Atomic-scale modeling of the thermal decomposition of titanium(IV)-isopropoxide

Abstract

The metal-organic (MO) compound titanium(IV)-isopropoxide (Ti(OiPr)4, TTIP) has tremendous technological relevance for thin film growth and coating technologies, offering a low-temperature deposition route for titania and titanium-oxide-based compounds. Thermal decomposition via the release of organic ligands, a key process in any TTIP-based synthesis approach, is commonly assumed to take place only via the beta-hydride elimination process. Here, we present reactive force field molecular dynamics (ReaxFF-MD) and metadynamics simulations that challenge this conventionally assumed scenario by revealing different, energetically preferred reaction pathways. The complete reaction scheme for the TTIP thermolysis, along with the statistics for the different ligand liberation steps and the associated reaction barriers for the bond dissociation events is presented. ReaxFF-MD simulations performed in the dilute limit realistically capture typical thin film deposition conditions, which in combination with metadynamics data, which produces free energies, constitutes a very powerful tool to quantitatively analyze the reaction dynamics of MO-based thin film growth processes and provide an atomic-scale understanding of how the remaining organic ligands detach from different titanium-containing MO fragments. The approach presented here allows for effective and straightforward identification of the undesirable temperature biasing effects in ReaxFF-MD and represents a predictive framework to identify chemical reaction pathways relevant to film growth processes at the atomic scale under realistic, experimentally relevant conditions. It enables computationally informed engineering of MO molecules with tailored decomposition and reaction pathways, and thus rapid and cost-effective advancements in MO molecule design for existing and future applications of thin film deposition and coating processes.