UWCScholar :: Browsing by Author "Kotsedi, Lebogang"

Browsing by Author "Kotsedi, Lebogang"

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Aluminium induced crystallization of hydrogenated amorphous silicon thin films
(University of the Western Cape, 2005) Kotsedi, Lebogang; Knoesen, Dirk; Madjoe, Reginalt
This study was carried out to crystallize hydrogenated amorphous silicon (a-Si:H) thin films using the aluminium induced crystallization (AIC) technique. This was done to investigate whether is there any lateral crystallization of the a-Si:H thin film away from the aluminium covered surface of the film. The hot wire chemical vapour deposition system (HWCVD) was used to deposit hydrogenated amorphous silicon thin films (a-Si:H) on Corning glass 7059 substrates. The substrate temperature was kept at 300oC while the filament temperature was l600oC during the deposition. The aluminium top layer was deposited at room temperature using the electron beam evaporator. The aluminium deposited, only partially covered the sample, this was done to investigate whether lateral crystallization of the uncovered part will take place. Samples were then annealed at 450oC for times ranging from 30 to 150 minutes in incremental steps of 30 minutes. A temperature series of annealings at l00oC, 150oC, 200oC,300"C and 350oC for 60 minutes were also performed. Energy Dispersive Spectroscopy (EDS) was used for elemental identification after annealing. Rutherford Backscattering Spectrometry was used for the depth profiling of the diffused species. X-ray diffraction (XRD) technique was used for crystallization studies on the aluminium covered side, transmission electron microscopy (TEM) was used to study lateral crystallization and diffraction patterns of crystallized part were taken using selected area diffraction (SAD).
Bio-synthesised black α-Cr2O3 nanoparticles; experimental analysis and density function theory calculations
(Elsevier, 2021) Kotsedi, Lebogang; Sackey, Juliet; Morad, R
A selective single phase black α-Cr2O3 nanoparticles was bio-synthesised via simple straight-forward green synthesis approach. The process involves extraction of phytochemicals contained in peels of sweet potatoes. Extraction was done in distilled water under constant magnetic stirring at a temperature of 70–80 °C resulting in a dusty yellow colour aqueous extracts. Afterwards, chromic nitrate salt was added to extracts resulting in reduction of metal salt to metal nanoparticles. Obtained precipitates were dried and annealed in the air for 2 h ready to be applied without further post synthesis modifications. SEM and EDS analysis of annealed precipitates reveal distinct shapes and high purity of nanoparticles. The effects of the annealing temperature are evident in the nanoparticle sizes. SAED and XRD patterns expose bright diffraction peaks which are harmonized to the rhombohedral structure of pure Eskolaiteα-Cr2O3. By quantitative analysis of XRD data, it was noted that lattice parameters and crystal sizes slightly decrease w.r.t increase annealing temperature.
Eco-friendly synthesis, characterization, in vitro and in vivo anti-inflammatory activity of silver nanoparticle-mediated Selaginella myosurus aqueous extract
(Dovepress, 2018) Kedi, Philippe Belle Ebanda; Meva, Francois Eya’ane; Kotsedi, Lebogang; Nguemfo, Edwige Laure; Zangueu, Calvin Bogning; Ntoumba, Agnes Antoinette; Mohamed, Hamza Elsayed Ahmed; Dongmo, Alain Bertrand; Maaza, Malik
Introduction: There is emerging interest in medicinal plants in the biomedical field, due to their multitude of chemicals which show anti-inflammatory, antimicrobial, antiviral, or antitumoral potential. Research on medicinal plants has shown that nanotechnology could offer new solutions in the quality control, delivery aspects, or in sustaining herbal biological activities. This work reports on the preparation and characterization of silver nanoparticle-mediated Selaginella myosurus plant extract. Methods: Ultraviolet-visible spectroscopy, Fourier transform infrared spectroscopy, powder X-ray diffraction, energy dispersive X-ray spectroscopy, high-resolution scanning electron microscopy, high-resolution transmission electron microscopy, and selected area electron diffraction have been used to characterize the prepared silver nanoparticles. The synthetic stability was studied by varying concentrations and pH of reactants. Egg albumin denaturation and carrageenan-induced rat paw edema model were used to ascertain the anti-inflammation. Results: Ultraviolet-visible spectroscopy gave plasmon resonance ranging between 420 and 480 nm while Fourier transform infrared spectroscopy proved nano interface functionalized with organics. The powder X-ray diffraction pattern is in agreement with silver and silver chloride nanoparticles of crystallite size 33.7 nm and 44.2 nm for silver and silver chloride, respectively. Energy dispersive X-ray spectroscopy enables elemental characterization of the particles consisting of silver and silver chloride among main elements. Spherical silver grain of 58.81 nm average size has been depicted with high-resolution scanning electron microscopy and high-resolution transmission electron microscopy. Inhibitions of 99% and 60% were obtained in vitro and in vivo, respectively. Conclusion: The albumin denaturation and carrageenan-induced rat hind paw edema model to assess the anti-inflammatory potential of generated nanoparticles suggests that the silver nanoparticles may act as reducing/inhibiting agents on the release of acute inflammatory mediators. Hence, this work clearly demonstrated that silver nanoparticles mediated-Selaginella myosurus could be considered as a potential source for anti-inflammatory drugs.
Fabrication and characterization of a solar cell using an aluminium p-doped layer in the hot-wire chemical vapour deposition process
(University of the Western Cape, 2010) Kotsedi, Lebogang; Knoesen, Dirk; Madjoe, Reginaldt; Dept. of Physics
When the amorphous silicon (a-Si) dangling bonds are bonded to hydrogen the concentration of the dangling bond is decreased. The resulting film is called hydrogenated amorphous silicon (a-Si:H). The reduction in the dangling bonds concentration improves the optoelectrical properties of the film. The improved properties of a-Si:H makes it possible to manufacture electronic devices including a solar cell. A solar cell device based on the hydrogenated amorphous silicon (a-Si:H) was fabricated using the Hot-Wire Chemical Vapour Deposition (HWCVD). When an n-i-p solar cell configuration is grown, the norm is that the p-doped layer is deposited from a mixture of silane (SiH4) gas with diborane (B2H6). The boron atoms from diborane bonds to the silicon atoms and because of the number of the valance electrons, the grown film becomes a p-type film. Aluminium is a group 3B element and has the same valence electrons as boron, hence it will also produce a p-type film when it bonds with silicon. In this study the p-doped layer is grown from the co-deposition of a-Si:H from SiH4 with aluminium evaporation resulting in a crystallized, p-doped thin film. When this thin film is used in the n-i-p cell configuration, the device shows photo-voltaic activity. The intrinsic layer and the n-type layers for the solar cell were grown from SiH4 gas and Phosphine (PH3) gas diluted in SiH4 respectively. The individual layers of the solar cell device were characterized for both their optical and electrical properties. This was done using a variety of experimental techniques. The analyzed results from the characterization techniques showed the films to be of device quality standard. The analysed results of the ptype layer grown from aluminium showed the film to be successfully crystallized and doped. A fully functional solar cell was fabricated from these layers and the cell showed photovoltaic activity.
Influence of synthesis method on structural
(Springer, 2023) Noukelag, Sandrine Kamdoum; Noukelag, Sandrine Kamdoum; Ngqoloda, Siphelo; Kotsedi, Lebogang
This contribution reports on the development of two versatile and efcient methods, namely the green and gamma radiolysis for Fe-Ag nanoparticles (NPs) synthesis, characterization, and further their growth inhibition potential on some spoilage microorganisms. Green Ag/Fe2O3 NPs were obtained at Fe-Ag [3:1], annealing temperature of 800 °C for 2 h, and gamma irradiated Ag/Fe3O4 NPs were obtained at Fe-Ag [7:1], a 50 kGy dose. The characterization techniques were performed with these two samples whereby the sizes from crystallographic and microscopic analyses were 39.59 and 20.00 nm for Ag/Fe2O3 NPs, 28.57 and 15.37 nm for Ag/Fe3O4 NPs, respectively. The polycrystallinity nature observed from X-ray diffraction was in accordance with the selected area electron difraction. The vibrational properties confrmed the presence of bimetallic Fe-Ag NPs with the depiction of chemical bonds, Fe–O and Ag–O from attenuated total refection-Fourier transform infrared spectroscopy and elements Ag, Fe, O from energy-dispersive X-ray spectroscopy analyses. The magnetic properties carried out using a vibrating sample magnetometer suggested a superparamagnetic behavior for the Ag/Fe2O3 NPs and a ferromagnetic behavior for the Ag/Fe3O4 NPs. Overall, the green Ag/Fe2O3 NPs successfully inhibited the growth of spoilage yeasts Candida guilliermondii, Zygosaccharomyces fermentati, Zygosaccharomyces forentinus, and spoilage molds Botrytis cinerea, Penicillium expansum, Alternaria alstroemeriae.
Infuence of Synthesis Method on Structural, Morphological, Magnetic, and Antimicrobial Properties of Fe‑Ag Nanoparticles
(Springer, 2023) Noukelag, Sandrine Kamdoum; Ngqoloda, Siphelo; Mewa‑Ngongang, Maxwell; Kotsedi, Lebogang; Razanamahandry, Lovasoa Christine; Ntwamp, Seteno; Arendse, Christopher; Maaza, Malik
This contribution reports on the development of two versatile and efcient methods, namely the green and gamma radiolysis for Fe-Ag nanoparticles (NPs) synthesis, characterization, and further their growth inhibition potential on some spoilage microorganisms. Green Ag/Fe2O3 NPs were obtained at Fe-Ag [3:1], annealing temperature of 800 °C for 2 h, and gamma irradiated Ag/Fe3O4 NPs were obtained at Fe-Ag [7:1], a 50 kGy dose. The characterization techniques were performed with these two samples whereby the sizes from crystallographic and microscopic analyses were 39.59 and 20.00 nm for Ag/Fe2O3 NPs, 28.57 and 15.37 nm for Ag/Fe3O4 NPs, respectively. The polycrystallinity nature observed from X-ray diffraction was in accordance with the selected area electron difraction. The vibrational properties confrmed the presence of bimetallic Fe-Ag NPs with the depiction of chemical bonds, Fe–O and Ag–O from attenuated total refection-Fourier transform infrared spectroscopy and elements Ag, Fe, O from energy-dispersive X-ray spectroscopy analyses. The magnetic properties carried out using a vibrating sample magnetometer suggested a superparamagnetic behavior for the Ag/Fe2O3 NPs and a ferromagnetic behavior for the Ag/Fe3O4 NPs. Overall, the green Ag/Fe2O3 NPs successfully inhibited the growth of spoilage yeasts Candida guilliermondii, Zygosaccharomyces fermentati, Zygosaccharomyces forentinus, and spoilage molds Botrytis cinerea, Penicillium expansum, Alternaria alstroemeriae.
Isothermal and non-isothermal comparative study of Zn-sn system using real-time RBS
(2021) Mnguni, Mmangaliso Mpilonde; Kotsedi, Lebogang
Solid-state reactions of bi-metallic systems can be driven or activated by various external stimuli like pressure, energetic photons, energetic charged particles or heat. For an example, high pressure torsion can be applied to aluminium-copper (Al-Cu) to drive solid-state reaction [1.1]. Oh-ishi et al. [1.1] applied a pressure of 6 GPa to Al and Cu half discs. Following this, x-ray diffraction (XRD) and high-resolution transmission electron microscope (HRTEM) were used to confirm the formation of different intermetallic phases such as Al2Cu and Al4Cu9. One of the first reported case where photons were used to drive solid phase diffusion was reported in 1998 by Ditchfield et al. [1.2]. The study was carried out to study the non-thermal effects of photons illumination on surface diffusion, an important process in microelectronics fabrication. Surface diffusion governs several important steps in microelectronics fabrication including the formation of hemispherical grained silicon used in memory devices [1.2], filling of channels with metals for devices interconnection purposes among others [1.2]. In this study, germanium-indium (Ge-In) on silicon was used because the thermal diffusion of this system was well understood [1.3]. Surface diffusion was measured in ultrahigh vacuum via second harmonic microscopy when the sample was illuminated with pulsed Nd: YAG laser at a wavelength of 1064 nm [1.3]. This study showed conclusively that photons could be used to drive solid-state reactions.
Isothermal and non-isothermal comparative study of zn-sn system using real-time rbs
(University of the Western Cape, 2021) Mnguni, Mmangaliso Mpilonde; Kotsedi, Lebogang
Insight into the effects of isothermal and non-isothermal annealing on bi-metallic thin film is important for material synthesis and application in everyday use. The effects of isothermal annealing on bi-metallic thin films has long been studied using various heating methods from a resistively heated filaments, by transferring heat via conduction, convection and irradiation. The effect of each method have been widely reported in literature. The diffusion coefficient and activation energies of the constituent atoms can calculated for each annealing method. On the other hand, the effects of non-isothermal annealing on bi-metallic thin films has not been comprehensively studied, and there are areas of this annealing regime that need further investigation. In this study a femtosecond laser with a 1064 nm central wavelength was used to anneal bi-metallic thin films of Zinc-Tin (Zn-Sn) on a substrate.
Out of thermodynamic equilibrium reaction of zinc-molybdenum system monitored by real-time rutherford backscattering spectrometry
(University of the Western Cape, 2022) Sobhoyise, Ayanda; Kotsedi, Lebogang
Solid phase reaction of bi-metallic thin films of zinc-molybdenum was thermally induced in order to investigate the diffusion kinetics of this bi-metallic system. The Zinc-Molybdenum bilayers were prepared by depositing a 50 nm thin film of Zinc on a substrate, followed by deposition of 50 nm layer of Molybdenum onto the Zinc film. All this was done in the electron beam evaporation chamber in sequential manner without breaking vacuum. The substrate temperature was at room temperature, the deposition pressure and the power supply current were approximately 1 ´ 10-6 mbar and 25 mA respectively. The samples were isothermally annealed using in-situ real-time Rutherford backscattering spectrometry using the incident energy of 3.045 MeV. In-situ real-time Rutherford backscattering spectrometry enabled the tracking of atomic diffusion and depth profiling between Zinc and Molybdenum layers while heating the sample.

Browsing by Author "Kotsedi, Lebogang"

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