Synthesis and Characterization of Nanoplatelets and Nanoplatelet Heterostructures made with Thiourea and Selone Precursors

In Chapter 1, I give a basic introduction to the scientific background necessary for understanding the rest of the dissertation. I describe semiconductor nanocrystals and quantum confinement, how nanocrystals grow and a brief description of the various characterization methods. Finally, I provide some of the general considerations and chemical sources for the experiments performed in the thesis as a whole. In Chapter 2, I summarize the journey towards working with molecular precursors and show the advances and challenges in modeling and understanding conversion made a step into nanoplatelets more feasible. The chalcogenourea syntheses are not included and the modeling of the spherical nanocrystals is in a fairly summarized form here. This chapter is intended to give a brief overview of the highlights, key conclusions, and resulting questions upon which I designed my own experiments. In Chapter 3, I discuss applying precursor conversion method to nanoplatelets and focus on 3ML CdE growth. I briefly introduce nanoplatelets, explain the new conditions necessary to adapt the chalcogenourea library, demonstrate my efforts in characterizing the kinetics and growth mechanisms, and finally show the relationship of precursor reactivity and final nanoplatelet size. The “kobs catalogue” which summarizes the kinetics and sizing from STEM is an appendix at the end of the chapter. In this chapter, we put to the test the idea that we can control nanocrystal synthesis through precursor reactivity. The synthesis of nanocrystal heterostructures controlled by precursor conversion was discussed in Chapter 2. In Chapter 4, the same theory is applied to nanoplatelet synthetic conditions, but because nanoplatelet nucleation is fast compared to the total reaction time, the precursors should result in something closer to what is modeled without extraneous products. At the end of the chapter, a nanoplatelet alloy catalogue records many of the modeling and alloy experiments. Chapter 5 attempts to gather the various side projects that working with nanoplatelets has brought about. All these projects come together when thinking about how the solute supply and surface ligands might determine nanoplatelet formation, which I hope to shed some insight on. In the end, I hope to have gathered enough information to provide thoughtful answers for why nanoplatelets form, how they are ideal for studying compositional growth, and how nanocrystal alloying changes the structural and optical properties of these materials.