Dynamics of a Field Emitted Beam From a Microscopic Inhomogeneous Cathode

• Published in: IEEE transactions on electron devices Vol. 68; no. 5; pp. 2461 - 2466
• Main Authors: Torfason, Kristinn, Sitek, Anna, Manolescu, Andrei, Valfells, Agust
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.05.2021; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Anodes; Brightness; Cathodes; Diode physics; Electron beams; Electron microscopy; electron sources; Emittance; Field emission; Force; Molecular dynamics; Nonhomogeneous media; Patches (structures); Simulation; space–charge; vacuum electronics; Work functions
• ISSN: 0018-9383; 1557-9646
• DOI: 10.1109/TED.2021.3063210

We investigate by molecular dynamics simulations (Torfason et al. , 2015; 2016) a beam of electrons released via field emission from a planar cathode surface of <inline-formula> <tex-math notation="LaTeX">1~\mu \text {m}^{2} </tex-math></inline-formula> with an inhomogeneous two-level work function, <inline-formula> <tex-math notation="LaTeX">\phi _{\text {low}} </tex-math></inline-formula> and <inline-formula> <tex-math notation="LaTeX">\phi _{\text {high}} </tex-math></inline-formula>. A rectangular grid, where each cell can have one out of two values of the work function, is used as a model. The number of cells in the grid ranges from 6 <inline-formula> <tex-math notation="LaTeX">{\times } </tex-math></inline-formula> 6 to <inline-formula> <tex-math notation="LaTeX">96\times 96 </tex-math></inline-formula>. We compare a periodic checkerboard arrangement with disordered distributions of patches. We perform multiple simulations and randomize the pattern each time. We study the beam behavior by calculating the position and velocity of each electron, r.m.s. emittance, and the brightness of the electron beam. The emittance increases while brightness decreases, with the mean distance between patches with <inline-formula> <tex-math notation="LaTeX">\phi _{\text {low}} </tex-math></inline-formula> when they are in minority, and they switch the behavior versus the mean distance between patches with <inline-formula> <tex-math notation="LaTeX">\phi _{\text {high}} </tex-math></inline-formula> when these patches are in minority, respectively. The Coulomb interaction between all particles is fully included in our simulations.