Formation Mechanism of Rutile TiO₂ Rods on Fluorine Doped Tin Oxide Glass

We report the formation mechanism of rutile TiO₂ rods grown directly on fluorine doped tin oxide (FTO) glass by hydrothermal process at 130 °C. Through SEM images, we could monitor detailed nucleation and crystal growth process of TiO₂ nanorods. The TiO₂ nanorods started to nucleate and grow along the grain boundaries of SnO₂ on FTO glass. As the reaction time increased, fine TiO₂ nanorods started to encounter each other on (110) faces and merge, resulting in growth of micrometer scale rods in [001] direction. Through TEM, SAED, and XRD analyses, we propose that the nucleation of TiO₂ on SnO₂ grain boundaries occurs by Ostwald ripening (OR) while the merging of small TiO₂ nanorods for the formation of larger rods occurs through oriented attachment (OA). The merged nanorods grow toward [001] direction to reduce surface energy.