Online

Ackley, Brandon James

Chemistry

2020

Ph. D.

Semiconductor ceramics have been the subject of study for many years due to their usefulness in applications ranging from LED devices to computer chips. Despite the ubiquity of semiconductor ceramics in daily life, the synthesis and manufacturing of such devices is tedious, energy intensive, or have a high potential for danger. Manufacturing methods such as deposition require the use of toxic or pyrophoric gases as well as requiring the temperatures often exceeding 1,000 °C. One way to address the issues of toxicity and high thermal barriers can be found in the implementation of pre-ceramic materials; materials which are either molecular or polymeric, and can be thermolyzed to form ceramics. The hypothesis that group 13/15 compounds can be used as molecular pre-ceramic materials for the formation of III/V semiconductors was tested and found to be successful. Towards this effort, an earth-abundant iron-based catalyst was tested for catalytic activity in the activation of pnictogens and pnictogen-boranes. Additionally, stoichiometric syntheses of heavier group 13/15 compounds were explored, and the resultant compounds were found to be successful in the formation of III/V ceramics. Through the analysis of the reactivity of [CpFe(CO)2]2 as a more reactive hydrophosphination catalyst than the closely related CpFe(CO)2Me, a hypothesis that [CpFe(CO)2]2 would be a more active dehydrocoupling catalyst for phosphine-boranes than the closely related CpFe(CO)2PPh2BH3 was formed. This system was then expanded to the study of arsine-boranes, resulting in the discovery of a catalyst-free generation of a wide range of pre-ceramic materials which provide clean thermolysis to semiconductor ceramics at the lowest temperatures observed for these types of ceramics. Substitution effects, the impact of oxygen, and the effect of pre-heating treatments were analyzed during this work. Through this methodology, ceramics including BAs, BP, GaP, GaAs, and AlAs have been realized, with substantial progress made in the formation of BN, AlP, and GaN ceramics. The use of small phosphorus rings was employed as a potential replacement for the use of primary phosphines in phosphine-borane formation. This brought about the discovery of small phosphorus rings serving as precursors to the formation of primary phosphines through the reaction of the rings with a Lewis acid catalyst under hydrogenation conditions. Additionally, the expansion of classical Schmidt type chemistry where the phosphorus rings serve as a source of "RP" were examined. This enables the study of phosphinidene fragments without the need to synthesize clunky supporting groups or handle primary phosphines to transfer low valent phosphorus fragments.