TiO2–SiO2 sol–gel hybrid films and their sensitivity to gaseous toluene

In this work, different TiO2–R-SiO2 xerogel films (R = methyl) were obtained by the sol–gel method. The films were prepared with contents of the two principal components varied in large extent (100% TiO2, 80% TiO2–20% R-SiO2, 60% TiO2–40% R-SiO2, 40% TiO2–60% R-SiO2, 20% TiO2–80% R-SiO2, 15% TiO2–85% R-SiO2, 10% TiO2–90% R-SiO2, 5% TiO2–95% R-SiO2, and 100% R-SiO2) under several annealing temperatures (room temperature and 100 °C). Films were applied onto planar substrates and they were characterized by spectral ellipsometry. It was found that refractive indices of the prepared films ranged from 1.4 to 1.85 at 650 nm and that they increased with the TiO2 content as well as the packing density. Films were also applied onto silica optical fibers. These films were characterized in experiments where the fibers were excited by an inclined collimated beam at 670 nm and angular distributions of the output optical power were measured. Time responses of the films on the fibers to contact with toluene vapours were also determined and film compositions exhibiting high responses to toluene were determined from these measurements. A detection limit of about 0.07 vol.% of toluene was found for the film composition of 10% TiO2–90% R-SiO2.