Optical Absorption Layers for Infrared Radiation

Chapter

Abstract

Optical functional layers with high absorption have a large number of applications. Beside their use in infrared radiation (IR) detection, they can be applied to radiation cooling because good radiation absorbers are also good emitters. Another application is the thermography of electronic devices. Here, a thin black layer deposited on a heated device gives a defined emittance of the surface. In this way, the thermal profile is calibrated absolutely in temperature. However, the most noticeable application is their use in thermal infrared detectors to transform radiation into heat. Thereby, infrared absorbing layers have to meet the following demands: (i) high and spectrally homogeneous radiation absorption, (ii) very low thermal mass, (iii) high heat conductivity, (iv) good long-term stability and reproducibility of the properties and (v) their fabrication must be compatible with the detector manufacturing technology. In the past IR absorption technology had focussed on thin films whereby several solutions of optical absorption layers for infrared radiation have been proposed. The most important are: (i) ultrathin metal films, (ii) quarter-wavelength structures, (iii) highly porous metal-black coatings, and (iv) particulate-filled polymer coatings, respectively. In recent years, new opportunities for ultrathin infrared absorption layers are offered due to recent advances in nanotechnology and plasmonics research. This chapter gives an insight into established principles of infrared radiation absorption and presents two new approaches dealing with nano-structured surfaces and plasmon resonance in nanoparticles.

Keywords

Metal Film Gold Nanorods Absorption Layer Thin Metal Film Thermal Detector 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

References

  1. 1.
    Advena, D.J., Bly, V.T., Cox, J.T.: Deposition and characterization of far-infrared absorbing gold black films. Appl. Opt. 32(7), 1136–1144 (1993)CrossRefGoogle Scholar
  2. 2.
    Barker Jr, A.S., Ballman, A.A., Ditzenberger, J.A.: Infrared study of the lattice vibrations in \({\rm litao}_{3}\). Phys. Rev. B 2(10), 4233–4239 (1970)CrossRefGoogle Scholar
  3. 3.
    Barnes, R.B., Czerny, M.: Concerning the reflection power of metals in thin layers for the infrared. Phys. Rev. 38(2), 338–345 (1931)CrossRefGoogle Scholar
  4. 4.
    Bauer, S.: Optical properties of a metal film and its application as an infrared absorber and as a beam splitter. Am. J. Phys. 60, 257 (1992)CrossRefGoogle Scholar
  5. 5.
    Bauer, S., Bauer-Gogonea, S., Ploss, B.: The physics of pyroelectric infrared devices. Appl. Phys. B: Lasers and Optics 54(6), 544–551 (1992)CrossRefGoogle Scholar
  6. 6.
    Becker, W., Fettig, R., Ruppel, W.: Optical and electrical properties of black gold layers in the far infrared. Infrared Phys. Technol. 40(6), 431–445 (1999)CrossRefGoogle Scholar
  7. 7.
    Bernhard, C.G.: Structural and functional adaptation in a visual system. Endeavour 26, 79–84 (1967)Google Scholar
  8. 8.
    Berning, P.H.: Use of equivalent films in the design of infrared multilayer antireflection coatings. J. Opt. Soc. Am. 52(4), 431–435 (1962)CrossRefGoogle Scholar
  9. 9.
    Betts, D.B., Clarke, F.J.J., Cox, L.J., Larkin, J.A.: Infrared reflection properties of five types of black coating for radiometric detectors. J. Phys. E Sci. Instr. 18, 689–696 (1985)CrossRefGoogle Scholar
  10. 10.
    Bohren, C.F., Huffman, D.R.: Absorption and scattering of light by small particles. Wiley, New York (1983)Google Scholar
  11. 11.
    Born, M., Wolf, E., Bhatia, A.B.: Principles of optics. Pergamon Press, Oxford (1964)Google Scholar
  12. 12.
    Brioude, A., Jiang, X.C., Pileni, M.P.: Optical properties of gold nanorods: DDA simulations supported by experiments. J. Phys. Chem. B 109(27), 13138–13142 (2005)Google Scholar
  13. 13.
    Bruggeman, D.A.G.: Berechnung verschiedener physikalischer Konstanten von heterogenen Substanzen. I. Dielektrizitätskonstanten und Leitfähigkeiten der Mischkörper aus isotropen Substanzen. Ann. Phys. 416, 636–664 (1935)CrossRefGoogle Scholar
  14. 14.
    Butler, N.R., Blackwell, R.J., Murphy, R., Silva, R.J., Marshall, C.A.: Low-cost uncooled microbolometer imaging system for dual use. In: Proceedings of the SPIE, vol 2552, p.583. (1995)Google Scholar
  15. 15.
    Cepak, V.M., Martin, C.R.: Preparation and stability of template-synthesized metal nanorod sols in organic solvents. J. Phys. Chem. B 102(49), 9985–9990 (1998)CrossRefGoogle Scholar
  16. 16.
    Chang, S.S., Shih, C.W., Chen, C.D., Lai, W.C., Wang, C.R.C.: The shape transition of gold nanorods. Langmuir 15(3), 701–709 (1999)CrossRefGoogle Scholar
  17. 17.
    Chih-Ming, W., Ying-Chung, C., Maw-Shung, L., Kun-Jer, C.: Microstructure and absorption property of silver-black coatings. Jpn. J. Appl. Phys 39, 551–554 (2000)CrossRefGoogle Scholar
  18. 18.
    Chiu, C.H., Yu, P., Kuo, H.C., Chen, C.C., Lu, T.C., Wang, S.C., Hsu, S.H., Cheng, Y.J., Chang, Y.C.: Broadband and omnidirectional antireflection employing disordered GaN nanopillars. Opt. Express 16(12), 8748–8754 (2008)CrossRefGoogle Scholar
  19. 19.
    Cruz-Cabrera, A.A., Basilio, L.I., Peters, D.W., Wendt, J.R., Kemme, S.A., Samora, S.: Fabrication and testing of plasmonic optimized transmission and reflection coatings. In: Proceedings of the SPIE, vol. 6883, p. 68830R.(2008)Google Scholar
  20. 20.
    De Nivelle, M., Bruijn, M.P., De Vries, R., Wijnbergen, J.J., De Korte, P.A.J., Sanchez, S., Elwenspoek, M., Heidenblut, T., Schwierzi, B., Michalke, W., et al.: Low noise high-T superconducting bolometers on silicon nitride membranes for far-infrared detection. J. Appl. Phys. 82, 4719 (1997)CrossRefGoogle Scholar
  21. 21.
    Esumi, K., Matsuhisa, K., Torigoe, K.: Preparation of rodlike gold particles by UV irradiation using cationic micelles as a template. Langmuir 11(9), 3285–3287 (1995)CrossRefGoogle Scholar
  22. 22.
    Foote, M.C., Kenyon, M., Krueger, T.R., McCann, T.A., Chacon, R., Jones, E.W., Dickie, M.R., Schofield, J.T., McCleese, D.J., Gaalema, S., et al.: Thermopile detector arrays for space science applications. In: Proceedings of the SPIE 4999, vol. 443. San Jose (2003)Google Scholar
  23. 23.
    Fullam, S., Cottell, D., Rensmo, H., Fitzmaurice, D.: Carbon nanotube templated self-assembly and thermal processing of gold nanowires. Adv. Mater. 12(19), 1430–1432 (2000)CrossRefGoogle Scholar
  24. 24.
    Gans, R.: Über die Form ultramikroskopischer Goldteilchen. Ann. Phys. 37, 881–900 (1912)CrossRefGoogle Scholar
  25. 25.
    Gerlach, G., Dötzel, W.: Introduction to microsystem technology: a guide for students. Wiley Publishing, NewYork (2008)Google Scholar
  26. 26.
    Gluodenis, M., Foss Jr, C.A.: The effect of mutual orientation on the spectra of metal nanoparticle rod-rod and rod-sphere pairs. J. Phys. Chem. B 106(37), 9484–9489 (2002)CrossRefGoogle Scholar
  27. 27.
    Golay, M.J.E.: A pneumatic infra-red detector. Rev. Sci. Instr. 18(5), 357–362 (1947)CrossRefGoogle Scholar
  28. 28.
    Gombert, A., Glaubitt, W., Rose, K., Dreibholz, J., Blaesi, B., Heinzel, A., Sporn, D., Doell, W., Wittwer, V.: Subwavelength-structured antireflective surfaces on glass. Thin Solid Films 351(1–2), 73–78 (1999)CrossRefGoogle Scholar
  29. 29.
    Grann, E.B., Moharam, M.G.: Comparison between continuous and discrete subwavelength grating structures for antireflection surfaces. J. Opt. Soc. Am. A 13(5), 988–992 (1996)CrossRefGoogle Scholar
  30. 30.
    Grann, E.B., Moharam, M.G., Pommet, D.A.: Artificial uniaxial and biaxial dielectrics with use of two-dimensional subwavelength binary gratings. J. Opt. Soc. Am. A 11(10), 2695–2703 (1994)CrossRefGoogle Scholar
  31. 31.
    Grann, E.B., Varga, M.G., Pommet, D.A.: Optimal design for antireflective tapered two-dimensional subwavelength grating structures. J. Opt. Soc. Am. A 12(2), 333–339 (1995)CrossRefGoogle Scholar
  32. 32.
    Granqvist, C.G.: Radiative heating and cooling with spectrally selective surfaces. Appl. Opt 20, 2606–2615 (1981)CrossRefGoogle Scholar
  33. 33.
    Grosse, P.: Freie Elektronen in Festkörpern. Springer, Berlin (1979)CrossRefGoogle Scholar
  34. 34.
    Hadley, L.N., Dennison, D.M.: Reflection and transmission interference filters. J. Opt. Soc. Am. 37(6), 451–453 (1947)CrossRefGoogle Scholar
  35. 35.
    Hadni, A., Gerbaux, X.: Infrared and millimeter wave absorber structures for thermal detectors. Infrared Phys. 30, 465–478 (1990)CrossRefGoogle Scholar
  36. 36.
    Hadobas, K., Kirsch, S., Carl, A., Acet, M., Wassermann, E.F.: Reflection properties of nanostructure-arrayed silicon surfaces. Nanotechnology 11, 161–164 (2000)CrossRefGoogle Scholar
  37. 37.
    Hanson, C.M.: Uncooled IR detector performance limits and barriers. In: Proceedings of the SPIE, vol. 4028, p. 2 (2000)Google Scholar
  38. 38.
    Harris, L.: The optical properties of metal blacks and carbon blacks. Massachusetts Institute of Technology, Cambridge (1967)Google Scholar
  39. 39.
    Heavens, O.S.: Optical properties of thin films. Rep. Prog. Phys. 23, 1–65 (1960)CrossRefGoogle Scholar
  40. 40.
    Heavens, O.S.: Optical properties of thin solid films. Dover Publication, New York (1991)Google Scholar
  41. 41.
    Hilsum, C.: Infrared absorption of thin metal films. J. Opt. Soc. Am. 44, 188–191 (1954)CrossRefGoogle Scholar
  42. 42.
    Hulst, H.C.: Light scattering by small particles. Dover Publications, New York (1981)Google Scholar
  43. 43.
    Jackson, J.D.: Classical Electrodynamics, 3rd edn. Wiley, New York (1999)Google Scholar
  44. 44.
    Jana, N.R., Gearheart, L., Murphy, C.J.: Wet chemical synthesis of high aspect ratio cylindrical gold nanorods. J. Phys. Chem. B 105(19), 4065–4067 (2001)CrossRefGoogle Scholar
  45. 45.
    Kanamori, Y., Hane, K., Sai, H., Yugami, H.: 100 nm period silicon antireflection structures fabricated using a porous alumina membrane mask. Appl. Phys. Lett. 78, 142 (2001)CrossRefGoogle Scholar
  46. 46.
    Kanamori, Y., Sasaki, M., Hane, K.: Broadband antireflection gratings fabricated upon silicon substrates. Opt. Lett. 24(20), 1422–1424 (1999)CrossRefGoogle Scholar
  47. 47.
    Karabacak, T., Wang, G.C., Lu, T.M.: Quasi-periodic nanostructures grown by oblique angle deposition. J. Appl. Phys. 94(12), 7723–7728 (2003)CrossRefGoogle Scholar
  48. 48.
    Kelly, K.L., Coronado, E., Zhao, L.L., Schatz, G.C.: The optical properties of metal nanoparticles: The influence of size, shape, and dielectric environment. J. Phys. Chem. B 107(3), 668–677 (2003)CrossRefGoogle Scholar
  49. 49.
    Kerker, M.: The scattering of light and other electromagnetic radiation. Academic Press, New York (1969)Google Scholar
  50. 50.
    Kolzer, J., Österschulze, E., Deboy, G.: Thermal imaging and measurement techniques for electronic materials and devices. Microelectron. Eng. 31(1), 251–270 (1996)CrossRefGoogle Scholar
  51. 51.
    Kutsay, O.M., Gontar, A.G., Novikov, N.V., Dub, S.N., Tkach, V.N., Gorshtein, B.A., Mozkova, O.V.: Diamond-like carbon films in multilayered interference coatings for IR optical elements. Diamond Relat. Mater. 10(9–10), 1846–1849 (2001)CrossRefGoogle Scholar
  52. 52.
    Lang, W., Kuhl, K., Sandmaier, H.: Absorbing layers for thermal infrared detectors. In: International Conference on Solid-State Sensors and Actuators, 1991. Digest of Technical Papers, TRANSDUCERS’91, pp. 635–638 (1991)Google Scholar
  53. 53.
    Lehman, J., Theocharous, E., Eppeldauer, G., Pannell, C.: Gold-black coatings for freestanding pyroelectric detectors. Meas. Sci. Technol. 14, 916–922 (2003)CrossRefGoogle Scholar
  54. 54.
    Li, L., Dobrowolski, J.A., Sankey, J.D., Wimperis, J.R.: Antireflection coatings for both visible and far-infrared spectral regions. Appl. Opt. 31(28), 6150–6156 (1992)CrossRefGoogle Scholar
  55. 55.
    Liddiard, K.C.: Thin-film resistance bolometer IR detectors. Infrared Phys. 24, 57–64 (1984)CrossRefGoogle Scholar
  56. 56.
    Lintymer, J., Gavoille, J., Martin, N., Takadoum, J.: Glancing angle deposition to modify microstructure and properties of sputter deposited chromium thin films. Surf. Coat. Technol. 174–175, 316–323 (2003)CrossRefGoogle Scholar
  57. 57.
    Looyenga, H.: Dielectric constants of heterogeneous mixtures. Physica 31, 401–406 (1965)CrossRefGoogle Scholar
  58. 58.
    Macdonald, D.H., Cuevas, A., Kerr, M.J., Samundsett, C., Ruby, D., Winderbaum, S., Leo, A.: Texturing industrial multicrystalline silicon solar cells. Solar Energy 76(1–3), 277–283 (2004)CrossRefGoogle Scholar
  59. 59.
    Martin, B.R., Dermody, D.J., Reiss, B.D., Fang, M., Lyon, L.A., Natan, M.J., Mallouk, T.E.: Orthogonal self-assembly on colloidal gold-platinum nanorods. Adv. Mater. 11(12), 1021–1025 (1999)CrossRefGoogle Scholar
  60. 60.
    Maxwell Garnett, J.C.: Colours in metal glasses and metal films. Phil. Trans. R. Soc. Lond. A 203, 385–420 (1904)Google Scholar
  61. 61.
    McKnight, S.W., Stewart, K.P., Drew, H.D., Moorjani, K.: Wavelength-independent anti-interference coating for the far-infrared. Infrared Phys. 27, 327–333 (1987)CrossRefGoogle Scholar
  62. 62.
    Mie, G.: Beiträge zur Optik trüber Medien, speziell kolloidaler Metallösungen. Ann. Phys. 25(3), 377–445 (1908)CrossRefGoogle Scholar
  63. 63.
    Murmann, H.: Untersuchungen über die Durchlässigkeit dünner Metallschichten für langwellige ultrarote Strahlung und ihre elektrische Leitfähigkeit. Z. Phys. A: Hadrons and Nuclei 54(11), 741–760 (1929)Google Scholar
  64. 64.
    Nelms, N., Dowson, J.: Goldblack coating for thermal infrared detectors. Sens. Actuators A 120(2), 403–407 (2005)CrossRefGoogle Scholar
  65. 65.
    Novotny, L., Bian, R.X., Xie, X.S.: Theory of nanometric optical tweezers. Phys. Rev. Lett. 79(4), 645–648 (1997)CrossRefGoogle Scholar
  66. 66.
    Parsons, A.D., Pedder, D.J.: Thin-film infrared absorber structures for advanced thermal detectors. J. Vac. Sci. Technol. A Vacuum, Surfaces, and Films 6, 1686 (1988)Google Scholar
  67. 67.
    Pfund, A.H.: Bismuth black and its applications. Rev. Sci. Instr. 1, 397 (1930)CrossRefGoogle Scholar
  68. 68.
    Pfund, A.H.: Optical properties of metallic and crystalline powders. J. Opt. Soc. Am. 23(10), 375 (1933)CrossRefGoogle Scholar
  69. 69.
    Raguin, D.H., Morris, G.M.: Analysis of antireflection-structured surfaces with continuous one-dimensional surface profiles. Appl. Opt. 32(14), 2582–2598 (1993)CrossRefGoogle Scholar
  70. 70.
    Rancourt, J.: Optical thin films: user handbook. SPIE Press, Bellingham (1996)Google Scholar
  71. 71.
    Raschke, G., Kowarik, S., Franzl, T., Sönnichsen, C., Klar, T.A., Feldmann, J., Nichtl, A., Kurzinger, K.: Biomolecular recognition based on single gold nanoparticle light scattering. Nano Letters 3(7), 935–938 (2003)CrossRefGoogle Scholar
  72. 72.
    Rayleigh, L.: On reflection of vibrations at the confines of two media between which the transition is gradual. Proc. Lond. Math. Soc. s1–11(1), 51 (1879)Google Scholar
  73. 73.
    Robbie, K., Beydaghyan, G., Brown, T., Dean, C., Adams, J., Buzea, C.: Ultrahigh vacuum glancing angle deposition system for thin films with controlled three-dimensional nanoscale structure. Rev. Sci. Instr. 75(4), 1089–1097 (2004)CrossRefGoogle Scholar
  74. 74.
    Robbie, K., Brett, M.J.: Sculptured thin films and glancing angle deposition: Growth mechanics and applications. J. Vac. Sci. Technol. A 15(3), 1460–1465 (1997)CrossRefGoogle Scholar
  75. 75.
    Robitaille, P.M.: On the validity of Kirchhoff’s law of thermal emission. IEEE Trans. Plasma Sci. 31(6), 1263–1267 (2003)CrossRefGoogle Scholar
  76. 76.
    Rogalski, A.: Infrared detectors: status and trends. Progr. Quant. Electron. 27(2–3), 59–210 (2003)CrossRefGoogle Scholar
  77. 77.
    Sancho-Parramon, J., Janicki, V.: Effective medium theories for composite optical materials in spectral ranges of weak absorption. J. Phys. D Appl. Phys. 41, 215304 (2008)Google Scholar
  78. 78.
    Schossig, M., Norkus, V., Gerlach, G.: Broadband nickel-chromium thin-film absorber for thermal sensors. In: Proceedings of the Eurosensors XXII, pp. 873–876. Dresden, (2008)Google Scholar
  79. 79.
    Schossig, M., Norkus, V., Gerlach, G.: High-performance pyroelectric infrared detectors. In: Proceedings of the 11th International Conference and Exhibition on Infrared Sensors and Systems OPTO/IRS2, pp. 191–196 (2009)Google Scholar
  80. 80.
    Seo, D., Park, J.H., Jung, J., Park, S.M., Ryu, S., Kwak, J., Song, H.: One-dimensional gold nanostructures through directed anisotropic overgrowth from gold decahedrons. J. Phys. Chem. C 113(9), 3449–3454 (2009)CrossRefGoogle Scholar
  81. 81.
    Setiadi, D., He, Z., Hajto, J., Binnie, T.: Application of a conductive polymer to self-absorbing ferroelectric polymer pyroelectric sensors. Infrared Phys. Technol. 40(4), 267–278 (1999)CrossRefGoogle Scholar
  82. 82.
    Sharma, V., Park, K., Srinivasarao, M.: Colloidal dispersion of gold nanorods: Historical background, optical properties, seed-mediated synthesis, shape separation and self-assembly. Mat. Sci. Eng. R 65, 1–38 (2009)CrossRefGoogle Scholar
  83. 83.
    Shuxing, G.: Study on antireflective coatings of PbTe/PbSnTe heterojunction infrared detectors. Int. J. Infrared Millimeter Waves 11(11), 1285–1297 (1990)CrossRefGoogle Scholar
  84. 84.
    Silberg, P.A.: Infrared absorption of three-layer films. J. Opt. Soc. Am. 47(7), 575–578 (1957)CrossRefGoogle Scholar
  85. 85.
    Sipe, J.E., Boyd, R.W.: Nanocomposite materials for nonlinear optics based on local field effects. Top. Appl. Phys. 82, 1–18 (2002)CrossRefGoogle Scholar
  86. 86.
    Stuart, D.A., Haes, A.J., Yonzon, C.R., Hicks, E.M., Van Duyne, R.P.: Biological applications of localised surface plasmonic phenomenae. In: IEEE Proceedings of the Nanobiotechnology, vol. 152 (2005)Google Scholar
  87. 87.
    Suchaneck, G., Norkus, V., Gerlach, G.: Improving responsivity of uncooled IR sensor arrays by optimized antireflective coatings. In: Proceedings of the 6th International Conference and Exhibition on Infrared Sensors and Systems OPTO/IRS2, pp. 139–142 (2000)Google Scholar
  88. 88.
    Taflove, A., Hagness, S.C., et al.: Computational electrodynamics: The finite-difference time-domain method. Artech House, Norwood (1995)Google Scholar
  89. 89.
    Thelen, A.: Design of optical interference coatings. McGraw-Hill, New York (1989)Google Scholar
  90. 90.
    Ting, C.J., Huang, M.C., Tsai, H.Y., Chou, C.P., Fu, C.C.: Low cost fabrication of the large-area anti-reflection films from polymer by nanoimprint/hot-embossing technology. Nanotechnology 19, 205301 (2008)Google Scholar
  91. 91.
    Turnbull, A.A.: The application of heat-collector fins to reticulated pyroelectric arrays. In: J.S. Seeley (ed.) SPIE Conference Series, vol. 588, pp. 38–43 (1985)Google Scholar
  92. 92.
    Vollmer, M., Kreibig, U.: Optical properties of metal clusters. In: Springer Series in Material Science, vol. 25. Springer-Verlag, Heidelberg (1995)Google Scholar
  93. 93.
    Whatmore, R.W.: Pyroelectric devices and materials. Rep. Prog. Phys. 49(12), 1335–1386 (1986)CrossRefGoogle Scholar
  94. 94.
    Woltersdorff, W.: Über die optischen Konstanten dünner Metallschichten im langwelligen Ultrarot. Z. Phys. A Hadrons and Nuclei 91(3), 230–252 (1934)Google Scholar
  95. 95.
    Xi, J.Q., Schubert, M.F., Kim, J.K., Schubert, E.F., Chen, M., Lin, S.Y., Liu, W., Smart, J.A.: Optical thin-film materials with low refractive index for broadband elimination of Fresnel reflection. Nat. Photonics 1, 176–179 (2007)Google Scholar
  96. 96.
    Yang, W.H., Schatz, G.C., Van Duyne, R.P.: Discrete dipole approximation for calculating extinction and Raman intensities for small particles with arbitrary shapes. J. Chem. Phys. 103(3), 869–875 (1995)CrossRefGoogle Scholar
  97. 97.
    Ye, D.X., Karabacak, T., Lim, B.K., Wang, G.C., Lu, T.M.: Growth of uniformly aligned nanorod arrays by oblique angle deposition with two-phase substrate rotation. Nanotechnology 15(7), 817–821 (2004)CrossRefGoogle Scholar
  98. 98.
    Yon, J.J., Biancardini, L., Mottin, E., Tissot, J.L., Letellier, L.: Infrared microbolometer sensors and their application in automotive safety. In: Valldorf, J., Gessner, W. (eds.) Advanced Microsystems for Automotive Applications 2003, pp. 137–157. Springer-Verlag, New York (2003)Google Scholar
  99. 99.
    Yu, Z., Gao, H., Wu, W., Ge, H., Chou, S.Y.: Fabrication of large area subwavelength antireflection structures on Si using trilayer resist nanoimprint lithography and liftoff. J. Vac. Sci. Technol. B 21, 2874 (2003)CrossRefGoogle Scholar

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Authors and Affiliations

  1. 1.Solid-State Electronics LaboratoryTechnische Universität DresdenDresdenGermany

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