Atomic layer deposition of titanium phosphate on silica nanoparticles

Titanium phosphate was deposited on silica nanoparticles by atomic layer deposition (ALD). The precursors were titanium tetrachloride (TiCl4), trimethylphosphate ((MeO)(3)PO), and water. Depositions were done at 150-300 degrees C employing a variety of pulse sequences which altered the self-limiting deposition process. Using the pulse sequence TiCl4-H2O-(MeO)(3)PO-H2O, the process was self-limiting at 200 degrees C, and <= 0.3 at.% Cl was incorporated into the material. With the pulse sequence TiCl4-H2O-(MeO)(3)PO, the process was not completely self-limiting at 200 degrees C and slightly more Cl incorporation occurred. Using the pulse sequence TiCl4-(MeO)(3)PO, the process was not self-limiting at 175 or 250 degrees C, and Cl incorporation was 0.2-2 at.%. The surface area of the material decreased from 300 m(2)/g for uncoated silica to 46 m(2)/g for silica coated with 60 ALD cycles. (C) 2012 American Vacuum Society. [DOI: 10.1116/1.3664097]