Magister Scientiae - MSc (Physics)

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https://hdl.handle.net/10566/12433

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Browsing by Author "Arendse, Christopher"

Now showing 1 - 5 of 5
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    Carbon, magnesium implantation and proton irradiation on pulsed laser deposited thermochromic thin film of VO2
    (University of Western Cape, 2020) Mabakachaba, Boitumelo Mafalo; Maaza, M.; Arendse, Christopher
    When the spacecrafts orbit in space, it is subjected to significant thermal cycling variation. Thermal regulation of the spacecraft temperature is required to ensure a good operation of the small crafts such as CubeSats and the on-board equipment while minimizing the weight. Three methods employed for the Smart Radiator Devices (SRD) are (i) mechanical louvers, (ii) electrochromic coatings and (iii) thermochromic coatings (which is of interest in this study). Based on the characteristics of the thermochromic coatings, the passive smart radiator device is by far the most efficient option since there are no mechanical moving components and also no electric energy needed for the craft to operate.
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    Hot-wire chemical vapor deposition of silicon nitride thin films
    (2013) Adams, Abdulghaaliq; Arendse, Christopher; Muller, Theo; Malgas, Gerald
    Amorphous silicon nitride (a-SiN:H) thin films has a multitude of applications, stemming from the tunability of the material properties. Plasma enhanced chemical vapour deposition (PECVD) is the industrial workhorse for production of device quality a-SiN:H. However, this technique has drawbacks in terms of film quality, rooting from ion bombardment, which then results in undesirable oxidation. Hot wire chemical vapour deposition (HWCVD) has shown to be a viable competitor to its more costly counterpart, PECVD. A thin film produced by HWCVD lacks ion bombardment due to the deposition taking place in the absence of plasma. This study will focus on optimising the MVsystems ® HWCVD chamber at The University of the Western Cape, for production of device quality a-SiN:H thin films at low processing parameters. The effect of these parameters on the structural, optical and morphological properties was investigated, for reduction of production costs. The films were probed by heavy ion elastic recoil detection, energy dispersive spectroscopy, Fourier transform infrared spectroscopy, atomic force microscopy, Xray diffraction, and ultraviolet visible spectroscopy. It was shown that silicon rich, device quality a-SiN:H thin films could be produced by HWCVD at wire temperatures as low as 1400 °C and the films showed considerable resistance to oxidation in the bulk.
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    Hybrid two-dimensional perovskite semiconductor layers for electronic applications
    (Universty of the Western Cape, 2024) Mercuur, James Winston; Arendse, Christopher
    Perovskite materials have emerged as a frontier in advanced functional materials, offering a versatile platform for various applications ranging from solar cells to light-emitting devices. Among the different fabrication techniques, Chemical Vapor Deposition (CVD) stands out for its ability to produce high-quality thin films with precise compositional control. This study delves into synthesising a two-dimensional (2D) hybrid perovskite thin film (PEA)2PbCl4 on diverse substrates, marking a significant advancement in the scalable production of perovskite-based devices. Optimising CVD parameters enabled the deposition of a PbCl2 precursor thin film and its subsequent conversion to the perovskite through an intercalation reaction with PEACl. X-ray diffraction (XRD) analysis, complemented by Rietveld refinement and VESTA simulations, confirmed the hybrid 2D structure of the (PEA)2PbCl4 with an inorganic octahedral layer number (n) equal to one. Scanning electron microscopy revealed a uniform distribution of columnar structures (~120 nm in diameter) for PbCl2 and a woven-like morphology for the perovskite. Optical properties assessed via UV-Vis spectroscopy indicated a band gap of 3.47 eV (Tauc plot) and 3.644 eV (Elliott model) for the perovskite. The perovskite Urbach energy (EU) was estimated at ~236 meV (Urbach method), suggesting significant disorder within the film. However, exciton binding energies were approximately 20 meV, as per the Elliott fit. Photoluminescence spectroscopy showed broadband self-trapped exciton emissions centred at ~532 nm with a full width at half maximum (FWHM) of 140 nm, attributed to intrinsic lattice distortions. These findings contribute to understanding the structural and optical properties of 2D hybrid perovskites and the potential of CVD synthesis, with implications for their application in optoelectronic device fabrication.
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    Optical properties of annealed hydrogenated amorphous silicon nitride (a-SiNx:H) thin films for photovoltaic application
    (2013) Jacobs, Sulaiman; Muller, Theo; Arendse, Christopher; Malgas, Gerald
    Technological advancement has created a market for large area electronics such as solar cells and thin film transistors (TFT’s). Such devices now play an important role in modern society. Various types of conducting, semiconducting and insulating thin films of the order of hundreds, or even tens of nanometres are combined in strata to form stacks to create interactions and phenomena that can be exploited and employed in these devices for the benefit of mankind. One such is for the generation of energy via photovoltaic devices that use thin film technology; these are known as second and third generation solar cells. Silicon and its alloys such as silicon germanium (SiGex), silicon oxide (SiOx), silicon carbide (SiCx) and silicon nitride (SiNx) play an important role in these devices due to the fact that each material in its different structures, whether amorphous, micro or nano-crystalline or completely crystalline, has its own range of unique optical, mechanical and electrical properties. These structures and their material properties can thus exert a huge influence over the overall device performance. viii Chemical vapour deposition (CVD) techniques are most widely used in industry to obtain thin films of silicon and silicon alloys. Source gases are decomposed by the external provision of energy thereby allowing for the growth of a thin solid film on a substrate. In this study a variant of CVD, namely Hot Wire Chemical Vapour Deposition (HWCVD) will be used to deposit thin films of silicon nitride by the decomposition of silane (SiH4), hydrogen (H2) and ammonia (NH3) on a hot tantalum filament (~1600 C). Hydrogenated amorphous silicon nitride (a-SiNx:H) has great potential for application in optoelectronic devices. In commercial solar cell production its potential for use as anti-reflection coatings are due to its intermediate refractive index combined with low light absorption. An additional benefit is the passivation of interface and crystal defects due to the bonded hydrogen. This can lead to better photon conversion efficiency. Its optical properties including optical band gap, Urbach tail, and wavelength-dependent optical constants such as absorption coefficient and refractive index are crucial for the design and application in the relevant optoelectronic device. The final firing step in the production of micro-crystalline silicon solar cells, allows hydrogen to effuse into the solar cell from the a-SiNx:H, and drives bulk passivation of the grain boundaries. We therefore propose the exploration of annealing effects on the thin film structure. The study undertakes a comparison of optical and bonding structure of the as deposited thin film compared to that of the annealed thin film which would have undergone changes due to high temperature annealing under vacuum. However, it is difficult to simultaneously obtain all of these important ix optical parameters for a-SiNx:H thin films. Ultraviolet visible (UV-vis) spectroscopy will be the method of choice to investigate the optical properties. Infrared (IR) spectroscopy is a source of useful information on the microstructure of the material. In particular, the local atomic bonding configurations involving Si, N, and H atoms in a-SiNx:H films can be obtained by Fourier Transform Infrared Spectroscopy (FTIR). Therefore, this study will attempt to establish a relationship between film microstructure of a-SiNx:H thin films and their macroscopic optical properties.
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    Tin Catalyst preparation for Silicon Nanowire synthesis
    (University of the Western Cape, 2018) Modiba, Fortunate Mofao; Arendse, Christopher
    Solar cells offer SA an additional energy source. While Si cells are abundantly available they are not at an optimal efficiency and the cost is still high. One technology that can enhance their performance is SiNW. However, material properties such as the diameter, porosity and length determine their effectiveness during application to solar cell technology. One method of growing SiNW uses Sn catalysts on a Si substrate. As the properties of the Sn nanoparticle govern the properties of the SiNW, this thesis investigates their formation and properties by depositing a Sn layer on a Si wafer and then subjecting it to different temperatures, during process the layer forms into nanoparticles. At each temperature the morphology, composition and crystallinity will be determined using XPS, SEM, TEM and EDS. Thus, in Chapter 1 there is an overview, Chapter 2 deals with techniques used in this study, Chapter 3 will give the quantitative and qualitative results on the XPS analysis and Chapter 4 will illustrate the structural behaviour of the annealed Sn film samples.