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| Book/Report | FZJ-2018-02864 |
1988
Kernforschungsanlage Jülich, Verlag
Jülich
Please use a persistent id in citations: http://hdl.handle.net/2128/18480
Report No.: Juel-2201
Abstract: The ion-induced electron emission from clean and gas-covered gold, silver, palladium, copper, and titanium, as well as from stainless steel, brass, titanium nitride, and technical aluminium was investigated. Each surface was bombarded with up to 23 different ion types from Li$^{+}$ to Sn$^{+}$ with a kinetic energy of 20 keV. The results for clean metals show that the electron yield depends an the electronic structures of both projectile ion and target atom. The yield from gold, silver, and palladium exhibits in every case the same dependence an the atomic number of the projectile, Z$_{1}$. A different dependence is observed for each of copper and titanium. Electron emission is favoured when there is good agreement between the binding energies of the outer p-shells of projectile ion and target atom. Clearly, the Z$_{1}$-dependence is determined by the excitation mechanism, for which details of the band structure of the target seem to be of little importance. The adsorption of oxygen, hydrogen, or nitrogen causes a small decrease in the electron yield from silver, palladium, and copper in accord with the expected increase in work function. In contrast, an increase in the yield from titanium following adsorption of oxygen is observed and is explained by the formation of an oxide layer with agreater escape depth for electrons. Exoelectron emission from titanium can be observed in the presence of a high residual gas pressure. It is shown that this exoelectron emission is a result of the adsorption of oxygen. The investigation of the Z$_{1}$-dependence of the electron yield from the clean metals after exposure to air and from stainless steel, brass, titanium nitride, and technical aluminium reveals a universal Z$_{1}$-dependence. It is explained by the superposition of the yields from the various components of the surface layers of these targets.
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