Zirconia and Zirconia−ORMOSIL Planar Waveguides Prepared at Room Temperature

We describe the preparation of zirconia and hybrid zirconia−ORMOSIL planar waveguides by sol−gel technology at room temperature. Acetic acid was used as chelating agent to stabilize the zirconia precursor. Multimode light guiding was demonstrated for the first time in zirconia films prepared by the sol−gel method. The properties of the films, refraction index, thickness, and transparency as well as structural characterization using Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy (XPS), thermal analysis, and X-ray diffraction (XRD), were studied. The zirconia film contains propoxy, acetate, and hydroxyl ligands. In the zirconia−ORMOSIL films Zr−O−Si bonds were found, although homocondensation bonds are favored. The mechanism proposed for the structural results involves condensation of oligomeric species that react by ligand exchange. XRD show wide peaks at angles in area of 2ϑ = 4−10°. These peaks can be attributed to oligomeric structures with d spacing values of about 10 Å. The hybrid films are hydrophobic and XPS measurements shows that the surface is covered mainly by organic groups of the ORMOSIL. Films doped by pH indicator Methyl Red showed reversible response to acid and base vapors; this opens the possibility to use such films as waveguide-based optical sensors.