AP-MOVPE growth and characterisation of GaSb/GaAs quantum dots
- Authors: Tile, Ngcali
- Date: 2018
- Subjects: Quantum theory , Quantum electronics Quantum dots Semiconductors
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/36716 , vital:34047
- Description: GaSb/GaAs quantum dots (QD) were grown by atmospheric pressure (AP) metal-organic vapour phase epitaxy (MOVPE) using triethylgallium (TEGa), tertiarybutylarsine (tBAs) and trimethylantimony (TMSb) as gallium (Ga), arsenic (As) and (Sb) sources, respectively. The effect of AP-MOVPE growth parameters on the formation of GaSb QD structures on GaAs was studied. The formation of small, coherent GaSb dots on GaAs improved with decreasing V/III ratios, which were controlled through changing either the TMSb/TEGa ratio at a constant growth temperature or changing the growth temperature at a constant TMSb/TEGa ratio. The maximum effective V/III ratio for dot formation was 0.175. The dot density was more sensitive to growth time than to source mole fraction in the reactor, since time determines the amount of deposited material. The dot density increased with increasing growth time, while the shape and size of the dots were more sensitive to the source vapour mole fraction, which controls the growth rate. Lower mole fractions resulted in smaller sized dots with a more uniform distribution compared to higher mole fractions. Dome-shaped dots with densities as high as 4×1010 cm-2, average base length of 35 nm and average height of 5 nm were achieved. Capping of GaSb QDs at high temperatures caused flattening and the formation of a thin, inhomogeneous GaSb layer inside GaAs. No obvious QD photoluminescence (PL) peak was detected for these samples. A two stage process for capping the dots (involving growth of a low temperature GaAs cap, followed by a high temperature cap) led to the retention of the dot-like features in/on a wetting layer (WL) of GaSb and distinct PL peaks for both the QDs and WL. An increase in excitation power during PL measurements for this particular sample caused the QD and WL peaks to shift to higher energies. This is attributed to electrostatic band bending, leading to triangular potential wells, typical for type II band alignment between GaAs and strained GaSb. Variable temperature PL measurements showed the decrease in the intensity of the WL peak to be faster than that of the QD peak as the measurement temperature increased. A detailed high resolution transmission electron microscopy analysis was performed to study the morphology and chemical interaction between GaAs and GaSb regions for capped GaSb/GaAs QDs. The capped dots had dimensions similar to those of uncapped dots and had a higher concentration of Sb at their center, with the periphery being intermixed with GaAs. Measurement of lattice strain performed inside these dots revealed the strain to be distributed inhomogenously throughout the dot area. The effect of GaAs host matrix on excitonic behaviour in AP-MOVPE grown GaSb/GaAs quantum dots was investigated. Room temperature (RT) PL emission was achieved from a single layer of quantum dots by controlling the GaAs host matrix growth temperature. These samples were prepared using a GaSb dot growth temperature of 530 °C, followed by growth of a thin GaAs ‘cold’ cap, before depositing the final part of the GaAs capping layer at either 550 °C, 600 °C or 650 °C. PL measurements at 10 K revealed QD emission peaks for all the samples at around 1.1 eV. However, variable temperature PL revealed different thermal quenching rates of the emission, with the rates of quenching reduced with increasing GaAs growth temperature. This was ascribed to reduced defect densities in GaAs grown at higher temperature, which resulted in QD emission even at RT. This RT emission peaked at approximately 1 eV. The hole localisation energy determined for these samples at RT was approximately 470 meV.
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- Date Issued: 2018
Construction project manager health and safety interventions towards improving workers' performance
- Authors: Ayessaki, Winn-Yam Houdou
- Date: 2016
- Subjects: Construction industry -- Management -- Health aspects Construction workers -- Health aspects -- South Africa Construction workers -- Safety measures
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/12275 , vital:27050
- Description: Optimum construction worker (CW) performance is required to achieve project delivery within project parameters. It is not always the case as CWs are regularly exposed to hazards, involved in accidents, their productivity is poor, they suffer from ill health, suffer from work-related musculoskeletal disorders (WMSDs) and contractors lack resources to allocate towards H&S. However, the lack or the absence of health and safety (H&S) measures, which the aforementioned depend on, has a negative impact on workers’ performance. Two descriptive surveys were conducted among professional construction project managers (CPMs) registered with the South African Council for Project and Construction Management Professions (SACPCMP) and general contractors (GCs) registered with the East Cape Master Builders Association (ECMBA). Interviews were also conducted with CPMs registered with the SACPCMP residing in the Nelson Mandela Bay metropolitan area. The salient findings include: • Accidents, which occur on construction sites, impact workers’ performance; • Inadequate H&S implementation affects both CW skills and motivation, which in turn affects their performance; • Poor constructability is relevant to H&S and CWs’ skills; • Provision and maintenance of welfare facilities are commonly inadequate and affect workers’ performance, and • Projects do not benefit from the adequate financial provision for H&S. It was concluded that exposure to hazards, poor site conditions, inadequate provision of welfare facilities, WMSDs, and insufficient financial provision for H&S affect workers’ performance by either incapacitating or demotivating them. Recommendations include : CPMs should make better use of their influence on clients; they should improve communication channels between project stakeholders; legislators need to raise awareness regarding H&S and worker welfare, and training and education institutions need to empower workers and professionals with H&S knowledge.
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- Date Issued: 2016
Managing conflict in the library information services of selected universities
- Authors: Dos Santos, Desiree
- Date: 2015
- Subjects: Conflict management -- South Africa -- Eastern Cape , Academic libraries -- South Africa -- Eastern Cape -- Administration , Technology -- South Africa -- Eastern Cape -- Information services , Academic librarians -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MPhil
- Identifier: vital:8325 , http://hdl.handle.net/10948/d1020307
- Description: Academic libraries are not immune to conflict; various important external and internal factors underlie conflict. Change, both external and internal, leads to interpersonal conflict amongst librarians which is caused by differing goals, policies, rules and decisions. Technology has been the major change in the digital era and academic libraries embarking on meeting the needs of the users have to manage change. It is important to understand how change evolves in order to manage it and the faster the change, the more conflict can be expected. The main purpose of this study is to investigate change and conflict in library and information services. The study collected data from two selected academic libraries - Fort Hare and Walter Sisulu. The reason for this choice is that the two libraries are from the Eastern Border region and strategically located to serve the deep rural and poverty-stricken communities. Both libraries are from merged institutions, under-developed and faced with change and conflict. Data was gathered by means of a literature study and face-to-face, semi-structured interviews with six participants in each library: two librarians in senior, two middle management and two librarians occupying lower level positions. Purposive sampling was used to select participants who fit the criteria and who could contribute to the study. The findings reveal that library staff experience stress and conflict because of external and internal factors of change impacting the academic environment. The study generated important findings which are capable of guiding academic library management on how to manage change effectively in the „new‟ electronic environment. The findings show that understanding conflict also equips management with strategies and techniques to manage conflict effectively. This study offers valuable insights into the lived conflict experiences and perceptions of librarians and sheds much light on the role of conflict management in these environments. This study will contribute to the management of conflict in information services in university libraries and will be an innovative application of conflict theory to the library discipline.
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- Date Issued: 2015
Improving service quality at automotive dealerships
- Authors: Lekhelebana, Vuyokazi Anneline
- Date: 2013
- Subjects: SERVQUAL (Service quality framework) , Automobile industry and trade -- South Africa , Customer services -- South Africa
- Language: English
- Type: Thesis , Masters , MBA
- Identifier: vital:8804 , http://hdl.handle.net/10948/d1017204
- Description: The highly competitive landscape of the automotive industry places increasing pressure on automotive dealerships to continually improve the quality of services rendered to customers. Understanding customer expectations and customer perceptions is key to making improvements in areas that matter most to the customer. It is against this background that this study was conducted. The aim of this research was to measure service quality at automotive dealerships. The literature review focused on the gaps model which resulted in the SERVQUAL measuring tool. The SERVQUAL instrument is supported by literature as the optimal instrument for measuring service quality. The 22-item questionnaire was adapted and used to solicit feedback from customers on their expectations and perceptions of the service rendered by dealerships across the five SERVQUAL dimensions; namely, tangibles, reliability, responsiveness, empathy and assurance. Gaps between customer expectations and perceptions were calculated as an indication of areas where customer expectations were met, unmet or exceeded. In order to identify priorities for improvement, each of the SERVQUAL dimensions was ranked in order of importance by the customer. Convenience sampling was used as a sampling technique. A total of 142 Volkswagen owners who had their vehicles serviced or repaired at a franchised dealership were surveyed. The reliability of the SERVQUAL questionnaire was tested by calculating the Cronbach’s Alpha coefficient for each of the five dimensions. The calculation yielded an average coefficient of 0.83, indicating a high reliability of the measuring instrument and the data collected. The overall gap score of -0.7 indicates that customer expectations exceeded customer perceptions. The lowest customer perceptions and the largest gaps were reported in the reliability and responsiveness dimensions. These two dimensions were also rated as the most important dimensions customers use for evaluating service quality. This formed the basis for recommending that dealership employees and management focus most of their efforts on improving the reliability and responsiveness dimensions.
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- Date Issued: 2013
Population dynamics of the white shark, Carcharodon carcharias, at Mossel Bay, South Africa
- Authors: Ryklief, Rabiah
- Date: 2012
- Subjects: White shark -- South Africa -- Mossel Bay , Sharks -- South Africa -- Mossel Bay
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10717 , http://hdl.handle.net/10948/d1012077 , White shark -- South Africa -- Mossel Bay , Sharks -- South Africa -- Mossel Bay
- Description: Mossel Bay is internationally recognised as one of the centres of abundance of white sharks in South Africa. During 2008 – 2010 there were four sites within the bay i.e. Seal Island, Hartenbos, Kleinbrak and Grootbrak, which were sampled to gain insight into the population dynamics of this species. Currently, life history information on white sharks in this area is limited. This study used a combination of mark-recapture using photographic identification techniques and sight per unit effort methods. Inter-annual, seasonal and spatial patterns in abundance are assessed. The effects of environmental parameters on abundance are also investigated. Photographic identification techniques were employed to identify unique individuals within the sampled population. This modified mark-recapture approach is therefore non-invasive and cost-effective. Open population POPAN parameterization was used to analyse the data in software program MARK. The total population was estimated at 389 sharks (351 – 428; 95 percent CI). Over the three year period, a marginal (yet non-significant) decline in numbers was observed, in terms of both monthly and seasonal population estimates. Sightings per unit effort data were collected during sampling trips. The relative abundance and body size composition of white sharks demonstrated significant spatial and seasonal variation. The highest and lowest relative abundance was observed at Seal Island and Hartenbos, respectively, and is likely attributed to prey availability. Although white sharks were present year-round in Mossel Bay, the highest relative abundance occurred during summer and the lowest relative abundance occurred during spring. White sharks were grouped into three main size classes based on estimated total length (TL): Young of the year (YOY) (125 – 174cm), juvenile (175 – 324cm) and adult (325 – 524cm). YOY white sharks were most prevalent at Grootbrak, with juvenile and adult individuals concentrating at Seal Island. Although most size classes were present throughout the year, seasonal differences were observed. YOY individuals were most abundant in the autumn months, juvenile size-classes appeared to concentrate in the study area during winter, and the adult individuals were most abundant in the spring months. Overall, there was a high concentration of white sharks ranging in size between 175 – 324cm TL, and it was thus hypothesised that Mossel Bay represents an interim nursery or grow out area for white sharks in South Africa. Data collected from 2008 and 2009 was used to investigate the relationship between specific environmental parameters, i.e. sea surface temperature and vertical water clarity, in relation to the relative abundance of white sharks. Sea surface temperature and vertical water clarity observed in this study ranged from 9.3 - 22.7°C and 0 – 10m, respectively. Sea surface temperature did not have a significant influence on the relative abundance of white sharks and this may be attributed to the thermoregulatory capacity of the species. Vertical water clarity, however, did significantly influence the relative abundance. Furthermore, the combined effect of site and season significantly influenced the relative abundance of white sharks and is probably linked to the distribution and abundance of inshore prey resources.
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- Date Issued: 2012
An assessment of the supplier development practices at Volkswagen of South Africa
- Authors: Erasmus, Bradley Quentin
- Date: 2006
- Subjects: Volkswagen of South Africa (Firm) , Production management , Business logistics -- Management , Motor vehicle industry -- South Africa
- Language: English
- Type: Thesis , Masters , MBA
- Identifier: vital:8555 , http://hdl.handle.net/10948/500 , Volkswagen of South Africa (Firm) , Production management , Business logistics -- Management , Motor vehicle industry -- South Africa
- Description: The underlying objective of the research is to assess the nature of the supplier training at Volkswagen of South Africa (VWSA). To achieve this objective, a theoretical study was conducted to establish what literature reveals to be the most important theory of supply chain management as well as supplier development geared towards lean manufacturing. The information obtained in the literature study was analysed to solve the main problem namely, an assessment of the nature of the supplier training at Volkswagen of South Africa (VWSA). The research was divided into two questionnaires: The first questionnaire is targeted at the suppliers. This questionnaire has two sections namely section A, the biographical data and section B attempts to determine the quality systems and manufacturing requirements. It further attempts to gauge training support and needs as compared to other OEM’s. The second questionnaire is targeted at the Supplier Development Manager. The aim of this questionnaire is to establish what the current training offerings are, the source of what VWSA teachers and the awareness of the Toyota Training College.
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- Date Issued: 2006