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Item Ultrasensitive SERS detection of organophosphorus compounds via surface modified silver nanostructures : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Chemistry, School of Natural Sciences, Massey University, New Zealand(Massey University, 2022) Buzás Stowers-Hull, AndréThe detection of target analytes with high specificity and sensitivity within fluids or on substrates is essential in many analytical applications. Surface-enhanced Raman spectroscopy (SERS) is a variation on vibrational Raman spectroscopy which uses plasmonic nanostructures or nanoparticles to amplify the Raman signal of various molecules via the formation of surface plasmons; concentrated areas of surface plasmons are known as 'hot spots', often influenced by the morphology of the chosen nanostructure. SERS can be attractive because it can provide greatly improved sensitivity and selective identification of an analyte in a mixture without separation, despite having different selection rules to normal Raman scattering. A variation of this technique, the slippery liquid-infused porous substrate (SLIPS) method, has also been shown to increase SERS signal enhancement considerably, allowing the detection of certain compounds at even lower initial concentrations. SLIPS-SERS involves the use of a Teflon-based microporous filter coated with a polyfluorinated oil to dry a drop of nanoparticles to a single condensed spot, which increases the likelihood of hotspot interactions with analytes. Despite increasing the overall sensitivity of SERS, some analytes still pose a challenge in SLIPS-SERS. One way to overcome this is modifying the surfaces of chosen nanoparticles, in the case of this research, this is done with a thin outer layer of SiO₂ or TiO₂ (ideally less than 5 nm thick). This is known as Shell-isolated Nanoparticle Enhanced Raman Spectroscopy (SHINERS), which can increase sensitivity by another order of magnitude than normal SERS, decreases particle agglomeration and the oxidation of the plasmonic core. In this research, we combine known SERS techniques: SLIPS-SERS, SHINERS and utilizing various nanoparticle shapes to greatly increase the sensitivity and detection of organophosphorus compounds.Item The defect modes of MoS₂ : indirect double resonance Raman spectroscopy in transition metal dichalcogenides : a thesis presented in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Nanoscience at Massey University, Manawatū, New Zealand(Massey University, 2022) Brooke, Samuel JamesMolybdenum disulfide (MoS₂) is a layered two-dimensional (2D) semiconducting crystal which has been a focal point of 2D materials research since the isolation and characterisation of graphene in 2005, owing to its relative abundance and a wide range of potential applications in thin film electronics, photovoltaics, information storage, and catalysis to name a few. It has unique layer-dependent electronic properties, demonstrating intense photoluminescence in single-layers and tightly-bound excitons at room temperature. The excitonic properties of MoS₂ lead to an optical phenomenon known as double resonance Raman (DRR), whereby the excited state charge carriers of excitons can interact with lattice vibrations (phonons) to scatter throughout the Brillouin zone during optical absorption and Raman spectroscopy measurements. These processes reveal signatures of electron and hole scattering dynamics that govern the complex electronic and physical properties of the material. At the nanoscale, the edges of MoS₂ have significant influence over the material’s properties, altering the electronic structure and contributing to doping effects for semiconductor performance and photoluminescence tuning. In addition, these edges (and defects) are also the sites of catalytic reactions, leading to intense efforts in literature to optimise MoS₂ as a catalyst for the production of clean hydrogen fuels. Consequently, understanding the edges of these materials is of great interest. This work demonstrates the design of a home-built low-frequency scanning Raman microscope, used to probe DRR features in MoS₂, revealing for the first time a defect-mediated indirect DRR mechanism which allows the quantification of defects and determination of zigzag and armchair edge structures in MoS₂ materials. This mechanism reveals indirect scattering pathways in the Brillouin zone, and appears to be applicable to similar materials in the family of transition metal dichalcogenides (TMDs). This indirect resonance mechanism has immediate application in facilitating the development of catalytic materials and novel nanomaterial architectures, as well as potential applications in the characterisation of exotic TMD materials and next-generation spin-valley coupled information storage devices.Item Hydrothermal synthesis of inorganic nanoparticles for potential technological applications : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Chemistry at Massey University, Manawatū, New Zealand(Massey University, 2021) Etemadi, HosseinIron oxide nanoparticles (IONPs) are of interest in a diverse range of environmental and biomedical applications due to their intrinsic chemical, physical and thermal features such as superparamagnetism, high surface-to-volume ratios, high biocompatibility, low toxicity and easy magnetic separation. Many technological applications necessitate small (diameter < 20 nm) nanoparticles with narrow size distributions (< 5 %) and pronounced saturation magnetisation (Ms) for uniform physical and chemical effects. Historically, the synthesis of IONPs with controlled size and size distribution without particle agglomeration has proved challenging. In this thesis, we utilised an easy hydrothermal route and successfully synthesized two common phases of IONPs, namely Fe₃O₄ (magnetite) and α-Fe₂O₃ (hematite), using Fe(acac)₃ as iron source. By controlling the reaction conditions such as time, temperature, and the concentration of surfactants such as PVP and oleic acid, the different phases were selectively synthesized. The prepared nanoparticles were fully characterized with X-ray diffraction (XRD), transmission electron microscopy (TEM), dynamic light scattering (DLS), energy dispersive X-Ray spectroscopy (EDS), atomic absorption spectroscopy (AAS), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), vibrating-sample magnetometry (VSM), Brunauer-Emmett-Teller (BET) surface area measurements, photoluminescence (PL) and UV–Vis diffuse reflectance spectroscopy (UV–Vis/DRS). In Part I of this thesis, Fe₃O₄ and metal-doped spinel MxFe₃−xO₄ (M = Fe, Mg, Mn, Zn) nanoferrites were synthesised as agents for cancer treatment via a method called magnetic fluid hyperthermia (MFH). In Part II, α-Fe₂O₃ nanoparticles were hybridized with tin (II) sulfide (SnS) to create p-n heterojunction photocatalysts for efficient H2 production via ethanol photoreforming.