by Katerina Lazarova, Hussein Awala, Sebastien Thomas, Marina Vasileva, Svetlana Mintova and Tsvetanka Babeva
Sensors 2014, 14(7), 12207-12218; doi:10.3390/s140712207, http://www.mdpi.com/1424-8220/14/7/12207
Abstract: The preparation of responsive multilayered structures with quarter-wave design based on layer-by-layer deposition of sol-gel derived Nb2O5 films and spin-coated MEL type zeolite is demonstrated. The refractive indices (n) and thicknesses (d) of the layers are determined using non-linear curve fitting of the measured reflectance spectra. Besides, the surface and cross-sectional features of the multilayered structures are characterized by scanning electron microscopy (SEM). The quasi-omnidirectional photonic band for the multilayered structures is predicted theoretically, and confirmed experimentally by reflectance measurements at oblique incidence with polarized light. The sensing properties of the multilayered structures toward acetone are studied by measuring transmittance spectra prior and after vapor exposure. Furthermore, the potential of the one-dimensional photonic crystals based on the multilayered structure consisting of Nb2O5 and MEL type zeolite as a chemical sensor with optical read-out is discussed.

Keywords: one-dimensional photonic crystals; nanosized zeolites; sol-gel Nb2O5;
multilayered structures; optical sensors