Fabrication of titania-coated silica fibers and effect of substrate shape on coating growth rate

Titania coating was fabricated on fused silica glass fibers of 4-6 μm in diameter by the hydrolysis of Ti-tetraethoxide in ethanol at 20 °C. Changes in the coating thickness with the deposition time were examined by scanning electron microscopy and compared with those on flat soda-lime glass substrate examined by atomic force microscopy. Uniform titania coating was obtained, but severe cracking occurred on coatings thicker than 150 nm due to isotropic shrinkage during the drying process. The faster growth rate of coating on fiber than that on flat substrate could be explained by employing an ‘adhesion growth model.’ X-ray diffractometry showed that titania coating on fused silica glass plate was transformed to anatase-phase TiO₂ by annealing in air at 300 °C. This indicates that the titania coating on a fused silica glass substrate becomes crystalline after annealing at that temperature.