abstract
The mechanisms of growth of TiO2 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.
keywords
SURFACE-REACTION MECHANISMS; OXYGEN STRETCHING FREQUENCIES; TITANIUM-DIOXIDE; ACETIC-ACID; FTIR SPECTROSCOPY; CARBOXYLATE COORDINATION; OZONE; FORMATE; OXIDE; ALKOXIDES
subject category
Chemistry; Materials Science
authors
Ramos, KB; Clavel, G; Marichy, C; Cabrera, W; Pinna, N; Chabal, YJ
our authors
Groups
acknowledgements
The work at the University of Texas at Dallas was supported by the National Science Foundation (CHE-0911197) and partially by the NHARP of the Texas Higher Education Board. K.B.R. was partially supported by the Consejo Nacional de Ciencia y Tecnologia (CONACyT), Mexico. The work at the University of Aveiro was supported by the FCT project (PTDC/CTM/098361/2008) and FCT grant (SFRH/BD/71453/2010).