Browsing by Author "Njoroge, E.G."

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    Investigating the structural changes induced by SHI on W–SiC samples
    (Vacuum, 2020) Thabethe, T.T.; Ntsoane, T.P.; Biira, S.; Njoroge, E.G.; Hlatshwayo, T.T.; Skuratov, V. A.; Malherbe, J.B.
    The structural modification of tungsten-SiC samples irradiated with Xe26þ swift heavy ions (SHIs) was investigated. Tungsten (W) thin films were deposited on 6H–SiC using e-beam. After deposition, the W–SiC samples were irradiated by 167 MeV Xe26þ ions to fluences of 1012 cm􀀀 2, 1013 cm􀀀 2 and 1014 cm􀀀 2 at room temperature. The sample composition, phase identification, residual stress component and surface morphology were investigated with Rutherford backscattering spectrometry (RBS), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results indicated that the as-deposited samples were composed of W and SiC, with no reaction between them. The samples irradiated to a fluence of 1012 cm􀀀 2 showed that a reaction between W and SiC took place resulting in the formation of WSi2 and WC phases. The samples irradiated to fluences of 1013 and 1014 cm􀀀 2 showed further reactions between W and SiC with WSi2 and WC being the only phases formed. The SiC substrate had bi-axial compressive stress which did not excess 700 MPa after irradiating to the highest fluence. The W layer deposited on SiC was flat and homogeneous after deposition. A textured surface with identifiable grains was observed after the SHI irradiations.
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    Irradiation effects of swift heavy ions on palladium films deposited on 6H-SiC substrate
    (Nuclear Inst. and Methods in Physics Research B, 2019) Thabethe, T.T.; Nstoane, T.; Biira, S.; Njoroge, E.G.; Hlatshwayo, T.T.; Skuratovd, V.A.
    The irradiation effect of swift heavy ions on palladium (Pd) films deposited on 6H-SiC was investigated. The samples were irradiated by Xe26+ ions with the energy of 167 MeV at fluences of 1×1013 cm−2 and 3×1014 cm−2 at room temperature. Phase identification, residual stress and surface morphology were investigated with X-ray diffraction (XRD) and scanning electron microscopy (SEM). The XRD results showed that the as-deposited sample was composed of Pd and SiC with no evidence of a reaction between Pd and SiC. No reaction was observed for the lower irradiation fluence, only an increase in the Pd peak intensities was observed indicating improvement in the crystallinity of the material. A reaction between Pd and SiC forming PdSi and Pd2Si was observed after irradiation at a fluence of 3×1014 cm−2. The stress measurements indicated that the films were having tensile and biaxial stress not exceeding 200 MPa. A decrease in stress values was observed with an increase in irradiation fluence. The surface morphology of the as-deposited was flat and composed of small granules. There was an increase in granule sizes due to irradiation at 1×1013 cm−2. Irradiating at 3×1014 cm−2 caused grain agglomeration and clustering.
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    The role of ZrCl4 partial pressure on the growth characteristics of chemical vapour deposited ZrC layers
    (Ceramics International, 2017) Biira, S.; Crouse, P.L.; Bissett, H.; Hlatshwayo, T.T.; Njoroge, E.G.; Nel, J.T.; Ntsoane, T.P.; Malherbe, J.B.
    ZrC layers were deposited in a chemical vapour deposition (CVD) reactor on graphite substrates using a ZrCl4- Ar-CH4-H2 precursor mixture. The deposition was conducted at different ZrCl4 partial pressures at a constant substrate temperature of 1400 °C for 2 h at atmospheric pressure. The deposited ZrC layers were characterised using X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM). The effect of ZrCl4 partial pressure on the growth rate, microstructure and surface morphology of the deposited layers was studied. The ZrCl4 partial pressure was manipulated by changing the flow rate of the argon carrier gas through the sublimation chamber. The boundary layer thickness decreased as ZrCl4 partial pressures increased due increased argon flows. The increased ZrCl4 partial pressure increased the growth rate of ZrC layers linearly. It was found that the transport process of the source materials was laminar and forced convection flow. The flow process of source materials through the boundary layer to the reacting surface was also illustrated using a model. The average crystallite size increased with ZrCl4 partial pressures, whereas the lattice parameter, lattice strain and dislocation density decreased as ZrCl4 partial pressure increased. The surface morphology of the asdeposited ZrC layers varied with the ZrCl4 partial pressure. The size of crystals grew larger and the cavities surrounding them decreased in number and size as the ZrCl4 partial pressure increased.