Transmission Electron Microscope (TEM) studies have been carried out of emitter regions in polysilicon contacted emitter bipolar transistors. The preparation of suitable TEM thin foils is described. In addition a technique is developed for the observation and quant jtative interpretation of the break-up of the interfacial oxide layers observed in these samples. The effect of annealing the samples prior to emitter dopant implantation (pre-annealing) is investigated for phosphorus and arsenic doped samples, implanted into a polysilicon layer 0.4μm thick, with a dose of 1x10¹⁶cm². Two wafer pre-cleans have been used prior to polysilicon deposition to produce a thin oxide (0-8Å) and a thicker oxide (14Å). In the presence of the thinner oxide, the phosphorus doped samples enhance epitaxial regrowth of the polysilicon layer compared with the arsenic doped or undoped samples. In the presence of the thicker oxide, no difference is observed between the samples. A mechanism is proposed to explain this. The mechanisms controlling the gain of a phosphorus doped device are investigated and a model proposed to explain the observed electrical characteristics. It is concluded that there are two mechanisms responsible for the observed supression of hole current. Firstly tunnelling through the interfacial oxide and secondly some blocking effect of the interface. Carrier transport in the polysilicon is not believed to contribute to this supression. A dopant sensitive etch has been applied to TEM thin foils containing fully processed emitters in state-of-the-art devices. The shape of the emitter dopant distribution is revealed in such devices for the first time, and a 2-D profile is obtained from the emitter. It is shown that reduction in the emitter depth to 8OOÅ or less does not alter the emitter dopant geometry. The technique is demonstrated to be capable of resolving spatial separations of dopant iso-concentration contours of 100Å or less.

This thesis describes an investigation into the folding behaviour of hen lysozyme by characterisation of the structure and the dynamics of different conformational states of the protein. The native state, a partially structured state generated by the addition of a cosolvent, trifluoroethanol (TFE), and a highly denatured state of the protein in presence of urea at low pH, have been studied at equilibrium by circular dichroism (CD) and nuclear magnetic resonance (NMR) spectroscopy. The principal methods utilised in-fchis thesis are the measurement and interpretation of amide hydrogen exchange and ¹⁵ N relaxation data. Amide hydrogen exchange rates from a highly denatured state of hen lysozyme in 8 M urea, at pH 2.0, are well approximated by recent estimates for intrinsic exchange rates from unstructured polypeptides, implying that residual .structures cannot be persistent in this state. In the native protein, by contrast, protection factors are measured to be of the order of 10⁴-10⁸ and can be rationalised by the involvement of amides in secondary structure and burial from the protein surface. Surface accessibility has also been found to be an important determinant of the dynamics of main and sidechain groups monitored by ¹⁵N relaxation. For this purpose ¹⁵N resonances of native lysozyme were assigned and order parameters derived. The dynamic behaviour was considered in the light of features of the crystal and NMR structures, suggesting that a lack of van der Waals contacts is a major determinant for mobility. A denatured state of hen lysozyme, formed by addition of TFE cosolvent, has been developed as a model for a partially ordered conformation of the protein. Amide hydrogen exchange measurements show that sites with the highest protection factors, up to 250, are located in stable native-like helices. Near complete assignment of ¹⁵N-edited NMR spectra allowed a detailed description of secondary structure in the TFE denatured state. Non-native α-helical structure is present as extensions to the native helices and in a region of the polypeptide which forms part of the β-sheet in the native state. These structures have been shown to be in accord with the helical propensities of the primary sequence. Preliminary structure calculations suggest that, despite the absence of extensive and persistent tertiary interactions, topological restraints exist in parts of the TFE denatured state, resulting in considerable propensities for native-like arrangements of the secondary structure. Mainchain dynamics determined by ¹⁵N relaxation, although increased in magnitude, appear to be related to that of the native state and are dominated by the position of disulphide bonds and by chain hydrophobicity. Thus the structural and the dynamic behaviour of the polypeptide chain in the TFE denatured state could be rationalised, at least in part, by consideration of features of the primary sequence.

The thesis work discuss about how the materials mechanical properties are influenced by the microstructure. The most common way of altering the microstructure of the material is by heat treatment.The mechanical properties that are of interest are strength, toughness, ductility, creep and fatigue. The material under consideration iswidely used superalloy In718. Two different sets of specimens areheat treated at different temperatures and influence of heat treatmenton the grain size is analyzed. In order to get better understanding ofthe grain size on mechanical properties, microstructural investigation was done using SEM. Efforts are made to understand the influence of different elements on the overall characteristic of the material. The tensile, creep and stress relaxation tests were conducted and the results were discussed. / Master Thesis

Non-equilibrium plasma modification of polymer surfaces in an oxygen atmosphere provides a highly efficient, solventless method of raising the surface energy. The chemical and physical effects of non-equilibrium plasma treatment on polymer surfaces have been investigated. Oxygen glow discharge and silent discharge treatment of several polymers (polypropylene, polystyrene, polyphenylene oxide and polycarbonate) has been shown to cause both surface oxidation and chain scission at the polymer surface. This generates low molecular weight oxidised material on the polymer surface which conglomerates into globular features due to the difference in surface energy between the oxidised material and the untreated polymer. These features can be removed by solvent washing. Generally silent discharge treatment generates more low molecular weight oxidised material whereas oxygen glow discharge treatment generates more non-soluble oxidised material. Crystalline polymers react at a slower rate than amorphous material. During the treatment of a model crystalline polymer (hexatriacontane) the plasma attacks the edges of the crystal, rather than the surface, due to the greater chain mobility at the edge. Non-equilibrium plasma treatment of both miscible and immiscible polymer blends were investigated. The size and distribution of the globular features formed were found to be dependent on the blend composition. For the immicible polymer blend, non-equilibrium plasma treatment reveals the blend morphology mi sing from the difference in reaction rates of the parent polymers.

Alzheimer's Disease (AD) is a neurodegenerative disorder that is prevalent among the elderly population. Aß protein has been heavily implicated in the pathogenesis of AD. This protein in its fibrillar form is a major component in the senile plaques that form on neuronal cellular membranes during the course of AD. Despite substantial efforts the exact mechanism of Aß toxicity towards a cell membrane is not well-understood. The determination of this mechanism, however, is of utmost importance, since the membrane presents the first site of Aß interaction with neurons, which in turn maybe the origin of Aß neurotoxicity. The purpose of this study was to find a lipid composition that can be used as a model of neuronal membrane for subsequent studies of the role of topographical heterogeneity (domain formation) on Aß-membrane interaction as related to AD. The lipids used in the study were 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC), 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoglycerol (POPG), cholesterol (Chol), sphingomyelin (SM) and ganglioside GM1 (GM1). These lipids were combined in different proportions and deposited on a mica substrate to form supported monolayers. They were then imaged with an atomic force microscope (AFM) to determine if any of them exhibited domain formation. Three of the studied samples: POPC/POPG/SM 40:40:20 +5%Chol, POPC/SM/Chol 75:20:5 and POPC/SM/GM1/Chol 74:2:1:23 were found to possess interesting topography, rich in structural features: pores and domains. The average height difference between the domain features for each sample was found to be 0.58±015 nm, 0.61±0.12 nm and 0.27±0:07 nm.

<p>In this study we report on the effect of the deposition parameters on the morphology and structural properties of CNTs, synthesized by means of the hot-wire chemical vapour deposition technique. SEM, Raman and XRD results show that the optimum deposition conditions for the HWCVD synthesis of aligned MWCNTs, with diameters between 50 and 150 nm and lengths in the micrometer range are: Furnace temperature of 500 &ordm / C, deposition pressure between 150 and 200 Torr, methane/hydrogen dilution of 0.67 and a substrateto- filament distance of 10 cm.</p>

Bacteria are implicated in endodontic infections. They not only infect the root canal lumen but also invade the dentinal tubules where they may remain untouched by contemporary chemomechanical preparation during root canal therapy. The contentious issue is whether the bacteria within these tubules contribute to secondary infections. Many studies have shown that clinicians fail to completely eradicate them during root canal therapy. At present there are no techniques available to detect the effectiveness of the current chemomechanical treatment regime within dentinal tubules. It is difficult to detect bacteria within the dentinal tubules. Culturing techniques have been used routinely as they are versatile and easy to use. However, they are unable to show the distribution of the bacteria within the dentinal tubules. Scanning electron microscopy, on the other hand, shows detailed surface structure in association with bacteria. Histological examination of root dentine specimens under the light microscope also shows the distribution of bacteria within the specimen but not viability. The dilemma posed by these existing techniques is that the results offer limited information; either demonstrating bacterial viability or bacterial distribution within specimens. No techniques able to show both the viability and the distribution of bacteria within the dentinal tubules have been reported to date. Fluorescent stains, in particular SYTO�9 and propidium iodide (LIVE/DEAD� Baclight[TM] viability kit, Molecular Probes Inc., Eugene, Oregon), have made it possible not only to stain bacteria but to differentiate live and dead bacteria. The combination of these two stains has yet to be applied to dental hard tissue in situ and they provide the basis for this investigation. The aim of this study was to evaluate the potential of the LIVE/DEAD� Baclight[TM] stains in conjuction with confocal laser scanning microscopy in the development of a technique to evaluate the viability and distribution of bacteria within dentinal tubules. This was extended to demonstrate the application of this technique by examining three different means of root canal disinfection both qualitatively and quantitatively. An important aspect of this study was to maintain bacterial viability, as well as to get maximum bacterial invasion into dentinal tubules. Results indicated that when the root canals were instrumented with Protaper� files and then irrigated with sodium hypochlorite (NaOCl) and ethylene diaminetetraacetic acid with cetrimide (EDTAC), there was more bacterial invasion into the dentinal tubules than when the root canals were only irrigated with NaOCl and EDTAC. Daily replenishments of nutrients resulted in deeper bacterial invasion into the dentinal tubules. Bacteria colonized the dentinal tubules up to a distance of 594 � 133 [mu]m from the canal. In the untreated tubules, 96 � 4 % of bacteria remained viable (green-fluorescent), whereas the Amoxicillin-treated tubules contained 94 � 6 % dead (red-fluorescent) bacteria. The calcium hydroxide-treated tubules resulted in 92 � 7 % bacterial death while the laser-treated tubules contained 81 � 12 % dead cells, frequently displaying an inner zone of dead cells surrounded by an outer zone of viable cells. The application of the fluorescent stains combined with confocal microscopy offers a new method for assessing the in vitro efficacy of root canal disinfection regimens.

Thesis (PhDBiomedicalScience)--University of South Australia, 2001.

Thesis (PhD)--University of South Australia, 1997

This thesis demonstrates the effective use of low temperature molecular beam epitaxy to encapsulate planar Si:P (phosphorus-in-silicon) devices lithographically patterned by scanning tunnelling microscopy (STM) without significant redistribution of the dopants. To achieve this goal, low temperature magnetotransport is used in combination with STM, Auger electron spectroscopy and secondary ion-mass spectrometry to analyse Si:P ??-doped samples fabricated under different doping and growth conditions. An important aspect of this project is the use of large 1 ?? 1 cm2 Si(001) samples which are about five times larger than standard STM samples. The larger sample size is necessary for post-STM fabrication lithography processes in a cleanroom but presents problems for preparing atomically clean surfaces. The ability to prepare clean and atomically flat Si(001) surfaces for STM lithography on such 1 ?? 1 cm2 samples is demonstrated, and it is shown that Si:P ??-doped layers fabricated on these surfaces exhibit complete electrical activation. Two dopant sources (gaseous PH3 and solid GaP source) were investigated to assess their compatibility with STM-lithography on the H:Si(001) surface. The findings show that while the PH3 and GaP sources result in near identical electrical qualities, only PH3 molecules are compatible with H-resist based lithography for controlled nano-scale doping. For achieving complete activation of the P dopants, it is shown that an anneal to ??? 350 ???C to incorporate P atoms into the Si surface prior to encapsulation is critical. While it is known that the presence of H during growth degrades the quality of Si epitaxy, investigations in this thesis indicate that it has no significant effect on dopant activation. Systematic studies performed to assess the impact of growth temperature recommend an encapsulation temperature of 250 ???C for achieving optimal electrical qualities with minimal dopant segregation. In addition, it is shown that rapid thermal anneals (RTAs) at temperatures &lt 700 ???C provide only marginal improvement in the electrical quality of Si:P ??-doped samples encapsulated at 250 ???C, while RTA temperatures &gt 700 ???C should be avoided due to the high probability of dopant redistribution. To elucidate the nature of 2D transport in Si:P ??-doped devices, a detailed analysis of the low temperature magnetotransport for Si:P ??-doped layers with doping densities in the range ??? 0.2 ??? 2 ?? 1014 cm???2 was carried out. Using conventional 2D theories for disordered systems, both weak localisation (WL) and electron-electron interactions (EEI) are shown to contribute almost equal corrections to the 2D conductivity. In particular, it is found that EEI can introduce a significant correction in the Hall coefficient RH (hence Hall density) especially in the low density/temperature regime and the need to correct for this when using the Hall density to estimate the activated electron density is highlighted. While the electronic mean free path in such highly doped ??-layers is typically &lt 10 nm making ballistic transport in these devices difficult to observe, the phase coherence length can extend to almost 200 nm at about 0.3???0.5 K for doping densities of ??? 1 ??? 2 ?? 1014 cm???2. Finally, the optimised encapsulation strategy developed in this thesis is applied to a 2D square device fabricated by STM. The device exhibits Ohmic conductivity with complete dopant activation. An analysis of its low temperature magnetotransport shows that the device behaves similarly to a Si:P ??-doped layer encapsulated under similar conditions, thus highlighting that the STM patterning process had no adverse effect on device quality.