surface science Secondary electron emission studies

Secondary-electron-emission pr cesses 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-elec-tron-generation process, the crossed-field amplifier (CFA) is an example where the cathode requires an efficient secondary-electron-emission material. Secondary-electron-emission processes will be discussed by a three-step rocess: penetration of the primary electrons, transmission of the secondary electrons through the material, and final escape of the secondary electrons over the vacuum barrier. The transmission of the secondary electrons is one of the critical factors in determining the magnitude of the secondary-electron yield. The wide band-gap in an insulator prevents low-energy secondary electrons from losing energy through electron-electron collisions, thereby resulting in a large escape depth for the secondary electrons and a large secondary-electron yield. In general, insulating materials have high secondary-electron yields, but a provision to supply some level of electrical conductivity is necessary in order to replenish the electrons lost in the secondary-electron-emission process. Our secondary-emission study of diamond emonstrates 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. 1