Water-rich conditions during titania atomic layer deposition in the 100 °C-300 °C temperature window produce films with TiIV oxidation state but large H and O content variations

Abstract

Titania films prepared by atomic layer deposition attract great attention due to the widespread application of the oxide as a photocatalytic material, or more recently, as a promising charge storage material for lithium or proton batteries. We implement here advanced tools (Ion Beam Analysis and X-ray Photoelectron Spectroscopy, aided by Ellipsometry and X-ray Diffraction) to characterize films grown in the 100 °C-300 °C temperature window, using tetrakis(dimethylamino)titanium (TMDAT) as the metal precursor and water vapor as the oxidant. We examine the outcomes of the ALD process as a function of the deposition temperature, applying equal oxidant and precursor half-cycle time lengths, which contrasts with common deposition processes where the water half-cycle is considerably shorter than that of the metal precursor. Under the present ALD scheme, n-type conductive films are obtained where the oxidation state of titanium is overwhelmingly TiIV at all temperatures, while the hydrogen content (O/Ti ratio) varies considerably, from ∼ 15 at% (∼1.8) at 100 °C to ∼ 3 at% (∼2) at 300 °C. The ideality of the ALD process is discussed through the identification of nitrogen-containing molecules detected at the oxide surfaces. By extending the structural and compositional range of ALD titania films, new opportunities of application are expected to appear.