Multi–scale simulation of hybrid inorganic–organic films
University College Cork
The discovery of novel materials and associated process chemistries is crucial for the realization of higher performance electronic devices and the progress of nanotechnology in general. Hybrid materials are a special class of materials with unusual features which are attracting great interest for a wide range of applications. The unique properties of hybrid materials arise from the combination of advantages of both building blocks, i.e., inorganic and organic, which allow material functionalities that are not present in the individual components to be engineered. The properties of these materials can be also tuned depending on the requirements of the application by the choice of the components. Hybrid films are fabricated using molecular layer deposition (MLD) technique, a variant of the widely used atomic layer deposition (ALD) technique, which enables precision and control at the atomistic scale. In recent years, many MLD processes for hybrid films have been developed. However, much less is known about the growth mechanism of hybrid MLD films. In my thesis I used first principles density functional theory (DFT) simulations to investigate the key steps in the mechanism of hybrid film deposition through MLD, to address open questions around earlier MLD experiments and to predict the most suitable precursors for deposition processes. We build up an atomistic level understanding of the growth chemistry of different types of hybrid films by modelling the relevant MLD deposition processes. In particular, deep investigations on how precursor atomic structure determines film growth, stability and flexibility is carried out. We focus on the key MLD process chemistries, namely alucone and titanicone films, both of high interest for passivation layers in batteries. We assist the interpretation of experimental findings by showing for the first time why the ethylene glycol precursor performs poorly in making stable alucone films and why glycerol is better. For titaiocone films we highlight the role of the substrate and the titanium containing precursors on the initial MLD steps and in film production. We have also predicted that aromatic molecules are a good choice for stable hybrid films and their chemistry can be manipulated without impacting on the stability and this has been borne out by experimental work.Furthermore, we predict suitable MLD chemistries for production of hybrid antibacterial materials. We also study the diffusion phenomena of MLD precursors into polymeric substrates with the vapour phase infiltration (VPI) technique to understand the chemical interactions and corroborate the experimental data on Ru nanostructures and self-healing materials. Finally, we provide atomic level understanding around novel organometallic precursors and predict their applicability for deposition of oxide and hybrid thin films. The work in my thesis illustrates the key role of atomistic simulations in materials and process development.
DFT , Hybrid films , Organic/inorganic precursors , Growth mechanism , MLD , ALD
Muriqi, A. 2023. Multi–scale simulation of hybrid inorganic–organic films. PhD Thesis, University College Cork.