Deposition mechanism of oxide thin films on self-assembled organic monolayers

A mechanism for the deposition of oxide thin films from aqueous media at low temperatures onto functionalized organic self-assembled monolayers (SAMs) is proposed. TiO₂ films deposited on sulfonate (SO₃H-) SAMs on silicon consist of densely packed anatase crystallites, with a small quantity (10-20%) of amorphous TiO₂. ZrO₂-containing films deposited on SO₃H-SAMs on silicon contain nanocrystallites of tetragonal zirconia and amorphous basic zirconium sulfate. Amorphous thin films of basic yttrium carbonate (which crystallize to cubic Y₂O₃ on subsequent heating) were deposited on SO₃H-SAMs on silicon and also on bare silicon substrates. The proposed mechanism accounts for the formation of all of these films on the basis of aggregation processes between the deposition surface and the solid particles that are known to exist in the aqueous deposition medium. Estimates, calculated using DLVO theory, of the interaction energies between the SAM and the particles, and between the growing film and the particles, are consistent with the experimental observations.