Browsing by Author "Cummings, Franscious"

Now showing 1 - 8 of 8
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    Application of vertically aligned arrays of metal-oxide nanowires in heterojunction photovoltaics
    (University of the Western Cape, 2020) Ladan, Muhammad Bello; Cummings, Franscious; Muller, Theophillus
    The commercial need to improve the performance of low-cost organic solar cells has led to the idea for this research. The study discusses the synthesis of one dimensional TiO2 and ZnO nanowire arrays synthesised using a hydrothermal autoclave method and their application in bulk heterojunction inverted organic solar cells. Previous literature has shown that the precise manipulation, positioning and assembly of 1D nanostructures remain one of the greatest challenges in the field of nanotechnology, with much of the difficulty arising primarily from the lack of size and scale of the materials as well as the inability to visualise the nanostructures. In particular, one dimensional metal-oxides such as TiO2, ZnO and Fe2O3 have emerged as attractive alternatives to traditional semiconductor structures such as Si and GaAs as they are simple and inexpensive to manufacture, with research showing that application of ZnO nano-cones yield efficiencies of 8.4%, which is very attractive given the scope that exists in optimising the metal-oxide architecture. Much is still to be learned from the precise structural features of these materials and their influence on device performance. In this regard, this work largely focuses on this aspect of metal-oxide nanowires prior their application in organic solar cells.
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    Effect of calcination time on the physicochemical properties and photocatalytic performance of carbon and nitrogen co-doped TiO2 nanoparticles
    (MDPI, 2020) Mouele, Emile Salomon Massima; Dinu, Mihaela; Cummings, Franscious
    The application of highly active nano catalysts in advanced oxidation processes (AOPs) improves the production of non-selective hydroxyl radicals and co-oxidants for complete remediation of polluted water. This study focused on the synthesis and characterisation of a highly active visible light C–N-co-doped TiO2 nano catalyst that we prepared via the sol-gel method and pyrolysed at 350 ◦C for 105 min in an inert atmosphere to prevent combustion of carbon moieties
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    Effect of the annealing atmosphere on the layer interdiffusion in Pd/Ti/Pd multilayer stacks deposited on pure Ti and Ti-alloy substrates
    (University of the Western Cape, 2019) Halindintwali, Sylvain; Donald, Earl; Cummings, Franscious; Arendse, Christopher
    Pd(50 nm)/Ti(25 nm)/Pd(50 nm) multilayer stack has been deposited on Ti and Ti6Al4V substrates; we have studied the intermixing of layers upon annealing at the hydrogenation temperature of 550 °C, under vacuum, H/Ar gas mixture and pure hydrogen atmospheres. Scanning electron microscopy (SEM) micrographs indicated surface roughening in samples annealed under vacuum and H/Ar gas mixture while those annealed under pure H2 remained relatively smoother. Rutherford backscattering spectrometry (RBS) revealed intermixing of layers as evidenced by the diffusion of Pd toward the bulk, while XRD indicated the formation of PdTi2 phase in the samples annealed under vacuum and H/Ar gas mixture atmosphere. In-situ, real-time RBS showed that the annealing under pure H2 preserves the integrity of the Pd catalyst. No indication of the PdTi2 formation in the pure H2 annealed samples was observed; instead only the TiH2 phase appeared, indicating the absorption of H into the system.
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    Electrodeposited CuO thin film for wide linear range photoelectrochemical glucose sensing
    (Elsevier, 2022) Cummings, Franscious; Cory, Neville J; Chamier, Jessica; Sackey, Juliet; Chowdhury, Mahabubur
    Cupric oxide (CuO) has been used as a non-enzymatic glucose sensor for decades. However, there is a paucity of publications on bare CuO based photo electrochemical (PEC) glucose detection. In this study, a photo active CuO thin film was electrodeposited onto conductive glass and its band gap was tuned by etching in NH3 solution. A 6 W light-emitting diode (LED) bulb was used as the light source for PEC glucose oxidation. Various physical and electrochemical characterization techniques were used to study the PEC behavior of the CuO thin film electrode during glucose oxidation. The electrochemical oxidation of glucose was found to be an irreversible electron transfer process controlled by diffusion at the electrode surface under illumination and dark conditions. Electrochemical impedance spectroscopy (EIS) confirmed that the charge transfer resistance in the light decreases by several orders of magnitude. Good amperometric performance was obtained for the CuO film with a 4 s response time and negligible interference from other species present in human blood. The as prepared sensor exhibited a remarkable wide linear range up-to 29 mM.
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    A highly responsive nh3 sensor based on pd-loaded zno nanoparticles prepared via a chemical precipitation approach
    (ScienceDirect, 2019) Cummings, Franscious
    The gas-detecting ability of nanostructured ZnO has led to significant attention being paid to the development of a unique and effective approach to its synthesis. However, its poor sensitivity, cross-sensitivity to humidity, long response/recovery times and poor selectivity hinder its practical use in environmental and health monitoring. In this context, the addition of noble metals, as dopants or catalysts to modify the ZnO surface has been examined to enhance its sensing performance.
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    Opto-electronic properties of anodized TiO2 nanotube arrays investigated using electron energy loss spectroscopy
    (sciencedirect, 2019) Cummings, Franscious
    A study of the nanoscale crystallinity of anodized TiO2 nanotubes is reported with the aim of demonstrating its influence on the localized optical and electronic properties of the structure. By employing scanning transmission electron microscopy, coupled with electron energy loss spectroscopy, x-ray diffraction and electron energy filtered jump-ratio imaging to probe changes in the electron near edge fine structure of the Ti L3,2 ionization edge, it is found that nanotubes annealed at 450 °C in air for 3 h crystallize in the anatase polymorph along their walls, with the underlying thick oxide barrier layer being predominantly rutile.
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    Structural features of air-processible methyl ammonium lead triiodide (MAPbI3) perovskite thin films grown on Al-doped ZnO Nanowire Arrays
    (University of the Western Cape, 2023) Phakoe, Mpho; Cummings, Franscious
    The performance of air stable, mixed halide (MAPbI3-xClx) perovskite based solar cells is highly dependent on the quality and stability of the perovskite thin film, which in turn, is dependent on the substrate on which it is deposited. ZnO presents excellent optoelectronic properties such as high electron mobility and diffusion length, direct band gap with high exciton binding energy. An array of ZnO nanowires (NWs) grown vertically on a conducting substrate, benefits from a large surface area, direct electron transport pathway and reduced recombination rate of carriers when used in a solar cell. These arrays of ZnO NWs may be synthesised by a wide range of methods, with the chemical bath deposition (CBD) method considered to be the most simple and cost-effective.
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    Synthesis of One-Dimensional TiO2 Nanotube Arrays by Potentiostatic Anodisation
    (University of the Western Cape, 2017) Tshaka, Anele; Cummings, Franscious
    TiO2 nanomaterials, in particular nanotubes, are some of the most studied materials, as they are considerably important in technological and biological applications due to their unique electronic properties and biocompatibility. For example, vertically aligned TiO2 nanotubes play a crucial role in photovoltaics as they enhance the charge separation as a result of their excellent photo-catalytic properties in the presence of organic dye molecules, and provide a superior one-dimensional transport route compared to nanoparticle films. There are numerous techniques used to synthesise TiO2 nanotubes, such as chemical vapor deposition (CVD), template based techniques, anodisation, to name but a few. However, due to its non-toxicity environmental friendliness and cost-effectiveness, anodisation is the most common technique to synthesise TiO2 nanotubes. In addition anodisation allows for control over the morphology when tailoring the anodisation parameters such as voltage, concentration, temperature and duration. It is well-documented that the as-synthesised TiO2 nanotubes via anodisation technique are amorphous and require post-treatment at elevated temperature (above 280 degrees C) to induce crystallinity into anatase phase. Further increase in annealing temperature results in crystallisation in either rutile or mixed phase structure.