Advances in the design of heavy alkaline earth metal complexes as precursors for chemical vapor deposition
Date of Award
Doctor of Philosophy (PhD)
Alkaline earth metal, Chemical vapor deposition, Oxygen templating, Pyrazolates, Ketoiminates-beta, Electronic thin films
Chemistry | Materials Chemistry | Physical Sciences and Mathematics
The heavy alkaline earth metals, calcium, strontium, and barium, are components in thin films with electronic properties such as high-capacitance, superconductance and electroluminescence. The formation of these thin films by chemical vapor deposition (CVD) methods requires precursors that are volatile, but the high reactivity of the heavy alkaline earth metal precursors has made this challenging. Historically, heavy alkaline earth metal β-diketonates have been utilized as precursors, but their tendency towards aggregation and hydrolysis affords high molecular weight compounds with low volatility. The lack of a suitable heavy alkaline earth metal precursor is a major limiting factor in the production of these electronic thin films by CVD. As a result, improved precursor materials have been pursued, yet a number of drawbacks, including limited synthetic methodologies, lack of availability, and incorporation of undesired elements into the films, have prevented their widespread use in industry.
This thesis work focuses on the development of novel alkaline earth metal precursors based on pyrazolate and β-ketoiminate ligand systems, which are thermally robust, readily available, and devoid of undesired elements such as silicon and fluorine. One of the key factors in precursor design is control of the coordination environment of the metal, to prevent aggregation and hydrolysis, and to keep the volatility high. However, the coordination chemistry of the heavy alkaline earth metals is only in its infancy, which is a major roadblock in the design of future precursors. Concurrently with the development of new precursors, this thesis work uncovers new insights into their coordination chemistry, most significantly, the effects of agostic interactions on the thermal stability of the compounds. Secondary interactions, such as agostics and π-bonding, appear to play a large role in the coordination chemistry of these metals, with implications in the design of future precursors. Additional findings in this work reveal the reproducible formation of an alkaline earth metal-hydroxide framework with triply bridging pyrazolate ligands in novel binding modes. Furthermore, the effect of synthetic methodologies on a β-ketoiminate ligand system is presented, specifically, the use of direct metallation by ammonia activation.
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O'Brien, Anna Yosick, "Advances in the design of heavy alkaline earth metal complexes as precursors for chemical vapor deposition" (2005). Chemistry - Dissertations. Paper 45.