Thermal evaporated hyperbranched Ag nanostructure as an effective secondary-electron trapping surface coating

We study secondary electron yield (SEY) suppression of silver using a hyperbranched nanostructure obtained by thermal evaporation. First, we perform thermal evaporation at different residual gas pressures for studying the influence of pressure on surface morphologies. A self-assembled hyperbranched Ag nanostructure has been achieved at 100 Pa. Then, we further investigate the detailed formation process of the self-assembled hyperbranched Ag nanostructure qualitatively and find it to be dominated by "screening effect". Finally, we study the obvious SEY suppression effect of this special structure. We show that 100 Pa is the best process condition within our experimental scope from the SEY suppression point of view. It exhibits maximum SEY (δ_max) of ∼0.9. We also show that the combining of this nanostructure with the micro-porous surface we developed before can further improve its SEY suppression effect which leading to a δ_max of ∼0.8. We propose a novel 2D rectangular-hemisphere hybrid trap model to perform numerical simulation of secondary electron dynamics for interpretation of the experimental results. In total, this work provides guidance to controllable preparation of low SEY metallic surfaces for potential applications in particle accelerators, RF microwave components and satellite systems.