Magister Philosophiae - MPhil (Physics)

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https://hdl.handle.net/10566/14962

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Structural and thermodynamic properties of Tb2Ni2X, (X=Al, Ga
(University of the Western Cape, 2025) Mpupa, Zandile
The research reported in this thesis presents a comprehensive investigation into the structural, magnetic, and thermodynamic properties of the ternary polycrystalline Tb2Ni2X (X = Al, Ga) compounds through measurements of X-ray diffraction (XRD), magnetic susceptibility, χ (T), magnetization, M (µ0H), and heat capacity, Cp(T). The compounds were synthesized using an arc-melting furnace, and the ingots were cut using a slow cutter to ensure the formation of high-quality samples for further analysis. XRD analysis confirms the orthorhombic W2CoB2-type structure with the space group Immm. χ(T) at high temperature for both compounds follows the Curie–Weiss relationship giving an effective magnetic moment values µef f = 10.172(1) µB and 10.520(4) µB for Tb2Ni2Al and Tb2Ni2Ga compounds, respectively, which are close to that expected for the trivalent Tb ion of 10.72 µB. Negative Weiss temperature, θp was obtained for both compounds as expected for AFM exchange interactions between the Tb moments. χ (T) [Cp(T)] data indicate that both compounds order antiferromagnetically at TN = 41 K [40.4 K] and 41.5 K [41.4 K] for the Al and Ga compounds, respectively. χ(T) data in field-cooled (FC) and zero-field-cooled (ZFC) modes showed bifurcation below TN . M(µ0H) of Al compound exhibits hysteresis below 3 T, indicating magnetic domain structures and coercivity effects, while M(µ0H) for the Ga compound exhibits metamagnetic behavior above 6 T, suggesting a field-induced transition from antiferromagnetic to ferromagnetic states. Cp(T) data of the nonmagnetic counterparts Tb2Ni2X (X = Al, Ga) are well described by the Debye model given a Debye temperature, θD = 236.9(4) K and 225.3(2) K for the Al and Ga compounds, respectively. The low-temperature of the 4f-magnetic contribution to the total heat capacity, C4f (T) data can be well approximated according to the antiferromagnetic spin–wave dispersion, giving an energy gap, ∆sw = 47(3) K and 26(2) K for Al and Ga compounds, respectively. The 4f–magnetic entropy, S4f (T) for both compounds reaches the values of 2Rln(2) close to their respective TN values indicating a ground state doublet for these compounds.
Hı asymmetries and deficiencies in Alfalfa galaxies
(University of the Western Cape, 2025) Thobejane, Reshoketswe
This work focuses primarily on the effects that the environment of a galaxy has on the asymmetries observed in the Hı profiles of galaxies. Galaxies exhibit a wide range of observable properties and the environment in which a galaxy resides is known to impact its characteristics significantly. Thus, using the ALFALFA survey, which provides ∼ 31,500 Hı spectral profiles of galaxies out to redshifts of z < 0.06, this work generates two samples (the isolated and merger sample) to provide evidence of how the environment of a galaxy is one of the main drivers of the asymmetries observed in the Hı profiles of galaxies. The galaxy’s environment in this work, is defined according to the nearest galaxy neighbour. The merger sample galaxies are those galaxies that are found to have neighbouring galaxies within 25 kpc spatially and 750 km s−1 spectrally. The isolated sample galaxies are those that are found to have no neighbouring galaxies within 750 kpc spatially and 7500 km s−1 spectrally. In total, the merger sample consists of 205 galaxies and the isolated sample of 5604 galaxies which all have signal-to-noise (SNR)> 6.5. This work finds that on average, the most asymmetric profiles are in the merger sample which leads to a strong suggestion that the environment of a galaxy is one of the main drivers of asymmetries observed in the Hı profiles of galaxies. A further investigation on environment density as a function of Hı asymmetry is employed on the full ALFALFA galaxy sample for different cluster environments. This work finds that there is a correlation between environmental density and Hı asymmetry, that is, the galaxies residing in dense environments tend to have more asymmetric Hı profiles than those galaxies residing in the less dense environments.
Investigating the effectiveness of carbon nanotubes for low inactive component ni-rich cathodes for lithium-ion batteries
(University of the Western Cape, 2024) Hawksley, James Brendan
As society drives towards a greener economy, the requirement for technologies to support this transition is of the utmost importance. The Lithium-ion battery is already a well-established technology, being utilised in a wide range of industries. Nonetheless, from the perspective of the automotive industry, the current generation of batteries are still lacking in key characteristics, such as volumetric capacity and power performance. The use of high aspect ratio conductive additive materials, such as carbon nanotubes, have been proposed as a means to improve the overall performance of the cell. However, to the author’s best knowledge, no work has been done to assess the effect of these high aspect ratio materials on the behaviour of the electrode slurry, and by extension probing the optimization of the electrode slurry preparation process. The aim of this work is therefore to investigate the effect of using a binary conductive additive system – combining spherical carbon black conductive additive, and high aspect ratio carbon nanotubes – on the electrode slurry. Furthermore, extensive time is taken to correlate the behaviour of the slurry with the characteristics of the coated electrode sheet, comparing the rheology of the slurry, with the microstructure of the electrode, as well as its electronic conductivity performance. During the course of the work, the effect of the sequence of addition during the mixing stage, as well as the effect of the carbon nanotube concentration on the slurry, electrode microstructure and electronic conductivity is investigated.
Dynamical models of galaxies observed in Hı line emission with MeerKAT
(University of the Western Cape, 2025) Smith, Craig Bryan
The dynamics of galaxies play a crucial role in understanding the evolution of these cosmic structures. In this work, we use neutral atomic hydrogen (Hı) emission line observations to generate 3D dynamical models of two galaxies, ESO 418- G 006 and WISEA J033235.23- 275532.8. These two galaxies form part of the Looking At the Distant Universe with the MeerKAT Array (LADUMA) survey. The first Hı interferometric observations of these extragalactic systems are constituted by this survey. Due to the exquisite nature of MeerKAT data, dynamical models of these galaxies are constructed at ˜1000 resolution, with these models used to gain insights into di↵erent evolutionary aspects of these galaxies. Using the dynamical model and resulting rotation curve of ESO 418- G 006, the first mass model of this galaxy is constructed to constrain the radial distribution properties of its dark matter content. This analysis reveals that a declining rotation curve most accurately represents the kinematics of ESO 418- G 006. Using the resulting mass model, the dark matter halo of this galaxy is parameterized using both the spherical pseudoisothermal (ISO) and NFW halo models. From this parameterization, the dark matter halo of ESO 418- G 006 is found to be best described by a halo consisting of a constantdensity inner core, with a core radius Rc = 3.79 ± 0.73 kpc and a core density ⇢0 = 0.083 ± 0.026 Mpc3. Due to the interesting morphology of the second galaxy that this work focuses on, WISEA J033235.23-275532.8, di↵erent 3D dynamical models of this galaxy are constructed, incorporating a warped Hı disk and a flat Hı disk respectively. This is undertaken to identify the model that can best describe the overall kinematics of this galaxy. Through a rigorous comparison of these models, we find that those incorporating a flat Hı disk do suciently well in resembling the data of WISEA J033235.23-275532.8. The resulting rotation curve of WISEA J033235.23-275532.8, generated from the bestfound flat Hı disk model, is found to mainly exhibit the typical shape associated with disk galaxies, but also exhibits a kinematic anomaly.
Synthesis of bimetallic immiscible alloy nanoparticles through green and gamma radiolysis approaches for environmental remediation applications
(University of the Western Cape, 2022) Noukelag, Sandrine Kamdoum; Maaza, Malik
The synthesis of bimetallic immiscible alloy nanoparticles (NPs) using versatile routes, is a major concern since physio-chemical methods are not environmentally benign. Breaking down the immiscibility would generate NPs with remarkable properties and consequently more applications. As a result, it urges the development of one-step, eco-friendly, efficient, and reliable methods for getting more metastable bimetallic alloys from immiscible metals. To that aim, unconventional approaches such as green and gamma radiolysis were considered as the paths forward in this thesis. The wide immiscibility gaps of iron-silver (Fe-Ag), and iron-zinc (Fe-Zn) led to their selection
Synthesis of bimetallic immiscible alloy nanoparticles through green and gamma radiolysis approaches for environmental remediation applications
(University of the Western Cape, 2022) Noukelag, Sandrine Kamdoum; Maaza, Malik
The synthesis of bimetallic immiscible alloy nanoparticles (NPs) using versatile routes, is a major concern since physio-chemical methods are not environmentally benign. Breaking down the immiscibility would generate NPs with remarkable properties and consequently more applications. As a result, it urges the development of one-step, eco-friendly, efficient, and reliable methods for getting more metastable bimetallic alloys from immiscible metals. To that aim, unconventional approaches such as green and gamma radiolysis were considered as the paths forward in this thesis. The wide immiscibility gaps of iron-silver (Fe-Ag), and iron-zinc (Fe-Zn) led to their selection
Towards stimuli-responsive functional nanocomposites: Smart tunable plasmonic nanostructures au-v02
(University of the Western Cape, 2010) Kama Kama, Jean Bosco; Maaza, M; Knoesen, D
The fascinating optical properties of metallic nanostructures, dominated by collective oscillations of free electrons known as plasmons, open new opportunities for the development of devices fabrication based on noble metal nanoparticle composite materials. This thesis demonstrates a low-cost and versatile technique to produce stimuli-responsive ultrafast plasmonic nanostructures with reversible tunable optical properties. Albeit challenging, further control using thermal external stimuli to tune the local environment of gold nanoparticles embedded in V02 host matrix would be ideal for the design of responsive functional nanocomposites. We prepared Au-V02 nanocomposite thin films by the inverted cylindrical reactive magnetron sputtering (ICMS) known as hollow cathode magnetron sputtering for the first time and report the reversible tuning of surface plasmon resonance of Au nanoparticles by only adjusting the external temperature stimuli. The structural, morphological, interfacial analysis and optical properties of the optimized nanostructures have been studied. ICMS has been attracting much attention for its enclosed geometry and its ability to deposit on large area, uniform coating of smart nanocomposites at high deposition rate. Before achieving the aforementioned goals, a systematic study and optimization process of V02 host matrix has been done by studying the influence of deposition parameters on the structural, morphological and optical switching properties of V02 thin films. A reversible thermal tunability of the optical/dielectric constants of V02 thin films by spectroscopic ellipsometry has been intensively also studied in order to bring more insights about the shift of the plasmon of gold nanoparticles imbedded in V02 host matrix.
Towards stimuli-responsive functional nanocomposites: Smart tunable plasmonic nanostructures au-v02
(University of the Western Cape, 2010) Kama Kama, Jean Bosco; Maaza, M; Knoesen, D
The fascinating optical properties of metallic nanostructures, dominated by collective oscillations of free electrons known as plasmons, open new opportunities for the development of devices fabrication based on noble metal nanoparticle composite materials. This thesis demonstrates a low-cost and versatile technique to produce stimuli-responsive ultrafast plasmonic nanostructures with reversible tunable optical properties. Albeit challenging, further control using thermal external stimuli to tune the local environment of gold nanoparticles embedded in V02 host matrix would be ideal for the design of responsive functional nanocomposites. We prepared Au-V02 nanocomposite thin films by the inverted cylindrical reactive magnetron sputtering (ICMS) known as hollow cathode magnetron sputtering for the first time and report the reversible tuning of surface plasmon resonance of Au nanoparticles by only adjusting the external temperature stimuli. The structural, morphological, interfacial analysis and optical properties of the optimized nanostructures have been studied. ICMS has been attracting much attention for its enclosed geometry and its ability to deposit on large area, uniform coating of smart nanocomposites at high deposition rate. Before achieving the aforementioned goals, a systematic study and optimization process of V02 host matrix has been done by studying the influence of deposition parameters on the structural, morphological and optical switching properties of V02 thin films. A reversible thermal tunability of the optical/dielectric constants of V02 thin films by spectroscopic ellipsometry has been intensively also studied in order to bring more insights about the shift of the plasmon of gold nanoparticles imbedded in V02 host matrix.
Selection and optimization of the seeding procedure prior to the synthesis of Pd-based membranes
(University of the Western Cape, 2014) Mc Donald, Earl; Halindintwali, S.; Bladergroen, B.J.; Julies, B.
Pd based membranes are known for their incredible selectivity towards H2. In order for Pd membranes to display high H2 selectivity, a defect free layer of Pd needs to be deposited onto a support. Although various fabrication techniques do exist, many researchers have attempted to produce defect free Pd-based films, using electroless plating. The first step in the preparation technique involves “seeding” of the support structure. Even though these seeds, if well distributed and anchored to the support, are crucial in order to obtain the defect free Pd layer, they hardly ever received attention from the science community. This thesis reports findings on various seeding methods as well as the resulting microstructures of the Pd films formed as a result of the type of seeding method employed. Finally the quality of the membranes using the most promising seeding technique was determined by subjecting the membranes to permeance tests with N2 at both high and low temperatures as well as with H2 at high temperatures.
Selection and optimization of the seeding procedure prior to the synthesis of Pd-based membranes
(University of the Western Cape, 2014) Mc Donald, Earl; Halindintwali, S.; Bladergroen, B.J.; Julies, B.
Pd based membranes are known for their incredible selectivity towards H2. In order for Pd membranes to display high H2 selectivity, a defect free layer of Pd needs to be deposited onto a support. Although various fabrication techniques do exist, many researchers have attempted to produce defect free Pd-based films, using electroless plating. The first step in the preparation technique involves “seeding” of the support structure. Even though these seeds, if well distributed and anchored to the support, are crucial in order to obtain the defect free Pd layer, they hardly ever received attention from the science community. This thesis reports findings on various seeding methods as well as the resulting microstructures of the Pd films formed as a result of the type of seeding method employed. Finally the quality of the membranes using the most promising seeding technique was determined by subjecting the membranes to permeance tests with N2 at both high and low temperatures as well as with H2 at high temperatures.
Simulation of silicon and diamond detector systems by GEANT4 simulation techniques
(University of the Western Cape, 2014) Erasmus, Nicholas Rattray; Orce, J.N.; Halindintwali, S
There is a constant need for improvement in nuclear particle detection methods. Silicon surface barrier detectors have proved very valuable during the last decades. Diamond is a viable alternative to silicon as a semiconductor detector. It offers significant advantages over silicon due to its high radiation hardness and low drift currents. A Coulomb-excitation study has been carried out at TRIUMF using a 59.7 MeV 12C beam impinging on a 194Pt target. The particles underwent elastic Rutherford scattering in the target, and a double sided silicon S3 CD detector was used to measure the resulting particle energy spectra. These spectra were simulated in GEANT4 and compared to the experimental results. Subsequently, the silicon was replaced with diamond and the simulation was repeated. Such simulations of particle energy spectra, properly incorporating elastic Rutherford scattering, have not been carried out with GEANT4 before. An accurate simulation of the elastic peak obtained from particle spectra will provide a methodology for applying particle-gamma coincidence techniques. The study of the inelastic peak in 12C and similar nuclei will benefit from such developments. Such simulations will also offer high energy calibration points for the experimental data, and the possibility of testing the experimental conditions including the target thickness, beam energy, and linearity of electronic modules (e.g. the preamplifier). The simulation offered results comparable to the experimental case. GEANT4 was found to simulate the Rutherford cross sections at specific scattering angles as well as the position of the simulated energy peaks accurately when compared with the experimental case. As expected, the experimentally obtained particle energy spectra displayed more broadening than the simulated spectra, though the shape of the peaks was very similar. The simulation of the double sided diamond detector was a tentative first step in its testing as a particle detector. The sophisticated methods required to properly simulate and test diamond for nuclear physics experiments were not implemented. This simulation may serve as a starting point for further testing of diamond detectors, using advanced simulation techniques
Simulation of silicon and diamond detector systems by GEANT4 simulation techniques
(University of the Western Cape, 2014) Erasmus, Nicholas Rattray; Orce, J.N.; Halindintwali, S
There is a constant need for improvement in nuclear particle detection methods. Silicon surface barrier detectors have proved very valuable during the last decades. Diamond is a viable alternative to silicon as a semiconductor detector. It offers significant advantages over silicon due to its high radiation hardness and low drift currents. A Coulomb-excitation study has been carried out at TRIUMF using a 59.7 MeV 12C beam impinging on a 194Pt target. The particles underwent elastic Rutherford scattering in the target, and a double sided silicon S3 CD detector was used to measure the resulting particle energy spectra. These spectra were simulated in GEANT4 and compared to the experimental results. Subsequently, the silicon was replaced with diamond and the simulation was repeated. Such simulations of particle energy spectra, properly incorporating elastic Rutherford scattering, have not been carried out with GEANT4 before. An accurate simulation of the elastic peak obtained from particle spectra will provide a methodology for applying particle-gamma coincidence techniques. The study of the inelastic peak in 12C and similar nuclei will benefit from such developments. Such simulations will also offer high energy calibration points for the experimental data, and the possibility of testing the experimental conditions including the target thickness, beam energy, and linearity of electronic modules (e.g. the preamplifier). The simulation offered results comparable to the experimental case. GEANT4 was found to simulate the Rutherford cross sections at specific scattering angles as well as the position of the simulated energy peaks accurately when compared with the experimental case. As expected, the experimentally obtained particle energy spectra displayed more broadening than the simulated spectra, though the shape of the peaks was very similar. The simulation of the double sided diamond detector was a tentative first step in its testing as a particle detector. The sophisticated methods required to properly simulate and test diamond for nuclear physics experiments were not implemented. This simulation may serve as a starting point for further testing of diamond detectors, using advanced simulation techniques
Synthesis and characterization of Ceria with an optimal oxygen storage capacity as potential medium to remove SO2 from flue gas emissions
(University of Western Cape, 2013) Andrews, Gary Lyndl; Bladergroen, B.J.; Hallindintwali, S.; Julies, B.
Due to an increasing demand for energy, alternative renewable energy sources are investigated globally. However fossil fuels are still one of the main energy sources. The combustion of these fuels produces by-products such as SOx, NOx and CO2, which have detrimental effects on the environment and human health. Therefore, effective methods are needed to minimize the pollution and affects that these by-products cause. Catalysts are commonly employed to convert these by-products to less harmful and/or resalable products. Ceria and ceria based materials are good candidates for the removal and conversion of SOx and NOx. Ceria and ceria related materials are most effective as catalysts when they are in the nano-form with good crystallinity and nanoparticles that are uniform. The growth of nanoparticles is preceded by a nucleation process which can occur by solid-state restructuring of a gel or precipitation from a saturated solution. The precipitation method was selected to synthesize Ceria nanoparticles. Synthesis conditions such as temperature, solution type and ageing time and their effect on the physical and chemical forms of the Ceria particles were investigated. The morphology and structural properties were investigated using Scanning Electron Microscopy, X-ray diffraction and Transmission Electron Microscopy. X-ray Photoelectron Spectroscopy was used to investigate the chemical properties. It was found that low temperatures, low base volume and a solvent with a small dielectric constant favor the formation of small crystallites with a relatively large concentration of defects. These defects are desirable since they enhance the catalytic activity of ceria.
Synthesis and characterization of Ceria with an optimal oxygen storage capacity as potential medium to remove SO2 from flue gas emissions
(University of Western Cape, 2013) Andrews, Gary Lyndl; Bladergroen, B.J.; Hallindintwali, S.; Julies, B.
Due to an increasing demand for energy, alternative renewable energy sources are investigated globally. However fossil fuels are still one of the main energy sources. The combustion of these fuels produces by-products such as SOx, NOx and CO2, which have detrimental effects on the environment and human health. Therefore, effective methods are needed to minimize the pollution and affects that these by-products cause. Catalysts are commonly employed to convert these by-products to less harmful and/or resalable products. Ceria and ceria based materials are good candidates for the removal and conversion of SOx and NOx. Ceria and ceria related materials are most effective as catalysts when they are in the nano-form with good crystallinity and nanoparticles that are uniform. The growth of nanoparticles is preceded by a nucleation process which can occur by solid-state restructuring of a gel or precipitation from a saturated solution. The precipitation method was selected to synthesize Ceria nanoparticles. Synthesis conditions such as temperature, solution type and ageing time and their effect on the physical and chemical forms of the Ceria particles were investigated. The morphology and structural properties were investigated using Scanning Electron Microscopy, X-ray diffraction and Transmission Electron Microscopy. X-ray Photoelectron Spectroscopy was used to investigate the chemical properties. It was found that low temperatures, low base volume and a solvent with a small dielectric constant favor the formation of small crystallites with a relatively large concentration of defects. These defects are desirable since they enhance the catalytic activity of ceria.

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