Thin layers of MgO are applied in the Zeus panel to tower the field strength needed for electron transport. The layers can be applied by evaporation or spray pyrolysis. To achieve proper performance the layers should be smooth and at least 40 nm thick. MgO is easily degraded upon storage in air by the formation of a surface layer of magnesium carbonate and magnesium hydroxide. However, heating the contaminated layer briefly at a temperature of 450°C in air is sufficient to regenerate the MgO surface.@en