Function-layer-driven surface engineering for high-efficiency and stable secondary electron emission films

The modification of MgO thin films through surface engineering has been widely investigated to enhance secondary electron emission (SEE) and air stability. Here, we propose two progressive hierarchical strategies based on Al and Au co-doped MgO thin film, designed as bilayer and trilayer sandwich structures with MgO-based functional layers. The optimized surface bilayer structure achieves a SEE coefficient (SEY) at Ep = 200 eV (δ₂₀₀) above 4.5 with a low decay rate of ∼5 %. Integrating both strategies, the final surface sandwich structure shows excellent air stability, maintaining δ₂₀₀ = 4.5 and a decay rate of only 4.25 % after 72 h air exposure. Compared with the previously reported co-doped film with a 2 nm Al₂O₃ passivation layer (C_P2nm), our surface sandwich structure exhibits clear advantages in terms of SEE performance and stability. Specifically, the inital δ₂₀₀ increases by 12 % at a comparable decay rate, wheras after 72 h of exposure to air, These results demonstrate that the hierarchical sandwich design effectively enhances both SEE performance and air stability, offering a superior strategy for MgO-based electron emission films.