Atomic Layer Deposition of Photocatalytic TiO2 Thin Films from Titanium Tetramethoxide and Water

Titanium dioxide thin films were grown by atomic layer deposition (ALD) at 200–400 °C from a new titanium precursor, titanium tetramethoxide, and water. As compared with other titanium alkoxides studied earlier, titanium methoxide shows the highest stability with respect to thermal decomposition, and can thus be used over the widest range of temperatures. The films deposited at 250 °C and above were polycrystalline with the anatase structure, whereas those deposited at 200 °C were amorphous. Except for the film deposited at 200 °C, the films contained only minor amounts of carbon and hydrogen residues. The crystalline films were shown to have photocatalytic activity in decomposing both methylene blue in aqueous solution, and solid stearic acid coated on the film surface. A new Ti precursor is examined for the preparation of TiO2 thin films by ALD at 200–400°C. Titanium methoxide is identified as the alkoxide that allows the widest range of deposition temperatures. Films deposited from titanium tetramethoxide and water at 250 °C are shown to be crystalline anatase of high purity, and photocatalytically active in decomposing methylene blue in aqueous solution and solid stearic acid coated on the film surface. Films deposited at 200 °C are amorphous and photocatalytically inactive. With the exception of films prepared at 200 °C, films contain only minor amounts of carbon and hydrogen residues.