Monika Agarwal

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. TiO 2 films deposited on sulfonate (SO 3 H-) SAMs on silicon consist of densely packed anatase crystallites, with a small quantity (10-20%) of amorphous TiO 2 . ZrO 2 -containing films deposited on SO 3 H-SAMs on silicon contain nanocrystallites of tetragonal zirconia and amorphous basic zirconium sulfate. Amorphous thin films of basic yttrium carbonate (which crystallize to cubic Y 2 O 3 on subsequent heating) were deposited on SO 3 H-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.

Deposition of oxide thin films on silicon using organic self-assembled monolayers

Crystalline oxide thin films have been synthesized at low temperatures from aqueous liquid solutions. A key element of the approach is the use of organic self-assembled monolayers (SAMs) on the substrate to promote the growth of adherent inorganic films. A SAM is a close- packed, highly ordered array of long-chain hydrocarbon molecules, anchored to the substrate by covalent bonds. The terminating functional group on the SAM surface is chosen so as to initiate and help sustain the formation of the oxide film when the substrate is immersed in the oxide precursor solution. Synthesis, microstructural characterization, and properties of TiO2, ZrO2, SiO2, and Y2O3 films are surveyed. Crystalline films were formed either directly from solution, or through subsequent heat treatments at temperatures that in most cases were lower than typical sol-gel or vapor phase deposition processes. All depositions were from aqueous solutions onto single-crystal (100) silicon. The ability to produce patterned films on a micron scale has been demonstrated, taking advantage of the selective deposition characteristics towards different surface functional groups of the SAM. The role of the SAM in oxide film formation is discussed.