SECONDARY-ELECTRON EMISSION FROM DIAMOND SURFACES

Diamond exhibits very high, but widely varying, secondary-electron yie lds. In this study, we identified some of the factors that govern the secondary-electron yield from diamond by performing comparative studie s on polycrystalline films with different dopants (boron or nitrogen), doping concentrations, and surface terminations. The total electron y ield as a function of incident-electron energy and the energy distribu tion of the emitted secondary electrons showed that both bulk properti es and surface chemistry are important in the secondary-electron-emiss ion process. The dopant type and doping concentration affect the trans port of secondary electrons through the sample bulk, as well as the el ectrical conductivity needed to replenish the emitted electrons. Surfa ce adsorbates affect the electron transmission at the surface-vacuum i nterface because they change the vacuum barrier height. The presence o f hydrogen termination at the diamond surface, the extent of the hydro gen coverage, and the coadsorption of hydrocarbon-containing species a ll correlated with significant yield changes. Extraordinarily high sec ondary-electron yields (as high as 84) were observed on B-doped diamon d samples saturated with surface hydrogen. The secondary electrons wer e predominantly low-energy quasithermalized electrons residing in the bottom of the diamond conduction band. Two key reasons for the unusual ly high yields are (1) the wide band gap which allows the low-energy s econdary electrons to have long mean-free paths, and (2) the very low or even negative electron affinity at the surface which permits the lo w-energy quasithermalized electrons that reach the surface to escape i nto vacuum.