published_or_final_version / Urban Planning / Master / Master of Science in Urban Planning

published_or_final_version / Geography and Geology / Master / Master of Philosophy

Indium-gallium-zinc oxide (IGZO) and zinc-tin oxide (ZTO) are investigated for thin-film transistor (TFT) applications. Negative bias illumination stress (NBIS) is employed for electrical stability assessment. Unpassivated IGZO and ZTO TFTs suffer from severe NBIS instabilities. Zinc-tin-silicon oxide is found to be an effective passivation layer for IGZO and ZTO TFTs, significantly improving the NBIS stability. NBIS instabilities in unpassivated TFTs are attributed to an NBIS-induced desorption of chemisorbed oxygen from the channel layer top surface, exposing surface oxygen vacancies. A ZTSO layer protects the channel layer top surface from adsorbed gas interactions and also appears to reduce the density of oxygen vacancies. The best device architectures investigated with respect to TFT electrical performance are found to be staggered with aluminum electrodes for unpassivated TFTs and coplanar with ITO electrodes for ZTSO-passivated TFTs. Annealing in wet-O₂ is not found to be effective for improving the performance of IGZO or ZTO TFTs or for reducing the post-deposition annealing temperature. / Graduation date: 2012

Contact mechanical study of layered structures is useful to various fields of engineering, such as - mechanical engineering, civil engineering, materials engineering and biomechanics. Thin hard film coating on a compliant substrate used in cutting tool industry is an example of a layered structure. The protective coating saves the substrate from fracture and wear. However, due to film material brittleness, fracture in the films is of concern. We have developed an analytical model for a film-substrate bilayer system under normal contact loading, which helps us to obtain the stress distribution in the film and fracture behaviour. Our contact model is based on Hankel’s Transform technique, where we assume a Hertzian pressure boundary condition. At each depth of penetration of the indenter in the film-substrate system, we estimate effective modulus of the system based on Gao’s approach. We have validated our analysis by surface strain measurements and photoelastic stress study in the film on a substrate. Experimental observations from literatures show the dependence of different fracture modes in a thin hard film with columnar structure on film thickness and substrate plasticity. We perform fracture analysis, a parametric study of the fracture modes in the film under contact loading. When the film thickness is small and the substrate is relatively hard (e.g. tool steel), the film and the substrate deform conformally under contact loading and the columns of TiN slide against each other into the substrate. On the other hand, when the film is thicker and the substrate is soft (e.g. mild steel or aluminium), the strain mismatch between the film and substrate acts as an added traction at the interface and drives cracks, such as radial tensile stress driven bending cracks that start from the interface at the center of indentation; maximum shear stress driven inclined shear crack that starts inside the film and propagate at an angle to the indentation axis and tensile stress driven edge crack that starts from the free surface outside the contact. We can draw a fracture map based on these calculations which provides a guide to select film thickness depending on the substrate hardness, so that the benign mode of damage, i.e., columnar shear occurs in the film. Apart from generating the fracture map, we can obtain rationale for different fracture phenomenon in the film by studying the indentation stress field. Principal tensile stresses, responsible for driving edge cracks from the free surface outside the contact, become compressive as one approaches the substrate if the substrate is compliant. The cracks therefore do not penetrate deep into the film rather curve away from the axis of indentation. At the transition zone from one mode of damage to other in the fracture map, different modes of fracture may co-exist. The whole column may not shear, rather the shear can start from somewhere in the middle of the film, where the shear stress is maximum and it can end without reaching the interface. The indentation energy is then dissipated in other forms of damage. The contact analysis is further applied to TiN /AlTiN multilayered films having similar elastic properties. Experimental observations suggest that with decreasing layer thickness the fracture resistance of the multilayers increase and some plastic yielding occurs at the top layers of the film. However no substantial change in strain capacity (Hardness/ Young’s Modulus) of the film is observed. Hence we attribute the increase of fracture resistance of multilayers to film plasticity and mimic it by reducing the modulus of the film. The analysis validates the propensity of edge cracking and transgranular cracking as they decrease with increasing number of layers in a multilayer. We next extend our bilayer analysis to a more general trilayer problem where the moduli of the layers vary by several orders. The test system here is a mica-glue-glass system which is used in surface force apparatus experiments. Gao’s trilayer analysis is used to fit the experimental data obtained from surface force apparatus experiments, where a glass sphere indents the trilayer. The parallel spring model used in Gao’s approximation is found to be inadequate to rationalize the experimental data. We have modified Gao’s formulations by reducing the problem to a bilayer problem where the layers are the first layer (in contact) and an equivalent layer which has properties determined by a rule of mixture of the properties of all the layers excluding the top layer set out as a set of springs in series. The modified formulations give a better fit to the experimental data and it is validated from nanoindentation experiments on the same system. The formulation is used to obtain the compression of the glue, which contributes significantly to the deformation of the trilayer system in the SFA experiments. Thus, the analysis can be used to deconvolute the influence of glue in the actual mechanical response of the system in an SFA experiment, which has so far been neglected.

published_or_final_version / Architecture / Master / Master of Architecture

published_or_final_version / Urban Design / Master / Master of Urban Design

The Malaysian granitoids form the backbone of the Malay Peninsula and have long been recognized as composed of two distinct granitic provinces separated by the Bentong-Raub suture zone: <table><ol><li>Early Permian to Late Triassic Eastern Province (Indochina – East Malaya) with mainly “I-type” hornblende-bearing granitoids, associated with Cu-Au deposits, and subordinate hornblende-free pluton roof-zones hosting limited Sn-W deposits; and</li> <li>Late Triassic Main Range Province, western Malaysia (Sibumasu) with mainly “S-type” hornblende-free granitoids, associated with Sn-W deposits, and subordinate hornblende-bearing granitoids.</li></ol></table> Field observations and new geochemical data suggested that the division of the Eastern Province and Main Range granitoids using Chappell and White’s (1974) I-S classification could be problematic, as there is a large degree of overlap between the two granitic provinces in terms of lithology, mineralogy and metallogenic affinity. The Main Range granitoids are more fractionated than the hornblende-bearing Eastern Province. Although the two granitic provinces were emplaced into different continental terranes, both granitic provinces exhibit common trace element geochemistry in the enrichment of high field strength elements (HFSE) and rare earth elements (REE) compared to typical Cordilleran I-S granites. Such enrichment is interpreted as an inheritance signature from the protoliths. The Kontum massif (an analogue of Indochina lower continental crust) comprises intraplate ortho-amphibolites and para-gneisses, which could serve as two hypothetical source end-members for the Malaysian granitoids. The model suggests that the geneses of the parental magmas of the Eastern Province and the Main Range Province were related to hybridization of melts derived from protoliths, geochemically and isotopically similar to these two source end-members, but in differing proportions. The fact that the granites from the two granitic provinces are so similar compositionally and metallogenically, suggests that similar protoliths were involved in their source. The incorporation of sedimentary-sourced melt makes the Main Range granitoids transitional I/S-type in nature, but this is unlikely to be true for the less evolved Eastern Province fractionated I-type granitoids. The hybridization of igneous- and sedimentary-sourced melts, and granite fractionation promotes Sn metallogenesis in the Main Range granitic province. Previous ages were obtained using whole rock Rb-Sr and biotite K-Ar geochronology in the 1970s and 1980s, dating methods that almost certainly do not accurately represent the crystallization age of granites. New ion microprobe U-Pb zircon ages are presented that provide new temporal constraints for the Malaysian granitic magmatism. Eastern Province granitoids have U-Pb zircon ages that range from 289 to 220 Ma, while Main Range Province magmatism is constrained between 227 and 201 Ma. A progressive westward younging trend is apparent across the Eastern Province, but becomes less obvious in the Main Range Province. In addition, the U-Pb zircon analysis of the Malaysian granitoids suggests that both granitic provinces have Cambro-Ordovician and Mesoproterozoic inheritance signatures, which match the ages of the Kontum intraplate ortho-amphibolites and para-gneisses, the two source end-members of the suspected Indochina basement. Two different tectonic models have been suggested to explain the formation and the emplacement of the Malaysian granitoids. Both models involve an east-dipping subduction zone during the Early and Mid-Triassic with Palaeo-Tethys lithosphere rolling back along the Bentong-Raub suture zone to produce westward younging ages in the Eastern Province granitoids. The first model (modified after Searle et al. 2012) suggests the younger Main Range granitoids were produced by another Late Triassic – Cretaceous east-dipping (Neo-Tethyan) subduction to the west of Sibumasu, after the Sibumasu – East Malaya collision. The transitional I/S-type geochemistry of the Main Range granitoids was caused by the partial melting of the more heterogeneous Sibumasu basement. The second model (Oliver et al. 2014) suggests the younger Main Range granitoids were produced by the westward underthrusting of Indochina crust of East Malaya beneath Sibumasu along the Bentong-Raub suture zone after the continental collision. In this model, the source of the Main Range granitoids was the pre-collision I-type Eastern Province granitoids. The second model is less likely, as no geological evidence for such underthrust is found in the Malay Peninsula.

published_or_final_version / abstract / Geography and Geology / Master / Master of Philosophy

published_or_final_version / Criminology / Master / Master of Social Sciences

published_or_final_version / Geography and Geology / Master / Master of Philosophy