金纳米结构表面二次电子发射特性

使用低气压蒸发工艺制备了金纳米结构,研究了金纳米结构的二次电子发射特性及其对表面形貌的依赖规律,表征了金纳米结构表面出射二次电子能量分布.实验结果表明:蒸发气压升高时,金纳米结构孔隙率增大,表面电子出射产额降低;能量分布表明金纳米结构仅对低能真二次电子有明显抑制作用,对背散射电子的作用效果则依赖于表面形貌.使用由半球和沟槽构成的复合结构,并结合二次电子发射唯象概率模型,对金纳米结构进行模型等效及电子发射特性仿真,模拟结果表明:纳米结构中的半球状纳米颗粒对两种电子产额均有增强作用;沟槽对真二次电子产额有强抑制作用,而对背散射电子产额仅有微弱抑制作用.本工作深入研究了金纳米结构表面电子发射机理,对于开发空间微波系统中纳米级低电子产额表面有重要参考价值.

Secondary electron emission characteristics of gold nanostructures

Secondary electron emission (SEE), which is a frequent phenomenon in space high power microwave systems, is one of the basic inducement of multipactor in space microwave components. It is already verified that lowering SEE is an effective method to mitigate the undesirable effect. Metal black nanostructures have ever been reported to suppress SEE remarkably, however, the SEE characteristics of the gold nanostructures are rarely investigated. In this work, we use the thermal evaporation to fabricate the gold nanostructures under various evaporation gas pressures, and further analyze their SEE characteristics as well as energy distribution information. Experimental results reveal that the evaporation gas pressure determines the morphology of gold nanostructure, and the morphology dominates the SEE level of the gold nanostructure. To be specific, as the evaporation gas pressure rises, the porosity of the nanostructure increases and the SEE yield decreases. The energy distribution information indicates that the gold nanostructure just suppresses the true secondary electrons (TSEs) effectively. However, the effect of the nanostructure on the back scattered electrons (BSEs) is heavily dependent on the surface morphology. Specifically, the nanostructure fabricated at 70 Pa suppresses the BSEs weakly while the nanostructures fabricated at 40-60 Pa enhance the BSEs to some degree. To theoretically explain the experimental phenomena, we establish an equivalent model, which is made up of the periodical combination of a hemisphere and a composite groove, to imitate the fabricated gold nanostructure and simulate its SEE characteristics based on the SEE phenomenological probability model. Simulation results indicate that the hemisphere induces more TSEs and BSEs while the composite groove suppresses them, besides, the groove suppresses the TSEs much more remarkably than the BSEs. The SEE level of the nanostructure model is determined by the weighted average effect of both the hemisphere and the groove. The simulations qualitatively explain the experimental phenomena. This work in depth reveals the SEE mechanism for the gold nanostructures, and is of considerable significance for developing the low SEE surface on a nanometer scale in a space high power microwave-system.