Oxidised porous silicon impregnated with Congo Red for chemical sensoring applications
Résumé
A method to impregnate OPS by means of a suitable CR solution has been developed, taking into account properties of solvent (e.g. b.p. polarity, etc.) and environmental conditions (e.g. vacuum and heating) in order to enhance and optimise drying and filling of the pores of the material. Presence of CR in depth has been investigated by means of micro-Raman spectroscopy. A good transmittance of the porous layer, before impregnation, has been found by means of spectroscopic measurements in the visible spectral range, in Specular Reflectance mode. An absorption band, centred on about 490 nm, related to the presence of CR inside the pores, appears after impregnation by the dye, whereas that shifts to ~ 650 nm after exposition to acid vapours. The shift is reversible, that is the initial conditions are restored by exposition to basic vapours. This composite material is interesting for achievement of waveguides acting as chemical sensors optically monitored. By this way, bilayers of porous material have been performed for the realisation of planar waveguides. Several porosity values for the guiding layer have been attempted to define the bestconfiguration for the waveguides at 633 nm. After filling with CR, how the light is guided depending on the pH has been studied.