The implantation of helium ions into lithium niobate produces a reduction in its refractive indices, due to radiation damage produced close to the end of the ion trajectories. This reduction can be utilised to form the boundaries of optical waveguides, which form the basis of any integrated optical circuit. Stripe waveguide fabrication using ion implantation has been demonstrated for the first time in this work. Firstly a buried damage layer was formed to define the depth of the waveguide, followed by additional implants around a gold mask to form the waveguide sidewalls. The gold mask was used to protect the guiding region during the latter implantation process. The waveguides were evaluated using the end-fire coupling technique to excite individual modes. Propagation loss and modal dimensions were determined experimentally for the fundamental mode of each guide, and it was shown that these properties are sensitive to both the ion energy of the wall implants, and the number of wall implants. Each of these two variables affects the propagation loss in the opposite sense to the other, and therefore the lowest propagation loss becomes dependant on the trade off between these two effects. The lowest loss of the waveguides presented in this thesis was found to be ~1 dB/cm, and it is expected that this figure may be further reduced by the optimisation suggested in the conclusions of this work. Additional results are presented which consider the electrooptic and photorefractive properties of ion implanted LiNbO3. Previous work of others suggested that the electrooptic effect would be considerably reduced in the implanted material, but the results were much more encouraging, showing a reduction of only ~20% in the r13 electrooptic coefficient. Furthermore, one of the most serious drawbacks of Ti:indiffused waveguides is the undesirable reduction of the output intensity due to the photorefractive effect, which has been shown not to affect the waveguides presented in this thesis.

M.Ing. (Electrical & Electronic Engineering Science) / Please refer to full text to view abstract

Design and fabrication of three-dimensional (3D) ICs is one the newest and hottest trends in semiconductor manufacturing industry. In 3D ICs, multiple 2D silicon dies are stacked vertically, and through silicon vias (TSVs) are used to transfer power and signals between different dies. The electrical characteristic of TSVs can be modeled with equivalent circuits consisted of passive elements. In this thesis, we use “dummy” TSVs as electrical delay units in 3D SRAMs. Our results prove that dummy TSVs based delay units are as effective as conventional delay cells in performance, increase the operational frequency of SRAM up to 110%, reduce the usage of silicon area up to 88%, induce negligible power overhead, and improve robustness against voltage supply variation and fluctuation.

Exotic invasive aquatic weeds such as alligator weed (Alternanthera philoxeroides) threaten native ecosystems by interfering with native plant communities, disrupting hydrology, and diminishing water quality. Development of new tools to combat invaders is important for the well being of these sensitive areas. Integrated pest management offers managers an approach that combines multiple control methods for better control than any one method used exclusively. In a greenhouse and field study, we tested the effects of selective herbicide application frequency, native competitor plant introduction, and their integration on alligator weed. In the greenhouse study, alligator weed shoot, root, and total biomass were reduced with one herbicide application, and further reduced with two. Alligator weed cumulative stem length and shoot/root ratio was only reduced after two applications. In the greenhouse, introduction of competitors did not affect alligator weed biomass, but did affect shoot/root ratio. The interaction of competitor introduction and herbicide did not significantly influence alligator weed growth in the greenhouse study. In the field, alligator weed cover was reduced after one herbicide application, but not significantly more after a second. Introduction of competitor species had no effect on alligator weed cover, nor did the interaction of competitor species and herbicide application. This study demonstrates that triclopyr amine herbicide can reduce alligator weed biomass and cover, and that two applications are more effective than one. To integrate selective herbicides and native plant introduction successfully for alligator weed control, more research is needed on the influence competition can potentially have on alligator weed growth, and the timing of herbicide application and subsequent introduction of plants.

Insect defoliation thresholds were reevaluated to determine their effectiveness during vegetative and reproductive stages of soybean. Field experiments were planted with maturity group IV soybeans and subjected 17, 33, 66, and 100% defoliation during R3, R5, and R6 growth stages. In addition to different amounts of defoliation for each growth stage, defoliation occurring within different portions of the plant canopy was also evaluated. Results of this experiment confirmed that soybeans during R3 and R5 stages are more susceptible to yield loss at high levels (>57%) of defoliation than R6 growth stage. However, yield loss was not significantly different below 57% defoliation. No significant yield difference was observed from defoliation occurring in the top or bottom part of the canopy. Yield loss from various levels of defoliation during the vegetative stages was significant at V6. No yield loss was observed from defoliation during the V3 growth stage. Both maturity group IV and V soybeans behaved similarly to each level of defoliation. Results from these experiments were used to determine dynamic economic injury levels for each growth stage based on yield loss equations, value of the crop, and cost of control and can be used to make insecticide application recommendations based on the amount of defoliation at a particular reproductive growth stage. Soybean looper, Chrysodeixis includens (Walker), is an economic pest of soybeans that has developed resistance to several insecticide classes. New insecticides have recently been labeled for control of lepidopteran pests in soybeans, including soybean loopers. Field reference strains were collected in 2010 and 2011 from soybean fields in Mississippi and Louisiana and subjected to insecticide incorporated diet treated with flubendiamide, chlorantraniliprole, and methoxyfenozide. Susceptibility of soybean loopers to flubendiamide and chlorantraniliprole did not differ. However the overall susceptibility to methoxyfenozide was greater than chlorantraniliprole. Diet incorporated assays determined a 9.4 fold variation in susceptibility to flubendiamide among the seven soybean looper populations tested. Variation to chlorantraniliprole was 6.25 fold and variation for methoxyfenozide was 5.37 fold. These data can be used as a benchmark for referencing future soybean looper populations in Mississippi and Lousiana.

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