Surface Engineering of All-Inorganic Nanocrystals for Electronic and 3D Printing Applications

Abstract

Nanocrystals (NCs) have received a lot of attention because they exhibit unique size- and shape-dependent physicochemical characteristics such as electronic, magnetic, and optical properties. Based on such unusual properties, NCs have provided unique solutions to solve unresolved issues in a wide range of application fields such as electronic, optoelectronic, and energy devices from a practical point of view. The major challenge for these applications of NCs is the chemical design of the surfaces of NCs, in which the electronic structures of individual NCs as well as the many-body interactions in NC solids should be controlled. For example, the recently developed inorganic ligands for NCs enhance the electronic coupling among NCs by the reduction of interparticle distance, which dramatically improves the charge carrier transport properties of NC arrays. These inorganic ligands-capped NCs, “all-inorganic NCs” can provide nanoscale building blocks to build up functional not only two-dimensional (2D) thin films but also 3D macroscale architectures. This dissertation describes the synthesis of 2D functional building blocks of CdSe and the development of new-typed inorganic ligands for the surface engineering of NCs for electronic and 3D printing applications. Firstly, I synthesized inorganic-organic hybrid structures of 2D CdSe slabs-diaminooctane (DAO) porous quantum nets. The formation of the net structures originated in the strong van der Waals interaction between the long-hydrocarbon chains in the assembled DAO, exerting intense compressive stress on CdSe slab's surface. And it also offset tensile stress on the other side, leading to the decomposition of the CdSe slabs, consequently a net-like morphology. Secondly, I investigated the enhancement of photoluminescence (PL) properties of CdSe NCs capped with inorganic MoS42- ligands by introducing photo-oxidation treatment on the NC surface. This treatment contributed to the preferential formation of stable MoSxOy oxide layers on the surface of CdSe NCs without changing the electronic structure of the NCs, leading to an increase in quantum yield (QY) by more than 50%. Besides, I also investigated the charge transport properties of MoS42--capped PbS NCs through the fabrication of the field-effect transistor (FET) and the photodetector. It showed clear gate modulation and the flow of photocurrent. Thirdly, I presented novel chemistry to prepare polyphosphide precursor solution that can serve as ink for solution-based fabrication of crystalline fibrous phosphorus thin films. These polyphosphide precursors can enable the fabrication of semiconducting fibrous phosphorus thin film without the addition of mineralizing agents. In addition, they successfully utilized as a new type of inorganic surface-capping ligands for various NCs. Finally, I developed the 3D nano-architecturing process of functional all-inorganic NCs that fabricates the 3D nanoarchitecture through photochemically active nano-building blocks. By using this process, I successfully fabricated 3D nanoarchitectures of different shapes with various sizes ranging from tens of micrometers to millimeters.