Self-organization of TiO2 nanoparticles in thin films

Nanocrystalline titanium dioxide colloids have been synthesized using a sol-gel technique followed by growth under hydrothermal conditions in a basic environment at temperatures between 190 and 270 degrees C. Thin films have been made from aqueous suspensions of these colloids. X-ray analysis showed the colloids to be primarily the anatase crystal phase. Scanning electron microscopy (SEM) revealed a predominantly rodlike particle morphology after growth at lower temperatures and the formation of principally truncated tetragonal or tetrahydral bipyramidal nanocrystallites following growth at higher temperatures. The rodlike particles self-organize into regular cubic arrays with the long axis of the rods aligned perpendicular to the film surface. This self-organization is dependent upon the base used in colloidal synthesis and also upon the dielectric constant of the medium used during film formation.