No description available.

No description available.

The emergence of novel electronic, optical and magnetic properties in ordered two-dimensional (2D) nanoparticle ensembles, due to collective dipolar interactions of surface plasmons or excitons or magnetic moments have motivated intense research efforts into fabricating functional nanostructure assemblies. Such functional assemblies (i.e., highly-integrated and addressable) have great potential in terms of device performance and cost benefits. Presently, there is a paradigm shift from lithography based top-down approaches to bottom-up approaches that use self-assembly to engineer addressable architectures from nanoscale building blocks. The objective of this dissertation was to develop appropriate processing tools that can overcome the common challenges faced in fabricating floating gate memory devices using self-assembled 2D metal nanoparticle arrays as charge storage nodes. The salient challenges being to synthesize monodisperse nanoparticles, develop large scale guided self-assembly processes and to integrate with Complementary Metal Oxide Semiconductor (CMOS) memory device fabrication processes, thereby, meeting the targets of International Technology Roadmap for Semiconductors (ITRS) – 2017, for non-volatile memory devices. In the first part of the thesis, a simple and robust process for the formation of wafer-scale, ordered arrays using dodecanethiol capped gold nanoparticles is reported. Next, the results of ellipsometric measurements to analyze the effect of excess ligand on the self-assembly of dodecanethiol coated gold nanoparticles at the air-water interface are discussed. In a similar vein, the technique of drop-casting colloidal solution is extended for tuning the interparticle spacing in the sub-20 nm regime, by altering the ligand length, through thiol-functionalized polystyrene molecules of different molecular weights. The results of characterization, using the complementary techniques of Atomic Force Microscopy (AFM) and Field-Emission Scanning Electron Microscopy (FESEM), of nanoparticle arrays formed by polystyrene thiol (average molecular weight 20,000 g/mol) grafted gold nanoparticles (7 nm diameter) on three different substrates and also using different solvents is then reported. The substrate interactions were found to affect the interparticle spacing in arrays, changing from 20 nm on silicon to 10 nm on a water surface; whereas, the height of the resultant thin film was found to be independent of substrate used and to correlate only with the hydrodynamic diameter of the polymer grafted nanoparticle in solution. Also, the mechanical properties of the nanoparticle thin films were found to be significantly altered by such compression of the polymer ligands. Based on the experimental data, the interparticle spacing and packing structure in these 2D arrays, were found to be controlled by the substrate, through modulation of the disjoining pressure in the evaporating thin film (van der Waals interaction); and by the solvent used for drop casting, through modulation of the hydrodynamic diameter. This is the first report on the ability to vary interparticle spacing of metal nanoparticle arrays by tuning substrate interactions alone, while maintaining the same ligand structure. A process to fabricate arrays with square packing based on convective shearing at a liquid surface induced by miscibility of colloidal solution with the substrate is proposed. This obviates the need for complex ligands with spatially directed molecular binding properties. Fabrication of 3D aggregates of polymer-nanoparticle composite by manipulating solvent-ligand interactions is also presented. In flash memory devices, charges are stored in a floating gate separated by a tunneling oxide layer from the channel, and the tunneling oxide thickness is scaled down to minimize power consumption. However, reduction in tunneling oxide thickness has reached a stage where data loss can occur due to random defects in the oxide. Using metal nanoparticles as charge-trapping nodes will minimize the data loss and enhance reliability by compartmentalizing the charge storage. In the second part of the thesis, a scalable and CMOS compatible process for fabricating next-generation, non-volatile, flash memory devices using the self-assembled 2D arrays of gold nanoparticles as charge storage nodes were developed. The salient features of the fabricated devices include: (a) reproducible threshold voltage shifts measured from devices spread over cm2 area, (b) excellent retention (>10 years) and endurance characteristics (>10000 Program/Erase cycles). The removal of ligands coating the metal nanoparticles using mild RF plasma etching was found, based on FESEM characterization as well as electrical measurements, to be critical in maintaining both the ordering of the nanoparticles and charge storage capacity. Results of Electrostatic Force Microscope (EFM) measurements are presented, corroborating the need for ligand removal in obtaining reproducible memory characteristics and reducing vertical charge leakage. The effect of interparticle spacing on the memory characteristics of the devices was also studied. Interestingly, the arrays with interparticle spacing of the order of nanoparticle diameter (7 nm) gave rise to the largest memory window, in comparison with arrays with smaller (2 nm) or larger interparticle spacing (20 nm). The effect of interparticle spacing and ligand removal on memory characteristics was found to be independent of different top-oxide deposition processes employed in device fabrication, namely, Radio-frequency magnetron sputtering (RF sputtering), Atomic Layer Deposition (ALD) and electron-beam evaporation. In the final part of the thesis, a facile method for transforming polydisperse citrate capped gold nanoparticles into monodisperse gold nanoparticles through the addition of excess polyethylene glycol (PEG) molecules is presented. A systematic study was conducted in order to understand the role of excess ligand (PEG) in enabling size focusing. The size focusing behavior due to PEG coating of nanoparticles was found to be different for different metals. Unlike the digestive ripening process, the presence of PEG was found to be critical, while the thiol functionalization was not needed. Remarkably, the amount of adsorbed carboxylate-PEG mixture was found to play a key role in this process. The stability of the ordered nanoparticle films under vacuum was also reported. The experimental results of particle ripening draw an analogy with the well-established Pechini process for synthesizing metal oxide nanostructures. The ability to directly self-assemble nanoparticles from the aqueous phase in conjunction with the ability to transfer these arrays to any desired substrate using microcontact printing can foster the development of applications ranging from flexible electronics to sensors. Also, this approach in conjunction with roll-to-roll processing approaches such as doctor-blade casting or convective assembly can aid in realizing the goal of large scale nanostructure fabrication without the utilization of organic solvents.

Gold nanoparticles (GNPs) have recently attracted considerable interest for use in radiation therapy due to their unique physical and biological properties. Of interest, GNPs (and other high-atomic-number materials) have been used to enhance radiation dose in tumors by taking advantage of increased photoelectric absorption. This physical phenomenon is well-understood on a macroscopic scale. However, biological outcomes often depend on the intratumoral and even intracellular distribution of GNPs, among other factors. Therefore, there exists a need to precisely visualize and accurately quantify GNP distributions. By virtue of the photoelectric effect, x-ray fluorescence (XRF) photons (characteristic x-rays) from gold can be induced and detected, not only allowing the distribution of GNPs within biological samples to be determined but also providing a unique molecular imaging option in conjunction with bioconjugated GNPs. This work proposes the use of this imaging modality, known as XRF imaging, to develop experimental imaging techniques for detecting and quantifying sparse distributions of GNPs in preclinical settings, such as within small-animal-sized objects, tissue samples, and superficial tumors. By imaging realistic GNP distributions, computational methods can then be used to understand radiation dose enhancement on an intratumoral scale and perhaps even down to the nanoscopic, subcellular realm, elucidating observed biological outcomes (e.g., radiosensitization of tumors) from the bottom-up. Ultimately, this work will result in experimental and computational tools for developing a better understanding of GNP-mediated dose enhancement and associated radiosensitization within the scope of GNP-aided radiation therapy.

This diploma thesis presents the results of the study of historical exploitation of gold in Vodňany, which were partly introduced in previous bachelor thesis. The core of the thesis is a list of locations that have been researched mainly through studying lidar pictures, field and heavy minerals prospecting, professional literature and geological maps. Based on the observation of common or different features of the individual areals, the thesis further solved questions related to the morphology of the areals, the probable occurrence of gold, the method of its mining, and, consequently, property and settlement links.

Les nanoparticules d'or de petite taille (< 5 nm) sont des matériaux qui présentent une bonne activité catalytique dans des réactions d'oxydation, et ce dans des conditions relativement douces. Cependant, il est difficile d'obtenir des nanoparticules monodisperses et de taille inférieure à 5 nm. En ce sens, les clusters d'or sont intéressants, car ce sont des composés atomiquement définis avec une formulation propre. Cela signifie que dans un cluster, le nombre d'atomes d'or et de ligands le stabilisant est déterminé. Comme ils peuvent être isolés purs, ils constituent donc une classe de nanoparticules parfaitement monodisperses. Nous nous sommes intéressés, dans le cadre de cette thèse, à la synthèse de clusters d'or et à leur assemblage afin d'avoir des catalyseurs atomiquement définis. Les nanoparticules d'or sont souvent utilisées après dépôt sur un support, résultant en la perte de surface accessible. Nous voulons donc utiliser ces clusters (i) comme espèces moléculaires déposées sur un support et (ii) comme briques moléculaires pour l'assemblage de réseaux tridimensionnels où la porosité permettrait la diffusion des réactifs/produits pour s'affranchir des effets de supports. Notre étude porte donc sur la synthèse de clusters d'or et nous nous sommes également intéressés aux polymères de coordination d'or (I), un intermédiaire de réaction important dans la synthèse de clusters et à ses propriétés photophysiques. Afin d'avoir des clusters avec une fonction externe permettant de les assembler ou de les déposer sur un support, nous avons développé une nouvelle voie de synthèse de clusters stabilisés par des ligands de type thiophénolates para-substitués. Nous avons ainsi isolé de nouveaux clusters stabilisés par des ligands hétérotopiques comme [Au25(SPh-pNH2)17]. Ces composés ont ensuite été déposés sur un support mésoporeux (SBA-15) et utilisés comme catalyseurs dans différentes réactions d'oxydation. Nos résultats montrent que les clusters d'or sont donc des précurseurs moléculaires permettant de préparer des catalyseurs efficaces, ayant une petite taille de particules (1-2 nm) et présentant des activités catalytiques très élevées comparativement aux matériaux de référence / Small gold nanoparticles (< 5 nm) are materials presenting a good catalytic activity in oxidations reactions, especially under soft conditions of temperature and pressure. However, it can be difficult to obtain monodisperse particles with a diameter less than 5 nm. In this sense, gold clusters are interesting, because they are atomically defined compounds, presenting a proper formulation. This means that the number of gold atoms and of stabilizers in the clusters are defined and, as they can be isolated pure, they constitue a novel class of perfectly monodisperse nanomaterials. Therefore, we are interested, in this thesis, in the synthesis and assembly of gold clusters. Indeed, gold nanoparticles are usually deposited on a support, resulting in the loss of accessible area. We therefore wanted to use gold clusters as (i) molecular species deposited on a support and (ii) as building blocks to assemble and organize tridimensional networks where the porosity permits the substrates/products diffusions and avoid the support effects. Our study deals with the synthesis of gold clusters, and we are also interested in the gold (I) coordination polymers, which are important reaction intermediates formed during the clusters synthesis and to its photophysical properties. In order to have clusters presenting external functions enabling their assembly or deposition on a support, we developed a novel synthesis suitable for para-substituted thiophenolates. We managed to isolate new clusters stabilized by heterotopic ligands such as [Au25(SPh-pNH2)17]. Those compounds have been deposited on a mesoporous support and used as oxidative catalysts. Our results show that gold clusters are molecular precursors that permit to prepare effective catalysts with narrow particle size (1-2 nm) and presenting high catalytic activity compared to the one exhibited by reference materials

Disease prevalence varies with geographic location. This research pursues a medical geographic perspective and examines the spatial variations in disease patterns between Obuasi, a gold mining town and Asankrangwa, a non gold mining town in Ghana, West Africa. Political ecology/economy and the human ecology frameworks are used to explain the prevalence of diseases. Mining alters the environment and allows disease causing pathogens and vectors to survive more freely than in other similar environments. Certain diseases such as upper respiratory tract infections, ear infections, sexually transmitted diseases such as HIV/AIDS and syphilis, certain skin diseases and rheumatism and joint pains may have a higher prevalence in Obuasi when compared to Asankrangwa due to the mining in Obuasi.

Costs saving measures are important for South African gold producers due to increasing energy costs and decreasing production volumes. Demand Side Management (DSM) is an effective strategy to reduce electricity consumption and costs. DSM projects have been implemented widely on South African mining systems such as pumping, refrigeration, rock transport and compressed air. Implementations have, however, been limited on gold processing plants despite the significant amounts of energy that this section consumes. The main objective of gold processing plants is production orientated and energy management is not a primary focus. This rationale is re-evaluated owing to high electricity price inflation and availability of DSM incentives. This study investigated the cost saving potential of DSM interventions on gold plants. Electrical load management was identified as a key opportunity that can deliver substantial cost savings. These savings were shown to be feasible in respect of the required capital expenditure, effort of implementation and maintenance of operational targets. Investigation procedures were compiled to identify feasible load management opportunities. The most potential for electricity cost savings was identified on comminution equipment. Consequently, a methodology was developed to implement electrical load management on the identified sections. The methodology proposed simulation techniques that enabled load management and subsequent electricity cost optimisation through production planning. Two electrical load management case studies were successfully implemented on comminution equipment at two gold processing plants. Peak period load shift of 3.6 MW and 0.6 MW, respectively, was achieved on average for a period of three months. The annual cost savings of these applications could amount to R1.4-million and R 660 000. This results in specific electricity cost reductions of 3% and 7% for the two respective case studies. Results from the two case studies are an indication of potential for electrical load management on South African gold processing plants. If an average electricity cost saving of 5% is extrapolated across the South African gold processing industry, the potential cost savings amount to R 25-million per annum. Although the costs saving opportunities are feasible, it is influenced by the reliability of the equipment and the dynamics of ore supply. This insight plays a decisive role in determining the feasibility of DSM on gold processing plants. / MIng (Mechanical Engineering), North-West University, Potchefstroom Campus, 2015

The South African gold mining sector consumes 47% of the mining industry’s electricity. On a deep level gold mine, 20% of the energy is consumed by the refrigeration system. The refrigeration system cools 67 ˚C virgin rock temperatures underground. Underground cooling demand increases significantly with deeper mining activities. Various cooling systems are available for underground cooling. This study focuses on the electricity usage of an ice storage system versus a chilled water system for underground cooling. An energy-savings approach was developed to determine possible power savings on the surface refrigeration system of Mine M. The savings approach involved converting an ice storage system to a chilled water system and varying the water flow through the system. The water flow was varied by installing variable speed drives on the evaporator and condenser water pumps. The feasibility of the energy-efficiency approach was simulated with a verified simulation model. Simulation results indicated the feasibility of converting the thermal ice storage to a chilled water system and implementing the energy-efficiency approach on Mine M. Simulated results indicated a 9% electricity saving when using a chilled water system. Various problems encountered by the mine were also a motivation to convert the thermal ice storage system. Converting an ice storage facility to a chilled water system for energy efficiency on a deep level gold mine Energy management is achieved through the monitoring, controlling and reporting of the implemented savings approach. Converting the glycol plant and recommissioning the chilled water plant gave the mine an additional chiller as backup to sufficiently meet underground demand. An annual summer power saving of 1.5 MW was achieved through the conversion and control strategy. It is concluded that conversion of the thermal ice storage system on Mine M results in an energy- and cost saving. / MIng (Mechanical Engineering), North-West University, Potchefstroom Campus, 2015

Costs saving measures are important for South African gold producers due to increasing energy costs and decreasing production volumes. Demand Side Management (DSM) is an effective strategy to reduce electricity consumption and costs. DSM projects have been implemented widely on South African mining systems such as pumping, refrigeration, rock transport and compressed air. Implementations have, however, been limited on gold processing plants despite the significant amounts of energy that this section consumes. The main objective of gold processing plants is production orientated and energy management is not a primary focus. This rationale is re-evaluated owing to high electricity price inflation and availability of DSM incentives. This study investigated the cost saving potential of DSM interventions on gold plants. Electrical load management was identified as a key opportunity that can deliver substantial cost savings. These savings were shown to be feasible in respect of the required capital expenditure, effort of implementation and maintenance of operational targets. Investigation procedures were compiled to identify feasible load management opportunities. The most potential for electricity cost savings was identified on comminution equipment. Consequently, a methodology was developed to implement electrical load management on the identified sections. The methodology proposed simulation techniques that enabled load management and subsequent electricity cost optimisation through production planning. Two electrical load management case studies were successfully implemented on comminution equipment at two gold processing plants. Peak period load shift of 3.6 MW and 0.6 MW, respectively, was achieved on average for a period of three months. The annual cost savings of these applications could amount to R1.4-million and R 660 000. This results in specific electricity cost reductions of 3% and 7% for the two respective case studies. Results from the two case studies are an indication of potential for electrical load management on South African gold processing plants. If an average electricity cost saving of 5% is extrapolated across the South African gold processing industry, the potential cost savings amount to R 25-million per annum. Although the costs saving opportunities are feasible, it is influenced by the reliability of the equipment and the dynamics of ore supply. This insight plays a decisive role in determining the feasibility of DSM on gold processing plants. / MIng (Mechanical Engineering), North-West University, Potchefstroom Campus, 2015