Deposition mechanism of anatase TiO2 from an aqueous solution and its site-selective deposition

We have developed a novel method for site-selective deposition (SSD) of anatase TiO2 thin films using a seed layer based on the knowledge obtained by the evaluation of deposition mechanism. The nucleation and initial growth of anatase TiO2 were found to be accelerated on amorphous TiO2 thin films compared with the substrates modified by silanol, amino, phenyl or octadecyl groups. Micropattern having octadecyl group regions and amorphous TiO2 regions was immersed in the aqueous solution at pH 1.5 to be used as a template for SSD. Anatase TiO2 was selectively deposited on amorphous TiO2 regions to form a micropattern of anatase TiO2 thin film in an aqueous solution. Furthermore, deposition mechanism of anatase TiO2 in an aqueous solution has been evaluated in detail. The adhesion of homogeneously nucleated particles to the amino group surface by attractive electrostatic interaction caused rapid growth of TiO2 thin films in the supersaturated solution at pH 2.8. On the other hand, TiO2 was deposited on self-assembled monolayers (SAMs) without the adhesion of TiO2 particles regardless of the type of SAM in the solution at pH 1.5 whose degree of supersaturation is low due to high concentration of H+. Additionally, the orientation of films deposited on all SAMs was shown to be improved by enlarging the reaction time regardless of the kind of SAM or pH. It is conjectured that the adsorption of anions to specific crystal planes caused c-axis orientation of anatase TiO2.