Abstract

It is a common finding that titanocene-derived precursors do not yield TiO2 films in atomic layerdeposition (ALD) with water. For instance, ALD with Ti(OMe)4 and water gives 0.5 A ˚ /cycle,while TiCp*(OMe)3 does not show any growth (Me = CH3, Cp* = C5(CH3)5). From massspectrometry we found that Ti(OMe)4 occurs in the gas phase practically exclusively as amonomer. We then used first principles density functional theory (DFT) to model the ALDreaction sequence and find the reason for the difference in growth behaviour. Both precursorsadsorb initially via hydrogen-bonding. The simulations reveal that the Cp* ligand ofTiCp*(OMe)3 lowers the Lewis acidity of the Ti centre and prevents its coordination to surface O(‘densification’) during both of the ALD pulses. The effect of Cp* on Ti seems to be both steric(full coordination sphere) and electronic (lower electrophilicity). This crucial step in the sequenceof ALD reactions is therefore not possible in the case of TiCp*(OMe)3 + H2O, which means thatthere is no deposition of TiO2 films.

Published in

Physical Chemistry Chemical Physics
2012, volume: 14, number: 22, pages: 7954-7964

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