This award in the Chemical Synthesis (SYN) program supports work by Professor Zi-Ling (Ben) Xue at the University of Tennessee, Knoxville, to carry out fundamental studies of the reactions of transition metal complexes with oxygen and water. Competitive oxidation in the complexes by oxygen and their gradual conversion to metal oxides by oxygen and water will be investigated. The properties of reaction intermediates will be investigated, and thermodynamic and kinetic data will be gathered to understand their conversion to metal oxides. A mentoring program through the University of Tennessee Math and Science Center will help advance the careers of first-generation college students in Tennessee and attract them to the sciences. The studies will also help develop the research infrastructure in Tennessee, an EPSCoR (Experimental Program to Stimulate Competitive Research) state.
The reactions to be studied here have been used in chemical vapor deposition/atomic layer deposition processes to make the state-of-the-art microelectronic metal oxides that are a key component of the newest and smallest transistors. An understanding of the basic chemistry of the reactions may lead to better precursors for and new chemical routes to the microelectronic materials.
Reactions of d0 early transition metal complexes with oxygen (O2) or water have been used to make microelectronic metal oxide materials through chemical vapor deposition (CVD) or atomic layer deposition (ALD) processes. The metal oxides, as high-k (dielectric constant) gate insulator materials (Scheme 1), are one key component in new generations of transistors. There have been relatively few studies of the reactions between O2 and d0 complexes. Scheme 1. Gate insulators in microelectronic devices that are used in computers and cell phones. The metal atoms in the d0 early transition metal complexes are at high-oxidation states. Reactions between the d0 complexes and O2 usually involve ligand oxidation, and the reactions are not well understood. In comparison, reactions of dn late transition metal complexes with O2 often lead to metal oxidation. In other words, pathways in the reactions of O2 with d0 complexes are different from those of dn complexes. Since O2 is a diradical, many of its reactions are radical in nature and are challenging to investigate. Our research group has observed and characterized an unusual peroxo complex in the reaction of O2 with a zirconium(IV) complex before the formation of the oxo compounds. In addition, studies from this NSF grant have helped point out pathways in the formation of microelectronic materials. The research also provided a very good opportunity to train students to become future scientists in an interdisciplinary area. Female students as well as high school students from areas of Tennessee with high poverty rates participated in the research. They helped the high school students to become potential first generation college students in their families. New materials are at the heart of the advances in microelectronic devices. Replacing silicon oxide by metal oxides as the gate material is of intense current interest to allow further device miniaturization. Scientists in the microelectronic industry have indicated that our NSF-supported research helped them understand the CVD/ALD reactions and assisted in increasing yields/purity of the precursors. Papers from our research group have pointed out, for example, that impurities in the precursor syntheses are from the reactions of the precursors with trace air. In other words, the NSF-funded studies have helped improve the manufacture of the microelectronic materials.
