Ion-induced secondary electron emission coefficient of metal surfaces analysed in an ion beam experiment

Electron emission of surfaces upon ion impact is one of the most fundamental plasma-surface-interactions. Many experimental (e.g [1-3]) and theoretical (e.g.[4-6]) approaches address the ion-induced secondary electron emission coefficient (SEEC=amount of released electrons per incident ion) in literature. However, the SEEC determination may remain rather indirect though, as the process of electron emissionn occurs often not isolated from all other plasma-surface-interactions. SEEC are especially important for magnetron sputtering discharges, because target conditions strongly affect electron emission of  targets and thus have an impact on the discharge itself. In reactive magnetron plasmas the impact of the SEEC is even more difficult to assess, because reactive species such as oxygen or nitrogen react also at the target surface and alter the SEEC. Data of such oxidized targets are very sparse and may even contain significant systematic errors, because they were often measured by modeling the complex behavior of plasma discharges. Using beam experiments avoids this complication and allows a precise SEEC determination. SEECs of clean, untreated (air-exposed) and intentionally oxidized copper and nickel surfaces are investigated in such a beam experiment. Metal foil and oxidized metal foils are exposed to beams of singly charged argon ions with energies of 200eV-10keV. SEECs of oxidized metal targets for a large ion energy range are determined precisely. A model for the electron emission of a partly oxidized surface is presented to explain the data. 

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