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Masters Degrees (Physics)

Permanent URI for this collectionhttps://hdl.handle.net/10413/6604

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Browsing Masters Degrees (Physics) by SDG "SDG4"

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    Improved collection of photogenerated current using bi-metal nanoparticles.
    (2024) Jili, Ncedo.; Mola, Genene Tessema.
    The energy demand has been continuously growing owing to the shortage of sources of traditional energy (such as fossil fuels), due to the growing population of the world, and increased industrialization, which prompted the need for more energy. However renewable energy (such as photovoltaics) has attained attention due to its reliance on the infinite energy source (sun) which provides an hour long energy flow that fulfil the yearly energy of the glob. Not only that, renewable energy sources offer clean energy, that is meant to contribute to decarbonization in the future and reduce environmental changes. Solar cell materials that can effectively capture photons and conduct charges are continuously investigated for the last six decades. Contrarily to silicon based solar cells, organic solar cells are among the most promising solar cells in terms of offering cheap device fabrication, flexibility, high absorption, etc. However, these solar cells still suffer from low efficiency compared to traditional silicon solar cells due to poor absorption, low mobility, and poor stability. Numerous strategies have been employed to improve the efficiency of OSC devices, these include Ternary OScs, Tandem OSCs, and the inclusion of nanoparticles in OSC devices. Nanoparticles remain the best candidate to feature in OSC devices because Tandem OSCs require multi-absorber layers which leads to high device cost, whereas nanoparticles can be produced at a small scale and still offer good results. This study takes advantage of the features offered by the nanoparticles and uses them to investigate the effect of Nickel doped with cobalt bi-metal nanoparticles(Ni/Co BMNPs) in the PEDOT:PSS buffer layers of the P3HT: PCBM-based devices. Solar cells were successfully fabricated with four different concentrations of Ni/Co BMNPs as 0.05 %(0.5 mg), 0.15 %(1.5 mg), and 0.25 %(2.5 mg). Significant improvements were achieved for the 0:05% with the Fill factor of 58:52 %, and current density of 15.31 mA/cm2, and maximum efficiency of 5:05 % which displayed 67:8 % improvement from the undoped device. The investigation was further conducted by simulation program called SCAPS to confirm the contribution of the metal nanoparticles on the device performance. The results were reproduced in SCAPS where the energy band gap of the P3HT:PCBM and the shallow conduction density of electrons of the PEDO:PSS were simultaneously varied. All results are comparable with the experimental results and found to be similar. The device that was made to mimic the 0:05 % device produced a FF of 57:76 %, Jsc of 15.76 mA/cm2, and maximum efficiency of 5:76 % which displayed 88 % improvement from the undoped device. This study further provides factors that contributed to the high/low device performance due to the inclusion of the BMNPs in the OSC device and some of the necessary background and theory are provided to support these findings.
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    Synthesis and characterization of magnetic iron oxide nanoparticles.
    (2022) Ndlovu, Nkanyiso Linda.; Masina, Colani John.
    Three high-purity cubic spinel-type crystalline magnetic iron oxides i.e. Fe3O4, CoFe2O4, and NiFe2O4 nanoparticles were successfully synthesized by co-precipitation method. X-ray diffraction (XRD) showed the formation of stoichiometric phases with average particle size of 11.7 nm, 23.6 nm, and 16.4 nm for the as-prepared Fe3O4, CoFe2O4, and NiFe2O4 nanoparticles, respectively. Transmission electron microscopy (TEM) observation for all three samples revealed spherical morphology with single magnetic domain structure. From high resolution TEM (HR-TEM) imaging, lattice fringes with d-spacing of 0.473 nm and 0.248 nm corresponding to (111) and (311) reflections planes, were observed for both the Co-doped and Ni-doped samples. Energy-dispersive x-ray spectroscopy (EDX) analysis showed the presence and homogeneous distribution of main elements Fe, O, Co, and Ni in the samples. Quantitative EDX results confirmed the formation of stoichiometric CoFe2O4 and NiFe2O4 phases with the experimentally measured weight wt% of the samples closely equal to the theoretical calculated wt% values i.e. Fe = 46.35 wt%, O = 26.79 wt%, and Co = 26.87 wt% for CoFe2O4, and Fe = 47.02 wt%, O = 27.27 wt%, and Ni = 24.75 wt% for NiFe2O4. The magnetic properties of these nanoparticles were investigated by 57-Fe Mossbauer spectroscopy (MS) and Vibrating Sample Magnetometer (VSM) techniques. Room temperature MS spectrum for the pure Fe3O4 phase consist of two superimposed sextets with isomer shifts (0.321, 0.463) mm/s and hyperfine field (57.3, 43.4) T attributed to tetrahedral (A-sites) and octahedral (B-sites). The CoFe2O4 and NiFe2O4 samples both showed room temperature MS spectra consisting of two sextets and a single central paramagnetic doublet. The two sextets in each sample had almost equal isomer shifts for both A- and B-sites i.e. 0.2956 & 0.3247 mm/s and 0.3784 & 0.2761 mm/s for each of the sites of the CoFe2O4 and NiFe2O4 sample, respectively. The paramagnetic doublet was fitted with isomer shift of 0.3272 mm/s for the CoFe2O4 sample and 0.3249 mm/s for the NiFe2O4 sample. Temperature dependence M-T magnetization curves measured at H = 500 Oe inthe zero-field-cooled (ZFC) and field-cooled (FC) conditions showed the superparamagnetic nature of all three particles. The MZFC magnetization curve showed a maximum (cusp) at 225 K, 300 K, and 228 K corresponding to blocking temperature (TB), for Fe3O4, CoFe2O4, and NiFe2O4, respectively. For the CoFe2O4 sample the irreversibility temperature (Tirr) was equal to the blocking temperature (TB). While measured Tirr for Fe3O4 and NiFe2O4 was 300 K for both samples. The M-H magnetization curves at 300 K for all three samples revealed the coexistence of ferrimagnetic and superparamagnetic behaviour of the nanoparticles. At 300 K all three samples exhibit symmetrical and almost "closed" hysteresis loops with coercivity approximately 36, 70, and 117 Oe and remanence magnetization of approximately 5, 3, and 4 emu/g, for Fe3O4, NFe2O4, and CoFe2O4, respectively. Furthermore, M-H measurements at 300 K showed a high saturation magnetization of 89 emu/g for the Fe3O4 sample compared to 37 emu/g and 26 emu/g for the CoFe2O4, and NiFe2O4, respectively. M-H measurements recorded at low temperatures showed rather "opened" hysteresis loops compared to loops measured at 300 K. In contrast to saturated magnetization M-H curves for the Fe3O4 and NiFe2O4 nanoparticles, unsaturated M-H loops were observed for CoFe2O4 sample in the temperature range 10 - 100 K. A significant increase in coercivity to 102 Oe, 391 Oe, and 2.4 kOe was observed for Fe3O4, NiFe2O4, and CoFe2O4, respectively, when the temperature was reduced from 300 K to 10 K. For the CoFe2O4 sample, a highest coercivity of 2.7 kOe was measured at 100 K. And finally, M-H data at 10 K showed high saturation magnetization of 100 emu/g, 51 emu/g, and 31 emu/g, for the pure magnetite, CoFe2O4, and NiFe2O4 samples, respectively.
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    Wigner functionals and ghost imaging.
    (2023) Durgapersadh, Akshay.; Konrad, Thomas.; Roux, FiIippus Stefanus.
    This dissertation discusses Wigner functionals and an application, namely ghost imaging. Wigner functionals aim to provide more accurate measurement results due to the inclusion of all the degrees of freedom of light. The main concepts discussed are spontaneous parametric down-conversion (SPDC), the evolution equation for light through the SPDC crystal, the probability distribution for the ghost image, conditional probability distribution, and the point spread function. The ghost imaging calculation is done for the rational thin crystal and extreme thin crystal limits. It is shown that the probability distribution produced is the same for the rational thin crystal and extreme thin crystal limits, and consequently, the point spread function, and conditional probability distributions are the same.