SECONDARY-ELECTRON EMISSION STUDIES

Secondary-electron-emission processes under electron bombardment play an important role in the performance of a variety of electron devices. While in some devices, the anode and the grid require materials that suppress the secondary-electron-generation process, the crossed-field amplifier (CFA) is an example where the cathode requires an efficient secondary-electron-emission material. Secondary-electron-emission proc esses will be discussed by a three-step process. penetration of the pr imary electrons, transmission of the secondary electrons through the m aterial, and final escape of the secondary electrons over the vacuum b arrier. The transmission of the secondary electrons is one of the crit ical factors in determining the magnitude of the secondary-electron yi eld. The wide band-gap in an insulator prevents low-energy secondary e lectrons from losing energy through electron-electron collisions, ther eby resulting in a large escape depth for the secondary electrons and a large secondary-electron yield. In general, insulating materials hav e high secondary-electron yields, but a provision to supply some level of electrical conductivity is necessary in order to replenish the ele ctrons lost in the secondary-electron-emission process. Our secondary- emission study of diamond demonstrates that the vacuum barrier height can have a strong effect on the total yield. The combined effect of a large escape depth of the secondary electrons and a low vacuum-barrier height is responsible for the extraordinarily high secondary-electron yields observed on hydrogen-terminated diamond samples.