Influence of activation parameters on the thickness of MgO thin film on Ag-3Mg alloy and its secondary electron emission property

Highlights: • MgO films with controlled thicknesses on Ag-3Mg alloys were prepared by activation in low vacuum with oxygen. • Superior secondary electron yield was obtained for the Ag-3Mg alloy with proper thickness of MgO film. • Oxygen pressure during the activation process is crucial for obtaining good secondary electron yield for Ag-3Mg alloys. • The mechanism of secondary electron emission in MgO films is discussed. - Abstract: MgO thin films of different thicknesses were prepared on polished Ag-3wt%Mg alloy by an activation process at 500–650 °C under oxygen pressures of 0.5–10.0 Pa. The influence of the thickness of MgO film on the secondary electron yield of the Ag-3wt%Mg alloy is investigated. The alloy with an MgO film of moderate thickness of 65 ± 1 nm shows the highest secondary electron yield of 10. Oxygen pressure below 10.0 Pa is crucial for the formation of intact MgO film on the top surface. Computational simulation analysis reveals that the maximum yield occurs when the penetration depth of primary electrons is 13–18 nm less than the thickness of MgO film. Electron supply of this extra MgO film is allowed by an electron tunneling mechanism under certain bias voltage. The replenishment of new electrons to the electron deficient surface is crucial for obtaining optimized secondary electron yields for Ag-Mg alloy cathodes.