| Abstract [eng] |
In this work, the influence of aluminum doping on silver mirrors was investigated. The main parameters observed were the reflection coefficient of the mirrors and the surface roughness. The coating of Ag-Al (silver-aluminum) mirrors was deposited using a magnetron sputtering system from the Kurt J. Lesker Company. The coating layer structure of the differently doped mirrors was maintained the same and the thickness of the reflective layer was the same for all specimens at - 150 nm. To investigate the dependence of the optical and physical parameters of Ag-Al mirrors on the level of Al doping, the aluminum concentrations of five different samples were used – 0 %, 5 %, 8 %, 10 %, and 15 %. In the study of the resistance of deposited samples to accelerated helium ions, the particle density (ϕ) was varied - 9,5 × 10^14 p^+/〖cm〗^2, 2,8 × 10^15 p^+/〖cm〗^2, 8,5 × 10^15 p^+/〖cm〗^2 ir 1,8 × 10^16 p^+/〖cm〗^2, with E = 25 keV. A decrease in the surface roughness from Rq = 1.7 nm (0 % Al) to Rq = 0.8 nm (15 % Al) was observed with increasing Al doping in the silver coatings. This effect happened due to the properties of Al to form denser and smaller atomic structures. Along with the surface roughness, the value of the reflection coefficient of the mirrors decreased. Reflection decrease depends on the structure alteration of the silver valence band which is effected by Al doping. This effect of reflectance decrease is most dominant in the UV and VIS areas, which was also observed in the course of this work. In the study of the radiation resistance of Ag-Al mirrors to the space environment, different values of helium ion particle density were chosen, and the maximum value corresponds to the density of particles affecting optical coatings in space for more than five years. A significant change in the reflectance value of the mirrors was observed only at a highest value of particle density ϕ=1,8 × 10^16 p^+/〖cm〗^2, and in this experiment, the surface roughness changed the least in the sample with 8 % Al doping. The change in the roughness of the speciments was caused by the implanted helium ions, which recombine and form hillock structures with a height of ≈ 30 nm inside the reflective layer. The sample with the lowest surface roughness value decrease after radiation tests, was 8 % Al doped mirror. This mirror could be successfully applied for space missions in optical systems, even under energetically difficult conditions. |
