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 degrees 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.