Quantum chemical simulations of organometallic systems: Atomic layer deposition of dielectric films and ethylene/styrene copolymerization using a titanium metallocene catalyst

Quantum chemical simulations from first principles are advantageous because results and conclusions can be extrapolated to analogous cases without the need for reparameterization. In this work, we study two organometallic systems containing Group IV transition metals.; The use of high-kappa materials as the gate dielectric in future metal-oxide-semiconductor field effect transistors could solve the problem of exponentially increasing leakage currents due to shrinking gate oxide thicknesses. Atomic layer deposition (ALD) is an ideal candidate process for depositing high-kappa materials because it allows for excellent control of the film thickness as it deposits the material one atomic layer per exposure cycle. We have investigated the use of alternative ALD precursors such as organometallic alkylamides. In the alkylamide ALD process, an electron density halo around the metal center destabilizes the intermediate complex that traps the reaction in the metal chloride process. The relative strengths of the bonds being formed and broken result in an exothermic reaction. The favorable kinetics and thermodynamics help explain the better deposition characteristics seen experimentally. With this knowledge, guidelines for precursor selection have been developed.; Syndiotactic polystyrene (sPS) is a semi-crystalline chemically-resistant thermoplastic with high melting (Tm = 270°C) and glass transition (Tg = 100°C) temperatures. One approach to improving the physical properties of sPS is to incorporate polyethylene (PE) blocks into the sPS chain. Many attempts to prepare sPS/ethylene block copolymers have failed. In an effort to elucidate the mechanisms, we performed quantum chemical calculations for the olefin insertion processes during catalysis. The Ti(IV)+ species polymerizes ethylene. The Ti(III) species CpTiMe+ was found to be active for both ethylene and styrene polymerization in the gas phase; however, coordination of an aromatic molecule to the Ti(III) + center inhibits ethylene polymerization in solution. A stable radical could be used to change the oxidation state of titanium in situ if the titanium-radical bond is sufficiently weak. The effect of substituting alternative electron-donating ligands on the titanium-radical bond energy is found to be much larger than generally expected previously.