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采用氧化激活AgMg合金在表面形成MgO薄膜, 以及采用射频反应溅射沉积法在不锈钢基片上分别制备了MgO薄膜和掺杂CoO的MgO薄膜, 研究了制备工艺对薄膜二次电子发射系数及耐电子束轰击能力的影响. 结果表明, 薄膜厚度对其耐电子束轰击能力有显著影响, 随着薄膜厚度的增加, 耐电子束轰击能力明显增强, 而射频反应溅射沉积可通过调整镀膜时间获得不同厚度的MgO薄膜. 射频反应溅射的氧分压比对MgO薄膜表面质量有较大影响, 随着沉积过程中氧分压比增大, MgO薄膜表面粗糙度增大, 不利于二次电子发射. CoO掺杂改善了MgO薄膜表面质量, 使其表面更加平整、光滑, 提高了薄膜的二次电子发射系数, 而且降低了薄膜表面质量对氧分压比变化的敏感性. 550 ℃真空热处理1 h使CoO掺杂的MgO薄膜发生热分解失氧且表面质量变差, 导致二次电子发射系数大幅下降. 在沉积过程中, 提升基片温度或提高氧分压, 会使薄膜中存在金属态Mg且薄膜表面质量变差, 使二次电子发射系数小幅下降.

High, stable and durable secondary electron emission is an essential property for the application of dynodes of electron multipliers and photomultiplier tubes. The MgO film have been widely used as dynode materials for the applications owing to its good secondary electron emission properties. In this work, MgO and CoO doped MgO films, as secondary electron emission films, were prepared by radio-frequency reactive sputtering deposition on the stainless steel substrate, and also another MgO film at the surface of activated AgMg alloy was prepared. The effect of preparation processes on the secondary electron emission properties of the films was focused. It was found that the film thickness significantly affected the resistance to electron beam bombardment. With the increase of film thickness, the resistance to electron beam bombardment was significantly enhanced. Radio-frequency reactive sputtering deposition could control the film thickness by varying deposition time. The surface quality of MgO film is quite sensitive to the oxygen partial pressure of the deposition atmosphere. Higher oxygen partial pressure caused higher surface roughness, which was harmful to the secondary electron emission. After doping with CoO, the surface of MgO films were much flatter and smoother, resulting in the improvement of the secondary electron emission coefficient. The CoO doping also reduced of the sensitivity of film surface quality to the oxygen partial pressure. The secondary electron emission coefficient of CoO doped MgO film sharply decreased after heated at 550 ℃ for 1 h due to the surface quality degrading and the thermal decomposition induced loss of oxygen. Elevating the substrate temperature or oxygen partial pressure during deposition accounted for the presence of metallic Mg in film and the degrading of surface quality, which finally lead to lower secondary electron emission coefficient.