Role of titanium and organic precursors in molecular layer deposition of "titanicone" hybrid materials.

The development of hybrid inorganic-organic films with well-controlled properties is important for many applications. Molecular layer deposition (MLD) allows the deposition of these hybrid films using sequential, self-limiting reactions, similar to atomic layer deposition (ALD). In this paper, we use first principles density functional theory (DFT) to investigate the growth mechanism of titanium-containing hybrid organic-inorganic MLD films, known as "titanicones". We investigate in detail the chemistry between the most common Ti precursors, namely titanium tetrachloride (TiCl 4 ) and tetrakis(dimethylamido)titanium (Ti(DMA) 4 ), and ethylene glycol (EG) and glycerol (GL) as the organic precursors. We analyse the impact of the substrate on the initial MLD reactions in titanicone film growth using three different surface models: anatase TiO 2 , rutile TiO 2 and Al 2 O 3 . Calculated energetics show that while TiCl 4 is reactive towards the anatase and rutile TiO 2 surfaces, it is not reactive towards the Al 2 O 3 surface. Ti(DMA) 4 is reactive towards all surfaces. This is attributed to the stronger Ti-Cl bonds in TiCl 4 compared to Ti-N bonds in Ti(DMA) 4 . Ti(DMA) 4 also shows high reactivity to the organics compared to TiCl 4 . Double reactions of EG and GL with the TiCl 3 species from TiCl 4 and TiDMA species from Ti(DMA) 4 are also explored to better understand the origin of the different thicknesses of EG-titanicone and GL-titanicone films observed in experimental work. We find that EG and GL coupled with TiCl 4 can orient in a flat lying configuration on anatase while on rutile, the preferred orientation is upright. When combined with Ti(DMA) 4 , EG and GL prefer the flat lying configuration on all surfaces. This work shows that the choice of the surface and the metallic precursor has a major impact on the behaviour of organic species. DFT findings provide motivation to develop a low temperature rutile TiO 2 /titanicone film suggesting that the desired film growth could be achieved.