Dependence of asperity depth on secondary electron emission coefficient

Surface discharges at the solar array on the spacecrafts are originated from electrification. Now, estimation of the electrical potential of the spacecraft by electrification is carried out. But, the reliability of the calculated results depends on the accuracy of the physical properties. One of the desired property is the secondary electron emission coefficient (SEEC): δ (The number of secondary electrons/Primary electrons). In this study, SEEC was obtained down to 200 eV using the original irradiation system. In the preliminary experiment using the Au sample, the magnitude of the maximum δ was 1.6 which was obtained around the primary electron energy Ep≈800 e V. It is reported that roughness on surface materials by atomic oxygen (AO) in the low earth orbit increase remarkably. Thus, the authors tried to make asperity forming island structures by evaporating Au. AFM (Atomic Force Microscope) was used for observing the surface geometry. The result showed that the height of several tens nanometers was able to be controlled. The magnitude of SEEC of evaporated sample increased compared with the untreatment sample.