Complex materials structures based on metal oxide and metal composites have been proposed for novel photonic sensors. Materials involved include: SiOx
SnO_x, InO_x , ITO, TiO_x, ZnO_x, WO_x and metals such as Pt, Pd, Cu, Ag etc. They have been grown on glass and metal substrates by magnetron sputtering techniques. Special designs include optical structures that can be affected by exposure to simple oxidizing and reducing gas chemical agents as well as to external physical parameters. Zinc and tin oxide structures have been shown to offer significant temperature response and further studies are underway to induce enhanced chemical sensitivity.

In a alternative approach, hybrid materials composed of polymer or sol-gel derived silica matrices containing cobalt chloride nanocrystals are fabricated and evaluated as hybrid humidity sensors. The composite films were produced by either spin coating or casting the initial polymer/CoCl₂ or Si(EtO)₄/CoCl₂ solutions on glass substrates. CoCl₂ nanocrystallites are formed within the films due to polymer or silica cobalt chloride interactions. At various degrees of humidity the formation of such molecular complexes affects severely the surface morphology due to changes of the molecular volume which results in significant and controlled diffractive and scattering effects. The variation of the complex refractive index may also affect the process, however, playing a secondary role, in contrast to the well known colorimetric effects.

Work supported by the grant from the European Comission NANOPHOS (contract IST-2001-39112).