Masters Degrees (Physics)
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Browsing Masters Degrees (Physics) by Author "Bharuth-Ram, Krishanlal."
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Item 57 Fe Mössbauer studies of 57 Mn* implanted III-V semiconductors InP and InAs.(2011) Dlamini, Wendy Bonakele.; Naidoo, D.; Bharuth-Ram, Krishanlal.III-V compound semiconductors such as Gallium Arsenide, Indium Phosphide as well as Indium Arsenide have recently demonstrated the capability of applications in high speed semiconductor devices compared to those made from Silicon. As a result, III-V compound semiconductors have drawn attention of material researchers, in particular in understanding the effects that may occur during manufacturing of these devices. Optical and electrical properties of a device may alter when a foreign atom is introduced during the manufacturing of the device. However, the foreign atom may also lead to the formation of lattice disorder (defects). A convenient way of introducing impurity atoms into a substrate and tailoring their functionality for particular applications is by ion implantation. Mössbauer spectroscopy is a useful technique usually utilized for understanding site location of the impurity atoms in a lattice and the formation of defect complexes. The focus of this dissertation is the study of lattice location of ion implanted ⁵⁷Mn/⁵⁷Fe ions in the III-V semiconductors InP, n-type InAs and p type InAs, and the annealing of implantation induced lattice damage in these samples. ⁵⁷Fe Mössbauer spectroscopy studies have been conducted on III-V semiconductors InP, n-type InAs and p-type InAs with the 57Fe Mössbauer state being populated following the implantation of radioactive ⁵⁷Mn⁺ ions which has the advantage that extremely low fluence implantations are sufficient to give data with good statistics. The ⁵⁷Mn⁺ ions were accelerated to 60 keV at the ISOLDE/CERN facility and implanted with fluences of up to 2x10¹² ions/cm² into single crystal samples which were held at 300 –700 K in an implantation chamber. βdecay of the Mn⁺ imparts an average recoil energy of 40 keV to the daughter ⁵⁷*Fe which are then re-distributed onto interstitial and/or substitutional sites, or trapped in defect complexes and damage sites. The Mössbauer spectra were collected with a light-weight parallel plate avalanche counter, with ⁵⁷Fe enriched stainless steel electrodes, mounted on a conventional drive unit outside the implantation chamber. The spectra were analyzed with the Mössbauer fitting code VINDA which allowed for simultaneous fits of the set of spectra for each sample collected at different temperatures. Acceptable fits to the Mössbauer spectra of the InP, n-type InAs and p-type InAs samples required three components: an asymmetric doublet attributed to Fe atoms in implantation induced damaged environments, a single line assigned to Fe on substitutional In sites, and a weak symmetric doublet assigned to impurity-vacancy complexes. In InP there is already an appreciable substitutional Fe (Feѕ) fraction on implantation at room temperature; while in the InAs samples FeS only becomes significant above 400 K. In all samples, the asymmetric doublet dominates the spectra below 400 K. Implantation damage, however, anneals quite rapidly and at high temperatures (above 400 K), the single line due to Feѕ dominates the spectra while the Fe-defect complex dissociates at 500 K. The implantation induced damage is observed to anneal fast in the arsenide samples compared to the phosphide sample. The slow annealing of the damage in InP was supported by the higher Debye temperature (290 K) extracted from the temperature dependence of the site population for the damage site in InP compared with InAs (194 K and 200 K for n-type and p-type, respectively). Variations in the isomer shift and quadrupole splitting for the damage site in InP at high temperatures (above 400 K) suggest structural changes in the neighborhood of the ⁵⁷Fe probe. Furthermore, the isomer shifts of the spectral components were consistent with near trivalent state and fully trivalent state i.e., Fe³⁺ with d⁵ electron configuration for Fe ions in the damage site and at the substitutional (In) site, respectively. The impurity Fe atoms associated with vacancies are identified to be in the Fe²⁺ state with a d⁶ electron configuration.Item Magnetic cluster formation in Al₂O₃.(2017) Adoons, Vanthini Nelson.; Moodley, Mathew.; Bharuth-Ram, Krishanlal.Abstract available in PDF file.Item Mössbauer study of the hyperfine magnetic field and electric field gradient at Fe sites in synthetic diamond.(1992) Govender, Nadaraj.; Bharuth-Ram, Krishanlal.Mossbauer Spectroscopy has been used to investigate the site of Fe inclusions in a suite of synthetic diamonds (de Beers MDAS). Information on the hyperfine magnetic fields and electric field gradients at Fe sites in the diamond grains were obtained from Mossbauer Spectroscopy of diamond grains ranging in size from 25 to 250 um. The Fe inclusions in these samples resulted from the synthesis of the diamond grains in which Fe was used as a catalytic solvent. The Mossbauer measurements were carried at room temperature with a constant acceleration spectrometer operating in transmission geometry. The samples with the largest grain size of 180-250 um gave a well defined six component magnetically split spectrum, similar to the Zeeman split sextet obtained for natural iron. As the grain sizes decreased the intensity of the magnetically split components became greatly reduced and a strong paramagnetic component appeared. At grain sizes 105-45 um the spectra are dominated by a central single line with some evidence of an asymmetric doublet. For the finest grain size 38-25 um, the reappearance of the six magnetic hyperfine splitting components together with the strong central single paramagnetic component was observed. The change in the Mossbauer patterns observed with decreasing grain size suggest that a rapid phase transition of the Fe inclusions from ferromagnetic to superparamagnetic takes place. The analysis of Mossbauer spectra yielded a value of the hyperfine magnetic field of Bhf = -32.4(4) T and an electric field gradient in the range of Vzz = 1.4(4) 1.8( 7) X 10'8 V.cm- 2 at the site of the probe s7Fe nucleus. These values compare favourably with other measurements.Item Nuclear structure studies with (n,d) reactions.(1988) Naidoo, Ravenderan Yagambaram.; Bharuth-Ram, Krishanlal.; McMurray, W. R.The ²⁷AI(n,d)²⁶Mg and ⁵⁶Fe(n,d)⁵⁵Mn reactions have been studied at 22 MeV incident energy. The 6MV Van de Graaff facility at the National Accelerator Centre, Faure was used for the experimental aspects. An (n, charged particle) spectrometer was used to detect the energy and angle of the outgoing deuterons. The spectrometer allows for accumulation of particle discriminated data over an angular range of 80⁰. The intrinsic geometry of the spectrometer limits its' angular resolution to ~ 5⁰ (FWHM). The spectrometer has an energy resolution of ~ 0.7MeV(FWHM). A detailed study of the experimental system has been conducted and the proportional counters in particular were extensively investigated. A review of the relevant nuclear models for the target and residual nuclei is presented, together with a theoretical outline of the reaction mechanism for the (n,d) reaction. The distorted waves method approach is used in the analysis of the reaction cross sections. Optical potentials are used to simulate the incoming and outgoing distorted waves and thus generate the theoretical cross sections for the (n,d) reactions. The shapes of the angular distributions of the reaction cross sections for different orbital angular momentum transfers are compared to obtain a fit. Comparison of experimental and theoretical cross sections produce the spectroscopic factors which reveal the occupancy or vacany of level states and hence the single particle nature of these states. It was concluded from the study that the shell model of the nuclei under investigation gives a very good description of the results obtained for the (n,d) reactions.Item A study of the 90Zr(n,d)89Y reaction.(1986) Bawa, Ahmed Cassim.; Bharuth-Ram, Krishanlal.; McMurray, W. R.A study has been made of the 90 Zr(n,d) 89 Y reactlion at an incident neutron energy of 22 MeV. The experimental aspect of the study was performed at the Van der Graaf facility at the National Accelerator Centre, using a particle spectrometer developed by K Bharuth-Ram and W R McMurray for the study of neutron-induced charged-particle emissions. The spectrometer, which consists of a telescope of three multiwire proportional counters and a curved plastic scintillator, permits the simultaneous accumulation of data over an angular range of 80°. Solid-angle- calculations have been performed to correct for the effect of the geometry of the system on the angular distribution of the cross-sections. A review has been made of the shell model of the nucleus, the optical potential model and the distorted waves method (or DWBA) for the analysis of direct nuclear reactions. A distorted-waves method analysis of the reaction is performed with the code DWUCK 4 and the resulting angular distribution of the various cross-sections are compared with the experimentally obtained data. ThIs comparison produces spectroscopic factors which are used to perform some analysis of the nuclear structure of the 90 Zr nucleus.