First Principles Modelling of Growth of Alucone Thin Films from Aromaticalcohol and Amine Precursors

Abstract

Hybrid materials composed of organic and inorganic components offer the opportunity to develop interesting materials with well-controlled properties. Molecular Layer Deposition (MLD) is a suitable technique for the controlled growth of thin, conformal hybrid films. Despite growing interest in these materials, there is, however, insufficient understanding of the atomistic mechanism of MLD film growth.In this contribution, we present a first principles investigation of the molecular mechanism of the growth of hybrid organic−inorganic thin films of aluminium alkoxides, known as ”alucones”, grown by MLD. We investigate in detail the chemistry of the MLD process between the post-TMA pulse methyl-terminated Al2O3 surface and the homo- or hetero- bifunctional aromatic compounds with hydroxy and/or amino groups as reactive groups: hydroquinone (HQ), 4-aminophenol (AP) and p-phenylenediamine (PDA). Double reactions of HQ, AP and PDA with the alumina surface are explored in detail to assist the interpretation of the experimental findings regarding the differences in alucone films grown with HQ, AP and PDA. DFT calculations show that all aromatic precursor molecules bind favorably to the methyl terminated Al2O3, via formation of Al-O and Al-N bonds and CH4 elimination. However, reaction energetics suggest lower reactivity of the amino groups with TMA in comparison to the hydroxyl groups. Therefore, we expect that in the case of the heterobifunctional precursor, AP, for which one of the groups is more reactive (OH) than the other (NH2), the unwanted double surface reactions are reduced and the organic molecule can be self-assembled in a more up-right configuration, which leads to higher growth per rates. We also analyze the reactions between the methyl-terminated Al2O3 with 2-methylhydroquinone, 2-methoxyhydroquinone, 2-chlorhydroquinone and 2-nitrohyrdoquinone to examine the influence of the activating groups –CH3, -OCH3 and deactivating groups –Cl and –NO2 on the interaction between the O site of the organic molecule and the Al site of TMA. This study contributes to the understanding of growth process of HQ-alucones, AP-alucones and PDA-alucones at the molecular level and is valuable in supporting experimental data on hybrid film growth.