Titanium oxide (TiO2) thin films can be prepared by controlled hydrolysis of a titanium tetrachloride (TiCl4) precursor in an aqueous solution at temperatures below 100°C. As part of an effort to understand the formation of such TiO2 films, the kinetics of the nucleation, growth, and aggregation of TiO2 nanoparticles in aqueous solutions of TiCl4 were studied using dynamic light scattering and a transmission electron microscope (TEM). A higher degree of supersaturation, produced by a higher solution temperature, a higher concentration of TiCl4, or a higher pH, results in a shorter nucleation induction time, a faster initial growth/aggregation rate, and a larger aggregate size. The interfacial energy of TiO2 nanoparticles was found to be 0.072 J/m2 from the homogeneous nucleation theory. Further investigations by a high‐resolution scanning electron microscope (SEM) and TEM for the as‐deposited films showed the structure hierarchy organized from nanocrystalline particles precipitated in the supersaturated solution. As a result, the effect of solution conditions on the nucleation, growth, and aggregation of TiO2 nanoparticles can provide useful guidance for tailoring of microstructures of the TiO2 films.

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We explored effects of the degree of supersaturation, which depends on solution concentration, pH, and temperature, on the development of microstructures of the TiO 2 thin films deposited from the controlled hydrolysis of TiCl 4 aqueous solutions. It was shown that, with precursor (TiCl 4 ) solution of low degree of supersaturation, a porous flower-like dendritic structure was synthesized, while a densely packed particulate nanostructure was obtained with that of high degree of supersaturation. The former morphology was attributed to the directional growth of TiO 2 crystals from the already-deposited films, whereas the latter to the bulk precipitated TiO 2 nanoparticles nucleated in the solution, followed by their attachment and self organization. By establishing the processing-microstructure relations, this study provided a means of generating a wide spectrum of reproducible TiO 2 microstructures using the low-temperature aqueous solution processing.

In our previous reports (Part I and II), we have identified precursor “supersaturation” as a key parameter to control the precipitation behavior of titania nanoparticles in a temperature‐driven hydrolysis process from the chemical bath of soluble titanium salt. Through this protocol, a methodology was developed to grow titania films with controlled microstructures and phases. In this study, we deposited titania films containing anatase or rutile as a dominant phase along with microstructures of various film densities, which were characterized for their dielectric, optical, photoelectrochemical, and mechanical properties. Specific microstructures and the constituting phases were responsible for a wide variation of such properties of titania thin films. This study aims to provide the systematic explanation for evolution of the phases as a function of the degree of supersaturation, along with the discussion of their effects on the aforementioned engineering properties.

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