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Novel nanostructures in transition metal chalcogenide systems

Denholme, Saleem J. (2011) Novel nanostructures in transition metal chalcogenide systems. PhD thesis, University of Glasgow.

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Abstract

This thesis discusses the synthesis of transition metal chalcogenide nanostructures (where the chalcogen is either sulfur, selenium or tellurium) through the use of standard chemical vapour transport (CVT) and chemical vapour deposition (CVD) techniques. The resultant structures are characterised with a variety of methods and comparisons of their properties are made with their bulk counterparts. A discussion into how some of these structures form during the reaction is also given. Highly symmetrical, isotropic, nickel disulfide (NiS2) nanocubes have been synthesised via a Physical Vapour Transport (PVT) method in which sulfur vapour generated in situ is reacted with nickel-coated silica substrates. Systematic studies demonstrate the effect of the reactant ratio, substrate, metal layer thickness and reaction temperature on the synthesis and growth process. The evolution of structure and composition has been followed by diffraction and scanning electron microscopy (SEM). The size of the NiS2 cubes can be varied from below 200 nm to 1 -2 1m across. Magnetic properties of the disulfide nanomaterials have been determined using superconducting quantum interference device (SQUID) magnetometry. Initial experiments also demonstrate that related CVT techniques can be exploited to produce alternative compositions in the Ni-S system with varying morphologies that can be controlled via chemical and physical reaction parameters. Surface Assisted Chemical Vapour Transport (SACVT) methods have been employed to grow flower-like nanostructures of titanium disulfide (TiS2) and titanium trisulfide (TiS3) on titanium coated silica substrates. Systematic studies demonstrate the role of the reactant ratio and reaction temperature on the synthesis and growth process. The evolution of structure and composition has been followed by powder X-ray diffraction (PXD) and electron microscopy techniques such as and transmission electron microscopy (TEM). Magnetic properties of the disulfide nanomaterials have been determined using SQUID and Raman spectroscopy has been used to confirm the identity of the sulfides. Investigations into nanostructured materials of the group IV transition metals zirconium and hafnium resulted in the successful synthesis of nanostructures of zirconium trisulfide/selenide (ZrS3/Se3) and hafnium trisulfide/selenide (HfS3/Se3). The unusual effects on structure that can occur when reactant time and synthesis temperature are varied and when a balance between these two factors is successfully found, nanostructures other than tubes and wires can be formed. Each of these systems were characterised with a variety of techniques including, TEM, PXD and SQUID.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Keywords: Nanostructure, Chalcogenide, transition metals
Subjects: Q Science > QC Physics
Q Science > QD Chemistry
Q Science > Q Science (General)
Colleges/Schools: College of Science and Engineering > School of Chemistry
Supervisor's Name: Gregory, Prof. D.H.
Date of Award: 2011
Depositing User: Mr Saleem Denholme
Unique ID: glathesis:2011-3077
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 10 Jan 2012
Last Modified: 10 Dec 2012 14:03
URI: http://theses.gla.ac.uk/id/eprint/3077

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