Developing novel vapor precursors for vapor depositions such as atomic layer deposition (ALD) is critical for enabling new thin film materials... Show moreDeveloping novel vapor precursors for vapor depositions such as atomic layer deposition (ALD) is critical for enabling new thin film materials and advanced processes. 2D materials such as transition metal dichalcogenides (TMDs) are promising materials for TFETs and diffusion barriers due to their narrow, direct band gap, and atomic thickness. In the potential electronic applications of TMDs materials, low-temperature, non-corrosive process is desired and even required to avoid thermal budget to the devices and sensitive components. Besides novel organometallic precursors, understanding the surface reaction mechanism is also necessary to achieve well-controlled material growth and obtain crystalline materials at lower temperature. In this dissertation, two novel synthetic methods to obtain crystalline TMDs materials such as tungsten disulfide (WS2) were developed, utilized metal hydride compound to synthesize at room temperature and heteroleptic compound to illustrate reaction mechanism. Reaction mechanism on the surface to produce metals chalcogenides including oxidation state changes and ligand behaviors during the nucleation using organometallic precursor on surfaces were investigated and observed with synchrotron X-ray absorption spectroscopy (XAS). Conventional tellurium sources have very limited reactivity towards tungsten. To overcome the low reactivities between W and Te sources, redox potential of organometallic Te and W precursors was utilized and achieved low-temperature synthesis of tungsten ditelluride (WTe2). Novel heteroleptic precursors design was also extended to Zr and Hf precursors. Heteroleptic Zr and Hf precursors were synthesized with high volatility and thermals stability. The heteroleptic precursors also showed high reactivity toward proton sources and selectivity between ligands. Metal chalcogenides deposition would be preferred with oxygen-free precursors. Organometallic precursors are typically more reactive than simple metal carbonyls or metal halides, and those organometallic precursors with a clear proton-transfer mechanism can allow ligands to be removed easily and obtain materials with high purity. Currently, tungsten precursors to synthesis TMDs material are commonly limited in metal carbonyls and metal chlorides, and the sulfurizations were performed at high temperature. By using more reactive organometallic precursors, the reaction between tungsten and chalcogenide sources can be initiated at lower temperature, highly reactive metal hydride and redox potential of metal complex were also utilized to boost reactivity. Well-designed ligands structures were employed to chemically enhance the crystallinity through the selectivity between ligands. Heteroleptic precursors are typically expected to have a better self-limiting control in synthesis, due to the different type of ligands could selectively react in each step. These enhanced precursor chemistries and understanding mechanism lead to better control of the synthesis of materials. Ph.D. in Chemistry, May 2018 Show less
