Abstract
Atomic/molecular layer deposition (ALD/MLD) processes based on TiCl4 as the metal source, and hydroquinone (HQ), 4-aminophenol (AP), p-phenylenediamine (PDA) or 4,4′-oxydianiline (ODA) as the organic precursor are systematically investigated to shed light on the factors affecting the inorganic-organic thin film growth. All the four ALD/MLD processes yield amorphous Ti-organic thin films which are here characterized by ex-situ X-ray reflectivity and Fourier transform infrared measurements for the film thickness and bonding scheme. First principles modelling results are presented to explore differences in the interaction of organic precursors with surface-bound TiCl4. For the TiCl4+AP process the high growth rate achieved, i.e. ca. 10 Å per one ALD/MLD cycle, essentially corresponds to the ideal thickness of the [Ti-O-C6H4N-Ti] building unit. For both the ODA- and PDA-based processes the growth rates are considerably lower, while the TiCl4+HQ process yields the hybrid film with an intermediate growth rate. We attribute these observations to (i) the higher reactivity of the OH groups in comparison to the NH2 groups towards TiCl4, and (ii) the higher tendency of a heterobifunctional organic precursor to orientate vertically and avoid unwanted double reactions on the surface.
Highlights
Inorganic-organic hybrid materials have potential to possess exciting combinations of properties singly seen for inorganics or organics in conventional materials
Atomic/molecular layer deposition (ALD/MLD) processes based on TiCl4 as the metal source, and hydroquinone (HQ), 4-aminophenol (AP), p-phenylenediamine (PDA) or 4,4′-oxydianiline (ODA) as the organic precursor are systematically investigated to shed light on the factors affecting the inorganic-organic thin film growth
It should be emphasized that the steric hindrance is a common phenomenon even in conventional Atomic layer deposition (ALD) of simple inorganic thin films [4,12], while the double-surface-reaction issue has been observed in ALD/MLD when using for example ethylene glycol as the organic precursor [8,11]
Summary
Inorganic-organic hybrid materials have potential to possess exciting combinations of properties singly seen for inorganics or organics in conventional materials. It should be emphasized that the steric hindrance is a common phenomenon even in conventional ALD of simple inorganic thin films [4,12], while the double-surface-reaction issue has been observed in ALD/MLD when using for example ethylene glycol as the organic precursor [8,11] Until this day there are already a wide variety of ALD/MLD processes for different hybrid inorganic-organic materials, in particular the approach has been extended – besides those of typical ALD elements (Al, Zn, Ti, Zr) – to a number of different metal components (transition metals, lanthanides, s-block elements) [14,15,16,17,18,19,20,21,22,23,24,25]. First princi ples density functional theory (DFT) simulations give further insights into the binding of the different organic functional groups and help rationalise the experimental results
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