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Diamond exhibits very high, but widely varying, secondary-electron yields. In this study, we identified some of the factors that govern the secondary-electron yield from diamond by performing comparative studies on polycrystalline films with different dopants (boron or nitrogen), doping concentrations, and surface terminations. The total electron yield as a function of incident-electron energy and the energy distribution of the emitted secondary electrons showed that both bulk properties and surface chemistry are important in the secondary-electron-emission process. The dopant type and doping concentration affect the transport of secondary electrons through the sample bulk, as well as the electrical conductivity needed to replenish the emitted electrons. Surface adsorbates affect the electron transmission at the surface-vacuum interface because they change the vacuum barrier height. The presence of hydrogen termination at the diamond surface, the extent of the hydrogen coverage, and the coadsorption of hydrocarbon-containing species all correlated with significant yield changes. Extraordinarily high secondary-electron yields (as high as 84) were observed on B-doped diamond samples saturated with surface hydrogen. The secondary electrons were predominantly low-energy quasithermalized electrons residing in the bottom of the diamond conduction band. Two key reasons for the unusually high yields are (1) the wide band gap which allows the low-energy secondary electrons to have long mean-free paths, and (2) the very low or even negative electron affinity at the surface which permits the low-energy quasithermalized electrons that reach the surface to escape into vacuum.

Computer codes are presently being developed for the purpose of improving the understanding of Crossed-Field Amplifier (CFA) performance. These codes require a more complete and reliable database of the secondary electron emission properties of the electrode materials than exists in the literature. We describe an experimental method and present results of the secondary emission yield measurements on molybdenum surfaces, both clean and gas-exposed. The surface cleanliness was monitored by Auger Electron Spectroscopy (AES), and all measurements made under ultra-high vacuum conditions (better than 1 x lO-''torr). Our results differ from the existing data for which the surface cleanliness was not determined. The secondary electron emission yields were measured as a function of the primary electron energy and also of the angle of incidence. The results were fitted with the analytical expressions of Vaughan, and the comparison found good overall agreement if Vaughan's formulas are slightly modified from the originally proposed form.

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