Silver nanopillar coatings grown by glancing angle magnetron sputtering for reducing multipactor effect in spacecrafts

We have studied nanometric high aspect ratio Ag nanopillar coatings exhibiting reduced secondary electron emission for the mitigation of multipactor effect in radio-frequency space devices of high frequency and high power. The Ag nanopillars have been grown by glancing angle deposition with DC magnetron sputtering. Some samples have been covered by a gold capping layer to reduce oxidation and aging effects. The secondary emission yield of the surfaces of these samples has been measured and compared to those of flat Ag and Au reference samples. The results show that high aspect ratio surface roughness at the nanometer scale significantly reduce the secondary emission yield of the surface. This reduction is more important for low electron energies, which is the most influencing energy range of electrons for multipactor. The multipactor region for the nanopillar coating presenting the best secondary emission yield properties has been simulated, finding practical suppression of multipactor effect. The high-frequency surface resistance of these samples has also been estimated from published computations for similar surface roughness patterns. It was found that such nanopillar coatings are compatible with the best accomplishments of present space industry.