COMPUTATIONAL PREDICTION OF MATERIAL DEGRADATION AND REACTIVITY

<p dir="ltr">Materials are the backbone of all modern human technological advancement, from high tech semiconductor infrastructures to everyday household utensils. Hence, their properties, both chemical and mechanical, are as diverse as their wide range of applications. This necessitates a case-by-case investigation of the properties of these materials to ensure their usability in each of these applications. However, this would not only be time consuming to achieve but also resource intensive. To address this and to enable the development of high performing materials, this work studied the properties and reactivities of a wide range of organic materials, notably polymers and small molecules for semiconductor applications, using first principles – quantum chemical and semiempirical methodologies. The insights drawn from these results elucidated the reactive mechanisms of these materials and the impact of environmental stressors such as dioxygen, water and electro potential and heat on their long-term usage.</p><p dir="ltr">Dioxygen is an important material degradant that is ubiquitous in atmosphere. Due to this, numerous computational investigations in combination with experiments have sought to understand the reactions that accompanies the oxidative degradation of materials, especially polymers. However, with a multireference character owing to the closely lying frontier orbitals in its ground state, the qualitatively correct quantum chemical description of such reactions cannot be routinely investigated with popular quantum mechanical (QM) techniques such as density functional theory (DFT) or Hartree Fock-based (HF) methods. This limits the application of automated reaction prediction algorithms such as, yet another reaction package (YARP), which are mostly run on QM and semi-empirical physical methods, in its study. Hence, in addition to the DFT-based degradation reaction network that was constructed for polyethylene glycol (PEG), to study the mechanistic details of its oxidative transformation, complete active space self-consistent field method (CASSCF) computations that captures the multireference properties was carried out for a subset of the network. The resulting network is the largest reported to date for the oxidative degradation of PEG and includes pathways out to all degradants observed in earlier experimental studies with other new alternative pathways discovered. The findings captured demonstrate the applicability of reaction network characterization for efficiently exploring thermo-oxidative reaction landscapes with multireference character.</p><p dir="ltr">Conjugated polymers, otherwise known as organic semiconductors (OSCs), are unique and desired for their color changing property under electro- or chemical potential. Traditionally, they are often colored in their neutral form and transparent in oxidized form. A new class of OSCs known as anodically colored electrochromes (ACEs) which are in contrast colored in their neutral state and transparent in oxidized form show significant performance improvements over the conventional ones especially in terms of optical constrast. To ensure its commercial applicability, this work also investigated the electronic properties and the susceptibility of this material to degradation on long term exposure to oxygen, water and heat to design more stable conjugated polymers. Energy pathways for several potential reactions were explored using quantum chemistry and quantified by their Gibbs free energy and heats of reaction.</p><p dir="ltr">Lastly, this work looked into the reactivities of propargyl-based small molecule inhibitors (SMIs) in area selective depositions (ASD) to elucidate their mechanism of inhibition. ASD take advantage of the chemical contrast between material surfaces in device fabrication, where a film can be selectively grown by chemical vapor deposition on metal versus a dielectric, for instance, and can provide a path to non-traditional device architectures as well as the potential to improve existing device fabrication schemes. While ASD can be accessed through a variety of methods, the incorporation of reactive moieties in inhibitors present several advantages such as increasing the thermal stability and limiting precursor diffusion into the blocking layer. Alkyne terminated small molecule inhibitors (SMIs) – propargyl, dipropargyl and tripropargylamine – were evaluated as metal selective inhibitors. Modeling these SMIs provided insight into the binding mechanism, influence of steric and the complex polymer network formed from the reaction between inhibitors consisting of alkene, aromatic and network branchpoints. While a significant contrast in the binding of the SMIs on copper versus a dielectric was observed, residual amounts were detected on the dielectric surfaces leading to variable ALD growth rates dependent on pattern critical dimensions. This behavior can be controlled and utilized to direct film growth on patterns only above a threshold critical dimension; below this threshold both the dielectric and metal features were protected. This method provides another design parameter for ASD processes and may extend its application to more broad ranging device fabrication schemes.</p>