Block copolymer templates for metal oxide nanostructures
- Authors: Talla, Assane
- Date: 2019
- Subjects: Nanotechnology , Nanostructured materials Metal oxide semiconductors
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/43889 , vital:37075
- Description: Recent advances in technology have increased the need for fabrication of devices with feature sizes of tens of nanometers, such as ultra-fine filters or membranes, and high density data storage media, to name a few. For this reason, research is now focused on block copolymer nanolithographic processes, particularly the fabrication of nanoscale templates with domains well below 100 nm. Block copolymers have the tendency to self-organise into various structures, such as lamellae, spheres or cylinders on a nanometer scale. Among these possible configurations, the perpendicular cylindrical structure is most desirable, because it can be used for templates or masks for feature development, in particular, oriented wires or rods. In this work, the aim is to create a nano-mask from a di-block copolymer thin film, for zinc oxide nanorods growth. For this purpose poly (styrene-block-methylmethacrylate) (PS-b-PMMA) was investigated as a potential nano-mask. Samples were characterized using X-ray reflectometry to determine the thicknesses of the PS-b-PMMA thin films, while scanning probe microscopy and scanning electron microscopy was used to investigate the surface morphology of the samples. PS-b-PMMA thin films were produced on a random copolymer (poly (styrene-random-methylmethacrylate) (PS-r-PMMA) coated onto a silicon substrate. The PS-r-PMMA permits a non-preferential interaction between the di-block constituents and the substrate. Thermal annealing in vacuum of PS-b-PMMA on PS-r-PMMA led to perpendicular cylinders of PMMA within a PS matrix in the di-block. The typical thicknesses measured for the di-block copolymer films ranged between 33 nm and 37 nm. During this study, a perpendicular orientation of the di-block components was also produced when PS-b-PMMA was spun onto a layer of zinc oxide nanoparticles and thermally annealed in vacuum. It was shown that the ZnO nanoparticles created a corrugated surface on silicon which induced perpendicular cylinders of PMMA within the PS matrix. This was possible for a specific surface roughness parameter and film thickness. In this case, the typical thickness determined for the di-block copolymer ranged between 33 and 35 nm and the surface roughness parameter was 0.07. For the fabrication of a di-block template or PS nano-mask, the vertically oriented PMMA cylindrical nanodomains in the PS matrix were removed by exposing the film to ultraviolet radiation at an adequate dose, followed successively by washing in acetic acid and de-ionized water. It was shown that ultraviolet exposure is necessary to ensure the degradation of PMMA. A subsequent rinse in glacial acetic acid and DI water of the film exposed to ultraviolet, left an array of ordered nanoscopic pores with sizes ranging between 10 nm and 20 nm. Finally, the growth of ZnO nanorods on the di-block template produced on zinc oxide nanoparticles, was attempted using an aqueous solution based-method, namely chemical bath deposition. The rods did not grow inside the nanopores, probably due to poor capillary action. In additional experiments, the di-block template was removed by toluene (a selective solvent for PS) followed by the growth of ZnO rods on the exposed nanoparticle surface. Vertical and well separated ZnO rods formed on this surface, in places where the underlying seed layer had been attacked by the acetic acid treatment during removal of the PMMA. The observed ZnO rod morphology can be used in applications such as solar cell.
- Full Text:
- Date Issued: 2019
- Authors: Talla, Assane
- Date: 2019
- Subjects: Nanotechnology , Nanostructured materials Metal oxide semiconductors
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/43889 , vital:37075
- Description: Recent advances in technology have increased the need for fabrication of devices with feature sizes of tens of nanometers, such as ultra-fine filters or membranes, and high density data storage media, to name a few. For this reason, research is now focused on block copolymer nanolithographic processes, particularly the fabrication of nanoscale templates with domains well below 100 nm. Block copolymers have the tendency to self-organise into various structures, such as lamellae, spheres or cylinders on a nanometer scale. Among these possible configurations, the perpendicular cylindrical structure is most desirable, because it can be used for templates or masks for feature development, in particular, oriented wires or rods. In this work, the aim is to create a nano-mask from a di-block copolymer thin film, for zinc oxide nanorods growth. For this purpose poly (styrene-block-methylmethacrylate) (PS-b-PMMA) was investigated as a potential nano-mask. Samples were characterized using X-ray reflectometry to determine the thicknesses of the PS-b-PMMA thin films, while scanning probe microscopy and scanning electron microscopy was used to investigate the surface morphology of the samples. PS-b-PMMA thin films were produced on a random copolymer (poly (styrene-random-methylmethacrylate) (PS-r-PMMA) coated onto a silicon substrate. The PS-r-PMMA permits a non-preferential interaction between the di-block constituents and the substrate. Thermal annealing in vacuum of PS-b-PMMA on PS-r-PMMA led to perpendicular cylinders of PMMA within a PS matrix in the di-block. The typical thicknesses measured for the di-block copolymer films ranged between 33 nm and 37 nm. During this study, a perpendicular orientation of the di-block components was also produced when PS-b-PMMA was spun onto a layer of zinc oxide nanoparticles and thermally annealed in vacuum. It was shown that the ZnO nanoparticles created a corrugated surface on silicon which induced perpendicular cylinders of PMMA within the PS matrix. This was possible for a specific surface roughness parameter and film thickness. In this case, the typical thickness determined for the di-block copolymer ranged between 33 and 35 nm and the surface roughness parameter was 0.07. For the fabrication of a di-block template or PS nano-mask, the vertically oriented PMMA cylindrical nanodomains in the PS matrix were removed by exposing the film to ultraviolet radiation at an adequate dose, followed successively by washing in acetic acid and de-ionized water. It was shown that ultraviolet exposure is necessary to ensure the degradation of PMMA. A subsequent rinse in glacial acetic acid and DI water of the film exposed to ultraviolet, left an array of ordered nanoscopic pores with sizes ranging between 10 nm and 20 nm. Finally, the growth of ZnO nanorods on the di-block template produced on zinc oxide nanoparticles, was attempted using an aqueous solution based-method, namely chemical bath deposition. The rods did not grow inside the nanopores, probably due to poor capillary action. In additional experiments, the di-block template was removed by toluene (a selective solvent for PS) followed by the growth of ZnO rods on the exposed nanoparticle surface. Vertical and well separated ZnO rods formed on this surface, in places where the underlying seed layer had been attacked by the acetic acid treatment during removal of the PMMA. The observed ZnO rod morphology can be used in applications such as solar cell.
- Full Text:
- Date Issued: 2019
The impact of open-plan office design on the productivity of City of Cape Town employees
- Authors: Nghona, Ziyanda
- Date: 2017
- Subjects: Labor productivity -- South Africa -- Cape Town , Performance -- Measurement Interior architecture Space (Architecture)
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/48080 , vital:40469
- Description: Comprehensive research studies on identifying the positive and negative impact of open-plan office designs on employees’ work productivity were long initiated and still continually debated in developed nations such as USA, Canada and UK. As a result, the researcher decided to undertake research in order to determine whether the salient negative and positive factors, identified in international literature about open-plan office designs, are applicable in the South African context. The aim was not to reduce the accrued positive and negative factors, emanating from open-plan offices, but rather to identify and determine how they impact employees work productivity. The study had the following objectives, namely: (1) to investigate the employees satisfaction level with the physical environment as a result of working within the open-plan office design layout; (2) to determine the employees' stress levels as a result of working within the open-plan office design layout; (3) to determine the team members or co-workers satisfaction level as a result of working within the open-plan office design layout; and lastly, (4) to determine the positive and negative impact of the open-plan office design layout on employees work productivity. The data gathering approaches included survey self-administered questionnaires to the Built Environment related employees working within the open-plan offices of the City of Cape Town Municipality within the CBD area. The sample consisted the following departments: Facilities Management; Sports & Recreation; Human Settlement and Solid Waste. A purposeful random sampling method was followed to identify participants for the study. Concerning the first objective, it was clear from the analysis that employees are unsatisfied with the physical environment of the open-plan office design layout. Their dissatisfaction pointed to several issues such as less control or flexibility to rearrange or reorganise their office furniture to meet their work needs; limited or no available quiet and undisturbed time. As a result, it was not surprising that employees in open-plan office experience high job-related stress levels. However, in a positive light, concerning the team members or co-workers relations on working within open-plan offices, it was reported that employees are satisfied reporting high exchange of job related information and thus learning from each other. Lastly and more importantly, in terms of the overall aim of this study, the study revealed that the employees’ work productivity is affected negatively as a result of the open-plan office design in the City of Cape Town. Initially identification of how open-plan offices impact employees work productivity is the critical first-step in an attempt to reduce the negative and increase the positive impact and this constitutes the contribution of this study. However, this study was limited in that it only requested respondents to agree or disagree with the relationships among measurable variables that already exist in previous studies done in developed countries. The study survey was also limited by the selected sample within the City of Cape Town Municipality public offices. As a result, the study only sampled five Built Environment related openplan offices and thus the generalisability of the findings is limited. Further studies with large and wider survey can thus benefit this study topic in developing economies like South Africa.
- Full Text:
- Date Issued: 2017
- Authors: Nghona, Ziyanda
- Date: 2017
- Subjects: Labor productivity -- South Africa -- Cape Town , Performance -- Measurement Interior architecture Space (Architecture)
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/48080 , vital:40469
- Description: Comprehensive research studies on identifying the positive and negative impact of open-plan office designs on employees’ work productivity were long initiated and still continually debated in developed nations such as USA, Canada and UK. As a result, the researcher decided to undertake research in order to determine whether the salient negative and positive factors, identified in international literature about open-plan office designs, are applicable in the South African context. The aim was not to reduce the accrued positive and negative factors, emanating from open-plan offices, but rather to identify and determine how they impact employees work productivity. The study had the following objectives, namely: (1) to investigate the employees satisfaction level with the physical environment as a result of working within the open-plan office design layout; (2) to determine the employees' stress levels as a result of working within the open-plan office design layout; (3) to determine the team members or co-workers satisfaction level as a result of working within the open-plan office design layout; and lastly, (4) to determine the positive and negative impact of the open-plan office design layout on employees work productivity. The data gathering approaches included survey self-administered questionnaires to the Built Environment related employees working within the open-plan offices of the City of Cape Town Municipality within the CBD area. The sample consisted the following departments: Facilities Management; Sports & Recreation; Human Settlement and Solid Waste. A purposeful random sampling method was followed to identify participants for the study. Concerning the first objective, it was clear from the analysis that employees are unsatisfied with the physical environment of the open-plan office design layout. Their dissatisfaction pointed to several issues such as less control or flexibility to rearrange or reorganise their office furniture to meet their work needs; limited or no available quiet and undisturbed time. As a result, it was not surprising that employees in open-plan office experience high job-related stress levels. However, in a positive light, concerning the team members or co-workers relations on working within open-plan offices, it was reported that employees are satisfied reporting high exchange of job related information and thus learning from each other. Lastly and more importantly, in terms of the overall aim of this study, the study revealed that the employees’ work productivity is affected negatively as a result of the open-plan office design in the City of Cape Town. Initially identification of how open-plan offices impact employees work productivity is the critical first-step in an attempt to reduce the negative and increase the positive impact and this constitutes the contribution of this study. However, this study was limited in that it only requested respondents to agree or disagree with the relationships among measurable variables that already exist in previous studies done in developed countries. The study survey was also limited by the selected sample within the City of Cape Town Municipality public offices. As a result, the study only sampled five Built Environment related openplan offices and thus the generalisability of the findings is limited. Further studies with large and wider survey can thus benefit this study topic in developing economies like South Africa.
- Full Text:
- Date Issued: 2017
A mathematical study on optimal prevention and control strategies for tuberculosis: case study for Port Elizabeth, South Africa
- Authors: Zembe, Pumelela Vincent
- Date: 2016
- Subjects: Tuberculosis -- South Africa -- Port Elizabeth -- Prevention Tuberculosis -- Mathematical models , Tuberculosis -- Case studies
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/12823 , vital:27124
- Description: In this treatise a SEIR model for the transmission of tuberculosis was proposed. It assumes that the latent infected individuals progress to active tuberculosis through endogenous reactivation and exogenous re-infection and that the individuals who have recovered from the disease through treatment are not immune to tuberculosis re-infection. While most features of the original model were kept, the model was modified to incorporate two control measures in the form of post-exposure tuberculosis prophylaxis for the treatment of latent individuals and tuberculosis therapeutics for the treatmentof individuals with active tuberculosis. Mathematical analysis of the modelwas done under the assumption that the two control measures are positiveconstants. The disease-free equilibrium point was locally asymptotically stable when the basic reproduction number was less than unity and unstable when this epidemic threshold exceeds unity. An optimal control problem was formulated and the necessary conditions for optimality were derived.The numerical results based on data from Port Elizabeth suggest that using both forms of control measures simultaneously is more effective in reducing the total number of infected individuals than applying single controls separately.
- Full Text:
- Date Issued: 2016
- Authors: Zembe, Pumelela Vincent
- Date: 2016
- Subjects: Tuberculosis -- South Africa -- Port Elizabeth -- Prevention Tuberculosis -- Mathematical models , Tuberculosis -- Case studies
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/12823 , vital:27124
- Description: In this treatise a SEIR model for the transmission of tuberculosis was proposed. It assumes that the latent infected individuals progress to active tuberculosis through endogenous reactivation and exogenous re-infection and that the individuals who have recovered from the disease through treatment are not immune to tuberculosis re-infection. While most features of the original model were kept, the model was modified to incorporate two control measures in the form of post-exposure tuberculosis prophylaxis for the treatment of latent individuals and tuberculosis therapeutics for the treatmentof individuals with active tuberculosis. Mathematical analysis of the modelwas done under the assumption that the two control measures are positiveconstants. The disease-free equilibrium point was locally asymptotically stable when the basic reproduction number was less than unity and unstable when this epidemic threshold exceeds unity. An optimal control problem was formulated and the necessary conditions for optimality were derived.The numerical results based on data from Port Elizabeth suggest that using both forms of control measures simultaneously is more effective in reducing the total number of infected individuals than applying single controls separately.
- Full Text:
- Date Issued: 2016
The production of Omega 3 fatty acids by a mixed microalgae culture
- Authors: Kimono, Diana Agnes
- Date: 2013
- Subjects: Omega-3 fatty acids , Algae culture , Microalgae
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/6498 , vital:21097
- Description: Background and Aim: Microalgae are a potential economical source of omega-3 fatty acids, which are known for their health benefits. Omega-3 fatty acids derived from microalgae are however still expensive due to high costs involved in production. These costs can partly be attributed to cultivation of microalgae in unialgal cultures, which are prone to contamination, difficult to scale up and require stringent control of growth conditions. This study therefore is aimed to investigate the feasibility of using a mixed microalgae culture for the production of omega-3 fatty acids. Methods and materials: The microalgae were grown under uncontrolled conditions in a hanging-bag photo-bioreactor, with only the phosphorus-nitrogen ratio (P:N-ratio) varied. Variations in the different population proportions in the culture were studied and related to the biomass, total fatty acid and omega-3 fatty acid productivity of the culture. Finally, a comparison was made between the results obtained in this study and similar studies found in literature. Results and discussion: The mixed culture used was composed of several green microalgae, whose proportions varied with P:N-ratio, season, and age of the culture. Different interactions between the populations were observable, and these were thought to influence the culture’s biomass, total fatty acids (TFAs) and omega-3 fatty acid productivity. The TFA content of the culture was ~10-20% by the end of the exponential phase, depending on the nutrients supplied. The fatty acids were composed of mostly unsaturated fatty acids, the majority of which were omega-3 fatty acids; C18:3ω3 (up to 50% of TFA), C16:4ω3 (up to 15%) and C18:4ω3 (up to 5%). Other fatty acids observed included C16:0 (up to 25%), C18:1ω9/C18:1ω8 (up to 20%), C18:2ω6 (up to 5%), traces of C18:0, C18:3ω6, C17:0, C16:3ω3 and C16:1ω7 were also detected. The presence of these fatty acids was found to vary depending on season, P:N-ratio, and age of the culture. When compared to studies in the literature, the mixed culture was found to perform better than, or as well as reported studies, where unialgal cultures were cultivated under controlled laboratory conditions. Conclusion: In view of the reported advantages of cultivating mixed cultures, the production of omega-3 fatty acids via such cultures appears attractive. More research however is needed to optimise the culture; study interactions between the organisms and their effect on biomass, total fatty acid and omega-3 fatty acid productivity. Finally, the economic implications of using mixed cultures need to be evaluated as well.
- Full Text:
- Date Issued: 2013
- Authors: Kimono, Diana Agnes
- Date: 2013
- Subjects: Omega-3 fatty acids , Algae culture , Microalgae
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/6498 , vital:21097
- Description: Background and Aim: Microalgae are a potential economical source of omega-3 fatty acids, which are known for their health benefits. Omega-3 fatty acids derived from microalgae are however still expensive due to high costs involved in production. These costs can partly be attributed to cultivation of microalgae in unialgal cultures, which are prone to contamination, difficult to scale up and require stringent control of growth conditions. This study therefore is aimed to investigate the feasibility of using a mixed microalgae culture for the production of omega-3 fatty acids. Methods and materials: The microalgae were grown under uncontrolled conditions in a hanging-bag photo-bioreactor, with only the phosphorus-nitrogen ratio (P:N-ratio) varied. Variations in the different population proportions in the culture were studied and related to the biomass, total fatty acid and omega-3 fatty acid productivity of the culture. Finally, a comparison was made between the results obtained in this study and similar studies found in literature. Results and discussion: The mixed culture used was composed of several green microalgae, whose proportions varied with P:N-ratio, season, and age of the culture. Different interactions between the populations were observable, and these were thought to influence the culture’s biomass, total fatty acids (TFAs) and omega-3 fatty acid productivity. The TFA content of the culture was ~10-20% by the end of the exponential phase, depending on the nutrients supplied. The fatty acids were composed of mostly unsaturated fatty acids, the majority of which were omega-3 fatty acids; C18:3ω3 (up to 50% of TFA), C16:4ω3 (up to 15%) and C18:4ω3 (up to 5%). Other fatty acids observed included C16:0 (up to 25%), C18:1ω9/C18:1ω8 (up to 20%), C18:2ω6 (up to 5%), traces of C18:0, C18:3ω6, C17:0, C16:3ω3 and C16:1ω7 were also detected. The presence of these fatty acids was found to vary depending on season, P:N-ratio, and age of the culture. When compared to studies in the literature, the mixed culture was found to perform better than, or as well as reported studies, where unialgal cultures were cultivated under controlled laboratory conditions. Conclusion: In view of the reported advantages of cultivating mixed cultures, the production of omega-3 fatty acids via such cultures appears attractive. More research however is needed to optimise the culture; study interactions between the organisms and their effect on biomass, total fatty acid and omega-3 fatty acid productivity. Finally, the economic implications of using mixed cultures need to be evaluated as well.
- Full Text:
- Date Issued: 2013
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