Electron emission from ferroelectric plasma cathodes

Recent and not so recent experimental data are analyzed to show that the reason for strong electron emission from dielectric cathodes is the incomplete discharge occurring on the dielectric surface due to the electric field there being tangentially nonzero. The places of origin of such discharges are the metal–dielectric–vacuum triple junctions (TJs). As the discharge plasma moves over the surface of the dielectric electrode, the bias current arises, and an electric microexplosion occurs at a TJ. If the number of TJs is large, as it is for a metal grid held tightly to a ferroelectric, electron currents of up to $10^4$ A with densities of more than $10^2$ A cm$^{-2}$ can be achieved. A surface discharge is initiated by applying a triggering pulse to the metal substrate deposited beforehand onto the opposite side of the ferroelectric. If this pulse leads the accelerating voltage pulse, the electron current is many times the Child–Langmuir current. The reason for the ferroelectric effect is the large permittivity ($\varepsilon>10^3$) of the materials used (BaTiO$_3$, PLZT, PZT). Although these devices have come to be known as ferroelectric cathodes, we believe ferroelectric plasma cathodes would be a better term to use to emphasize the key role of plasma effects.