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This thesis describes a novel concept for a field-effect transistor based on metallic channels. Latest research demonstrates that the bulk (3D) properties of many materials begin to change when confined to 2D sheets, or 1D nanowires. Particularly, the bandgap increases and the density of states decreases. In this work, this effect is explored further to demonstrate its application to field-effect transistors. Certain metals such as Gold and Silver in these dimensions have extremely low density of states in particular energy regions and through gate modulation can be partially depleted from electrons thus creating conditions for field-effect. A simulation study of Gold channel FET demonstrates ION/IOFF of 30 and superior current driving capability compared to the state-of-the art 22nm SiGe ETSOI as well as 30nm nanotube transistors.

This thesis describes a novel concept for a field-effect transistor based on metallic channels. Latest research demonstrates that the bulk (3D) properties of many materials begin to change when confined to 2D sheets, or 1D nanowires. Particularly, the bandgap increases and the density of states decreases. In this work, this effect is explored further to demonstrate its application to field-effect transistors. Certain metals such as Gold and Silver in these dimensions have extremely low density of states in particular energy regions and through gate modulation can be partially depleted from electrons thus creating conditions for field-effect. A simulation study of Gold channel FET demonstrates ION/IOFF of 30 and superior current driving capability compared to the state-of-the art 22nm SiGe ETSOI as well as 30nm nanotube transistors.

Introduction Irradiation of gold with protons provides access to no-carrier-added 197mHg and 197Hg. Interests in these radionuclides were awakened by the unique chemical and physical properties of mercury and its compounds combined with convenient nuclear properties like suitable half life (197mHg: T1/2 = 23.8 h, 197Hg: T1/2 = 64.14 h), low energy gamma radiations for imaging, Auger – and conversion electrons for therapy. The high thermal conductivity of gold enables high current irradiations and the monoisotopic natural abundance of 197Au supersedes expensive enrichment of the target material. The 197Au(p,n)197(m)Hg reaction was applied until now only for beam monitoring1, stacked foil meas-urements2 or very small scale tracer production. Material and Methods The irradiations were performed at a Cyclone 18/9 (IBA, Louvain la Neuve, Belgium). Its beam-line was sealed with a 1.0 mm vacuum foil (high purity aluminum, 99.999 %) from Goodfellow (Huntingdon, England). High purity gold disks (23 mm diameter, 2 mm thickness, 99.999% pure, 1 ppm Cu) as target material were purchased from ESPI (Ashland, USA). Gold foils as alternative gold targets (12.5×12.5 mm, 0.25 mm thickness, 99.99+ %, 1 ppm Cu) between an aluminum disk (22 mm diameter, 1 mm thickness, 99.0 %, hard) and an aluminum lid (23 mm diameter, 99.0 %, hard) were purchased from Goodfellow (Huntingdon, England). Hydrochloric acid (30%) and nitric acid (65%) were purchased from Roth (Karlsruhe, Germany) in Rotipuran® Ultra quality. Deionized water with > 18 MΩcm resistivity was prepared by a Milli-Q® system (Millipore, Molsheim, France). For separation of target material and side products a liquid-liquid extraction method (Gold was extracted with methyl isobutyl ketone (MIBK) from 2 M HCl target solution) and an ion exchange method (cation exchange resin (Dowex50W-x8, 100–200 mesh, H+ form) were applied. Results and Conclusion No-carrier-added 197(m)Hg was produced from gold via the 197Au(p,n)197(m)Hg reaction at proton energies of 10 MeV in sufficient quantity and quality for imaging studies. Two different methods were studied for the separation of Hg radionuclides generated from Au targets. The results demonstrate the possibility to produce 197(m)Hg from gold at low proton energies. Combined with the presented radiochemical separation methods, the 197Au(p,n) reaction could be the basis for repeatable production of 197(m)Hg for imaging and therapy research on sufficient activity level.

This thesis presents the study of films derived from the reduction of aryldiazonium salts at gold surfaces. The properties of bare polycrystalline surfaces were investigated via the observation of the electrochemical oxidation and reduction of the gold. Films derived from diazonium salts were electrochemically grafted to the gold surface. The structure and stability of these interfaces was examined through the use of redox probes, gold oxide electrochemistry and water contact angle measurements. The spontaneous reduction of aryldiazonium salts at gold surfaces was investigated and the possible applications it presented towards printing and patterning of the gold surface with films were explained. Polycrystalline gold surfaces were prepared and subjected to various treatments, to observe the behaviour of gold oxide formation and reduction at the surface. Various effects on the surface structure were observed after treatment in solvents and electrolyte solutions. The surface structure of the gold atoms frequently changed due to the high mobilities of the gold atoms, and it is difficult to achieve a reproducibly stable surface. The electrochemical modification of gold surfaces via the reduction of aryldiazonium salts was investigated. Surfaces were modified with methylphenyl and carboxyphenyl films and exposed to various treatments. Monitoring the gold oxide reduction changes enabled the surface coverage of modifier directly attached to the surface to be calculated. The films appear to be stable, loosely packed and porous. The films are flexible in nature; redox probe responses showed reversible changes after repeated sonication in solvents of differing polarities and hydrophilicities. Contact angle measurements further support the notion of films that can reorganise in response to their environment. The spontaneous reduction of aryldiazonium salts at gold surfaces was observed. Film coverage was significantly lower at the spontaneously grafted surface than for films grafted electrochemically. Gold surfaces were successfully modified via microcontact printing, and surface coverages similar to the spontaneously grafted film were achieved. Microcontact printing was also used to pattern surfaces with films derived from diazonium salts. Feature sizes down to 100 µm were successfully achieved.

On the verge of entering the post-antibiotic era, numerous efforts are in place to regain the losing potential of antibiotics which are proving ineffective against common bacterial infections. Engineered nanomaterials, especially gold nanoparticles (GNPs) capped with antibacterial agents are proving to be an effective and novel strategy against multi-drug resistant (MDR) bacteria. In this study, we report a one-step synthesis of kanamycin-capped GNPs (20 ± 5 nm) utilizing the combined reducing and capping ability of the aminoglycoside antibiotic, kanamycin. Antibacterial assays showed dosedependent broad spectrum activity of Kan-GNPs against Gram-positive (Staphylococcus epidermidis and Enterococcus durans), Gram-negative (Escherichia coli and Enterobacter aerogenes) and Kan-resistant and MDR bacterial strains. A significant reduction in the minimum inhibitory concentration (MIC) of Kan-GNPs was observed as compared to free kanamycin against all the sensitive and resistant bacterial strains tested. Mechanistic studies using TEM and fluorescence microscopy showed that Kan- GNPs exerted their bactericidal action through disrupting the cellular membrane resulting in leakage of cytoplasmic content and death of bacterial cells. Results of this study provide a novel method in the development of antibiotic capped GNPs as potent next-generation antibacterial agents.

Monothiolate protected gold nanoclusters with near IR luminescence underwent a five-to-ten fold enhancement of quantum efficiency by heating in the presence of excess thiols. Two monothiolate nanoclusters, mercaptosuccinic acid and tiopronin, were shown to benefit from this procedure. Emission maximum around 700-900 nm is favorable for bioimaging applications due to reduction of background signal from autofluorescence. Dithiolate lipoic acid protected gold nanoclusters with higher near IR quantum efficiency present an interesting candidate for biological imaging due to the difference in hydrophobicity, resistance to quenching by divalent cations and cell growth media, and retained quantum efficiency when coupled to agents such as polyethylene glycol. Intracellular and nuclear internalization of mercaptosuccinic gold nanoclusters demonstrate a potential vector for delivery of nuclear targeting agents. The small size, chemical stability, high luminescence, and potential for targeting various intracellular domains make gold nanoclusters worthwhile for further studies as potential bioimaging probes.

Hydrogen cyanide gas (HCN{g)) is formed during the process of extracting gold from ore and may pose a risk to the health of the workers at the gold refinery (Mill/plant), especially the risk of detrimental effects on the central nervous system and the cardiovascular system. The measurement of the personal airborne HCN(g) exposure of a worker using sorbent tubes, provides the concentration of the chemical that the worker breaths in. The measurement of the urinary thiocyanate (SCN~) concentration provides the total HCN exposure experience by the worker through all possible routes of exposure. The study's aim was to determine if the workers were exposed to HCN(g) concentrations that was higher than the occupational exposure limit (OEL) , which would mean that the workers are exposed to excessive and possibly harmful levels of HCN. The monitored workers were divided into three homogenous exposure groups or HEGs, according to the their potential level of exposure. The results were compared between the three HEGs and between three work description groups, namely the Mill/plant workers, SGS laboratory assistants and members of the environmental department. The study found that all the workers were exposed to personal airborne HCN(9) concentrations below the OEL. A statistical significant difference was found the personal airborne exposure experienced by the three HEGs and between the Mill/plant workers and the members of the environmental department. No statistical significant difference was found between the urinary SCN" concentration found in the three HEGs or the between the three work description groups. Confounding factors such as smoking, the consumption of cassava, the exposure to fire smoke and the amount of time worked at the mine did not influence the urinary SCN~ concentration. The implementation of a biological monitoring program would enable the identification of any worker that is exposed to excessive levels of HCN. / Thesis (M.Sc. (Occupational Hygiene))--North-West University, Potchefstroom Campus, 2009.

This research emphasizes on the use of seeded growth in synthesis of noble metal nanocrystals with precise control over the size, shape, and composition. In the first part of this work, I have produced Au nanocrystals with single-crystal structure and truly spherical profiles and investigated their optical properties and self-assembly as induced by dilution with water. These Au nanospheres were generated in high yield and purity, together with controllable sizes continually increased from 5 to 150 nm. I also found these Au nanospheres self-assembled into dimers, larger aggregates, and wavy nanowires, respectively, as diluted with water. In the second part of this work, I demonstrate the kinetic control can be implemented to control the shape of mono- and bi-metallic nanocrystals in seeded growth. The as-prepared single-crystal nanospheres of Au were employed as seeds to synthesize of tetrahedral Au nanocrystals and Au@Pd core-shell nanocrystals with six distinct shapes. The success of the two demonstrations relies on manipulation of reaction kinetics to achieve different product shapes. The reaction kinetics was controlled by varying a set of reaction parameters, including the type and concentration of capping agent, the amount of reductant, and the injection rate of metal precursor solution. In the final part of this work, I will discuss an unusual change in crystallinity observed in seeded growth of Au nanocrystals on Au seeds. In particular, single-crystal Au seeds treated with a chemical species could develop twin defects during the seed-mediated growth process to yield multiply twinned products.