Synthesis and Characterisation of Metal Chalcogenide Nanocrystals

<p>Nanomaterials are defined as materials which possess features with dimensions of less than 100 nm. Nanocrystals are a subclass of nanomaterials, where the absolute dimensions of individual particles are within this range. Various effects become evident at such small scales, including notably: alterations in electronic structure and magnetic behaviour; and the predominance of surface chemistry. Consequently, the synthesis of nanocrystals with tailored properties via chemical methodology has become an area of some interest. Metal chalcogenides form an important class of inorganic materials, which includes many technologically important semiconductors. Metal chalcogenides feature prominently among semiconductor nanocrystals synthesised to date, but the development of magnetic nanocrystals has focused primarily on metal, and metal oxide phases. Thus the aim of this project was the investigation and development of synthetic methodology for producing nanocrystals, focusing on the metal chalcogenides, with specific emphasis on magnetic metal chalcogenides (iron sulfides). Properties of nanocrystals and metal chalcogenides are discussed in Chapter 1. As described in Chapter 2, metal chalcogenide nanocrystals were synthesised by high temperatures solution-phase reactions, and all samples were characterised by Transmission Electron Microscopy (TEM), Energy Dispersive X-ray Spectroscopy (EDS) and Electron Diffraction (ED). Powder X-ray Diffraction (XRD), Scanning Quantum Interference Device magnetometry (SQUID), Thermogravimetric analysis (TGA), Ultraviolet-visible (UV-vis) absorption and fluorescent emission spectroscopy were also used extensively. CdSe nanocrystals with diameters <10 nm are noted for their size-dependent absorption and emission in the visible region. As described in Chapter 3, an established synthesis was used to produce CdSe nanocrystals in order to explore the size-dependence of the optical properties of the nanocrystals, and to explore the possibility of transferring the nanocrystals to aqueous media. As described in Chapter 4, high temperature reaction of iron salts and elemental sulfur in non-aqueous coordinating solvents was used to produce Fe1-xS and Fe3S4 nanocrystals. The factors affecting phase-selectivity, particle size and morphology were ascertained; and the magnetic properties of pure Fe1-xS, pure Fe3S4 and mixtures of Fe1-xS and Fe3S4 were investigated. As described in Chapter 5, thermal decomposition of iron salts in a coordinating solvent was used to synthesis iron metal or iron oxide intermediates, which could either be oxidised to iron oxide spinel; or sulfidised in situ to iron thiospinel (Fe3S4) nanocrystals. This approach proved to be a good source of small, monodisperse iron oxide spinel and iron thiospinel nanocrystals with the same average dimensions. The magnetic properties of the highly-researched iron oxide spinel nanocrystals were determined, and contrasted to those of the their far less investigated thioanalogues. As described in Chapter 6, metal polysulfido complexes of the type [M(N-MeIm)x]Sy/MSy(N-MeIm)x (M = Fe, Zn, Mg; N-MeIm = N-methylimidazole) were synthesised from metal powders, elemental sulfur and N-MeIm; then thermolysed in coordinating solvents to afford metal sulfide nanocrystals. Thus establishing a new general route for synthesis of metal sulfide nanocrystals from low-cost starting materials.</p>

Synthesis and Characterisation of Metal Chalcogenide Nanocrystals

<p>Nanomaterials are defined as materials which possess features with dimensions of less than 100 nm. Nanocrystals are a subclass of nanomaterials, where the absolute dimensions of individual particles are within this range. Various effects become evident at such small scales, including notably: alterations in electronic structure and magnetic behaviour; and the predominance of surface chemistry. Consequently, the synthesis of nanocrystals with tailored properties via chemical methodology has become an area of some interest. Metal chalcogenides form an important class of inorganic materials, which includes many technologically important semiconductors. Metal chalcogenides feature prominently among semiconductor nanocrystals synthesised to date, but the development of magnetic nanocrystals has focused primarily on metal, and metal oxide phases. Thus the aim of this project was the investigation and development of synthetic methodology for producing nanocrystals, focusing on the metal chalcogenides, with specific emphasis on magnetic metal chalcogenides (iron sulfides). Properties of nanocrystals and metal chalcogenides are discussed in Chapter 1. As described in Chapter 2, metal chalcogenide nanocrystals were synthesised by high temperatures solution-phase reactions, and all samples were characterised by Transmission Electron Microscopy (TEM), Energy Dispersive X-ray Spectroscopy (EDS) and Electron Diffraction (ED). Powder X-ray Diffraction (XRD), Scanning Quantum Interference Device magnetometry (SQUID), Thermogravimetric analysis (TGA), Ultraviolet-visible (UV-vis) absorption and fluorescent emission spectroscopy were also used extensively. CdSe nanocrystals with diameters <10 nm are noted for their size-dependent absorption and emission in the visible region. As described in Chapter 3, an established synthesis was used to produce CdSe nanocrystals in order to explore the size-dependence of the optical properties of the nanocrystals, and to explore the possibility of transferring the nanocrystals to aqueous media. As described in Chapter 4, high temperature reaction of iron salts and elemental sulfur in non-aqueous coordinating solvents was used to produce Fe1-xS and Fe3S4 nanocrystals. The factors affecting phase-selectivity, particle size and morphology were ascertained; and the magnetic properties of pure Fe1-xS, pure Fe3S4 and mixtures of Fe1-xS and Fe3S4 were investigated. As described in Chapter 5, thermal decomposition of iron salts in a coordinating solvent was used to synthesis iron metal or iron oxide intermediates, which could either be oxidised to iron oxide spinel; or sulfidised in situ to iron thiospinel (Fe3S4) nanocrystals. This approach proved to be a good source of small, monodisperse iron oxide spinel and iron thiospinel nanocrystals with the same average dimensions. The magnetic properties of the highly-researched iron oxide spinel nanocrystals were determined, and contrasted to those of the their far less investigated thioanalogues. As described in Chapter 6, metal polysulfido complexes of the type [M(N-MeIm)x]Sy/MSy(N-MeIm)x (M = Fe, Zn, Mg; N-MeIm = N-methylimidazole) were synthesised from metal powders, elemental sulfur and N-MeIm; then thermolysed in coordinating solvents to afford metal sulfide nanocrystals. Thus establishing a new general route for synthesis of metal sulfide nanocrystals from low-cost starting materials.</p>

Properties of multicomponent (Mn-Ni-Co-Al-Si-Ti) oxide spinel hierarchically organized nanostructures deposited by magnetron sputtering in two temperatures.

Multicomponent spinel films were deposited on Ag/Si substrates by magnetron sputtering. Two substrate temperatures were used. XRD diffraction measurements show that the layers are composed of three metals oxides (Mn2O3, NiO, CoO). The presence of spinel phase is poorly visible. However, electron diffraction measurements (RHEED) clearly confirmed the presence of nanostructured spinel structure on top of the samples. Moreover, AFM measurements show that nanostructured spinel islands are present on the sample surface. The measurements validated that indeed, hierarchically organized spinel-oxides nanostructures were obtained. A possible model growth of the spinel nanostructures at different temperatures is discussed.

Research Progress of Cathode Materials for Lithium-ion Batteries

Lithium-ion batteries have attracted widespread attention as new energy storage materials, and electrode materials, especially cathode materials, are the main factors affecting the electrochemical performance of lithium-ion batteries, and they also determine the cost of preparing lithium-ion batteries. In recent years, there have been a lot of researches on the selection and modification of cathode materials based on lithium-ion batteries to continuously optimize the electrochemical performance of lithium-ion batteries. This article introduces the research progress of cathode materials for lithium ion batteries, including three types of cathode materials (layer oxide, spinel oxide, polyanionic compound) and three modification methods (doping modification, surface coating modification, nano modification method), and prospects for the future development of lithium ion battery cathode materials.