely successful and further researched. Limitations in device efficiency and materials have thus far restricted large-scale energy generation sources based on thermionic and photoemission. However, recent advances in the fabrication of nanoscale emitters suggest promising routes for improving both thermionic and photo-enhanced electron emission along with newly developed research concepts, e.g., photonically enhanced thermionic emission. However, the abundance of new emitter materials and reduced dimensions of some nanoscale emitters increases the complexity of electron-emission theory and engender new questions related to the dimensionality of the emitter. This work presents derivations of basic two and three-dimensional thermionic and photo-emission theory along with comparisons to experimentally acquired data. The resulting theory can be applied to many different material types regardless of composition, bulk, and surface structure.

Work Function Characterization of Potassium-Intercalated, Boron Nitride Doped Graphitic Petals

“…An alternative model was developed by Westover and McCarthy (Westover et al, 2010;McCarthy et al, 2014) as an extension of the theory developed by Fowler and DuBridge (Fowler and Nordheim, 1928;DuBridge, 1933) and offers a generalized approach for predicting photoemission with regard to specific material properties. As with the thermionic theory embodied in Eq.…”

“…Equation 2 is termed the normal energy model. Westover and McCarthy further improved this model by weighting the number of electrons available for emission based on the angle of electron emission, for which the derivation is provided elsewhere (Westover et al, 2010;McCarthy et al, 2014). The angle of photonic illumination is referenced to the surface normal.…”

Solar energy conversion with photon-enhanced thermionic emission

“…in [22], including the nonlinear dependence on carrier concentration and on temperature. The boundary conditions are analogous to equation (8), duplicated for both holes and electrons [18], and applied to the component of charge carrier transport in the direction of the surface normaln :ˆ ⋅ n J n andˆ ⋅ n J p for electrons and holes, respectively. For the potential, it is convenient to apply a zero value at the cathode contact, and a Neumann type boundary condition on the electric field at the electron emission surface, which depends on the applied device voltage [18].…”

Thermionic Energy Conversion in the Twenty-first Century: Advances and Opportunities for Space and Terrestrial Applications

“…The purpose of this article is not only to discuss recent advances but also to offer some perspectives on the field in terms of possibilities as well as challenges, from the collective wisdom of the workshop participants. We do note that it is not the intent of the article to provide a detailed review of recent research, and for that we point the reader to other recent review articles (Khoshaman et al, 2014;McCarthy et al, 2014;Khalid et al, 2016;Trucchi and Melosh, 2017).This perspective article is organized into several sections as follows. "Background and Fundamentals" gives background on thermionic emission and TEC, including establishing the fundamentals of TEC and the terminology that will be used throughout this article as well as opportunities for TEC implementation.…”

“…The purpose of this article is not only to discuss recent advances but also to offer some perspectives on the field in terms of possibilities as well as challenges, from the collective wisdom of the workshop participants. We do note that it is not the intent of the article to provide a detailed review of recent research, and for that we point the reader to other recent review articles (Khoshaman et al, 2014;McCarthy et al, 2014;Khalid et al, 2016;Trucchi and Melosh, 2017).…”