Nanoporous glass-ceramics transparent in infrared range to be used as optical sensor-Mechanical and viscoelastic properties of the TAS (Te-As-Se) glass
GeS₂-Sb₂S₃-CsCl glass-ceramics with nanoporous surfaces were synthesized and tested as optical elements. The nanoporosity is obtained through a two-step process, including controlled nucleation of CsCl nuclei in the glass matrix followed by selective etching of the nuclei with an acid solution. The porous surface is several hundred nanometers thick and results in a surface area increase of almost four orders of magnitudes. The pores size is approximately 150 nm and can be tailored by controlling the nucleation process and the etching time. It is shown that the creation of the nanoporous surface does not critically affect the optical transmission of these infrared transparent glass-ceramics. These materials can therefore be used for the design of optical elements and an ATR (Attenuated Total Reflections) plate with nanoporous surface was fabricated and tested as an optical infrared sensor. The porous element shows higher detection sensitivity in initial experiments with a coating of silane molecules. The TAS (Te₂As₃Se₅) infrared glass, used as optical sensor in many fields of applications (medicine, environment, etc), exhibits poor mechanical properties rapidly that enable it to be used. Its mechanical properties have been investigated as a function of time and environment. From a general observation, air and vacuum have dramatic effects on TAS fibers tensile strength. When ageing under static stress, they exhibit an increase of tensile strength. The structural relaxation phenomenon is hypothesized to explain these results. The coordination number, , which is a rough measure of the network rigidity, has an influence on the TAS mechanical properties. It is shown that the TAS glass exhibits photosensitive effects. This effect seems to be only a surface effect, not a volume effect in the sense that light has no influence on the kinetic of a stress relaxation experiment. Due to their low glass transition temperature, TAS fibers exhibit viscoelastic behavior at room temperature. The study of the change of radius curvature allows for the determination of constitutive laws both for the stress relaxation kinetics and the delayed elasticity process which are well described by a stretched exponential function KWW (Kolraush-Williams-Watt).
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