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13 May 2010 Mesostructured thin films as photonic crystal building blocks for sensing applications
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One-dimensional photonic crystals (1DPC) made by sequential deposition of TiO2 and SiO2 dense thin films can be used as environmental sensors by incorporating some responsive coating capable of selectively capturing the targeted molecules. The material chosen is a porous TiO2 mesostructured thin film with a narrow pore size distribution, which endows it with size selectivity adsorption properties. The deposition of such thin layer onto the dense 1D PC produces a modulation in the reflectance spectrum highly sensitive to modifications of the environment. In order to study the evolution of the optical response with the environmental changes both purely dense and hybrid multilayers were introduced into a close chamber and the partial pressure of the solvent was increased. The optical spectrum of the dense 1DPC remains unaltered by the environmental changes, while the same structure coupled to a designed mesoporous thin film displays clear and gradual modifications of the reflectance spectra when the partial vapour pressure is increased. The analysis of these spectra provides well-defined isotherms due to the adsorption and condensation of the vapour onto the pore walls presented in the mesoporous coating. Depending of the size of the pores, which is controlled by synthetic procedures, the condensation of a specific molecule can be prevented, totally different isotherms being attained.
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Nuria Hidalgo, Mauricio E. Calvo, and Hernán R. Mìguez "Mesostructured thin films as photonic crystal building blocks for sensing applications", Proc. SPIE 7713, Photonic Crystal Materials and Devices IX, 77131I (13 May 2010);

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