Secondary electron emission characteristics of nanostructured silver surfaces

Multipactor induced by secondary electron emission (SEE) is a potential risk for many high-power systems. It is of great importance to suppress the total electron emission yield (TEEY) to mitigate the detrimental effect. Metal black has been reported as effective TEEY suppressor, but the theoretical model for describing its SEE characteristics is still scarce. In this work, we propose a periodic nanostructure model, with each unit composed of a combination of a top hemispherical nanograin and a fractal rectangular groove-like gap, to describe the silver black nanostructure. Using this model, we investigate the SEE characteristics of the silver black nanostructure theoretically. Simulation results indicate that the groove-like gaps in the nanostructure suppress the TEEY, while the top hemispherical nanograins enhance it; and the suppression on the true secondary electron yield is much stronger than that on the back-scattered electron yield (BSEY). In addition, we observe two interesting phenomena: first, the nanostructure enhances the BSEY even if it suppresses the TEEY when the proportion of top nanograins reaches 30%; second, the suppression on TEEY of the nanostructure becomes weak at relatively high primary electron energy. To verify the simulation results, we fabricate several silver nanostructures by thermal evaporation with gas pressure varied from 40 to 70 Pa. Measurement results indicate that all the fabricated nanostructures can suppress TEEY to some degree; and the more top hemispherical nanograins the nanostructure possesses, the higher TEEY revealed. For the measured SEE characteristics of the nanostructures fabricated at 40 and 45 Pa, we observe a higher BSEY than that of the flat surface. These experimental results qualitatively verify the simulated estimations. This work is of significance to comprehend SEE characteristics in related applications such as multipactor suppression. Published by AIP Publishing.