Atomic layer deposition of photocatalytic TiO2 thin films from TiF4 and H2O.

Titanium dioxide (TiO2) thin films were grown by atomic layer deposition (ALD) at 300-500 degrees C using TiF4 and H2O as precursors. The films were characterized by FESEM, EDX, UV/Vis and XRD techniques. Two glass types, soda lime and borosilicate, were used as the substrate materials. It was found that the type of the glass substrate had a very strong influence on the growth and properties of the resulting films. At substrate temperatures of 400 and 500 degrees C, the growth rates on borosilicate were 0.8 and 1.0 A per cycle, respectively, and the films were mainly anatase. With the same deposition conditions on soda lime, rutile phase was formed and the growth rates were 1.1 and 1.5 A per cycle, respectively. Growth saturation was confirmed for both glass substrates at 400 degrees C by varying the pulse lengths of the precursors. Both anatase and rutile films prepared at 400-500 degrees C possessed photocatalytic activity in degrading stearic acid under UV and visible light, whereas the films prepared at 300 degrees C had virtually no activity. All the films, including those prepared at 300 degrees C, turned superhydrophilic under UV light.