Dynamical level-crossing model for the time-dependent electron emission from dielectric surfaces in symmetric dielectric barrier discharges

Abstract

In field emission plasmas, electrons that initiate plasma formation come from the surface of a metallic electrode, or wall, with emission controlled by the electron-work function of the wall, and can be computed via the Fowler-Nordheim formula. Impinging ions modify the rate at which electrons leave the surface, and are accounted via the coefficient of secondary electron emission. However, in the case of dielectric surfaces, the microscopic mechanism by which electrons are emitted is not as well understood. While simulations of dielectric barrier discharge plasmas assume an initial density of electrons in a time-dependent simulation, whether the presence of electrons is a necessary ambient condition or whether it is a result of emission from a surface is not clear. This is particularly relevant in the context of micro and nanoscale plasma generators when surface-related effects become more important. Here we consider electron emission from dielectric surfaces in the context of dielectric barrier discharges. The configuration of interest consists of two parallel-plate metallic electrodes, each covered by a dielectric layer. Assuming that the initial electrons for plasma formation arise from the surface, we compute the rate of charge transfer from surfaces, which is a necessary, but not sufficient, condition for plasma formation. The novelty of this work is the application of the theory of nonadiabatic transitions (dynamical level-crossing) to the problem of electron emission from dielectric surfaces in dielectric barrier discharges. The microscopic model of electron transfer described here has potential applications in the design of micro and nano-scale plasma generators.

Secondary electron emission and photoemission from a negative electron affinity semiconductor with large mean escape depth of excited electrons

“…Therefore, NEASs have more applications in current amplifiers, photo-injectors (such as RF photocathode guns in accelerators) and x-ray sources. [3][4][5][6] Therefore, NEASs are an important topic. [7][8][9][10][11] A NEAS with high E pom (> 20.0 keV) and large λ (> 1.0 × 10 4 Å) is called a NEAS with large λ (NEASLD), where λ is mean escape depth of secondary electrons and E pom is the incident energy of primary electrons E po corresponding to δ m .…”