Browsing by Author "Comrie, Craig"

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    Controlling CoSi2 formation temperature by reactive deposition
    (2008) Ahmed, Hind Ali Mohmmed; Comrie, Craig
    When cobalt is evaporated under ultra high vacuum conditions onto a heated silicon substrate, the reaction between the cobalt and the silicon starts immediately and cobalt silicides are formed directly - a technique referred to as reactive deposition. This procedure was used to grow silicide films over a variety of temperatures ranging between 375 - 550 ce. It was found that a disilicide film is formed directly for substrate temperature maintained at T
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    Development of a Time of Flight - Energy spectrometer for applications in Heavy Ion - Elastic Recoil Detection thin film analysis
    (2010) Msimanga, Mandlenkosi; Comrie, Craig; Pineda-Vargas, Carlos A
    Two principal aims of this work were firstly, to build and characterise a Time of Fight –Energy spectrometer and demonstrate its usability in Heavy Ion – Elastic Recoil Detection thin film materials analysis, and secondly, to measure stopping powers of heavy ions in thin foil compound materials using the newly built spectrometer. Key to the performance of the assembled spectrometer was its timing resolution. Characterisation measurements using a 27.5 MeV Kr15+ incident beam showed that the best timing resolution could be obtained when measurements are performed without timing preamplifiers in the signal processing chain. The best example was that of a resolution of 190 ps for 18 MeV 40Ca ions. The resultant depth resolution was found to be 6.8 nm for 40Ca recoils ejected from the surface layers of a CaF2 film on a Si substrate. A mass calibration procedure was devised for identification of light impurities in known sample structures, and the mass resolution, also a direct result of time resolution, was found to range between 0.8 u and 1.7 u in the atomic mass range 12 u to 40 u, respectively. Spectrum analysis was implemented using the software code KONZERD, enabling elemental quantification and measurement of film thickness. The lowest detectable atomic concentrations measured were 0.46 at.% for carbon and 0.84 at.% for oxygen. The analytical depth was up to 0.6 μm. Measurements were also carried out to determine stopping powers of ZrO2 and Mylar foils for 12C, 16O, 19F, 24Mg, 27Al and 28Si ions in the 0.1 – 0.6 MeV/u energy range. Of these, 27Al and 24Mg stopping power data generated in this work are the first such measurements for ZrO2, and 24Mg and 19F for Mylar.
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    The effects of annealing on phase transformation in platinum-molybdenum coatings
    (2012) Khumalo, Zakhelumuzi Mesuli; Blumenthal, M; Comrie, Craig
    The thermodynamic study of platinum binary systems has both fundamental and applied aspects. It is due to the fact that the formation of ordered phases increases the strength and surface hardness and could also have an impact on surface activity and chemical properties. The changes in mechanical, physical and chemical properties could be of significant importance in enhancing the performance of platinum-based systems in their respective applications, such as gas sensors, catalyst, fuel cells and superconductors. In this investigation, the phase transformation in Pt-Mo coated systems induced by thermal annealing was studied by X-ray diffraction, scanning electron microscope, transmission electron microscope, energy dispersive X-ray emission and Rutherford backscattering spectrometry. The phase analysis showed the presence of several intermetalic phases, Pt2Mo, PtMo and Pt2Mo3 which were observed to nucleate in sequence when the annealing time and temperature were extended. RBS analysis showed an increase in coating thickness after annealing which has been attributed to the formation of the Pt-Mo phases.
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    The formation of epitaxially stabilized nickel and cobalt silicides by pulsed laser annealing
    (2001) Kubeka, Thulani M; Comrie, Craig
    The formation of epitaxially stabilised nickel and cobalt silicides by pulsed laser annealing has been investigated. Thermally grown NiSi and CoSi and Si<111> substrate were irradiated with laser pulses in the energy density range between 0.4 - 1.0 J/cm² in an attempt to produce epitaxially stabilized silicides. The analysis was carried out using well established RBS and channelling techniques. In the bulk form, and in thin films, NiSi has an orthorhombic MnP crystal structure and cannot grow epitaxially on the cubic silicon substrate and channelling is nto observed in the silicides thus prepared. Since NiSi melts at a temperature 400°C below silicon, it is possible to melt the whole NiSi film without melting the substrate. The presence of channelling in the NiSi film observed after laser annealing at lower energy densities was an indication that complete melting of the film had occured allowing for re-ordering of atoms in the melt.
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    Optimisation of accelerator optics and the application of nuclear microscopy to the biomedical field
    (2005) Eisa, Mohamed Eltayeb M; Comrie, Craig; Conradie, Lowry; Pineda-Vargas, Carlos A
    With the aim of improving the reliability and stability of the beams delivered to the nuclear microprobe at IThemba LABS, as well as optimization of the beam characteristics along the Van de Graaf acceleratore beamlines in general, relevant modifications were implemented. The design and layout of the beamlines in general, relevant modifications were implemented. The design and layout of the beamlines were revised. The beam-optical characteristics through the accelerator, from the ion source up to the analysing magnet directly after the accelerator, were calculated and the design optimised, using the computer codes TRANSPORT, IGUN and TOSCA. The ion source characteristics and optimal operating conditions were determined on an ion source test bench. The measured optimal emittance for 90% of the beam intensity was bout 50π mm mrad for an extraction voltage of 6kV. These changes allow operation of the Nuclear Microprobe at proton energies in the range 1 MeV to 4 meV with beam intensities of tens of a pA at the target surface. The capabilities of the nuclear micropobe facility were evaluated in the improved beamline, with particular emphasis to the characertisation of hard human calcium-rich tissue materials. The process of demineralization in teeth erosion due to exposure to acidic media was investigated in a group of test and control healthy human molar teeth. Samples were cut in cubes of