Synthesis and Characterization of Light-Emitting Magnetic Bi-Functional Nanocrystals

Abstract

The combination of two different materials into a single nanostructure is of great interest due to the potential in creating structures where two distinct properties are displayed in a single composite nanostructure. This can be achieved by combining two types of materials, each having a distinct property, through interfaces in various spatial configurations, such as those of core-shells and heterodimers. Self-assembly of these composite nanostructures into thin films and bulk materials could lead to hybrid materials with enormous design flexibility, structural complexity and multifunctionality. These hybrid materials may have great potential in applications in various fields, including biomedical applications, catalysis of organic reactions, energy generation and conservation and other industrial applications. The focus of this thesis is the solution phase synthesis of hybrid nanostructures made of magnetic and semiconductor materials, which can lead to potentially bi-functional nanostructures. A seeded growth approach was employed in synthesizing these hybrid nanostructures, where magnetic seed particles were synthesized in the first step and the fluorescent semiconductor material was grown on the magnetic seeds in the second step. The morphology, crystal structure, crystallinity and chemical composition of the synthesized nanostructures were studied through transmission electron microscopy (TEM), selected area electron diffraction (SAED), energy dispersive X-ray spectroscopy (EDS) and powder X-ray diffraction (XRD). Optical characterizations such as UV-Vis spectroscopy and photoluminescence measurements as well as magnetic measurements were carried out on selected samples. Chapter 1 and 2 introduced the background of this thesis and the experimental methods used in this research. The magnetic components involved included spherical nickel nanoparticles of 40, 20 and 10nm in size, nickel nanocubes (13nm) and iron oxide nanocubes (15nm). The semiconductor components involved included CdSe, CdS and CdTe. In Chapter 3, 4 and 5, the synthesis and characterization of core-shell nanostructures involving the above magnetic and semiconductor materials were presented. The factors governing the formation of semiconductor shell layers on the surface of the magnetic seeds were investigated. In particular, the surface properties of the magnetic seeds played a dominant role in the formation of the semiconductor shell layers. In addition, the reactivity of the reagents used can affect the chemical composition and the morphology of the resultant core-shell structures. In Chapter 6, analysis of high resolution TEM images was carried out on selected samples of semiconductor coated nickel nanoparticles. Through studying the crystallographic facets of Ni and CdSe, the presence of preferential orientation between the Ni and CdSe phases was identified and determined. This analysis resulted in further understanding of the growth behavior of the semiconductor components on the nickel cores. These result chapters are followed by Chapter 7, which is the conclusion chapter. Also included in the conclusion chapter is potential future work of this research.