Deposition mechanism of anatase TiO 2 from an aqueous solution and its site-selective deposition

Abstract

We have developed a novel method for site-selective deposition (SSD) of anatase TiO 2 thin films using a seed layer based on the knowledge obtained by the evaluation of deposition mechanism. The nucleation and initial growth of anatase TiO 2 were found to be accelerated on amorphous TiO 2 thin films compared with the substrates modified by silanol, amino, phenyl or octadecyl groups. Micropattern having octadecyl group regions and amorphous TiO 2 regions was immersed in the aqueous solution at pH 1.5 to be used as a template for SSD. Anatase TiO 2 was selectively deposited on amorphous TiO 2 regions to form a micropattern of anatase TiO 2 thin film in an aqueous solution. Furthermore, deposition mechanism of anatase TiO 2 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 TiO 2 thin films in the supersaturated solution at pH 2.8. On the other hand, TiO 2 was deposited on self-assembled monolayers (SAMs) without the adhesion of TiO 2 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 TiO 2.