Synthesis of 3-Glycidoxypropyltrimethoxysilane-TiO2 UV-sensitive waveguides

A hybrid organic-inorganic sol-gel material based on 3-(glycidoxypropyl)-trimethoxysilane (GPTMS), an organically modified alkoxide containing an epoxy ring in the organic functional group, and titanium isopropoxide Ti(OPri)4 has been synthesised. The presence of Ti alkoxide is important in order to increase the refractive index and to improve the mechanical and physical properties of the film. A basic catalysis has been used to perform the hydrolysis/condensation reactions of the inorganic network and to preserve the presence of unreacted epoxy rings. The epoxy groups are thus available in the final solid state films for the UV-photopolymerization process. The photopolymerization allows one to increase the refractive index and to pattern the film directly. The modification of the hybrid sol–gel TiO2 matrix microstructure during the thermal treatment and the interaction with the UV light have been investigated by FT-IR and UV-Vis spectroscopies, DTA and TGA thermal analysis. The sol-gel film thickness and roughness have been analyzed by a profilometer: the films possess high optical quality and well controlled thickness, ranging from 500 nm to 2 μm. The refractive index of sol-gel thin films was measured by m-line spectroscopy and ellipsometry. An increase of the refractive index in the range 0,02÷0,1 was achieved, depending on the UV irradiation dose.