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The ability to fabricate structures and engineer materials on the nanoscale leads to the development of new devices and the study of exciting phenomena. Nanostructures attached to the surface of a substrate, in a manner that renders them immobile, have numerous potential applications in a diverse number of areas. Substrate-supported nanostructures can be fabricated using numerous modalities; however the easiest and most inexpensive technique to create a large area of randomly distributed particles is by the technique of thermal dewetting. In this process a metastable thin film is deposited at room temperature and heated, causing the film to lower its surface energy by agglomerating into droplet-like nanostructures. The main drawbacks of nanostructure fabrication via this technique are the substantial size distributions realized and the lack of control over nanostructure placement. In this doctoral dissertation, a new pathway for imposing order onto the thermal dewetting process and for manipulating the size, placement, shape and composition of preformed templates is described. It sees the confinement of substrate-supported thin films or nanostructure templates by the free surface of a metal film or a second substrate surface. Confining the templates in this manner and heating them to elevated temperatures leads to changes in the characteristics of the nanostructures formed. Three different modalities are demonstrated which alters the preformed structures by: (i) subtracting atoms from the templates, (ii) adding atoms to the template or (iii) simultaneously adding and subtracting atoms. The ability to carry out such processes depends on the choice of the confining surface and the nanostructured templates used. A subtractive process occurs when an electroformed nickel mesh is placed in conformal contact with a continuous gold film while it dewets, resulting in the formation of a periodic array of gold microstructures on an oxide substrate surface. When heated the gold beneath the grid selectively attaches to it due to the surface energy gradient which drives gold from the low surface energy oxide surface to the higher surface energy nickel mesh. With this process being confined to areas adjacent to and in contact with the grid surface the film ruptures at well-defined locations to form isolated islands of gold and subsequently, a periodic array of microstructures. The process can be carried out on substrates of different crystallographic orientations leading to nanostructures which are formed epitaxially and have orientations based on underlying substrate orientations. The process can be extended by placing a metallic foil of Pt or Ni over preformed templates, in which case a reduction in the size of the initial structures is observed. Placing a foil on structures with random placement and a wide size distribution results, not only in a size reduction, but also a narrowed size distribution. Additive processes are carried out by using materials which possess high vapor pressures much below the sublimation temperature of the template materials. In this case a germanium substrate was used as a source of germanium adatoms while gold or silver nanostructures were used as heterogeneous nucleation sites. At elevated temperatures the adatoms collect in sufficient quantities to transform each site into a liquid alloy which, upon cooling, phase separates into elemental components sharing a common interface and, hence, resulting in the formation of heterodimers and hollowed metal nanocrescents upon etching away the Ge. A process which combined aspects of the additive and subtractive process was carried out by using a metallic foil with a high vapor pressure and higher surface energy than the substrate surface (in this case Pd foil). This process resulted in the initial preformed gold templates being annihilated and replaced by nanostructures of palladium, thereby altering their chemical composition. The assembly process relies on the concurrent sublimation of palladium and gold which results in the complete transfer of the templated gold from the substrate to the foil, but not before the templates act as heterogeneous nucleation sites for palladium adatoms arriving to the substrate surface. Thus, the process is not only subtractive, but also additive due to the addition of palladium and removal of gold. / Mechanical Engineering

Terahertz region in the electromagnetic spectrum is the region between Infrared and Microwave. As the Terahertz region has both wave and particle nature, it is difficult to make a room temperature, fast, and sensitive detector in this region. In this work, we fabricated a Palladium based IR detector and a CNT based THz bolometer. In Chapter 1, I give a brief introduction of the Terahertz region, the detectors already available in the market and different techniques I can use to test my detector. In Chapter 2, I explain about the Palladium IR bolometer, the fabrication technique I have used, and then we discuss the performance of the detector. In Chapter 3, I explained about the Roll to Roll based THz bolometer, its working and fabrication techniques, and at the end we discussed its performance.

Ceria is a lanthanide series element that can exist as Ce3+ or Ce4+. Cerium oxide nanostructures are being developed for use in industry as catalysts. Nanostructures often behave differently from their corresponding macrostructures and these new behaviors can result in novel and important biological and chemical properties. The free radical theory of aging suggests that free radicals many of which are reactive oxygen species, damage cellular macromolecules. This damage can contribute to degenerative diseases, cancer and aging. Recent research has shown that ceria oxide nanoparticles protected cells from UV and radiation damage as well as decrease intracellular reactive oxygen species in primary cell cultures. The enzyme superoxide dismutase (SOD) protects the cell from free radicals by reacting with superoxide, a reactive oxygen species. Chemicals that catalyze the same reaction as SOD are referred to as SOD mimetics. Another biologically significant free radical is nitric oxide, a reactive nitrogen species. Nitric oxide is an important signaling molecule in both the cardiovascular and nervous system; however it can also cause damage to proteins through nitrosylation. When superoxide and nitric oxide react with each other they form the highly potent free radical, peroxynitrite. This reaction naturally occurs in the phagolysosome of the macrophage and is utilized by the immune system to kill pathogens. Nanoceria was tested for activity against superoxide, nitric oxide and peroxynitrite. The results presented in this work show that ceria oxide nanoparticles exhibit SOD mimetic activity and reduce protein nitrosylation in vitro.

Dans ce manuscrit, nous mesurons la réponse mécanique à l’échelle nanométrique de divers systèmes issus de la matière molle en utilisant un microscope à force atomique basé sur un diapason à quartz. Utilisé comme un nano-rhéomètre, cet instrument permet une mesure quantitative des propriétés viscoélastiques des matériaux et des processus frictionnels et dissipatifs aux nanoéchelles. Nous montrons d’abord que les liquides ioniques confinés aux nanoéchelles peuvent subir un changement dramatique de leurs propriétés mécaniques, suggérant une solidification capillaire. Cette transition est favorisée par la nature métallique des interfaces confinantes, montrant la présence d’effets électrostatiques subtils dans ces électrolytes denses. Nous étudions ensuite les mécanismes de plasticité à l’échelle atomique en mesurant la réponse viscoélastique de jonctions d’or de quelques atomes de diamètre. Nous mettons en évidence une transition sous cisaillement entre un régime élastique, puis plastique, jusqu’à la liquéfaction complète de la jonction. Nous caractérisons ainsi de manière fine les mécanismes de plasticité dans ces systèmes moléculaires. Finalement, nous montrons les effets profonds que les interactions à l’échelle nanométrique peuvent avoir sur le comportement macroscopique de la matière molle. Nous mesurons le profil frictionnel entre paires de particules de suspensions de PVC et de maïzena. Nos mesures mettent en lumière le rôle dominant des interactions locales entre particules dans la rhéologie non-newtonienne des suspensions. / In this manuscript, we use a tuning fork based atomic force microscope to measure the mechanical response of various soft matter systems at the nanoscale. This instrument is used as a nano-rheometer, allowing quantitative measurements of viscoelastic material properties, and unprecedented characterization of friction and dissipation at the nanoscale. First, we show that ionic liquids can undergo a dramatic change in their mechanical properties when confined at the nanoscale, pointing to a capillary freezing transition. This transition is favored by the metallic nature of the confining substrates, suggesting the occurrence of subtle electrostatic effects in those dense electrolytes. Second, we probe plasticity at the individual atomic level, by measuring the viscoelastic rheological response of gold junctions of few atoms diameter. For increasing shear, we uncover a transition from a purely elastic regime to a plastic flow regime, up to the complete shear-induced melting of the junction. Our measurements give unprecedented insights on the plastic mechanisms at play in those molecular systems. Finally, we show that nanoscale interactions can have profound effects on the macroscopic behavior of soft materials. Focusing on the nonnewtonian flow behavior of concentrated suspensions of particles, we measure the nanoscale frictional force profile between pairs of particles of PVC and cornstarch suspensions. Our measurements highlight the dominant role of local interparticle interactions on the macroscale rheology of suspensions.

Thesis (M.Sc (Chemistry)) --University of Limpopo, 2013 / Since their discovery in 1991, CNTs have shown extraordinary properties and as result, these materials are being investigated for several different applications. Synthesis and electrochemical application of CNTs for hydrogen storage provide new possibilities for replacement of gasoline use in vehicles due to its cost and negative environmental impact. The study investigated the metal nanoparticles modified multi-walled carbon nanotubes as possible storage material for hydrogen. Herein, carbon nanotubes were successfully synthesized by pyrolysis of iron (II) phthalocyanine under Ar/H2 reducing atmosphere at 900 oC for 30 min. The micro-structural information of the as-prepared carbon nanotubes was examined by Transmission electron microscopy (TEM). It was found that the prepared CNTs were multi-walled with iron particles impurities present on the surface. Synthesized MWCNTs were found to have open tips as shown by TEM images. These materials were purified and functionalized with acid groups as confirmed by Fourier transform infra-red spectroscopy (FTIR). A successful decoration of MWCNTs by Cu, CuO, Fe, Fe2O3, Ni and NiO nanoparticles was confirmed by Scanning electron miscroscopy (SEM) and Transmission electron microscopy (TEM). TEM images showed that metal nanoparticles and metal oxides were well dispersed on the surface of the MWCNTs. The chemical composition of the as-prepared MWCNTs was confirmed by XRD (showing the presence of metal impurities and amorphous carbon). Synthesized materials were applied in electrochemical techniques such as cyclic voltammetry, chronopotentiometry and controlled potential electrolysis. These techniques have shown that modification of glassy carbon bare electrode (GCE) with carbon nanotubes decorated with metal nanoparticles (Cu, Ni and Fe), improves the current density, charge-discharge voltages and discharge capacity for hydrogen storage (in a 6 M KOH aqueous electrolyte). It was shown that MWCNTs exhibit high conductivity, porosity and high surface area for hydrogen storage. The increase in discharge capacity was as follows: GCE < GCE-MWCNT < GCE-MWCNT-M (M = Cu, Ni, Fe and/or metal oxides). This confirmed a successful modification of GCE with MWCNTs and MWCNT-M (M = Cu, Ni, Fe and/or metal oxides). The maximum discharge capacity of 8 nAh/g was obtained by GCE-MWCNTs-Ni electrode, corresponding to an H/C value of 28.32 x 10 It was confirmed that both Ni loading and MWCNTs loading have an impact on the current response, charge-discharge voltages and discharge capacity. A maximum current density and discharge current was reached when a 4wt% nickel was loaded. A decrease in current density and discharge current was observed for nickel loading of higher than 4wt%. Thus suggests a possible decrease in surface area of the adsorbed material on the surface of the electrode for hydrogen storage. As more MWCNTs were added, a decrease in current density was observed. A 2wt% MWCNTs gave higher discharge current and this was possibly due to less hindrance on the surface of the electrode for hydrogen to diffuse. It was shown that calcining the metal nanoparticles result in particles agglomeration, as confirmed by Transmision electron microscopy (TEM). This resulted in a decrease in surface area of the working electrode. A low current response was observed compared to the uncalcined Ni nanoparticles. The highest exchange current density was obtained while using a GCE-MWCNT-Nical as compared to the GCE-MWCNT-Niuncal electrode. The applied discharge current in CPE was also shown to have influence on the discharge capacity. An increase in discharge capacity for the GCE-MWCNT-Ni (2wt% MWCNTs and 4wt% Ni) electrode was observed as more discharge current was applied. A decrease in discharge capacity for hydrogen was observed as more content of the MWCNT-Niuncal nanocomposite are added on the active surface area of the glassy carbon electrode.

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