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Low-temperature electronic transport of metal doped carbon nanotube molecular hybrids and Nitrogen-doped nanocrystalline diamond
(University of the Witwatersrand, Johannesburg, 2024-08) Sodisetti, Venkateswara Rao; Bhattacharyya, Somnath
This thesis explores the magnetism and spin-related properties in carbon-based molecular hybrid materials, with a focus on expanding our understanding of low-dimensional carbon structures and their potential electronic applications. The investigation spans from one-dimensional systems, such as carbon nanotubes (CNTs) functionalized with single-molecule magnets (SMMs), to three-dimensional systems like nitrogen-doped ultra nanocrystalline diamond (UNCD). In these carbon structures, electronic transport is intricately tied to microstructural features, such as grain boundaries and impurity clusters, which hold significant potential for the development of all-carbon electronic devices. The research begins with a detailed examination of the chemical functionalization of multi-walled carbon nanotubes (MWCNTs) through controlled acid treatment to achieve precise metal doping. Using Raman spectroscopy and complementary techniques like ICP-MS and ToF-SIMS, we successfully demonstrate how functionalization levels influence the magnetic properties of CNT hybrids loaded with magnetic metals from the lanthanide series (Gd, Tb, Dy). The study reveals that low percentages of metal doping (0.5% to 1.0%) preserve the magnetic bistability of SMMs post-grafting, while higher doping levels lead to complex magnetic behaviors including super paramagnetism, quasi-ferromagnetism, and potential Kondo lattice behavior inCNT-heavy metal systems. We also explore the spin-phonon coupling in Gd-filled double-walled CNTs, where the onset of superparamagnetic properties at low temperatures is coupled with phonon mode stiffening observed via Raman spectroscopy. This enhanced coupling offers promising pathways for developing efficient molecular qubits through the modulation of spin-phonon interactions in one-dimensional systems. The second part of the thesis investigates into the microwave plasma-assisted chemical vapor deposition (MWCVD) growth of nitrogen-doped nanocrystalline diamond (NCD) thin films on different substrates. By pioneering upgrades to the MWCVD system, I was able to achieve reliable growth of high-quality nanocrystalline diamond thin films. Notably, I observed a novel nanostructure, termed Diaphite-a previously unreported feature, in these NCD films, consisting of nanodiamond grains coherently linked with graphene-like rings. This structure, along with the non-equilibrium growth conditions induced by nitrogen doping and secondary nucleation, presents unique polymorphic features in artificially grown diamonds. Detailed low-temperature transport measurements on four different samples—ranging from 7.5% to 20% nitrogen doping—uncovered complex transport phenomena such as 3D weak localization (WL), variable-range hopping (VRH), and unusual magnetoresistance (MR) behavior. In particular, the 7.5% N2-doped UNCD film on quartz exhibited 3D weak localization (WL) at low fields and anti-weak localization (AWL) at higher fields, with distinct magnetoresistance characteristics depending on the direction of the applied magnetic field. The 20% N2-doped films on both quartz and silicon showed more metallic-like behavior, with magneto-resistance characterized by a B1/2 dependence at low temperatures, suggesting an intricate relationship between doping level, microstructure, and electron transport. These findings significantly expand our understanding of the role that microstructural and chemical modifications play in determining the electronic and magnetic properties of carbon-based materials. This work provides a foundational platform for future research into carbon electronics, offering potential breakthroughs in spintronics, molecular transistors, quantum computing, and other advanced electronic applications.
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Beyond the click: Informed consent in the age of cookies
(University of the Witwatersrand, Johannesburg, 2024) Finger, Mokone; Visser, C.
Rapid evolution of technology and the internet has enabled vast data to be exchanged amongst people. These changes have introduced extraordinary data collecting methods that also recognise traces of personal information when users browse the internet. An example of such a tracking method is a cookie. Cookies, while they serve to enhance user experience, tend to collect and store personal information of data subjects without their knowledge and consent. For this reason, they raise a question of a threat to privacy and consent of data subjects. This research report principally examines the legal sufficiency of a mere click of a button in establishing valid consent for processing of personal information, which includes the collection, storage and transmission of personal information through cookies. The Protection of Personal Information Act 4 of 2013 (the POPI Act) was enacted to give effect to the constitutional right to privacy. Thus, the POPI Act operationalises the constitutional right to privacy by providing a framework for the processing of personal information, even though its application has shortcomings related to consent and cookies. In order to interpret the POPI Act, this paper will integrate the common law and the General Data Protection Regulation 2016/679, based on the adjudicative subsidiarity doctrine, as constitutional backdrop instruments to determine the threshold for consent in the POPI Act when using cookies.
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A practical review of the effectiveness of artificial intelligence in the automated review of legal contracts
(University of the Witwatersrand, Johannesburg, 2024) Fouché, Jacques Gerrit
This research report compares the performance of AI-driven automated contract review platforms with that of human contract reviewers, aiming to see improved effectiveness for the elements of time, cost and quality. An empirical study is done by comparing the specific performance of an automated contract review platform provider, Lawgeex, to the human contract reviewers of a business entity, Endress+Hauser. The results of the effectiveness assessment are reported on through dashboard data and questionnaires to the users of the platform. Recommendations are made both in general and specific to the two entities of the empirical study.
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Oil Price Shocks and Financial Stress in Sub-Saharan African Countries
(University of the Witwatersrand, Johannesburg, 2024) Frost, Callum
This study examines the nexus between financial stability and oil shocks within South Africa, a net-oil importer, and Nigeria, a net-oil exporter. A signal theory approach utilising pAUROC analysis is used to capture relevant indicators. Furthermore, sub-market indices are weighted using a diagonal BEKK-GARCH model, allowing for time-varying cross-correlations to determine sub-market weights, allowing the constructed financial stress index (FSI) for each economy to focus on systemic events of financial stress. The FSI for each economy is then incorporated into a SVAR model which disaggregates oil demand shocks into three components (economic activity, oil consumption demand, and oil inventory demand) following the framework of Baumeister and Hamilton (2019) to capture the effects of oil market shocks on financial stability. This paper finds that positive shocks to oil supply, economic activity, and oil inventory demand tend to reduce financial stress in South Africa. Interestingly, demand driven increases in the real price of oil reduces systemic stress, even though the economy is a net-oil importer. Oil supply shocks and economic activity shocks tend to have no significant effect on Nigerian financial stress while demand driven increases to real oil prices tend to decrease financial stress. Interestingly, shock increases in demand for oil inventories tends to raise financial stress.
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Deconstructing the debate around bank account closures on the pretext of institutional reputational risk
(University of the Witwatersrand, Johannesburg, 2024) Hayath, Iram; Kawadza, Herbert
The Supreme Court of Appeal in Bredenkamp v Standard Bank found that a bank has a contractual right to close a client’s accounts on reasonable notice, and that a bank is entitled to exercise this right if it perceives that a continued relationship with the client may result in reputational and business risks to the bank (albeit may be premised on allegations which the client denies). Banks have regulatory obligations to (amongst others): (i) manage their reputational risk; and (ii) take steps to avoid their accounts being used by clients to facilitate the proceeds of unlawful activities. Banks are at the receiving end of scrutiny for the latter, including from the media. Banks’ actions of closing accounts for institutional reputational risk are however, often challenged by clients on the basis that these decisions are informed by untrue allegations and are contrary to public policy. A particular consideration is the potential consequences of the clients becoming ‘unbanked’. There are also other issues of contention including that reputational risk is an elusive reason. The competing interests and public policy considerations at play have not yet been adjudicated by our courts. This research report argues that the complexities involved necessitates legislative reform to ensure certainty and fairness on both sides.