CEAS Space Journal

, Volume 11, Issue 4, pp 579–587 | Cite as

Protected silver coatings for reflectors

  • Stefan SchwindeEmail author
  • Mark Schürmann
  • Ralph Schlegel
  • Jan Kinast
  • Reinhold J. Dorn
  • Jean Louis Lizon
  • Sebastien Tordo
  • Norbert Kaiser
Original Paper


For ground- and spaced-based applications, Ag-coated reflectors are indispensable because of their high reflectivity. The transport, assembly, and storage of these reflectors take places over a long period before they are finally commissioned for application. To endure this period without a decrease of reflectivity, protective coatings with a final layer, which offers a high resistance to aqueous solutions, and a low mechanical stress should be used. These criteria were taken into account for the selection of a final layer for a protected Ag coating, which was applied for reflectors utilized in the CRIRES+-instrument (an IR spectrograph used at the VLT). Reactively sputtered Al2O3, SiO2 and Si3N4 layers were investigated with regard to these criteria. In aqueous (alkaline) solutions, the investigated Si3N4 layers are more stable than the SiO2 layers and the SiO2 layers more stable than the Al2O3 layers. This shows the influence of the intrinsic material properties. The mechanical stress of the sputtered layers depends on the deposition conditions and thus on the selected parameters. A Si3N4 layer with a high resistance to aqueous (alkaline) solutions also offers low and stable mechanical stress. Therefore, the deposition parameters used for this layer were applied for sputtering the final layer of the protected Ag coating for the reflectors.


Protective layer Coating Sputtering Silver Reflector Durability 



  1. 1.
    Wilson, R.N.: Reflecting Telescope Optics II. Springer, Berlin Heidelberg (2001)Google Scholar
  2. 2.
    Jean, M.B., Ashley, E.J.: Infrared reflectance and emittance of silver and gold evaporated in ultrahigh vacuum. Appl. Opt. 4(2), 221–224 (1965)CrossRefGoogle Scholar
  3. 3.
    Thomas, N., Wolfe, J.: UV-shifted durable silver coating for astronomical mirrors. Proc. SPIE 4003, 312–323 (2000)CrossRefGoogle Scholar
  4. 4.
    Veleva, L., Valdez, B., Lopez, G., et al.: Atmospheric corrosion of electro-electronics metals in urban desert simulated indoor environment. Corros. Eng. Sci. Technol. 43(2), 149–155 (2013)CrossRefGoogle Scholar
  5. 5.
    Vargas, O.L., Valdez, S.B., Veleva, M.L., et al.: The corrosion of silver in indoor conditions of an assembly process in the microelectronics industry. Anti-Corrosion Meth. Mater. 56(4), 218–225 (2009)CrossRefGoogle Scholar
  6. 6.
    Jobst, P.J., Stenzel, O., Schürmann, M., et al.: Optical properties of unprotected and protected sputtered silver films: surface morphology vs. UV/VIS reflectance. Adv. Opt. Technol. 3(1), 91–102 (2014)Google Scholar
  7. 7.
    Thomas, N.L., Siekhaus, W.J., Farmer, J.C., et al.: Prevention of corrosion of silver reflectors for the National Ignition Facility. Proc. SPIE 3427, 394–400 (1998)CrossRefGoogle Scholar
  8. 8.
    Hass, G., Heaney, J.B., Herzig, H., et al.: Reflectance and durability of Ag mirrors coated with thin layers of Al2O3 plus reactively deposited silicon oxide. Appl. Opt. 14(11), 2639–2644 (1975)CrossRefGoogle Scholar
  9. 9.
    Pellicori, S.F.: Scattering defects in silver mirror coatings. Appl. Opt. 19(18), 3096–3098 (1980)CrossRefGoogle Scholar
  10. 10.
    Vucina, T., Boccas, M., Araya, C., et al.: Gemini primary mirror in situ wash. Proc. SPIE 7012, 1–13 (2008)Google Scholar
  11. 11.
    Chu, C.-T., Fuqua, P.D., Barrie, J.D.: Corrosion characterization of durable silver coatings by electrochemical impedance spectroscopy and accelerated environmental testing. Appl. Opt. 45(7), 1583–1593 (2006)CrossRefGoogle Scholar
  12. 12.
    Folgner, K.A., Chu, C.-T., Lingley, Z.R., et al.: Environmental durability of protected silver mirrors prepared by plasma beam sputtering. Appl. Opt. 56(4), 75–86 (2017)CrossRefGoogle Scholar
  13. 13.
    Barrie, J.D., Fuqua, P.D., Folgner, K.A., et al.: Control of stress in protected silver mirrors prepared by plasma beam sputtering. Appl. Opt. 50(9), 135–140 (2011)CrossRefGoogle Scholar
  14. 14.
    Schwinde, S., Schürmann, M., Jobst, P.J., et al.: Description of particle induced damage on protected silver coatings. Appl. Opt. 54, 4966–4971 (2015)CrossRefGoogle Scholar
  15. 15.
    Herrmanna, M., Schilma, J., Michaela, G., et al.: Corrosion of silicon nitride materials in acidic and basic solutions and under hydrothermal conditions. J. Eur. Ceram. Soc. 23, 585–594 (2003)CrossRefGoogle Scholar
  16. 16.
    Lin, C.-H., Komeya, K., Meguro, T., et al.: Corrosion resistance of wear resistant silicon nitride ceramics in various aqueous solutions. J. Ceram. Soc. Japan 111, 452–456 (2003)CrossRefGoogle Scholar
  17. 17.
    Vogel, W.: Glaschemie. Springer-Verlag, Berlin (1992)CrossRefGoogle Scholar
  18. 18.
    Salh, R.: Defect related luminescence in silicon dioxide network: a review. InTech-Verlag, Rijeka (2011)CrossRefGoogle Scholar
  19. 19.
    Waters, P., Volinsky, A.A.: Stress and moisture effects on thin film buckling delamination. Exp. Mech. 47, 163–170 (2007)CrossRefGoogle Scholar
  20. 20.
    Leplan, H., Geenen, B., Robic, J.Y., et al.: Residual stresses in evaporated silicon dioxide thin films: correlation with deposition parameters and aging behavior. J. Appl. Phys. 78(2), 962–968 (1995)CrossRefGoogle Scholar
  21. 21.
    Schwinde, S., Schürmann, M., Kaiser, N., et al.: Investigation of SiO2–Al2O3 nanolaminates for protection of silver reflectors. Appl. Opt. 56, 41–46 (2017)CrossRefGoogle Scholar
  22. 22.
    Berg, S., Nyberg, T.: Fundamental understanding and modeling of reactive sputtering processes. Thin Solid Films 476, 215–230 (2005)CrossRefGoogle Scholar
  23. 23.
    Sheikh, D.A., Connell, S.J., Dummer, R.S.: Durable silver coating for Kepler Space Telescope primary mirror. Proc. SPIE 7010, 1–5 (2008)Google Scholar
  24. 24.
    Kinast, J., Schlegel, R., Kleinbauer, K., Steinkopf, R., Follert, R., et al.: Manufacturing of aluminum mirrors for cryogenic applications. Proc. SPIE 10706, 107063G-1–107063G-7 (2018)Google Scholar
  25. 25.
    Dorn, R.J., Anglada-Escude, G., Baade, D., et al.: CRIRES+: exploring the cold universe at high spectral resolution. Messenger 156, 7–11 (2014)Google Scholar
  26. 26.
    Berg, S., Larsson, T., Nender, C., et al.: Predicting thin-film stoichiometry in reactive sputtering. J. Appl. Phys. 63, 887–891 (1988)CrossRefGoogle Scholar
  27. 27.
    Särhammar, E., Strijckmans, K., Nyberg, T., et al.: A study of the process pressure influence in reactive sputtering aiming at hysteresis elimination. Surf. Coat. Technol. 232, 357–361 (2013)CrossRefGoogle Scholar
  28. 28.
    Software: OptiChar by A.V. Tikhonravov and M.K.Trusbetskov; Module of the software package Optilayer; OptiLayer GmbH; Version 12.12 (2013)Google Scholar
  29. 29.
    User manual: Tencor FLX-2320 user manual. Thin Film Stress Measurement. Tencore Instruments, 9.1–9.3 (1995)Google Scholar
  30. 30.
    Depla, D.: Magnetrons, reactive gases and sputtering. Ghent University Belgium, Ghent (2014)Google Scholar
  31. 31.
    Huheey, J.E., Keiter, E.A., Keiter, R.L.: Anorganische Chemie: Prinzipien von Struktur und Reaktivität. de Gruyter, Berlin (2003)Google Scholar
  32. 32.
    Cartledge, G.H.: “Studies on the Periodic system—the ionic potential as a periodic function”, 1. J. Am. Chem. Soc. 50(11), 2855–2863 (1928)Google Scholar
  33. 33.
    Sree, K.S.: Principle of physical vapor deposition of thin films. Elsevier, New York (2006)Google Scholar
  34. 34.
    Blasek, G., Bräuer, G.: Vakuum Plasma Technologien: Beschichtung und Modifizierung von Oberflächen. Eugen G. Leutze Verlag 87–101 (2010)Google Scholar
  35. 35.
    Thornton, J.A.: Influence of substrate temperature and deposition rate on structure of thick sputtered Cu coatings. J. Vacuum Sci. Technol. 11, 666–670 (1974)CrossRefGoogle Scholar
  36. 36.
    Hirsch, E.H.: Stress in porous thin films through absorption of polar molecules. J. Phys. D Appl. Phys. 13, 2081–2094 (1980)CrossRefGoogle Scholar
  37. 37.
    Stolz, C.J., Taylor, J.R., Eickelberg, W.K., et al.: Effects of vacuum exposure on stress and spectral shift of high reflective coatings. Appl. Opt. 32(28), 5666–5672 (1993)CrossRefGoogle Scholar
  38. 38.
    Nishikawa, T., Ono, H., Murotani, H., et al.: Analysis of long-term internal stress and film structure of SiO2 optical thin films. Appl. Opt. 50(9), 210–216 (2011)CrossRefGoogle Scholar
  39. 39.
    Scherer, K., Nouvelot, L., Lacan, P., et al.: Optical and mechanical characterization of evaporated SiO2 layers. Long-term evolution. Appl. Opt. 35(25), 5067–5072 (1996)CrossRefGoogle Scholar
  40. 40.
    Schulz, U., Jakobs, S., Norbert, K.: SiO2 protective coatings on plastic optics deposited with plasma-lAD. Proc. SPIE 2776, 169–174 (1996)CrossRefGoogle Scholar
  41. 41.
    Bräuer, G., Szczyrbowski, J., Teschner, G.: Mid frequency sputtering—a novel tool for large area coating. Surf. Coat. Technol. 94–95, 658–662 (1997)CrossRefGoogle Scholar
  42. 42.
    Besland, M.-P., Lapeyrade, M., Delmotte, F., et al.: Interpretation of stress variation in silicon nitride films deposited by electron cyclotron resonance plasma. J. Vacuum Sci. Technol. A 22(5), 1962–1970 (2004)CrossRefGoogle Scholar
  43. 43.
    Schürmann, M., Schwinde, S., Kaiser, N.: Optical element comprising a reflective coating Patent specification: EP3158370A1 (2015)Google Scholar
  44. 44.
    Schwinde, S., Schürmann, M., Kaiser, N., et al.: Protected and enhanced silver for mirrors: damage mechanisms and how to prevent them. Proc. SPIE 9627, 96271R-1–96271R-6 (2015)Google Scholar

Copyright information

© CEAS 2019

Authors and Affiliations

  • Stefan Schwinde
    • 1
    Email author
  • Mark Schürmann
    • 1
  • Ralph Schlegel
    • 1
  • Jan Kinast
    • 1
  • Reinhold J. Dorn
    • 2
  • Jean Louis Lizon
    • 2
  • Sebastien Tordo
    • 2
  • Norbert Kaiser
    • 1
  1. 1.Fraunhofer Institute for Applied Optics and Precision Engineering IOFJenaGermany
  2. 2.European Southern Observatory ESOGarching bei MuenchenGermany

Personalised recommendations