Low temperature epitaxial growth of III-Nitride semiconductors on silicon carbide templates by remote plasma metal-organic chemical vapor deposition

Group III-Nitride (III-N) semiconductors are of high interest due to their thermal and electrical properties. Opposed to other III-V group semiconductors III-N semiconductors are hexagonal wurtzite structures that have a direct bandgap across the entire composition range. This wide bandgap range covers from the deep ultra-violet to the infrared region of the electromagnetic spectrum. This makes the III-N semiconductor group ideal for LEDs, laser diodes and photodetectors. This thesis presents an in-depth study to the growth of III-Nitrides on Silicon Carbide (SiC) templates. Due to the difficulty in growing bulk crystals for the III-Nitrides, non-native substrates must be used. Because of this, there exists a lattice mismatch between the substrates and thin films grown on top. SiC proves to be an ideal substrate as the lattice mismatch is around 3.5%. Thin films of III-N were grown upon commercially purchased SiC templates using remote plasma enhanced metal organic chemical vapor deposition (RP-MOCVD) in the Lakehead University Semiconductor Research Lab. Results were characterized using x-ray diffraction (XRD), atomic force microscope (AFM), Energy-dispersive X-ray spectroscopy (EDX) and Ramen spectroscopy

Saturation of the Raman amplification by self-phase modulation in silicon nanowaveguides

We experimentally show that the self-phase modulation of picosecond pump pulses, induced by both the optical Kerr effect and free-carrier refraction, has a detrimental effect on the maximum on-off Raman gain achievable in silicon on insulator nanowaveguides, causing it to saturate. A simple calculation of the Raman gain coefficient from the measured broadened output pump spectra perfectly matches the saturated behavior of the amplified Raman signal observed experimentally at different input pump powers.Comment: Accepted for publications in Applied Physics Letter

Development of a photoelectrochemical cell using III-V nitrides

Hydrogen production through Photoelectrochemical (PEC) water splitting is a source of clean and sustainable energy. Current energy production through the use of fossil fuels is rapidly depleting reserves and had been a direct cause of climate change. III-V nitrides offer a unique solution due to the variable band gap seen in Indium Gallium Nitride, which allows the semiconductor to capture the full spectrum of light by varying the quantities of Indium in the layer. In this work, different types of III-V were used as both photoanodes and photocathodes for the development of a III-V Nitride PEC cell. In addition, NaC1 was added to the electrolyte to act as simulated ocean water to reduce the cost of production for the cells, as current processes requires the use of distilled water for electrolyte preparation. Samples were grown in a custom built Metal Organic Chemical Vapor Deposition (MOCVD) reactor using a Flow Modulated Epitaxy (FME) method. Samples were tested in an acidic, neutral based PEC cells. In addition to III-V nitride photoelectrodes, Zinc Oxide layers created through dip coating were also tested. [...

Study of the evolution of the frontier in the central western area of Mato Grosso

Following the national strategy of regional occupation, colonization projects initiated both by the Brazilian government and private companies played a major role in the process of deforestation and development of the State of Mato Grosso in the 1970’s, especially in the municipios of Tangará da Serra, Diamantino and Campo Novo do Parecis. The effective colonization of Tangará da Serra began in 1966 with the installation of the first pioneers of the SITA, Sociedade Imobiliária Tupã para Agricultura. At this time, 3-4 million coffee-plants were set over 3000 ha in 500 minifundios. But rapidly grasslands took the place of coffee trees. Since 1970-75, major private companies settled as well in the central western area of Mato Grosso : this process involved the expansion of crops such as soybean, maize and cotton in the cerrados of the Chapada dos Parecis and stock breeding in areas of forest and older settlements. Satellite images allow us to monitor and understand the evolution of rural landscapes through the various colonization phases

Light localization induced enhancement of third order nonlinearities in a GaAs photonic crystal waveguide

Nonlinear propagation experiments in GaAs photonic crystal waveguides (PCW) were performed, which exhibit a large enhancement of third order nonlinearities, due to light propagation in a slow mode regime, such as two-photon absorption (TPA), optical Kerr effect and refractive index changes due to TPA generated free-carriers. A theoretical model has been established that shows very good quantitative agreement with experimental data and demonstrates the important role that group velocity plays. These observations give a strong insight into the use of PCWs for optical switching devices.Comment: 6 page

Structural Variations in Hybrid All-Nanoparticle Gibbsite Nanoplatelet/Cellulose Nanocrystal Multilayered Films

Cellulose nanocrystals (CNCs) are promising bio-sourced building blocks for the production of high performance materials. In the last ten years, CNCs have been used in conjunction with polymers for the design of multilayered thin films via the layer-by-layer assembly technique. Herein, polymer chains have been replaced with positively charged inorganic gibbsite nanoplatelets (GN) to form hybrid “nanoparticle-only” composite films. A combination of atomic force microscopy and neutron reflectivity experiments was exploited to investigate the growth and structure of the films. Data show that the growth and density of GN/CNC films can be tuned over a wide range during preparation by varying the ionic strength in the CNC suspension and the film drying protocol. Specifically, thin and dense multilayered films or very thick, more porous mixed slabs, as well as intermediate internal structures could be obtained in a predictable manner. The influence of key physicochemical parameters on the multilayer film build up was elucidated and the film architecture was linked to the dominating interaction forces between components. The degree of structural control over these hybrid nanoparticle-only films is much higher than that reported for CNC/polymer films, which offers new properties and potential applications as separation membranes or flame retardant coatings

Mutations in Eml1 lead to ectopic progenitors and neuronal heterotopia in mouse and human.

Neuronal migration disorders such as lissencephaly and subcortical band heterotopia are associated with epilepsy and intellectual disability. DCX, PAFAH1B1 and TUBA1A are mutated in these disorders; however, corresponding mouse mutants do not show heterotopic neurons in the neocortex. In contrast, spontaneously arisen HeCo mice display this phenotype, and our study revealed that misplaced apical progenitors contribute to heterotopia formation. While HeCo neurons migrated at the same speed as wild type, abnormally distributed dividing progenitors were found throughout the cortical wall from embryonic day 13. We identified Eml1, encoding a microtubule-associated protein, as the gene mutated in HeCo mice. Full-length transcripts were lacking as a result of a retrotransposon insertion in an intron. Eml1 knockdown mimicked the HeCo progenitor phenotype and reexpression rescued it. We further found EML1 to be mutated in ribbon-like heterotopia in humans. Our data link abnormal spindle orientations, ectopic progenitors and severe heterotopia in mouse and human

Tropomodulin1 is required for membrane skeleton organization and hexagonal geometry of fiber cells in the mouse lens

The spectrin–actin network is disrupted in Tmod1 mutants, disturbing fiber cell morphology, and disordering lens cell organization

Engineering of III-nitride semiconductors on low temperature Co-fired ceramics

This work presents results in the field of advanced substrate solutions in order to achieve high crystalline quality group-III nitrides based heterostructures for high frequency and power devices or for sensor applications. With that objective, Low Temperature Co-fired Ceramics has been used, as a non-crystalline substrate. Structures like these have never been developed before, and for economic reasons will represent a groundbreaking material in these fields of Electronic. In this sense, the report presents the characterization through various techniques of three series of specimens where GaN was deposited on this ceramic composite, using different buffer layers, and a singular metal-organic chemical vapor deposition related technique for low temperature deposition. Other single crystalline ceramic-based templates were also utilized as substrate materials, for comparison purposes

Association of the PHACTR1/EDN1 genetic locus with spontaneous coronary artery dissection

Background: Spontaneous coronary artery dissection (SCAD) is an increasingly recognized cause of acute coronary syndromes (ACS) afflicting predominantly younger to middle-aged women. Observational studies have reported a high prevalence of extracoronary vascular anomalies, especially fibromuscular dysplasia (FMD) and a low prevalence of coincidental cases of atherosclerosis. PHACTR1/EDN1 is a genetic risk locus for several vascular diseases, including FMD and coronary artery disease, with the putative causal noncoding variant at the rs9349379 locus acting as a potential enhancer for the endothelin-1 (EDN1) gene. Objectives: This study sought to test the association between the rs9349379 genotype and SCAD. Methods: Results from case control studies from France, United Kingdom, United States, and Australia were analyzed to test the association with SCAD risk, including age at first event, pregnancy-associated SCAD (P-SCAD), and recurrent SCAD. Results: The previously reported risk allele for FMD (rs9349379-A) was associated with a higher risk of SCAD in all studies. In a meta-analysis of 1,055 SCAD patients and 7,190 controls, the odds ratio (OR) was 1.67 (95% confidence interval [CI]: 1.50 to 1.86) per copy of rs9349379-A. In a subset of 491 SCAD patients, the OR estimate was found to be higher for the association with SCAD in patients without FMD (OR: 1.89; 95% CI: 1.53 to 2.33) than in SCAD cases with FMD (OR: 1.60; 95% CI: 1.28 to 1.99). There was no effect of genotype on age at first event, P-SCAD, or recurrence. Conclusions: The first genetic risk factor for SCAD was identified in the largest study conducted to date for this condition. This genetic link may contribute to the clinical overlap between SCAD and FMD