Growth of Titanium Oxide Nanostructures on γ-Al2O3 by Atomic Layer Deposition

This paper presents results on control over the surface composition, surface structure, and pore texture of core/shell materials, as exemplified by the growth of conformal titanium oxide nanocoatings on gamma-Al2O3 by atomic layer deposition via sequential and alternating exposure of the alumina to TiCl4 and H2O vapor. The alumina surface and growing titanium oxide layer are shown to influence the characteristics of the forming two-phase material. Increasing the amount of titanium via an increase in the number of deposition cycles leads to a systematic decrease in specific surface area, pore volume, and pore size, which points to conformal pore filling in the starting matrix by a titanium oxide layer. The composition and structure of the titanium oxide coating are influenced by its thickness and the nature of the starting matrix. The coordination state of the titanium oxide in monolayer structures is characteristic of the titanium oxide polyhedra in aluminum titanate. As the distance from the top monolayer to the surface of the matrix (coating thickness) increases, an X-ray amorphous layer is formed in which the oxygen coordination environment of the titanium is similar to that in an anatase-like phase of titanium dioxide.