Degradation Mechanism of Secondary Electron Emission in Plasma-Exposed MgO Films

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Degradation mechanism of secondary electron emission (SEE) properties in plasma-exposed MgO films was studied using three types of plasma ion; He+, Ne+, and Ar+. As the mass of impinging ions increased from He+ to Ar+, the SEE coefficient ($\gamma$) of MgO decreased from 0.0227 to 0.0175. Synchrotron radiation photoemission spectroscopy revealed that the Mg-to-O ratio significantly decreased from 1.00 to 0.79 in He plasma, to 0.73 in Ne plasma, and to 0.66 in Ar plasma. This was due to the preferential sputtering of Mg atoms by the high-mass ions, leading to the production of Mg vacancies (V centers) near the surface of MgO and the decrease in $\gamma$.
2009-07-25