In Situ Infrared Spectroscopic Study of Atomic Layer-Deposited TiO₂ Thin Films by Nonaqueous Routes

Abstract

The mechanisms of growth of TiO 2 thin films by atomic layer deposition (ALD) using either acetic acid or ozone as the oxygen source and titanium isopropoxide as the metal source are investigated by in situ Fourier transform infrared spectroscopy (FTIR) and ex situ X-ray photoelectron spectroscopy. The FTIR study of the acetic acid-based process clearly shows a ligand exchange leading to the formation of surface acetate species (vibrational bands at 1527 and 1440 cm −1 ) during the acetic acid pulse. Their removal during the metal alkoxide pulse takes place via the elimination of an ester and the formation of Ti−O−Ti bonds. These findings confirm the expected ester elimination condensation mechanism and demonstrate that the reaction proceeds without intermediate surface hydroxyl species. The in situ FTIR study of the O 3 -based ALD process demonstrates similarities with the process described above, with formation of surface formate and/or carbonate species upon exposure of the surface titanium alkoxide species to ozone. These surface species are removed by the subsequent titanium isopropoxide pulse, leading to the formation of Ti−O−Ti bonds.

Mechanistic Aspects in the Formation, Growth and Surface Functionalization of Metal Oxide Nanoparticles in Organic Solvents

“…[193,200] Esterification reactions were also appliedf or atomic layer deposition( ALD) of titania from titaniumi sopropoxide and acetic acid. [203] In situ FTIR and ex situ X-ray photoelectron spectroscopy investigations confirmed the formationo fs urface acetate speciesv ia ligand exchange of the alkoxy group by carboxylates (with the elimination of the corresponding alcohol) during the acetic acid pulse, followed by the elimination of ester,a nd formation of Ti-O-Tib onds during the titanium isopropoxide pulse. This reactionp athway agreedw ith the mechanism already suggested by Pinna and co-workers before.…”

“…Long chain carboxylic acids like oleic acid not only act as reactant for esterification, but also as capping and structure directing agent . Esterification reactions were also applied for atomic layer deposition (ALD) of titania from titanium isopropoxide and acetic acid . In situ FTIR and ex situ X‐ray photoelectron spectroscopy investigations confirmed the formation of surface acetate species via ligand exchange of the alkoxy group by carboxylates (with the elimination of the corresponding alcohol) during the acetic acid pulse, followed by the elimination of ester, and formation of Ti‐ O ‐Ti bonds during the titanium isopropoxide pulse.…”

Acetic Anhydride as an Oxygen Donor in the Non‐Hydrolytic Sol–Gel Synthesis of Mesoporous TiO2 with High Electrochemical Lithium Storage Performances

“…. Water formation can only be avoided in atomic layer deposition methods, in which reactants and by‐products are flushed after each alternate pulse of metal alkoxide and acetic acid . In 1996, Vioux et al.…”

“…[9,22,23] Water formation can only be avoided in atomic layer deposition methods, in whichr eactants and byproducts are flushed after each alternate pulse of metal alkoxide and acetic acid. [24,25] In 1996, Vioux et al proposed to form acetoxyg roups in situ by the reaction of acetic anhydride with an alkoxide [Eq. (4)].…”

Atomic layer deposition: an enabling technology for the growth of functional nanoscale semiconductors

“…The lattice mismatch between ZnO and GaN is lower which makes deposition of epitaxial high quality ZnO on GaN possible as well [86]. ALD of TiO 2 has been reported using several different compounds of Ti as precursors [87][88][89][90][91][92][93][94][95][96][97][98][99][100][101]. TiCl 4 is the most commonly used precursor which allows deposition of high quality TiO 2 material (refractive index as high as 2.6) at substrate temperatures ranging from 27°C to 600°C [89,99,102].…”