Radiation damage in GaAs and SiC
- Authors: Janse van Vuuren, Arno
- Date: 2011
- Subjects: Gallium arsenide semiconductors
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10515 , http://hdl.handle.net/10948/1477 , Gallium arsenide semiconductors
- Description: In this dissertation the microstructure and hardness of phosphorous implanted SiC and neutron irradiated SiC and GaAs have been investigated. SiC is important due to its application as a barrier coating layer in coated particle fuel used in high temperature gas cooled reactors. The characterisation of neutron irradiated GaAs has been included in this study in order to compare the radiation damage produced by protons and neutrons since proton bombardment of SiC could in principle be used for out-of-reactor simulations of the neutron irradiation damage created in SiC during reactor operation. The following SiC and GaAs compounds were investigated: As-implanted and annealed single crystal 6H-SiC wafers and polycrystalline 3C-SiC bulk material implanted with phosphorous ions. As-irradiated and annealed polycrystalline 3C-SiC bulk material irradiated with fast neutrons. As-irradiated and annealed single crystal GaAs wafers irradiated with fast neutrons. The main techniques used for the analyses were transmission electron microscopy (TEM) and nano-indentation hardness testing. The following results were obtained for the investigation of implanted and irradiated SiC and GaAs: Phosphorous Implanted 6H-SiC and 3C-SiC The depth of the P+ ion damage was found to be in good agreement with predictions by TRIM 2010. Micro-diffraction of the damage region in P+ implanted 6H-SiC (dose 5×1016 ions/cm2) indicates that amorphization occurred and that recrystallisation of this layer occurred during annealing at 1200°C. TEM analysis revealed that the layer recrystallised in the 3C phase of SiC and twin defects also formed within the layer. Micro-diffraction of the damage region in P+ implanted 3C-SiC (dose 1×1015 ions/cm2) indicates that amorphization also occurred for this sample and that recrystallisation of this layer occurred during annealing at 800°C. Nano-hardness testing of the P+ implanted 6H-SiC indicated that the hardness of the implanted SiC was initially much lower than unimplanted SiC due to the formation of an amorphous layer during ion implantation. After annealing the implanted SiC at 800°C and 1200°C, the hardness increased due to re-crystallisation and point defect hardening. Neutron Irradiated 3C-SiC TEM investigations of neutron irradiated 3C-SiC revealed the presence dark spot defects for SiC samples irradiated to a dose of 5.9×1021 n/cm2 and 9.6×1021 n/cm2. Neutron Irradiated GaAs TEM investigation revealed a high density of dislocation loops in the unannealed neutron irradiated GaAs. The loop diameters increased after post-irradiation annealing in the range 600 to 800 °C. The dislocation loops were found to be of interstitial type lying on the {110} cleavage planes of GaAs. This finding is in agreement with earlier studies on 300 keV proton bombarded and 1 MeV electron irradiated GaAs where interstitial loops on {110} planes became visible after annealing at temperatures exceeding 500 °C. The small dislocation loops on the {110} planes of the neutron irradiated GaAs transformed to large loops and dislocations after annealing at 1000 °C.
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- Date Issued: 2011
'n Dekonstruksie van 'n teks uit Die ongedanste dans van Breyten Breytenbach
- Authors: Vorster, Anton Ferreira
- Date: 1988
- Subjects: Breytenbach, Breyten -- Criticism and interpretation
- Language: Afrikaans
- Type: Thesis , Masters , MA
- Identifier: vital:3572 , http://hdl.handle.net/10962/d1002095 , Breytenbach, Breyten -- Criticism and interpretation
- Description: The thesis provides an interpretation of the poem ʺ(Taalstryd)ʺ (Lewendood, p.143) by employing deconstruction theory, particularly as it has been developed by Jacques Derrida. The main assumption is that the text is not a self-sufficient entity, but finds itself in a continually changing relationship with other texts, a relationship described by deconstructionists as intertextuality. This relationship, as it has been described by Julia Kristeva, does not only involve literary works, but also the world-as- text. In chapter one this point of view is illustrated in a discussion around the title of the poem. It is postulated that the title is not a neutral description of a period in the history of the development of the Afrikaans language. Rather, it represents an ideological concept which can be interpreted in various ways. The poem clearly lends itself to an interpretation of "the struggle for the Taal" as a struggle which has manifested itself in many different areas and historical periods within the South African context. In chapter two the discussion of the relationship between language, history and ideology is continued. It is shown how the ʺofficialʺ history represents a one-sided view of Afrikaans as a ʺEuropeanʺ language, greatly ignoring its African component. This representation relies on a logocentric approach to the relationship between language and writing. Breytenbach's poetry, like the writings of Derrida, can be regarded as a "deconstruction" of this approach. The ʺdisseminationʺ of meaning in ʺ(Taalstryd)ʺ is illustrated in terms of the poem's intertextual relationship with Breytenbachʾs ʺPlease don't feed the animalsʺ and Krigeʾs ʺLied van die Fascistiese bomwerpersʺ. Chapter three sets ʺ(Taalstryd)ʺ within the current debate surrounding Afrikaner survival. It is shown how the Afrikaner power base has been established and strengthened by way of legislation, the system of Christian National Education, as well as the creation of a nationalist-orientated history. This power base is currently in a state of crisis, in which different political groupings are continuing the ʺ(Taalstryd)ʺ
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- Date Issued: 1988