Dissertations / Theses on the topic 'Ultraviolet light'
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Porter, Michael Anthony. "Hyperspectral imaging using ultraviolet light /." Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2005. http://library.nps.navy.mil/uhtbin/hyperion/05Dec%5FPorter.pdf.
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Thesis (M.S. in Astronautical Engineering)--Naval Postgraduate School, December 2005.Thesis Advisor(s): Richard C. Olsen, Christopher Brophy. Includes bibliographical references (p.55-56). Also available online.
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Porter, Michael A. "Hyperspectral imaging using ultraviolet light." Thesis, Monterey, California. Naval Postgraduate School, 2005. http://hdl.handle.net/10945/1817.
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The LINEATE IMAGING NEAR ULTRAVIOLET SPECTROMETER (LINUS) instrument has been used to remotely detect and measure sulfur dioxide (SO2). The sensor was calibrated in the lab, with curves of growth created for the 0.29 0.31 æ - spectral range of the LINUS sensor. Field observations were made of a coal burning plant in St. Johnâ s, Arizona at a range of 537 m. The Salt River Coronado plant stacks were emitting on average about 100 ppm and 200 ppm from the left and right stacks respectively. Analysis of the LINUS data matched those values within a few percent. Possible uses for this technology include remote verification of industry emissions and detection of unreported SO2 sources.
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Brown, R. B. "Ultraviolet light mutagenesis in Myxococcus xanthus." Thesis, University of East Anglia, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.373103.
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Kim, Hyunsu. "Interference lithography with extreme ultraviolet light." Thesis, University of Southampton, 2016. https://eprints.soton.ac.uk/410353/.
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In photolithography, increasing pattern density is a key issue for development of semiconductor devices. Extreme ultraviolet (EUV) radiation is the next generation light source for overcoming the resolution limit of conventional photolithography in order to obtain nanostructures of higher density. In this thesis, we focus on investigating resolution limits of interference patterns produced by EUV radiation. Optical properties of interference fringes obtained using different types of compact EUV sources are studied with regard to increasing pattern density. Rigorous simulations of optical wave propagation of EUV radiation are performed to investigate the resolution limits of interference fringes for the fractional Talbot effect, the achromatic Talbot effect, and an image of Talbot carpet that has an optical property of ever-decreasing size of interference fringes. In experiments, interference lithography has been performed with three different types of compact EUV sources including a gas discharge produced plasma, a plasma based EUV laser, and a high-harmonic generation source. We analyze optical characteristics of particular EUV sources resulting in different capabilities of patterning. Also different optical system designs capable of overcoming the limitations of optical properties of EUV radiation are investigated. We expect that the study of EUV interference lithography can be helpful for understanding the upcoming photolithography resolution and also can be useful as a technology for fabricating very fine structures.
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Habtemichael, Yishak Tekleab. "Packaging designs for ultraviolet light emitting diodes." Thesis, Georgia Institute of Technology, 2012. http://hdl.handle.net/1853/45764.
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Aluminum Gallium Nitride (AlGaN) / Gallium Nitride (GaN) based deep ultraviolet (DUV) light emitting didoes (LEDs) with emission wavelengths between 200-280 nm enable key emerging technologies such as water/air purification and sterilization, covert communications and portable bio-agent detection/identification systems for homeland security, and surface and medical device sterilization. These devices produce a large amount of undesired heat due to low quantum efficiencies in converting electrical input to optical output. These low efficiencies are attributed to difficulties in the growth&doping of AlₓGa₁₋ₓN materials and UV absorbing substrates leading to excessive joule heating, which leads to device degradation and a spectral shift in the emission wavelength. With this regard, effective thermal management in these devices depends on the removal of this heat and reduction of the junction temperature. This is achieved by decreasing the package thermal resistance from junction-to-air with cost-effective solutions. The use of heat sinks, thermal interface materials, and high conductivity heat spreaders is instrumental in the reduction of the overall junction-to-air thermal resistance.
This thesis work focuses on thermal modeling of flip-chip packaged deep UV LEDs to gain a better understanding of the heat propagation through these devices as well as the package parameters that have the biggest contributions to reducing the overall thermal resistance. A parametric study focusing on components of a lead frame package is presented to ascertain the thermal impacts of various package layers including contact metallizations, thermal spreading sub-mounts, and thermal interface materials. In addition the use of alternative thermal interface materials such as phase change materials and liquid metals is investigated experimentally.
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Ahmed, Ibrahim Abdelhamid Soliman. "Vacuum Ultraviolet Light Irradiation towards Photochemical Surface Architectures." Kyoto University, 2017. http://hdl.handle.net/2433/227625.
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Natarajan, Shweta. "Thermal metrology techniques for ultraviolet light emitting diodes." Thesis, Georgia Institute of Technology, 2012. http://hdl.handle.net/1853/45891.
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AlₓGa₁₋ₓN (x>0.6) based Ultraviolet Light Emitting Diodes (UV LEDs) emit in the UV C range of 200 - 290 nm and suffer from low external quantum efficiencies (EQEs) of less than 3%. This low EQE is representative of a large number of non-radiative recombination events in the multiple quantum well (MQW) layers, which leads to high device temperatures due to self-heating at the device junction. Knowledge of the device temperature is essential to implement and evaluate appropriate thermal management techniques, in order to mitigate optical degradation and lifetime reduction due to thermal overstress. The micro-scale nature of these devices and the presence of large temperature gradients in the multilayered device structure merit the use of several indirect temperature measurement techniques to resolve device temperatures. This work will study UV LEDs with AlₓGa₁₋ₓN active layers, grown on sapphire or AlN growth substrates, and flip-chip mounted onto submounts and package configurations with different thermal properties. Thermal metrology results will be presented for devices with different electrode geometries (i.e., interdigitated and micropixel), for bulk and thinned growth substrates. The body of this work will present a comparative study of optical techniques such as Infrared (IR), micro-Raman and Electroluminescence (EL) spectroscopy for the thermal metrology of UV LEDs. The presence of horizontal and vertical temperature gradients within the device layers will be studied using micro-Raman spectroscopy, while the occurrence of thermal anomalies such as hotspots and shorting paths will be studied using IR spectroscopy. The Forward Voltage (Vf) method, an electrical junction temperature measurement technique, will also be investigated. The Vf method will be applied to the Thermal Resistance Analysis by Induced Transient (TRAIT) procedure, whereby electrical data at short time scales from an operational device will be used to discretize the junction-to- package thermal resistance pathway from the total junction- to-ambient heat path. The TRAIT procedure will be conducted on several LEDs, for comparison. The scope and applicability of each thermal metrology technique will be examined, and the merits and demerits of each technique will be exhibited.
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Boyce, J. M. "Repair of ultraviolet light damage in Saccharomyces cerevisiae." Thesis, University of Oxford, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.355722.
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Shangguan, Hanqun. "Novel Cylindrical Illuminator Tip for Ultraviolet Light Delivery." PDXScholar, 1993. https://pdxscholar.library.pdx.edu/open_access_etds/4647.
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The design, processing, and sequential testing of a novel cylindrical diffusing optical fiber tip for ultraviolet light delivery is described. This device has been shown to uniformly(+/- 15%) illuminate angioplasty balloons, 20 mm in length, that are used in an experimental photochemotherapeutic treatment of swine intimal hyperplasia. Our experiments show that uniform diffusing tips of < 400 micron diameter can be reliably constructed for this and other interstitial applications. Modeling results indicate that this design is scalable to smaller diameters. The diffusing tips are made by stripping the protective buffer and etching away the cladding over a length of 20 mm from the fiber tip and replacing it with a thin layer of optical epoxy mixed with A/203 powder. To improve the uniformity and ease of fabrication, we have evaluated a new device configuration where the tip is etched into a modified conical shape, and the distal end face is polished and then coated with an optically opaque epoxy. This is shown to uniformly scatter - 70% of the light launched into the fiber without forward transmission. To our knowledge, we are the first to use this device configuration, and we have achieved a uniform cylindrical pattern of laser energy with uniformity < ± 15% of the average value. A simple computational model suitable for the interpretation of laser energy irradiance along the bare core surface of multimode optical fiber tips is proposed and experimentally verified. The model used is based on geometrical optics and Gaussian approximation. Good agreement is obtained between the calculation and experiment. We have measured the optical properties of the tips through all the sequences of the fabrication. The performances of the diffusing tips for illuminating angioplasty balloons are then evaluated by Ultraviolet Light at 365 nm. A Ti:Sapphire Ring Laser System with a doubling crystal pumped by an argon ion laser is used to generate the wavelength in this study.
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Sou, Kun Tou. "Microorganism control for air conditioning systems using ultraviolet light." Thesis, University of Macau, 2002. http://umaclib3.umac.mo/record=b1446149.
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Mohammadbeygy, Tina. "Shelf life extension of preformed pizza using ultraviolet light." Thesis, McGill University, 2014. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=123317.
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Mold is a common post-processing contaminant in pizza. Since contamination could occur in post-baking process, other safety barriers in addition to packaging are needed to ensure the continued safety of preformed pizza. The present research investigated the use of pulsed UV-light for the purpose of decontaminating Penicillium roqueforti on the surfaces of agar media, bread and preformed pizza. In the first step in the present study, the spatial distribution of pulsed UV-light was investigated. The Petri plates inoculated with Penicillium roqueforti were treated for10 min in the first three effective levels in the treatment chamber (5, 10 and 15 cm). 30, 75 and 90 percent of the surface area of the tray was exposed to pulsed light at 5, 10 and 15 cm from pulsed light lamp, respectively. Apple juice inoculated with E. coli was treated with pulsed UV-light at the same distances (5, 10 and 15 cm) from the light source, 3 voltage inputs (400, 750 and 1,000 V) and 3 treatment times (1, 5 and 10 min). The log reduction in E. coli population treated by pulsed UV-light varied from 1.4 to 2.05 log CFU ml-1. In the second phase of the study, the consistency of mold growth on the surface of flat bread was investigated using two different methods of inoculation; random spot and spread. Two different inoculum populations (102 and 103 CFU ml-1) were also used to assess the effect of inoculum concentration on the distribution and consistency of mold growth. Samples inoculated with 102 CFU ml-1 yielded more homogenously distributed colonies. In the third phase of the study, sensory and microbiological analyses were used to evaluate the effectiveness of pulsed light treatment for shelf life extension of pizza and bread. Up to 40 days shelf-life extension was achieved for 8, 32, and 40 percent of samples with minimal, intermediate and maximal pulsed light treatment, respectively. In the fourth phase of the study, the effectiveness of pulsed light was evaluated for the decontamination of Penicillium roqueforti on the surface of solid agar. Process parameters evaluated were treatment time (1, 3, 5, 7 and 10 min) and voltage input (500, 750 and 1,000 V). The population of Penicillium roqueforti was reduced after 10 min of exposure to pulsed light by 3.74, 5.36 and 6.14 log CFU ml-1, respectively for 500, 750 and 1,000 V. The inactivation data were used to construct models to estimate the inactivation. The results presented in this study indicate that inactivation kinetics was best described by the Weibull model with the smallest root mean squared error (RMSE) (R2 ≥ 0.92). Finally in the last phase of study, culture-dependent and independent methods were applied to study the ecology of preformed pizza. The average population of mesophilic aerobic bacteria (MAB), mesophilic anaerobic bacteria (MANB), lactic acid bacteria (LAB), molds and yeasts (M+Y) were 6.6±0.5, less than 2.4, 2.8±0.6 and 5.4±0.4 log CFU g-1, respectively. Molecular methods incorporating conventional PCR targeting the 18S rRNA gene of fungi, TA cloning of PCR-amplified fragments and sequencing were carried out to detect spoilage fungi in naturally spoiled pre-formed pizza. The cloning approach enabled the putative identification of Saccharomyces cerevisiae, Saccharomyces sp. WW-W23, Penicillium expansum, Penicillium freii, Penicillium sp. HSL, Penicillium sp. ljg1, Rhodotorula mucilaginosa, Monascus fuliginosus, Hordeum jubatum, Galactomyces geotrichum strains as well as uncultured fungus and uncultured eukaryote clones. Overall, pulsed UV-light was found to have a potential use for the decontamination of spoilage microorganisms on the surfaces of solid agar and bakery products. However, further investigation using higher treatment voltages is necessary in order to achieve a higher target decontamination of P. roqueforti.La pizza pré-cuisinée est couramment contaminée par la moisissure. Puisque la contamination pourrait se produire durant les procédés d'après cuisson, d'autres mesures, en plus de l'emballage, sont nécessaires pour assurer la sécurité permanente des pizzas pré-cuisinée. Cette recherche a examiné l'utilisation de la lumière UV pulsée pour décontaminer Penicillium roqueforti sur la surface de l'agar solide, du pain et de pizzas préformées.Dans la première étape de la présente étude, les paramètres critiques du procédé ont été optimisés pour améliorer l'efficacité des traitements à la lumière pulsée. Les boîtes de Petri inoculées avec Penicillium roqueforti ont été traitées 10 min dans une chambre de traitement pour les trois premiers niveaux d'efficacité (5, 10 et 15 cm). Les résultats démontrent que 30, 75 et 90 pour cent de la surface du plateau a été exposée à la lumière pulsée à 5, 10 et 15 cm respectivement de la source lumineuse. La réduction en log de la population de E. coli traitée par la lumière UV pulsée varie de 1.4 à 2.05 log UFC ml-1.Dans la deuxième phase de l'étude, la cohérence de la croissance des moisissures (Penicillium roqueforti) sur la surface du pain plat a été étudiée en utilisant deux méthodes différentes d'inoculation : par inoculation ponctuelle aléatoire et par étalement. Deux populations d'inoculum différentes (102 et 103 UFC ml-1) ont également été utilisées pour évaluer l'effet de la densité de l'inoculum sur la distribution et la cohérence de la croissance de moisissures. Les échantillons inoculés avec 102 UFC ml-1 ont donné une distribution des colonies plus homogène. À la troisième phase de cette étude, l'analyse sensorielle et microbiologique, ont été utilisées pour évaluer l'efficacité du traitement à la lumière pulsée pour prolonger la durée de vie de la pizza et du pain. Jusqu'à 40 jours de prolongement de la durée de conservation a été obtenue pour 8, 32 et 40 pour cent des échantillons après un traitement à la lumière pulsée minimal, intermédiaire et maximal, respectivement. Dans la quatrième phase de l'étude, l'efficacité d'une lumière UV pulsée à large spectre a été évaluée pour la décontamination de Penicillium roqueforti sur la surface de l'agar solide. La population de Penicillium roqueforti a été réduite après 10 minutes d'exposition à la lumière pulsée par 3.74, 5.36 et 6.14 log UFC ml-1 respectivement pour 500, 750 et 1000 V. Les résultats présentés dans cette étude indiquent que d'inactivation a été mieux décrite par le modèle de Weibull avec la plus petite erreur de moyenne quadratique (RMSE) (R2 ≥ 0.92). Finalement, dans la dernière phase de l'étude, des méthodes dépendantes ou indépendantes des conditions de culture ont été appliquées pour étudier l'écologie des pizzas pré-cuisinées. La moyenne de la population des bactéries mésophiles aérobies (BMA), des bactéries mésophiles anaérobies (BMNA), des bactéries lactiques (BL), des moisissures et des levures (M+L) étaient respectivement de 6.6 ± 0.5, inférieur à 2.4, 2.8 ± 0.6 et 5.4 ± 0.4 log UFC g-1. Les méthodes moléculaires incorporant la PCR conventionnelle ciblant le gène de l'ARNr 18S des champignons, le clonage TA de fragments amplifiés par PCR et le séquençage ont été réalisées pour détecter les champignons altérant les pizzas pré-cuisinées naturellement contaminées. L'approche du clonage a permis l'identification présumée de souches de Saccharomyces cerevisiae, Saccharomyces sp. WW- W23, Penicillium expansum, Penicillium freii, Penicillium sp. HSL, Penicillium sp. ljg1, Rhodotorula mucilaginosa, Monascus fuliginosus, Hordeum jubatum , Geotrichum galactomyces ainsi que des champignons et eucaryotes non cultivés.Dans l'ensemble, la lumière UV pulsée a démontré avoir un potentiel d'utilisation pour la décontamination des microorganismes altérant les surfaces d'agar solide et les produits de boulangerie.
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Hudson, John G. "The application of ultraviolet light to bone marrow transplantation." Thesis, University of Bristol, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.296599.
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Ladin, Loren Guerrero 1959. "Effect of ultraviolet light on reproduction in Hydra littoralis." Thesis, The University of Arizona, 1989. http://hdl.handle.net/10150/277085.
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The "DNA Damage Hypothesis" pertaining to the evolution of sex was tested using Hydra littoralis. DNA damage was produced by irradiating whole live hydra with ultraviolet light. A curve of uv light dosage vs. survival was constructed. Estimations of threshold fluence and LD50 were made from the survival curve. In four separate experiments, using various combinations of environmental temperatures, uv doses, and number of doses, frequencies of asexual and sexual reproduction were observed and compared. The hydra that received uv treatments did not show an increase in the consequent amount of sexual reproduction, and actually showed a decrease. An increase in the amount of sexual reproduction following DNA damage is predicted by the DNA damage hypothesis, therefore these results do not support this theory. The data was also used to make contradictory observations regarding the "stress hypothesis" for the occurrence of sexual reproduction in hydra.
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Moodycliffe, Angus M. "Mechanism of immunosuppression induced by ultraviolet-B light irradiation." Thesis, University of Edinburgh, 1993. http://hdl.handle.net/1842/20025.
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Irradiation with ultraviolet-B light (UV-B) suppresses some cell-mediated immune responses to a variety of antigens, including contact sensitizers. Following UV irradiation there is a modulation of Langerhans cell markers, and keratinocytes are induced to synthesize and secrete tumour necrosis factor-alpha (TNF-α). It has been postulated that there is a photoreceptor in the skin which mediates the effects of UV-B radiation on the immune system. One candidate is urocanic acid (UCA) found naturally in the stratum corneum of the epidermis as the trans-isomer, which converts to the cis-isomer on irradiation. Cis-UCA has been demonstrated to suppress immune reponses in several experimental systems. The mechanism of UV-B induced suppression of contact hypersensitivity (CH) responses and the role of cis-UCA were examined using a murine model of CH. UV-B irradiation was demonstrated to suppress the induction of CH response whilst cis-UCA had little, if any, effect. Next, the migration of dendritic cells (DC) to draining lymph nodes (DLN) following UV-B irradiation or epicutaneous application of UCA isomers was examined in unsensitized mice and mice sensitized with FITC. It was found that UV-B irradiation alone induced DC migration to DLN with a maximum number of DC being present in DLN 48 h following irradiation. In addition UV-B irradiation followed by skin sensitization at the same site enhanced DC migration. In sensitized mice, the percentage of DC bearing FITC and the quantity of FITC per DC were unaltered by prior UV exposure. Further, the percentage of DC expressing Ia or ICAM-1 molecules and the amount of Ia or ICAM-1 expressed per DC was unaffected by UV-B irradiation. In contrast to these results with UV-B irradiation, neither isomer of UCA had any significant effect on DC numbers in DLN in sensitized or unsensitized mice.
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Ekström, Smedby Karin. "Ultraviolet light, autoimmune disorders and the etiology of malignant lymphomas /." Stockholm, 2005. http://diss.kib.ki.se/2005/91-7140-313-2/.
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Lee, Kean Boon. "Fabrication and Characterisation of AlGaN based Ultraviolet Light Emitting Diodes." Thesis, University of Sheffield, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.505540.
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Yam, Cheuk-sing, and 任卓昇. "The impact of ultraviolet light on cataract: a systematic review." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2010. http://hub.hku.hk/bib/B45174969.
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Swanson, Andrew K. "Ecophysiological adaptations of northeast Pacific kelp communities to ultraviolet light stress." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape2/PQDD_0022/NQ51923.pdf.
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Grady, George. "The effect of resveratrol on ultraviolet light-induced skin cell death." Marietta College Honors Theses / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=marhonors1366909727.
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Daloglu, Mustafa Ugur, Aniruddha Ray, Zoltan Gorocs, Matthew Xiong, Ravinder Malik, Gal Bitan, Euan McLeod, and Aydogan Ozcan. "Computational On-Chip Imaging of Nanoparticles and Biomolecules using Ultraviolet Light." NATURE PUBLISHING GROUP, 2017. http://hdl.handle.net/10150/623196.
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Significant progress in characterization of nanoparticles and biomolecules was enabled by the development of advanced imaging equipment with extreme spatial-resolution and sensitivity. To perform some of these analyses outside of well-resourced laboratories, it is necessary to create robust and cost-effective alternatives to existing high-end laboratory-bound imaging and sensing equipment. Towards this aim, we have designed a holographic on-chip microscope operating at an ultraviolet illumination wavelength (UV) of 266 nm. The increased forward scattering from nanoscale objects at this short wavelength has enabled us to detect individual sub-30 nm nanoparticles over a large field-of- view of > 16 mm(2) using an on-chip imaging platform, where the sample is placed at <= 0.5 mm away from the active area of an opto-electronic sensor-array, without any lenses in between. The strong absorption of this UV wavelength by biomolecules including nucleic acids and proteins has further enabled high-contrast imaging of nanoscopic aggregates of biomolecules, e.g., of enzyme Cu/Zn-superoxide dismutase, abnormal aggregation of which is linked to amyotrophic lateral sclerosis (ALS)-a fatal neurodegenerative disease. This UV-based wide-field computational imaging platform could be valuable for numerous applications in biomedical sciences and environmental monitoring, including disease diagnostics, viral load measurements as well as air-and water-quality assessment.
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Harlow, Greg Russell. "Isolation and characterization of ultraviolet light hypersensitive mutants of Arabidopsis thaliana." Diss., The University of Arizona, 1993. http://hdl.handle.net/10150/186569.
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UV resistance mechanisms have been extensively studied in bacteria, fungi, and mammalian cells, but little is known about these mechanisms in plant cells. We have developed a genetic screen to help identify mutant Arabidopsis plants that are hypersensitive to the damaging effects of UV light. Six mutants, designated uvh1 through uvh6, were isolated by this screening procedure. The uvh mutants, which behave as single recessive traits, form six complementation groups. Although isolated as hypersensitive to UV-C light wavelengths, all of the uvh mutants are also hypersensitive to small fluences of UV-B wavelengths that do not affect wild type plants. UV-induced damage in the uvh mutants could be reduced or eliminated by subsequent exposure to light containing photoreactivating wavelengths, suggesting that the damage is pyrimidine dimers. One of the mutants, uvh1, was shown not to be defective in protection of chloroplast and nuclear DNA from UV-induced damage, suggesting that the defect in uvh1 may be in repair or toleration of UV-induced damage. Further analysis revealed that levels of UV-induced DNA damage removal were the same in chloroplast and nuclear DNA of uvh1 and wild type plants. uvh1 was more sensitive than wild type to the rosette-inhibiting effects of ionizing radiation, suggesting a possible defect in recombinational repair in uvh1, however, the frequency of meiotic recombination was normal in uvh1. In a collaborative study with Dr. E. Signer, Department of Biology, Massachusetts Institute of Technology, uvh1 was shown to be defective in T-DNA integration, suggesting a defect in non-homologous genetic recombination. As a first step in isolating the gene by map-based cloning, genetic and RFLP mapping techniques were used to localize the uvh1 mutation to a region of chromosome 3.
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Fu, Wai Yuen. "Modelling and characterization of III-nitride heterostructures for ultraviolet light-emitting diodes." Thesis, University of Cambridge, 2014. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.708179.
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Greenwood, Verity Jane. "The effects of the artificial light environment on avian behaviour and physiological indicators of stress." Thesis, University of Bristol, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.274670.
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Liang, Yu-Han. "Deep Ultraviolet Light Emitters Based on (Al,Ga)N/GaN Semiconductor Heterostructures." Research Showcase @ CMU, 2017. http://repository.cmu.edu/dissertations/1008.
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Deep ultraviolet (UV) light sources are useful in a number of applications that include sterilization, medical diagnostics, as well as chemical and biological identification. However, state-of-the-art deep UV light-emitting diodes and lasers made from semiconductors still suffer from low external quantum efficiency and low output powers. These limitations make them costly and ineffective in a wide range of applications. Deep UV sources such as lasers that currently exist are prohibitively bulky, complicated, and expensive. This is typically because they are constituted of an assemblage of two to three other lasers in tandem to facilitate sequential harmonic generation that ultimately results in the desired deep UV wavelength. For semiconductor-based deep UV sources, the most challenging difficulty has been finding ways to optimally dope the (Al,Ga)N/GaN heterostructures essential for UV-C light sources. It has proven to be very difficult to achieve high free carrier concentrations and low resistivities in high-aluminum-containing III-nitrides. As a result, p-type doped aluminum-free III-nitrides are employed as the p-type contact layers in UV light-emitting diode structures. However, because of impedance-mismatch issues, light extraction from the device and consequently the overall external quantum efficiency is drastically reduced. This problem is compounded with high losses and low gain when one tries to make UV nitride lasers. In this thesis, we provide a robust and reproducible approach to resolving most of these challenges. By using a liquid-metal-enabled growth mode in a plasma-assisted molecular beam epitaxy process, we show that highly-doped aluminum containing III-nitride films can be achieved. This growth mode is driven by kinetics. Using this approach, we have been able to achieve extremely high p-type and n-type doping in (Al,Ga)N films with high aluminum content. By incorporating a very high density of Mg atoms in (Al,Ga)N films, we have been able to show, by temperature-dependent photoluminescence, that the activation energy of the acceptors is substantially lower, thus allowing a higher hole concentration than usual to be available for conduction. It is believed that the lower activation energy is a result of an impurity band tail induced by the high Mg concentration. The successful p-type doping of high aluminum-content (Al,Ga)N has allowed us to demonstrate operation of deep ultraviolet LEDs emitting at 274 nm. This achievement paves the way for making lasers that emit in the UV-C region of the spectrum. In this thesis, we performed preliminary work on using our structures to make UV-C lasers based on photonic crystal nanocavity structures. The nanocavity laser structures show that the threshold optical pumping power necessary to reach lasing is much lower than in conventional edge-emitting lasers. Furthermore, the photonic crystal nanocavity structure has a small mode volume and does not need mirrors for optical feedback. These advantages significantly reduce material loss and eliminate mirror loss. This structure therefore potentially opens the door to achieving efficient and compact lasers in the UV-C region of the spectrum.
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Fortner, Jason C. "Illuminating whole effluent toxicity testing : ultraviolet radiation, phototoxicity, and PAH-contaminated groundwater /." Online version, 2009. http://content.wwu.edu/cdm4/item_viewer.php?CISOROOT=/theses&CISOPTR=314&CISOBOX=1&REC=10.
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Pinos, Andrea. "Optical properties and degradation of deep ultraviolet AIGaN-based light-emitting diodes." Doctoral thesis, KTH, Fotonik, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-37917.
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Pardasani, Dheerja. "Induction of resistance to ultraviolet light in Escherichia coli by heat shock." Thesis, University of Ottawa (Canada), 1989. http://hdl.handle.net/10393/5898.
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Wells, Jessica Benoit. "SANITIZATION OF BROILER BREEDER HATCHING EGGS USING ULTRAVIOLET LIGHT AND HYDROGEN PEROXIDE." MSSTATE, 2009. http://sun.library.msstate.edu/ETD-db/theses/available/etd-06302009-132533/.
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Ultraviolet light (UV) and hydrogen peroxide (H2O2) decrease eggshell bacteria. However, when combined, the optimum amount of each and effects on hatchability are unknown. In Experiment 1, when compared to other concentrations of H2O2 and lengths of UV, the combination of 1.5% H2O2 and 8 minutes of UV yielded optimum results with a 3 log10 CFU/egg reduction in bacteria on the eggshell. In Experiment 2, exposing eggs to this optimum combination yielded a 1000 fold reduction in eggshell bacteria but only a numerical increase in hatch of set and hatch of fertile. In Experiment 3, eggs exposed to repetitive treatments of H2O2 and UV yielded a 4 log reduction in eggshell bacteria but no differences in hatchability or chick characteristics. In conclusion, the combination of H2O2 and UV proved to be effective for eggshell sanitization, especially when used repetitively, and did not alter hatchability.
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Cates, Ezra Lucas Hoyt. "Development of visible-to-ultraviolet upconversion phosphors for light-activated antimicrobial surfaces." Diss., Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/47619.
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A new form of antimicrobial surface was developed, which relies on an optical mechanism rather than chemical inactivation of microorganisms. Through the photoluminescence process of upconversion, low energy photons can be amplified into higher energy photons, and in this case, phosphors capable of converting visible light into germicidal UVC radiation were synthesized. Host crystals were doped with a praseodymium activator ion and shown to emit UVC photons upon excitation by blue or violet light. Surface coatings were prepared and proof-of-concept experiments demonstrated that, under exposure to a household fluorescent lamp, sufficient UVC radiation was emitted from the surfaces to achieve observable inactivation of surface bacterial spores and inhibition of biofilm growth. Material engineering was conducted to achieve higher optical conversion efficiency, wherein lithium codoping and development of alternative oxyfluoride host crystals were found to significantly improve upconversion emission. Implications of polychromatic excitation were investigated by conducting photoluminescence spectroscopy under combined laser beam excitation, while the effects of other application parameters are also discussed. These findings show that upconversion-based antimicrobial materials have strong potential for offering sustainable and effective technology for the prevention of diseases.
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Burdick, Steven Curtis. "Interactions between Ultraviolet Light and Soybean Aphid, Aphis Glycines Matsumura (Hemiptera: Aphididae)." Thesis, North Dakota State University, 2013. https://hdl.handle.net/10365/27225.
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Global increases in ultraviolet (UV) radiation have led to greater interest in its current and potential effects on organisms, including insects and plants. Here we report the short-term effects of UV on soybean aphids (Aphis glycines Matsumura), a common phytophagous pest of soybeans. We examined how modified amounts of UV radiation affect soybean aphids by focusing on changes in 1) soybean aphid densities and 2) within plant distribution. In a laboratory experiment artificially adding UV decreased soybean densities compared to a low UV control. In a field experiment blocking UV had minimal effects on soybean aphid densities. Further observations suggest that soybean aphid location could mediate UV effects; the soybean leaf may shield aphids from some direct harmful effects of UV. Our results demonstrate the potential importance of UV to insect herbivores and how insect behavior may mitigate negative effects.
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Morris, Joseph P. "Disinfection of Bacillus Subtilis Spores Using Ultraviolet Light Emitting Diodes." Ohio University / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1338575832.
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Flittner, David Edward. "Atmospheric ozone and sulfur dioxide from satellite measurements of backscattered ultraviolet light." Diss., The University of Arizona, 1994. http://hdl.handle.net/10150/186896.
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An iterative method of estimating total atmospheric O₃ and SO₂ is developed for currently available satellite measurements of backscattered ultraviolet (uv) radiation. This method utilizes a direct inversion of the equation of radiative transfer by using a first order Taylor expansion of this equation with respect to a guessed combination of total O₃ and total SO₂. A new guess is made so as to minimize the difference between the measurements and theoretically calculated values. This method is able to model an atmosphere with molecular scattering or one with scattering by both molecules and particulates. A sensitivity analysis is presented and, in the case of a molecular atmosphere, the errors in retrieved total O₃ are on the order of 20% and for total SO₂ are 25%. Estimates can be performed for an atmosphere containing both molecular scatters and particulate scatters for scattering angles of 110°-150°. In the case of volcanic ash and SO₂ mixed within the stratospheric eruption cloud, retrieval errors for these angles are within the same range as those of the molecular only atmosphere if: the index of refraction of the ash is known to within a factor of 1.5 and the mean radius is also known to within a factor of 2. Application of this method to total ozone measuring spectrometer (TOMS) Nimbus 7 data for scans of a volcanic cloud show the total O₃ amount within the cloud to be noticeably lower than those of positions out of the cloud. This is consistent with the results of others.
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Liu, Yi. "A STUDY OF BACTERIAL ADAPTATION TO ULTRAVIOLET LIGHT IN ULTRAPURE WATER SYSTEMS." Diss., The University of Arizona, 2009. http://hdl.handle.net/10150/193866.
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UV radiation is an essential unit operation in ultra pure water treatment systems forits efficiency in treating microbes and oxidizing organics. This research investigated allfactors that affect the ability of UV light to deactivate and kill microorganisms. Morespecifically, bacterial growth conditions and the UPW stimulation time were investigated.The two major UV lights sources, UV254 and UV 185, were compared. The resultingdeath rates of bacteria living in UPW indicate that UV 185 is very effective in killingbacteria, and even more powerful than UV254, providing there is no mass transferlimitations.The effect of UV light on bacteria surviving in UPW system was also investigated.Mutants with different phenotypes were found with both strains of bacteria used in thisresearch. Partial 16s rRNA test precluded the possibility of contamination. Fortunately,two types of mutation happened. One was sustainable across microbial generations whichsuggest a genetic variation. The other one may be from alteration in gene expressioncontrolled at the transcriptional level, since the strain readily reverted to the originalphenotype. Compared with original or wild type cells, mutants are more resistant to UVlight, indicating that bacteria in UPW have the ability to adjust and adapt to UV treatment.Fourier transform infrared spectroscopy was used to explore bacterial surface andstructural differences existing between the original and mutant bacteria. The goal was tounderstand some of the cell structure changes that occur after exposure to UV light. FTIRturned out to be a useful tool in this exploration, indirectly supplying information that themutant strain used in this research had a differently organized cell membrane, and a moreadhesive cell-wall. This observation is consistent with the well-known protectivemechanism for bacteria living in aquatic environment to form biofilms. The spectra alsoindicated a more stable protein structure in the mutant. Furthermore, the indication of anincrease in ribose-5-phosphate in the mutant suggested an increase in ability to repairnucleic acids. Overall, the FTIR spectra did give some indirect evidences in explainingthe higher UV resistant property of the mutant. One may find more help from FTIRspectra in the future, so that a breakthrough point in completely eliminatingmicroorganisms in UPW may be achieved based on the structural and componentchanges indicated by FTIR.
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Rocha, Artur Batista de Oliveira 1982. "Efeitos da radiação UV-C e da luz fluorescente no controle fitossanotário e na indução de resistência em batata-semente após a colheita." [s.n.], 2015. http://repositorio.unicamp.br/jspui/handle/REPOSIP/256741.
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Orientadores Sylvio Luis Honório, Claudio Luiz MessiasTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Agrícola
Made available in DSpace on 2018-08-27T23:01:54Z (GMT). No. of bitstreams: 1 Rocha_ArturBatistadeOliveira_D.pdf: 1714662 bytes, checksum: 577fdeb54b226ba61587e77781ac70cf (MD5) Previous issue date: 2015
Resumo: O cultivo da batateira (Solanum tuberosum L.) apresenta problemas fitossanitários decorrentes do ataque de pragas e doenças, o que acarreta altos cultos de produção. As principais doenças pós-colheita em batata-semente são: podridão seca (agente causal: Fusarium solani), rhizoctoniose (agente causal: Rhizoctonia solani) e podridão mole (agente causal: Pectobacterium carotovorum subsp. carotovorum). Os principais glicoalcaloides presentes na batata são a ?-chaconina e ?-solanina, os quais possuem propriedades antimicrobianas e podem ser estimulados por diversos fatores, com destaque para a luz. O objetivo desta pesquisa foi investigar a aplicação da radiação ultravioleta UV-C e da luz fluorescente no controle dos patógenos Fusarium solani, Rhizoctonia solani e Pectobacterium carotovorum subsp. carotovorum nas cultivares Ágata, Atlantic e Monalisa de batata-semente após a colheita. A pesquisa foi realizada em duas etapas: (I) avaliou-se in vitro o efeito da radiação UV-C no desenvolvimento das colônias de F. solani e de R. solani e na germinação dos conídios de F. solani. In vivo avaliou-se o efeito da radiação UV-C e da luz fluorescente na severidade e na incidência de podridão seca e de rhizoctoniose na brotação, na perda de massa e no teor de sólidos solúveis em batata-semente 'Agata' e 'Atlantic'; (II): avaliou-se in vitro o efeito da radiação UV-C no desenvolvimento das colônias de P. carotovorum subsp. carotovorum. In vivo avaliou-se o efeito da radiação UV-C e da luz fluorescente na severidade e na incidência da podridão mole, na concentração de ?-chaconina e de ?-solanina, na brotação, na perda de massa e no teor de sólidos solúveis em batata-semente 'Agata' e 'Monalisa'. A exposição de F. solani e R. solani a uma densidade de energia de 105,6 kJ.m-2 de radiação UV-C diminui o desenvolvimento das colônias desses fungos para estudos in vitro. Para a germinação de conídios de F. solani foi exposta a uma densidade de energia de 52,8 kJ.m-2 de radiação UV-C. Além disso, a luz fluorescente foi mais eficaz do que a radiação UV-C para o controle da podridão seca e da rhizoctoniose, sem afetar a brotação. A exposição de P. carotovorum subsp. carotovorum na densidade de energia de 34,5 kJ.m-2 de radiação UV-C inibiu o desenvolvimento das colônias para estudos in vitro. A luz fluorescente foi mais eficaz do que a radiação UV-C para controle da podridão mole em tubérculos de batata, assim como, estimulou a síntese de glicoalcaloides. O controle da podridão mole em tubérculos de batata está relacionado a maior concentração de ?-chaconina e ?-solanina, especialmente na periderme. Os teores de ?-chaconina (11,6 a 26,0 mg.kg-1P.F.) e ?-solanina (11,4 a 25,1 mg.kg-1P.F.) mostraram-se eficazes para o controle da podridão mole. Além disso, a brotação não foi afetada de forma adversa
Abstract: The cultivation of potato (Solanum tuberosum L.) in the tropics suffers the attack of pests and diseases, burdening the cost of production. The main postharvest diseases in potato seeds are the dry rot (pathogen: Fusarium solani), black scab (pathogen: Rhizoctonia solani) and wet rot (pathogen: Pectobacterium carotovorum subsp. carotovorum. The efficiency of UV-C against a wide variety of microorganisms has been reported and there is interest in applying for seed disinfection. Potato plants contain glycoalkaloids being ?-chaconine and ?-solanine the main ones. The accumulation of these glycoalkaloids can be stimulated by several factors, especially light, having them important antimicrobial properties. The aim of this research was to evaluate the the postharvest application of ultraviolet (UV-C) radiation and the fluorescent light to control the pathogens: F. solani, R. solani, and P. carotovorum subsp. carotovorum on 'Agata', 'Atlantic', and 'Monalisa' potato seeds. The research was conducted in two stages: (I) the evaluation in vitro of the effect of UV-C radiation on the growth of F. solani and R. solani colonies and F. solani conidias germination and the in vivo effect of UV-C radiation and fluorescent light on dry rot and black scab severity and incidence, mass loss and soluble solids content on 'Agata' and 'Atlantic' and (II) the evaluation in vitro of the effect of UV-C radiation on P. carotovorum subsp. carotovorum colonies and was reported in vivo the effect of UV-C radiation and the fluorescent light on the severity and incidence of wet rot, ?-chaconine and ?-solanine, concentration, tuber sprouting, weight loss and soluble solids on 'Agata' and 'Monalisa'. Exposure of R. solani and F. solani at an energy density of 105,6 kJ.m-2 of UV-C radiation decreases the development of fungi colonies in vitro. Energy density of 52,8 kJ.m-2 inhibited the F. solani conidias germination. Moreover the fluorescent light was more effective than UV-C radiation to control dry root and black scab, without affecting the sprouting. The in vivo experiments showed that treated and untreated. UV-C tubers stored under fluorescent light were more effective to control soft rot than the UV-C treated tubers and stored under darkness. Control tubers under fluorescent light, UV-C treated under darkness, and UV-C treated under fluorescent light showed an increased concentration of ?-chaconine (11,6 to 26,0 mg.kg-1F.W.) and ?-solanine (11,4 a 25,1 mg.kg-1F.W.) for both cultivars
Doutorado
Tecnologia Pós-Colheita
Doutor em Engenharia Agrícola
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Knowles, Haydn Scott. "The light activated alkylation of glycine." Thesis, University of York, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.341492.
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George, Kimberly Suzanne. "The Roles of Membrane Rafts in Ultraviolet Light-Induced Association of Apoptotic Proteins." Ohio University / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1320893267.
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Gabbai, Udi Edward. "Microbial inactivation using ultraviolet light-emitting diodes for point-of-use water disinfection." Thesis, University of Cambridge, 2015. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.708718.
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Kao, Chen-Kai. "Development of ultraviolet electroabsorption modulators and light emitting diodes based on AlGaN alloys." Thesis, Boston University, 2012. https://hdl.handle.net/2144/31573.
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Thesis (Ph.D.)--Boston UniversityPLEASE NOTE: Boston University Libraries did not receive an Authorization To Manage form for this thesis or dissertation. It is therefore not openly accessible, though it may be available by request. If you are the author or principal advisor of this work and would like to request open access for it, please contact us at open-help@bu.edu. Thank you.
The research in this dissertation addressed the development of ultraviolet (UV) electroabsorption modulators and ultraviolet light emitting diodes (UV-LEDs), covering the spectral range from 360 to 265 nm. The materials system for both types of devices is the AlGaN alloys, either in bulk or quantum well (QW) form, grown by plasma-assisted molecular beam epitaxy (MBE). Potential applications of these devices either individually or in combination include UV non-line-of-sight free-space-optical communications, UV sensing and spectroscopic systems, Q-switched pulsed lasers, water/air purification and various medical applications. Optical modulators based on cubic III-V semiconductors have been the subject of extensive research over the past several years. Such devices are typically based on the quantum-confined Stark effect to modify the absorption spectrum of multiple-quantumwell active regions. On the other hand, in wurtzite III-Nitride semiconductors, strong electric fields are already present in the quantum wells due to intrinsic and piezoelectric polarizations; as a result, an even greater change in absorption is achievable, especially if the internal fields are compensated by the external bias so that the net field in the quantum wells is reduced. A number of UV electroabsorption modulators based on Schottky barriers on bulk GaN and GaN /AlGaN multiple quantum wells (MQWs) were designed, fabricated and characterized. Record modulation ratio of 30 % was obtained from bulk GaN Schottky barrier modulators at the excitonic resonant energy of 3.45 eV (360 nm) upon the application of 12 V reverse bias. Similarly, record modulation ratio of 43% was obtained from GaN I AlGaN MQWs Schottky barrier modulators at the excitonic resonant energy of 3.48 eV (356 nm) upon the application of 17 V reverse bias. The external quantum efficiency (EQE) of AlGaN based deep UV LEDS is relatively low ( ~ 1% at 270 nm). This is generally attributed to the poor internal quantum efficiency (IQE) of this material system due to the high concentration of line and point defects. In the current work the deep UV-LED structures were grown on inexpensive and widely available sapphire substrates, which resulted in materials with dislocation density of 1010 cm-2. To prevent the non-radiative recombination of the injected electron-hole pairs, the active region of the devices were grown under conditions which lead to band structure potential fluctuations, which lead to exciton localization and thus efficient radiative recombination. Using such a growth method AlGaN MQWs emitting at 265 nm with an IQE as high as 58.8% were demonstrated. Using such QWs a number UV LEDs emitting in the spectral region from 340 to 265 nm were fabricated and evaluated at the die level. A number of milliwatt output power LEDs emitting at 280 nm were demonstrated.
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Matta, Samuel. "AlGaN quantum dots grown by molecular beam epitaxy for ultraviolet light emitting diodes." Thesis, Montpellier, 2018. http://www.theses.fr/2018MONTS042/document.
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Ce travail porte sur la croissance par épitaxie sous jets moléculaires (EJM) et sur les propriétés structurales et optiques de boîtes quantiques (BQs) AlyGa1-yN insérées dans une matrice AlxGa1-xN (0001). L’objectif principal est d’étudier le potentiel des BQs en tant que nouvelle voie pour la réalisation d’émetteurs ultraviolets (UV) efficaces.Tout d'abord, nous avons étudié la croissance des BQs GaN en utilisant soit une source plasma (N2, appelée PAMBE) soit une source ammoniac (NH3, appelée NH3-MBE) afin de choisir la meilleure approche pour former les BQs les plus efficaces. Il a été montré que le procédé de croissance est mieux contrôlé en utilisant l’approche PAMBE, conduisant à la croissance de BQs GaN avec des densités plus élevées, une meilleure uniformité en taille et des intensités de photoluminescence (PL) jusqu’à trois fois plus élevées. En outre, l'influence de la contrainte épitaxiale sur le processus d'auto-assemblage des BQs a été étudiée en fabriquant des BQs GaN sur différentes couche tremplins d’AlxGa1-xN (avec 0,5 ≤ x ≤ 0,7). Nous avons montré que des BQs avec des densités plus élevées et des hauteurs plus faibles sont formées en augmentant le désaccord de paramètre de maille (c.à.d en utilisant des tremplins avec xAl plus élevé). Cependant, les mesures de photoluminescence (PL) indiquent un fort décalage de l'énergie d'émission vers le rouge lorsque xAl augmente, en raison de l'augmentation de la discontinuité du champ électrique interne de 3 à 5,3 MV/cm.Ensuite, des études approfondies sur les conditions de croissance et les propriétés optiques des BQs Al0,1Ga0,9N / Al0,5Ga0,5N ont été présentées, montrant les différents défis pour fabriquer des BQs efficaces. L’optimisation de la procédure de croissance, notamment l’étape de recuit post-croissance, a montré une modification de la forme des BQs. Plus précisément, un changement d’une forme allongée (pour un recuit à 740 °C), à une forme symétrique (pour un recuit à une température proche de ou supérieure à 800°C) a été observé. En plus, une bande d’émission supplémentaire vers les plus grandes longueurs d’onde a également été observée pour les BQs formées avec un recuit à 740°C. Cette bande a été attribuée à une fluctuation de composition des BQs, induisant la formation d’une famille additionnelle de BQs avec des hauteurs plus grandes et une compostions en Al inférieure à 10 %, estimée proche de l’alliage binaire GaN. Enfin, il a été démontré qu’en faisant un recuit à plus haute température (≥ 800°C), l’émission de PL de cette famille supplémentaire de BQs (BQs riche en Ga ou (Al)GaN) diminue très fortement. De plus, cette étape de recuit impacte fortement la forme des BQs et a conduit à une amélioration de leur efficacité radiative d’un facteur 3. Ensuite, la variation de la composition en Al des BQs AlyGa1-yN (0,1 ≤ y ≤ 0,4), ainsi que la quantité de matière déposée ont permis d’évaluer la gamme de longueurs d’onde d’émission accessibles. En ajustant les conditions de croissance, l’émission des BQs a été déplacée de l’UVA vers l’UVC, atteignant une émission autour de 270 - 275 nm (pour les applications de purification de l’eau et de l’air) avec des rendements radiatifs élevés. Les mesures de photoluminescence résolue en temps (TRPL), combinées avec les mesures de PL en fonction de la température, nous ont permis de déterminer les efficacités quantiques internes (IQE) des BQs GaN / AlxGa1-xN (0001). Des valeurs d’IQE comprises entre 50 % et 66 % ont été obtenues à basse température, avec la possibilité d’atteindre un rapport d’intensité intégré de PL, entre 300 K et 9 K, allant jusqu’à 75 % pour les BQs GaN et 46 % pour les BQs AlyGa1-yN (contre 0,5 % pour des structures équivalents à base de puits quantiques).Enfin, nous avons montré la possibilité de fabriquer des DELs à base de BQs (Al,Ga)N couvrant une grande gamme de longueurs d’onde allant du bleu-violet jusqu’à l’UVB (de 415 nm à 305 nm)This PhD deals with the epitaxial growth, structural and optical properties of AlyGa1-yN quantum dots (QDs) grown on AlxGa1-xN (0001) by molecular beam epitaxy (MBE), with the aim to study their potential as a novel route for efficient ultraviolet (UV) emitters.First, we have studied the growth of GaN QDs using either plasma MBE (PAMBE) or ammonia MBE (NH3-MBE) to find the most adapted nitrogen source for the fabrication of UV emitting QDs. It was shown that the growth process is better controlled using PAMBE, leading to the growth of GaN QDs with higher densities, better size uniformity and up to three times higher photoluminescence (PL) intensities. Also, the influence of the epitaxial strain on the QD self-assembling process was studied by fabricating GaN QDs on different AlxGa1-xN surfaces (with 0.5 ≤ x ≤ 0.7). We showed that QDs with higher densities and smaller sizes (heights) are formed by using a larger lattice-mismatch (i.e. a higher xAl composition). However, photoluminescence (PL) measurements indicated a strong redshift in the emission energy as the Al content of the AlxGa1-xN template increases due to the increase of the internal electric field discontinuity from 3 to 5.3 MV/cm.Next, in-depth investigations of the growth conditions and optical properties of Al0.1Ga0.9N QDs / Al0.5Ga0.5N were done presenting the different challenges to be solved to grow efficient QDs. Changing the growth procedure, especially the post-growth annealing step, has shown a modification of the QD shape from elongated QDs, formed with an annealing at 740°C, to symmetric QDs, formed with an annealing at a temperature around or above 800°C. An additional band emission at lower energies was also observed for QDs grown with a lower annealing temperature (740°C). This additional band emission was attributed to the formation of QDs with higher heights and a reduced Al composition less than the nominal one of 10 % (i.e. forming Ga-rich QDs). The influence of the annealing step performed at higher temperature has been shown to strongly decrease the PL emission from this additional QD family. In addition, this annealing step strongly impacted the QD shape and led to an improvement of the QD radiative efficiency by a factor 3. Then, the AlxGa1-xN barrier composition (0.5 ≤ x ≤ 0.7), the AlyGa1-yN QD composition (0.1 ≤ y ≤ 0.4) as well as the deposited amount were varied in order to assess the range of accessible emission energies. Also, the influence of varying the AlxGa1-xN barrier composition on the QD formation was studied. By varying these growth conditions, the QD wavelength emission was shifted from the UVA down to the UVC range, reaching a minimum wavelength emission of 270 - 275 nm (for water and air purification applications) with a high radiative efficiency. Time resolved photoluminescence (TRPL) combined with temperature dependent PL measurements enabled us to determine the internal quantum efficiencies (IQE) of AlyGa1-yN QDs / AlxGa1-xN (0001). IQE values between 50 % and 66 % were found at low temperature, combined with the ability to reach a PL integrated intensity ratio, between 300 K and 9 K, up to 75 % for GaN QDs and 46 % for AlyGa1-yN QDs (versus 0.5 % in a similar quantum well structure emitting in the UVC range).Finally, the demonstration of AlyGa1-yN QD-based light emitting diode prototypes, emitting in the whole UVA range, using GaN and Al0.1Ga0.9N QDs, and in the UVB range down to 305 nm with Al0.2Ga0.8N QDs active regions, was shown
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Parikh, Priti P. "Efficacy of Ultraviolet Light and Antimicrobials to Reduce Listeria monocytogenes in Chill Brines." Diss., Virginia Tech, 2007. http://hdl.handle.net/10919/29618.
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Chill brines used in ready-to-eat meat processing may be an important source of post-processing contamination by Listeria monocytogenes. The purpose of this study was to determine the efficacy of ultraviolet light (UV) in combination with antimicrobials to reduce L. monocytogenes in fresh and used chill brines. Three different antimicrobials were used in combination with UV; citric acid (CA, 0.2 and 0.5%), dimethyl dicarbonate (DMDC, 250 and 500 ppm), and hydrogen peroxide (HP, 2000 and 4000 ppm).
For fresh brine studies, brine (8.0% w/v NaCl) was prepared and inoculated with a cocktail of three L. monocytogenes strains (approximately 6 log CFU/mL). Brine was treated with UV alone, antimicrobials alone, and combination of UV and antimicrobials. Moreover, to observe the effect of treatment temperature and brine circulation through the UV system on survival of listeriae cells, inoculated brine was circulated through the system without any treatment that served as control for all the treatments. For UV treatment, inoculated brine solution was exposed to UV in an Ultraviolet Water Treatment Unit (Model: AMD 150B/1/2T D; Aquionics Inc., Peak output: 254 nm) fitted with an inline chiller to maintain brine temperature of -1°C. Samples were withdrawn at regular intervals for 120 minutes. When L. monocytogenes population was no longer detectable via direct plating on MOX, enrichment was performed and suspect colonies were confirmed using API-Listeria. For antimicrobial-only (i.e., no UV) treatments, a specific concentration of antimicrobial was added in inoculated brine and samples were taken for 120 minutes. For the brine that received combination of UV and antimicrobial treatments, UV was turned on once a specific concentration of antimicrobial was added in inoculated brine and samples were withdrawn at regular intervals for 120 minutes.
When treated with UV alone, L. monocytogenes population decreased from approximately 6 log CFU/mL to below the detection limit (i.e., 1 log CFU/mL) in 15 minutes with the reduction rate of 0.87 log CFU/mL per minute. However, cells were detectable by enrichment through 120 minutes. The highest rate of decline (0.90 log CFU/mL per minute) was achieved by the combination of UV and 500 ppm DMDC (UV+500 ppm DMDC), which was not significantly different from the reduction rates of UV and UV+0.5% CA. UV+500 ppm DMDC reduced L. monocytogenes to the detection limit in 15 minutes and the organism was not detected by enrichment after 60 minutes. Though the reduction rate of UV+0.5% CA was not significantly lower than the rate of UV+500 ppm DMDC (P>0.05), the former treatment resulted in non-detectable levels more quickly (45 minutes) than the latter (60 minutes). Thus, based on enrichment studies UV+0.5% CA was the most effective treatment in reducing the population of L. monocytogenes in fresh brine. Moreover, when brine was treated with 0.5% CA alone the population decreased to below detection limit in 15 minutes with the rate significantly lower than UV+500 ppm DMDC and UV+0.5% CA (P<0.05). However, L. monocytogenes was not detectable by enrichment from 60 minutes. To summarize, through enrichment studies we observed that UV+0.5% CA, UV+500 DMDC, and 0.5% CA Control were more effective than other treatments in reducing the listeriae population to a non-detectable level.
Spent brine is recycled brine that was obtained from a frankfurter processor after its maximum usage. Results of spent brine studies showed that when brine was treated with UV+4000 ppm HP and UV+2000 ppm HP, L. monocytogenes population decreased to the detection limit in 45 minutes and was not detected by enrichment from 120 minutes. These treatments were observed to be the most effective treatments with a reduction rate of 0.12 log CFU/mL per minute. The reduction rate of some other treatments such as, UV+250 and 500 ppm DMDC, UV+0.2% and 0.5% CA, and UV alone was not significantly different from UV+4000 and 2000 ppm HP. However, the population was detected through enrichment up to 120 minutes in all other treatments.
The results of these studies indicate that combinations of UV and antimicrobial may be more effective than either treatment alone (except 0.5% CA treatment) to process fresh chill brines. However, the antimicrobials and UV were less effective for controlling L. monocytgoenes in spent brine; presumably due to the presence of organic matter.Ph. D.
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Huang, Qiuyun. "Study on Ultraviolet Light Cured Resin Bond Grind/Lap for Aluminum Oxide Ceramics." University of Toledo / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1461592358.
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Aubuchon, Matthew D. "Biological and physical factors affecting catch of house flies in ultraviolet light traps." [Gainesville, Fla.] : University of Florida, 2006. http://purl.fcla.edu/fcla/etd/UFE0013838.
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Sivis, Murat. "Extreme-ultraviolet light generation in plasmonic nanostructures." Doctoral thesis, 2013. http://hdl.handle.net/11858/00-1735-0000-0022-5E08-0.
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Fang, Chun Chieh, and 方俊傑. "Ultraviolet Light Protective Layer for OTFTs Encapsulation." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/28361866999927670765.
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碩士國立交通大學
顯示科技研究所
97
In this thesis, we fabricated N,N′-bis(naphthalen-1-y)-N,N′-bis(phenyl) benzidine (NPB) passivation to protect the organic thin-film transistors (OTFTs) from degradation under UV-light illumination. With a thermally-deposited NPB film on the OTFTs, it was found that UV-light induced degradation could be significantly reduced. For example, after about 120 minutes UV-light the change of field effect mobility was only 37 % and the change of threshold voltage was within 10%. On the contrary, the OTFTs without NPB film suffered serious degradation. The field-effect mobility was reduced by about 90%, and the threshold voltage was increased by more than 40%. UV-light induced degradation on OTFTs was also discussed; Through surface morphology analysis by atomic force microscopy ( AFM ) and electron Spectroscopy for Chemical Analysis ( ESCA ) , the surface oxidation and destroyed pentacene grains pentacene film was the dominative factor that influenced OTFT’s properties. We conclude that our NPB passivation is a promising way to protect pentacene TFTs. Finally, I would like to address that the work is conducted under the leading of my supervisor and also Mr. Kuo-His Yen, Ph. D student in our lab. The result is shared with all the co-workers in this research.
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Yang, Chen-Yu, and 楊琛喻. "Study of Ultraviolet Organic Light Emitting Diodes." Thesis, 2004. http://ndltd.ncl.edu.tw/handle/16476759216930984311.
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Pan, Chang-Chi, and 潘昌吉. "Investigation of InGaN Ultraviolet Light-Emitting Diodes." Thesis, 2007. http://ndltd.ncl.edu.tw/handle/6hdab3.
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博士國立中央大學
電機工程研究所
96
This dissertation includes the growth and characterization of InGaN/(Al)GaN multiple-quantum-well ultraviolet light-emitting diode (UV LED) structures grown by metalorganic chemical vapor deposition. The main work can be divided into the following four parts. First, a series of measurements have conducted to investigate the luminescence efficiency behaviors of 400 nm UV LEDs with 5 In0.06Ga0.94N/GaN quantum wells. The emission luminescence efficiency of In0.06Ga0.94N/GaN quantum well near UV LED structures were studied for the purpose to clarify the dominant factor to cause low efficiency of UV LEDs and compared with 470 nm blue LED structures with same periods of quantum well in the active region. It is shown that the behavior of luminescence efficiency at low current density for UV and blue LEDs is different due to the different emission mechanisms in the quantum well. Based on their injection current-dependent characteristics under dc and pulsed operation, it can be concluded that carrier overflow is the dominant factor that affects the quantum efficiency of UV LED before thermal effects take over. The constant external quantum efficiency of the blue or UV LEDs at high current densities rule out the carrier saturation effect unambiguously. It is also experimentally shown that increasing the number of quantum wells from 5 to 10 is found to be effective in the utilization of injected carriers for radiative recombination and hence in improving the luminescence efficiency of the UV LEDs. Second, the methods of low defect density buffer layer growth, carrier confinement improvement in the quantum wells and p-type AlxGa1-xN cladding layer are introduced for further improving the output power of UV LEDs. Etch pits density is improved by almost one order of magnitude with the use of three SiNx layers as an interlayer in the LED structure. It is also found that adding a little amount of Al into GaN to form a barrier layer does not degrade the crystal quality. Instead, it leads to better carrier confinement in shallower In0.06Ga0.94N quantum well. The luminescence intensity of the UV LED structure with Al0.05Ga0.95N barrier layers is about four-fold higher than that of its counterpart, revealing that the carrier confinement ability and material quality both are significantly improved by introducing a little Al and SiNx interlayers into barrier layers and the n-GaN underlying buffer layer, respectively. The emission intensity of 400 nm UV LED with a graded p-AlxGa1-xN layer is also greatly improved, because of the effective increase in the hole injection effect from p-GaN to the quantum well layers and the increase in the recombination emission rate of electron and hole pairs. Third, the effects of etching depth and stripe orientation on the structural and optical properties of the GaN epilayer as well as LEDs are investigated. It is found that much better material quality and light output power are obtained when GaN epilayer and LEDs are grown on a 0.9 μm-deep patterned sapphire substrate with stripes along the <1-100>sapphire direction. According to the results of scanning electron microscopy, transmission electron microscopy (TEM), and cathodoluminescence (CL) studies on these samples, the growth modes of GaN epilayer along the <11-20>sapphire and <1-100>sapphire directions are proposed and used to explain the anisotropic material properties between them. Normalized far field emission patterns of the LEDs show that the emitted light are scattered predominantly toward the vertical direction with increasing the groove depth. Their radiation angles, however, are stripe-orientation independent, implying that the light extraction efficiency is almost the same for the LEDs grown on PSSs with stripes along the <11-20>sapphire and <1-100>sapphire directions. Otherwise, the analysis of the internal quantum efficiency (IQE) and light extraction efficiency (LEE) in these two sets of UV LEDs was also investigated. It was also found that the improvement in the output power was mainly due to the enhancement of the LEE and then been changed to the contribution of the IQE by reducing the dislocation density when the LED structure was grown on PSS with stripes along the <11-20>sapphire and <1-100>sapphire directions, respectively. Finally, we can conclude that the maximum contribution of the LEE was about 44.9 % obtained using the 0.9 μm-deep stripe-PSS along either the <11-20>sapphire or <1-100>sapphire direction. However, an improvement of the IQE by as much as 2.785 times higher can be obtained for a LED structure grown on 0.9 μm-deep stripe-PSS along the <1-100>sapphire direction than its counterpart. It is therefore concluded that the superior performance of LED on the <1-100>sapphire stripe is attributed to its lower defect density. Finally, sapphire substrates with stripe SiON patterns which has adjustable refractive index to match sapphire substrate have been shown effective in improving the output power of light-emitting diodes. The output power of 400 nm UV LEDs grown on the stripe-SIONPSS is increased as much as 60 % compared to the LEDs grown on planar one. In the other work, the estimated values of the IQE and LEE in these LED grown on stripe-SIONPSS and planar substrate are obtained by temperature-dependent PL measurement. The IQE and LEE in the LED grown on stripe-SIONPSS are 28.6 % and 37.62 %, respectively. The increments of the IQE and LEE are about 26.55 % and 26.9 %, respectively, comparing with that of its counterpart. It shows that the power output enhancement of our devices is due not only to the reduction of dislocation density but also to the light extraction contributed by the geometric shape of the SiON stripe patterns. These results indicate that SiON stripe pattern on sapphire substrate is a promising approach to achieve high efficiency LEDs.
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Chu, Yen-Chang, and 朱延章. "The Study of Ultraviolet- and Blue-Light-Inhibited White Light-Emitting Diode." Thesis, 2016. http://ndltd.ncl.edu.tw/handle/89m7bf.
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博士逢甲大學
電機與通訊工程博士學位學程
104
White light-emitting diodes (LEDs) are an optimal candidate for generating white light source. Compared with traditional lighting sources, white-light LEDs offer the benefits of low energy consumption, are free of mercury pollution, and are small, lightweight, durable, and reliable. However, most products exist in blue light, UV leakage, and glare problems with commercial phosphor-based white-light LEDs. The long-time exposure to blue or UV light can damage the skin, eyes, and endocrine system of humans. Therefore, if LEDs are to be promoted as a next-generation light source, problems related to the safety of these devices must be solved. Accordingly, this thesis devotes to investigates of UV- and blue-light-inhibited white LEDs. Firstly, an RGB phosphor-converted white LEDs with a coating layer of photocatalyst is proposed. Using the absorption spectrum in the blue and UV regions of the bismuth oxide photocatalysts, the blue light and UV leakage problems of phosphor-converted white LEDs can be significantly reduced; meanwhile, the coating layer of photocatalyst can act as an air purifier and diffuser to reduce glare. In order to optimize the suppressed ratio of UV-light and increase the luminous efficiency, the improved design of an RGB-phosphor-converted white LED is proposed. In the design, the LED package is covered with a substrate that has an optical reflection coating on the underside and a bismuth oxide photocatalyst coating on the topside. The wavelengths below 400 nm are reflected back to re-excite the red-green-blue phosphors and consequently enhance luminous efficiency. The absorption spectrum of bismuth oxide photocatalysts is below 521 nm, and the leaked UV and blue light can be absorbed, thereby exciting electron-hole pairs and producing the photocatalytic effect. Thus, blue light and UV leakage can be suppressed appreciably and the luminous efficiency can be increased markedly. Finally, a packaged design of different viscid epoxy resin on RGB phosphor-converted white light-emitting diodes to improve the problem of phosphor precipitation is proposed. Because the more viscid epoxy resin has a uniform distribution of RGB phosphors in SMD-LED lead frame, which can be more efficiently excited by ultraviolet (UV) LED chip. Therefore, the uniform distributions of RGB phosphor with the higher viscid epoxy resin can provide uniformed light field and comfortable visual experience. Accordingly, the concepts of above packaged can be applied effectively to implement a health, safe and environment benign white LED light source.
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Chang, Wei-En, and 張維恩. "Light Extraction Enhancement of AlGaN-based Ultraviolet-C Light-Emitting Diodes device." Thesis, 2019. http://ndltd.ncl.edu.tw/cgi-bin/gs32/gsweb.cgi/login?o=dnclcdr&s=id=%22107NCHU5159051%22.&searchmode=basic.
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碩士國立中興大學
材料科學與工程學系所
107
In this study, Ultraviolet C Light Emitting Diodes (UV-C LEDs) were used in epitaxial structure on sapphire by Metal Organic Chemical-Vapor Deposition (MOCVD) system. The SiO2/Al reflectors were coated on the inclined sidewalls of the active mesa stripes upon the shape of finger electrode (pin) by using the Flip-Chip process of typical photolithography(i.e., the optical path from the active layer toward the sapphire substrate). In addition, P-type gallium nitride (p-GaN) epitaxial film thickness changed 50 nm for 150 nm with surface texture of the active mesa stripes were formed on the inclined sidewalls by using electrochemical etching. Transverse Electric mode (TE mode) and Transverse Magnetic mode (TM mode) were investi-gated by using the Integrating sphere (IS), X-ray diffractometer (XRD), Scanning Electron Microscope (SEM), and polarization-dependent Electroluminescence (EL). The effect of the light extraction efficiency (LEE) were investigated in various num-ber of active mesa stripes、angles of the inclined sidewalls, and thickness of the p-GaN layer. According to the result of experiment、2D-DDCC simulation, and ray tracing measurement, the result in current crowding due to increasing the contact resistance of the ITO and resistance of the p-GaN layer, which contribute to the side-wall-emission-enhanced UV-C LED breaks through the fundamental limitations caused by the intrinsic properties of AlGaN, thus shows a remarkable improvement in light output power by 40% result from total internal reflection, which improves the LEE of TM mode compare with the 5pin 75o inclined sidewalls. On the other hand, the 25pin 30o inclined sidewalls enhanced the LEE of TE mode and TM mode due to increasing the light escape rate.
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Armstrong, John David. "Mutational specificity of ultraviolet light in Saccharomyces cerevisiae." 1993. http://hdl.handle.net/1993/17494.
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Lu, Tzu-Chun, and 盧姿君. "Investigation of ultraviolet ZnO nanostructure light emitting diodes." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/06641211305651346737.
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碩士國立臺灣大學
光電工程學研究所
98
ZnO related materials together with nanostructure LEDs have attracted great interests as the new short wavelength lighting source due to the superior optical and electrical characteristics of ZnO. For there are still difficulties in realizing ZnO homojunction LEDs, GaN is the most suitable substitute for p type material due to many of the physical properties are similar to ZnO. Many groups make effort to fabricate ZnO/p-GaN heterojunction LEDs, but how to suppress the defect related emission and thus achieve high purity ultraviolet (UV) light emission from ZnO are still under concerned. To overcome these problems, we demonstrate ZnO/p-GaN LEDs with high quality ZnO thin film by RF sputtering at room temperature together with the post annealing. Asymmetric SiO2 confinement barriers of properly designed with ZnO in between are then carried out to exhibit UV radiative recombination in the ZnO layer. Moreover, by improving the interface of ZnO and p-GaN using surface treatments, the UV light emission with suppressing defect states from simple ZnO/p-GaN heterostructures without any confinement layers can be further realized. For the superior physical properties of nanostructures, ZnO nanowire/p-GaN LEDs are also fabricated using hydrothermal synthesis for the single crystal ZnO nanowire arrays growth. MgO blocking layer between ZnO nanorod and p-GaN are inserted to enhance the UV emission from ZnO nanowires. Furthermore, the “inverted triangle” profile is formed due to the deposition of SiNx on ZnO nanorods. This special shape of nanorod arrays not only makes the continuous contact but also suppresses the deep level emission. We further extract the UV emission under low temperature, the luminescence together with the temperature effect are also discussed. All the results mentioned above lead us to realize pure UV emission with great suppressed defect band in both ZnO thin film/p-GaN LEDs and ZnO nanowire/p-GaN LEDs. With low cost, low temperature, easily fabrication method and properly designed of structures, ZnO based LEDs indeed have great potential to become the UV light sources.