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arXiv:2603.16033

Summary overview of present state of basic electrostatic field electron emission theory

Richard G. Forbes

cond-mat.mes-hallcond-mat.mtrl-sciquant-phSubmitted Mar 17, 2026• Announced Mar 18, 2026
arXivHTMLPDF

Abstract

This technical note provides a high-level overview of the present state of basic field electron emission (FE) theory, as suitable for use in the context of technological applications of FE theory. At present there is much theoretical confusion in FE literature, and a partial breakdown of the peer review system. Even in sensitive technological contexts, many papers have stated and used out-of-date theory that makes current-density predictions that are several hundred times less than those of modern FE theory. A primary aim of this note is to help reduce the confusion and error in future published FE literature. It is not intended as a detailed review of FE theory.

Comments
13 pages, 1 two-component figure

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This technical note provides a high-level overview of the present state of basic field electron emission (FE) theory, as suitable for use in the context of technological applications of FE theory. At present there is much theoretical confusion in FE literature, and a partial breakdown of the peer review system. Even in sensitive technological contexts, many papers have stated and used out-of-date theory that makes current-density predictions that are several hundred times less than those of modern FE theory. A primary aim of this note is to help reduce the confusion and error in future published FE literature. It is not intended as a detailed review of FE theory.
Field electron emission (FE) and electrostatic field ionization (ESFI) are quantum-mechanical tunnelling processes that provide basic theory for important technologies. However, the basic theories of FE and ESF1 are not yet completely understood. This paper attempts to identify related fundamental quantum mechanical issues, problems and relevances. The following topics have been identified as deserving closer investigation or discussion. (a) The implication that if a "real electron" cannot have negative kinetic energy, then this necessarily implies that a "real electron" is a distributed object rather than a point object. (b) The implication that the language we use to discuss quantum mechanics needs to be changed in order to avoid referring to the "position of a (point) electron". (c) The idea that "quantum mathematics" (i.e., the mathematics of quantum mechanics) has different utilisations, namely the "matter distribution" and "pathway choice" utilisations, with "measurement" being observed pathway choice. (d) Difficulties with the present formulations of the uncertainty principle and wave-particle duality. (e) Fundamental difficulties in the exact calculation of exchange-and-correlation effects in both FE and ESFI theory. (f) Conceptual problems associated with "seeing electrons" in the field electron (emission) microscope. (g) Field emission tunnelling and the arrow of time. (h) The choice between tunnelling-integral and overlap-integral formulations of tunnelling theory, and the apparent incompleteness of both types of formulation.
In these notes I have given a personally flavored exposé of static density-functional theory (DFT). I have started from standard many-body physics at a very elementary level and then gradually introduced the basic concepts of DFT. Successively more advanced topics are added and at the end I even discuss a few not yet published theories. The discussion represents many of the personal views of the author and there is no attempt at being comprehensive. I fully realize that I am often 'unfair' in treating the achievements of other researchers. Many topics of standard DFT are deliberately left out like, e.g., time-dependence, excitations, and magnetic or relativistic effects. These notes represent a compilation of a series of lectures given at at the EXC!TING Summer School DFT beyond the ground state at Riksgränsen, Sweden in June of 2003.
Field emission (FE) electron sources are made close to atomic-scale to reach the highest spatial resolution as well as stable emission for electron microscopy, electron beam inspection and lithography. At present, no single agreed method exists of using FE current-voltage data to extract the apparent emission area, which is needed for predicting some beam properties. The 1956 theory of Murphy and Good (MG) is better physics than the 1920s theory of Fowler and Nordheim (FN) and colleagues, but many researchers use simplified FN theory to analyse experimental data. The present paper reports an experimental method of finding apparent emission area, based on using field ion and field electron microscopes (FIM-FEM). The discrepancy of emission area between the FIM-FEM method and MG-based analysis is a factor of 7.4, while that with simplified FN-based analysis is about 25, confirming MG theory is better for FE data analysis. The result allows deduction of key indicators, including source energy spread, reduced brightness and emission efficiency. A downloadable program is made available to help analysis. Our work provides a new experimental method of characterizing FE electron sources, especially the atomic-scale cold cathode, for which existing plot-based data-analysis methods are not suitable.
While nonclassical light sources are fundamental to quantum communication and computing, solid-state platforms like color centers and quantum dots require cryogenic temperatures to reach the performance levels necessary for practical applications. Over the past decade, low-temperature engineering has transitioned from manual handling of liquid cryogens to automated closed-cycle cryostats. This review details the principles behind modern cooling hardware ranging from flow cryostats to mechanical cryocoolers and dilution refrigerators, with a specific focus on the requirements of optical quantum devices. Aimed at the practicing scientist, this overview provides the technical insights and historical context needed to navigate the current cryogenic landscape and evaluate its role in the future of quantum technology deployment.