Dissertations / Theses on the topic 'In compositional fluctuations'

Thesis (D.M.A.)--University of North Texas, 2006.
System requirements: Adobe Acrobat Reader. Accompanied by 4 recitals, recorded June 28, 1999, Jan. 24, 2000, Jan. 29, 2001, and Apr. 10, 2006. Includes bibliographical references and discography (p. 66-70).

Dans des conditions de croissance spécifiques, des sections nanofilaires d’AlGaN peuvent croître en épitaxie sur des bases nanofilaires de GaN. De telles croissances, effectuées par épitaxie par jets moléculaires dans le cadre dans le cas présent, permettent la caractérisation ultérieure de petits volumes d’AlGaN exempt de défauts étendus communément observés dans les couches planaires. Cette absence de défauts rend ces fils prometteurs pour les dispositifs optoélectroniques émettant dans l’ultraviolet. Cependant, la réalisation de tels composants nécessite de mieux comprendre les propriétés fondamentales des fils.La question des inhomogénéités d’alliage à l’échelle nanométrique reste notamment à éclaircir. Afin d’y voir plus clair, ces dernières ont été dans un premier temps étudiées dans cette thèse. Pour nos expériences, des nanofils d’AlGaN non-intentionnellement dopés (NID) ont été crûs dans des conditions variées afin d’ajuster potentiellement les fluctuations de composition de l’alliage et ainsi sonder éventuellement des centres de localisation de porteurs de taille et composition différentes. Il a premièrement été observé au moyen de méthodes de caractérisation structurale que la longueur des sections plus riches Al qui nucléent préférentiellement au sommet des fils de GaN peut être ajustée en variant les paramètres cinétiques de croissance, mettant en lumière un mécanisme de croissance gouverné par la cinétique. Des études optiques ont ensuite démontré que les fluctuations de composition induisent de la localisation et présentent un comportement de type boîte quantique. Ce dernier a été observé quel que soit les conditions de croissance explorées dans ce travail. Il est ensuite démontré que les régions plus riches Ga spontanément formés durant la synthèse de l’AlGaN partagent des propriétés µ-optiques similaires sur une plage de longueur d’onde d’émission donnée, pour toutes les conditions de croissance utilisées dans cette étude. De telles régions, émettrices de photons uniques, sont présentes à très petite échelle, puisque elles ont été également mises en évidence dans des nanodisques quantiques d’AlGaN très fins.En outre, le dopage des nanofils d’AlGaN, surtout de type p, est loin d’être totalement compris. En particulier, En particulier, le problème de l’incorporation ainsi que de l’activation optique et électrique dans les fils demeure nébuleux. Cette question a été étudiée pour des jonctions pn nanofilaires d’AlGaN dopées avec des atomes Mg et Si. Premièrement, des signatures propres à l’incorporation des dopants dans les nanofils ont été mises en exergue au travers de techniques de caractérisation structurale, avant que des jonctions pn AlGaN soient mises en évidence électriquement. De plus, des analyses optiques ont mis en lumière des dopants de type n et p optiquement actifs. Néanmoins, les dopants Mg ne sont que partiellement actifs électriquement en raison de la passivation par l’hydrogène mise en évidence par l’observation de complexes Mg-H. Pour résoudre ce problème, des recuits post-croissance ont été effectués. En parallèle, des jonctions pn nanofilaires d’AlN ont été préliminairement examinées et présentent des caractéristiques morphologiques intéressantes. En effet, des creux profonds ont été observés dans les fils et associés au dopage Mg effectué à basse température de croissance. La morphologie des fils peut être ajustée en jouant sur les paramètres cinétiques de croissance et sur l’effet surfactant des atomes Mg. En augmentant la température, les creux disparaissent tandis que la forme du sommet des fils, usuellement hexagonale, change pour devenir « étoilée », mettant en exergue des conditions de croissance très éloignées de l’équilibre thermodynamique. L’activation électrique des dopants n’a pas été observée jusqu’à présent dans ces jonctions pn d’AlN
Using specific growth conditions, AlGaN nanowire (NW) sections can be grown in epitaxy on top of GaN NW templates. Such NW growth, performed by plasma-assisted molecular beam epitaxy in the present case, allows the subsequent characterization of very small volume of material free of extended defects commonly observed in planar structures. This absence of defects makes these NWs very promising for optoelectronic devices operating in the ultraviolet. However, achieving such devices requires a better understanding of the NW fundamental properties.The issue of alloy inhomogeneity at nanoscale has notably remained obscure so far. In order to make it clearer, the latter has been first investigated in the present work, especially through optical characterization. For our experiments, non-intentionally doped (NID) AlGaN NWs have been grown in various conditions in order to potentially tune the compositional fluctuations within the AlGaN alloy and therefore possibly probe for carrier localization centers of different size and Al composition. It has been firstly observed through structural characterization that the length of Al-rich sections preferentially nucleating on top of GaN NWs can be tuned by varying the growth kinetical parameters, emphasizing a growth mechanism governed by kinetics. Optical studies have then evidenced that compositional fluctuations induce carrier localization and exhibit a quantum dot-like behavior. The latter has been observed whatever the growth conditions explored in this work. Our results are consistent with the spontaneous formation during growth of tiny Ga-richer regions shown to share similar micro-optical features over a given emission wavelength range for all investigated growth conditions. Such regions exhibiting the single-photon emission character are present at very small scale, as signs of their existence have been also evidenced in thin NID AlGaN quantum disks.In addition, doping in Al(Ga)N NW, especially p-type, is far from being fully comprehended. In particular, the issue of dopant incorporation as well as optical and electrical activation in such NWs remains unclear. The latter has been examined in Al(Ga)N NW pn junctions doped with Mg and Si atoms. First, signatures specific to dopant incorporation in NWs have been highlighted through structural characterization, before evidencing AlGaN pn junctions electrically. Moreover, optical analysis have exhibited optically active both dopant types. Nonetheless, Mg dopants are but partially active electrically due to passivation by hydrogen emphasized by the observation of Mg-H complexes. To cope with the latter issue, post-growth annealing experiments have been attempted. Concomitantly, AlN NW pn junctions have been also preliminarily investigated and present interesting morphological features. Indeed, deep hollows have been observed in NWs and associated with Mg doping carried out at low growth temperature. The NW morphology can be tuned by varying growth kinetical parameters and by using the surfactant effect of Mg atoms. When increasing growth temperature, these hollows disappear, while the NW top shape has been observed to switch from hexagonal to star-like, emphasizing growth conditions very far from thermodynamical equilibrium. Electrical activation of dopants has not been evidenced so far in AlN NW pn junctions

Les semi-conducteurs nitrures (AlN, GaN, InN) focalisent une activité de recherche intense en raison de nombreuses applications comme les diodes électroluminescentes, les composants de puissance ou hyperfréquence. Dans cette recherche, nous avons abordé le travail sous deux angles: a) la conduction électrique dans les couches d'InN produites par croissance épitaxiale aux jets moléculaires assistée par plasma (PAMBE) et une recherche sur l'origine de la forte émission bleue dans les puits de quantiques d'InGaN/GaN. L'accumulation d'électron en surface dans les couches d'InN constitue une limitation importante pour la fabrication de composants. Au cours de ce travail, nous avons exploré l'utilisation des mesures de bruit de basse fréquence sur les couches d'InN et pu accéder à leur conductivité électrique en volume. L'étude des puits quantiques d'InGaN/GaN, obtenue par croissance épitaxiale aux jets moléculaires (MBE) ou épitaxie en phase vapeurs aux organométalliques (MOVPE) , a été effectuée par analyses de la microstructure par microscopie électronique en transmission (MET, HRTEM et STEM) en corrélation avec les propriétés optiques d'un grand nombre d'échantillons provenant de conditions de croissance différentes. Ce travail nous a permis d'acquérir une vision plus critique du rôle des conditions de fabrication et des paramètres comme la morphologie, les fluctuations de composition et la présence des défauts en V sur les explications actuellement avancées pour la forte efficacité d'émission dans les puits quantiques d' InGaN/GaN
The nitride semiconductors (AlN, GaN, InN) are subject to a large research effort due to their numerous applications, such as light emitting diodes, high power and high frequency components. Following the trend, the aim of this dissertation has been twofold: first, we have probed the bulk electrical conduction in InN layers, second, we investigated the origin of the high emission efficiency in InGaN/GaN Quantum Wells (QWs). The surface electron accumulation in InN layers is still an important limitation to device applications. W have explored this point using low frequency noise measurements on Plasma Assisted Molecular Beam Epitaxy (PAMBE) InN layers and we demonstrated that the bulk electrical conductivity of InN can be accessed. The investigation of quantum wells produced by molecular beam epitaxy (MBE) or matalorganic vapour phase epitaxy (MOVPE), has been carried out through microstructural analyses by transmission electron microscopy techniques(TEM, HRTEM, STEM) in correlation with optica properties on a large number of samples grown in different growth conditions. This experimental work has allowed us to obtain a critical view on the role of the growth conditions and such parameters as the well morphology, composition fluctuations, as well as the V shaped defects on the current explanations of high emission efficiency in InGaN/GaN QWs

PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO
O Observatório Pierre Auger é um detector de raios cósmicos ultra-energéticos (E maior ou igual 1018 eV) com características híbridas, que combinam detectores de superfície e de fluorescência. A determinação da composição química primária destes raios cósmicos é um dos seus principais objetivos. Há indícios de que os primários dos raios cósmicos com E maior que 1018.5 eV tem massa maior, conclusão baseada nos resultados recentes sobre a evolução dos chuveiros atmosféricos extensos (cascatas de partículas formadas quando da colisão do raio cósmico primário no topo da atmosfera com moléculas de N2 ou O2). Encontrar parâmetros, que caracterizam o chuveiro, no processo de sua reconstrução e que forneçam informações associadas a este resultado, são essenciais para validar esta conclusão. Nesta tese estuda-se a evolução como função da energia, de parâmetros que caracterizam os chuveiros, que sejam sensíveis à sua composição primária. Mais especificamente aqueles determinados pelo detector de superfície, pois há uma estatística de chuveiros detectados significativamente maior. Damos especial atenção às flutuações intrínsecas – chuveiro-a-chuveiro – do parâmetro de inclinação (beta) da Função de Distribuição Lateral, que descreve a variação da densidade de partículas ao longo da direção perpendicular ao eixo do chuveiro, como função da distância a esse eixo. Os resultados indicam que a flutuação intrínseca em beta, para eventos inclinados (45-60 graus) com E maior que 1018.5 eV, possui uma tendência de diminuição com a energia até valores em torno de 1019.8 eV. Este resultado é consistente com o encontrado anteriormente em análises de composição química sobre a evolução com a energia da profundidade de máximo (Xmax) dos chuveiros atmosféricos extensosmedida pelos detectores do Auger em modo híbrido, em que em energias acima de 1018.5 eV, observase que os chuveiros tendem a atingir seu máximo numa região mais bem definida da atmosfera, levando, por conseguinte, a flutuações menores no sinal no solo.
The Pierre Auger Observatory is an ultra high energy cosmic ray detector (E more than or equal as 1018 eV) which has hybrid characteristics combining surface and fluorescence detectors. Determining the cosmic rays chemical composition is one of its most important challenges. There are evidences that cosmic ray primaries with energy above 1018.5 eV are heavy and this conclusion is based on recent results on the evolution of extensive air showers (cascades of particles formed by the collision of primary cosmic rays in the top of the atmosphere with nitrogen and oxygen molecules). Therefore, it is mandatory to find additional parameters supporting that conclusion. In this thesis, the evolution with energy of parameters characterizing the shower and with sensitivity to chemical composition are studied. More specifically, parameters determined by the surface detector are analyzed due to the high statistics in this operation mode. Special attention is given to the instrinsic - shower to shower - fluctuations of the slope parameter (beta) of the Lateral Distribution Function which describes the particles density variation in the plane perpendicular to the shower axis as a function of distance to that axis. The results show that the intrinsic fluctuation of Beta, for inclined showers (45-60 degrees) with energy above 1018.5 eV, where the detector resolution is small compared to the total fluctuation, has a trend to decrease with energy up to 1019.6 eV. This result is consistent with recent results on the energy evolution of the depth of shower maxima (Xmax) of extensive air showers, where above 1018.5 eV, the distributions of Xmax show less fluctuations, leading, in turn, to less fluctuations on the ground level.

Les nanostructures de nitrures d’éléments III sont considérées comme des candidats prometteurs visant à la réalisation de divers dispositifs innovants. Depuis quelques années, l'intérêt croissant des nano-LEDs basés sur l’InGaN a été relevé dans le domaine de l'éclairage et de l'affichage. Ce travail de thèse porte sur la croissance par épitaxie par jets moléculaires assistée plasma (PA-MBE) et sur la caractérisation d'hétérostructures InGaN/GaN à base de nanofils.Tout d'abord, un modèle de croissance cinétique de nanofils de nitrures d’éléments III a été établi, en vue d'une analyse en profondeur et d'un meilleur contrôle des processus cinétiques atomiques impliqués dans la croissance MBE. Ce travail de modélisation construit la base théorique et guide l'interprétation expérimentale dans cette thèse.Ensuite, les propriétés morphologiques, structurelles, compositionnelles et optiques des hétérostructures de nanofils GaN/InGaN/GaN axiaux ont été étudiées à nano-échelle par une combinaison de microscopie électronique (SEM / STEM / TEM), photoluminescence (PL), nano-cathodoluminescence (nano-CL), spectroscopie de rayons-X à énergie dispersive (EDX). Sur la base des résultats expérimentaux, nous avons obtenu une description statistique du paysage morphologique pour tous les NWs InGaN/GaN sous différentes conditions thermodynamiques et de flux atomiques. De plus, la corrélation entre les caractéristiques morphologiques & compositionnelles et les propriétés électroniques & optiques des NWs InGaN/GaN a été établie.En outre, divers types de superstructures InGaN à base de nanofils ont été étudiés. On constate que tant le taux de croissance axiale que la composition réelle d’Indium vont diminuer dans le cas de l'excès d'Indium, en raison de l'effet surfactant de l’Indium et d'un flux effectif d’azote réduit. En même temps, un élargissement spectaculaire des sections de l'InGaN a été observé sous des conditions riches en azote, suggérant que la condition riche en métal n'est pas nécessaire pour l'élargissement de l'InGaN. En conséquence, nous proposons le mécanisme de la croissance d’InGaN, pour lequel la croissance axiale est un processus cinétique déterminé par le flux et l'élargissement latéral est principalement induit par la contrainte.Enfin, nous avons étudié l'influence du processus de recuit pour l'efficacité de la luminescence et proposé nos recettes de croissance de plaques LEDs, visant à aborder la fabrication de plaques LED développées par MBE
Group-III-nitride nanostructures are considered as promising candidates aiming at the realization of various innovative devices, including fields from electronics, photonics, to biochemistry and energy. Since recent years, a growing interest of InGaN-based nano-LEDs has been raised in the field of lighting and display. This PhD work focuses on the growth by plasma-assisted molecular beam epitaxy and on the characterization of nanowire-based InGaN/GaN heterostructures.Firstly, a kinetic growth model of III-nitride nanowires has been established, aiming at an in-depth analysis and a better control of atomically kinetic processes involved in MBE growth. This modeling work constructs the theoretical basis and guides the experimental interpretation in this thesis.Then, the morphological, inner-structural, compositional and optical properties of axial GaN/InGaN/GaN nanowire heterostructures have been investigated at nano-scale by a combination of electron microscopy (SEM/STEM/TEM), photoluminescence (PL), nano-cathodoluminescence (nano-CL), energy-dispersive X-ray spectroscopy (EDX). On the basis of experimental results, we have achieved a statistical description of morphological landscape for all InGaN/GaN NWs under different thermodynamic and atomic fluxes conditions. Meanwhile, the correlation between the morphological & compositional features and the electronic & optical properties of InGaN/GaN NWs has been established.Furthermore, various types of NW-based InGaN superstructures have been grown and investigated. It is found that both axial growth rate and real In composition will decrease in the case of Indium excess, due to In surfactant effect and a reduced effective nitrogen flux. Meanwhile, a dramatic widening of InGaN sections has been observed under N-rich condition, suggesting the metal-rich condition is not necessary for the InGaN enlargement. Accordingly, we propose the driving mechanism of InGaN growth, for which the axial growth is a flux-determined kinetic process and the lateral widening is mainly strain-induced.Finally, we have investigated the influence of post-growth annealing process for the luminescence efficiency and proposed our growth recipes of LED plates, aiming at approaching the fabrication of MBE-grown LED plates

En raison de leurs applications prometteuses dans les domaines de l'optoélectronique et de l'électronique, les semiconducteurs III-V à base d'azote: les nitrures (AlN, GaN, InN) et leurs alliages (InAlN, InGaN, AlGaN), font l'objet, depuis les années 1990, d'une activité intense en recherche et développement. Dans ce travail, nous avons étudié les propriétés structurales des couches d'InN et de l'alliage InAlN dans les hétérostructures InAlN/AlN/GaN et InAlN/GaN en combinant les techniques AFM, IBA, DRXHR, Raman et MET. L'étude des couches d'InN a été menée par DRX afin de déterminer la contrainte résiduelle, et on a cherché à faire une corrélation avec la morphologie des surfaces par AFM. Les contraintes résiduelles obtenues par DRX ont été comparées aux résultats de spectroscopie Raman, et on a pu montrer que toutes les couches avaient une contrainte résiduelle qui n'est pas purement bi-axiale. Les hétérostructures InAlN pour transistors à haute mobilité électronique (HEMTs) sont des couches ultraminces de quelques monocouches atomiques à plusieurs dizaines de nanomètres d'épaisseur. De plus, leur structure peut être assez complexe dans le but d'optimiser le gaz d'électrons généré dans le canal du transistor. Dans l'idéal, on utilise une concentration en indium autour de 17%, qui est celle de l'accord de paramètres cristallins avec le GaN. Nos travaux ont mis en évidence qu'il n'est pas facile de contrôler la composition locale; en effet la structure et morphologie des couches sont très sensibles aux conditions de croissance.

Les semi-conducteurs nitrures (AlN, GaN, InN) focalisent une activité de recherche intense en raison de nombreuses applications comme les diodes électroluminescentes, les composants de puissance ou hyperfréquence. Dans cette recherche, nous avons abordé le travail sous deux angles: a) la conduction électrique dans les couches d'InN produites par croissance épitaxiale aux jets moléculaires assistée par plasma (PAMBE) et une recherche sur l'origine de la forte émission bleue dans les puits de quantiques d'InGaN/GaN. L'accumulation d'électron en surface dans les couches d'InN constitue une limitation importante pour la fabrication de composants. Au cours de ce travail, nous avons exploré l'utilisation des mesures de bruit de basse fréquence sur les couches d'InN et pu accéder à leur conductivité électrique en volume. L'étude des puits quantiques d'InGaN/GaN, obtenue par croissance épitaxiale aux jets moléculaires (MBE) ou épitaxie en phase vapeurs aux organométalliques (MOVPE) , a été effectuée par analyses de la microstructure par microscopie électronique en transmission (MET, HRTEM et STEM) en corrélation avec les propriétés optiques d'un grand nombre d'échantillons provenant de conditions de croissance différentes. Ce travail nous a permis d'acquérir une vision plus critique du rôle des conditions de fabrication et des paramètres comme la morphologie, les fluctuations de composition et la présence des défauts en V sur les explications actuellement avancées pour la forte efficacité d'émission dans les puits quantiques d' InGaN/GaN.

Etude de monocristaux de eumo::(6)s::(8) et d'echantillons frittes de yb::(1,2-x)eu::(x)mo::(6)s::(8) basee sur des mesures de transport sous pression et sous champ magnetique, des mesures de la susceptibilite magnetique et des mesures rpe; mise au point d'un dispositif automatise de mesures de transport. Correlations entre la temperature de transition structurale, la remontee de la resistivite a basse temperature et la transition supraconductrice sous pression; effets de la composition des echantillons frittes. Mise en evidence d'une valeur tres elevee du coefficient de chaleur massique electronique. Discussion des proprietes anormales dans le cadre d'un modele de melange de phases triclinique et rhomboedrique et d'un modele de supraconductivite propre

碩士
國立交通大學
電子物理系所
94
Effect of the composition fluctuation in InGaAsN/GaAs single quantum well is investigated by photoluminescence (PL), capacitance-voltage (C-V), admittance spectroscopy, deep-level transient spectroscopy (DLTS) and cross-sectional transmission electron microscope (TEM). Three samples were grown by molecular beam epitaxy (MBE) with different growth rates, 4.4, 2.8 and 0.506 Å/s, respectively. PL studies show that the composition fluctuation causes a splitting of the InGaAsN emission into a main emission and a low-energy bump. Lowering the growth rate degrades the composition fluctuation, as indicated by the broadening of the InGaAsN emission and enhancement of the low-energy bump, suggesting the presence of the local N-rich regions in the well. Further lowering the deposition rate leads to a three-dimensional growth, destroying the size-quantization effect of the well. According to the carrier distribution in the well, the existence of a carrier bump following an accumulation peak suggests the presence of an energy state below the ground state of the well. The activation energy of this energy state is comparable to the energy separation between the InGaAsN emission and the low-energy bump. Therefore, the local N-rich region probably induces an electron state below the ground state of the InGaAsN layer. From admittance and DLTS results, two defect states, one shallow at 0~83 meV and the other deeper at 0.21~0.25 eV, are present in the 0.506 Å/s sample due to composition fluctuation. Decreasing the growth rate is found to increase the activation energy of the deeper energy state from 0.1 eV(4.4 and 2.8 Å/s) to 0.25 eV(0.506 Å/s). Furthermore, the activation energy of the deeper state is more bias-dependent in 0.506 Å/s sample than others, implying that this state broadens into a band as a result of increased composition fluctuation. As to the shallow state, it is probably related to structural defects produced by lattice expansion or localized state due to composition fluctuation.

From June 2006 to March 2007, the concentrations of water soluble inorganic particulates and their associated precursor gases were semi-continuously measured adjacent to a high traffic street in downtown Toronto, Canada. Measurements underwent extensive quality assurance and control protocols. Seasonal and diurnal variations in HNO3 and NH3 partitioning to NH4NO3 were observed. Long range transported air masses from southwest of Toronto were the predominant source of measured SO4 2- for all seasons. The contributing sources of PM2.5 nitrate mass fluctuated between seasons: pNO3- was predominantly locally derived in the summer and resulted from long range transport in the winter. Comparison between measurements and ISORROPIA thermodynamic model predictions identified model weaknesses and was used to explore the effect of modulating primary gas concentrations on consequent particulate levels. SO2 emissions reductions were the most influential and direct method to reduce overall PM2.5 concentrations; however, limiting ammonia emissions was also another successful strategy.

碩士
長庚大學
光電工程研究所
95
Abstract In this thesis, the effects of migration and desorption reactions on the indium fluctuations in InGaN/GaN multiple quantum wells were investigated by introducing growth interruption method into the growth procedures. The growth interruption method was used to inspect the effects of migration and desorption reactions during the growth procedures of InGaN/GaN multiple quantum well (MQW) heterostructures. While the interruption time increases, the introduction of growth interruptions at the interfaces of the MQWs results in further influence the effects of migration and desorption reactions on the properties in quantum well structures. To characterize the indium fluctuations in the active layers, the X-ray diffraction, photoluminescence (PL), and electroluminescence (EL) spectra of InGaN/GaN MQW structures have been measured. First, the X-ray diffraction was analyzed to realize the variation of indium composition of InGaN/GaN multiple quantum well (MQW) heterostructures. Furthermore, the Schrödinger equations analysis were used to examine how the variation of indium composition influence on the band bending and carrier wave functions. Second, the PL and EL spectra were used to in-depth understand the effect of migration and desorption resulting in In fluctuation by emission peak shift, full width of half maximum (FWHM) and integrated intensity. Third, the life time, luminescence intensity and activation energy were investigated to realize the degree of the localization effect while the In coalescence mechanism from 2-dimension to 3-dimension like structure to form In-rich regions. These experimental results were indicated that not only the improvement the structural properties, but also inhibitions of nonradiative recombinations. Further, the effect of migration reaction would facilitate the structure of Indium from 2-dimension to 3-dimension resulting in the enhancement of localization effect.

The occurrence of total gas pressure gradients, which act as a driving force for the mass transport of fluids, may be common phenomena in plant organs. A gas-exchange system was devised to characterize changes in CO₂ emission rates of greenhouse tomato fruit (Lycopersicon esculentum L. Dombito), greenhouse green bell pepper fruit (Capsicum annum L. Doria), slicing cucumber fruit (Cucumis sativa L. Straight Eight and Sweet Success) and jumbo yellow onion bulbs (Allium cepa L.) in response to the imposition of total gas pressure gradients. Cyclical variations in atmospheric pressure induced significantly higher rates of gas exchange in peppers and onions but not in tomatoes and cucumbers. Oxygen concentration significantly affected carbon dioxide efflux rates in onions subjected to variable pressures. Temperature had no significant effect on relative efflux rates in any of the plant organs used in this study. Duration of the interval between varying pressure treatments was an important factor in CO₂ emission rate in onions, tomatoes and cucumbers. The differing response of various commodities to varying pressure treatments was probably due to differences in routes of gas exchange as well as intercellular space volumes and internal structure. To determine if variable pressure treatments had a metabolic effect on tissues, a dynamic head-space sampling technique was developed to collect and concentrate aroma volatiles for analysis by gas chromatography/mass spectrometry. Principal component analysis of pepper, onion and tomato volatiles revealed that variable pressure storage increased levels of compounds associated with oxidation compared to those stored under constant pressure. Data from peppers stored under 3% oxygen and variable pressures for 1 week indicated that compounds associated with off-flavours were lower than in peppers stored in air.

La fibrose kystique (FK) est la maladie autosomique récessive la plus fréquente chez les individus de race caucasienne. Elle est secondaire à la mutation du gène Cystic Fibrosis Transmembrane Regulator (CFTR). Grâce à des traitements plus agressifs, la médiane de l’espérance de vie des individus atteints de la FK a augmenté et cette augmentation est associée à l’émergence du diabète secondaire ou associé à la FK (DAFK), une complication associée à une augmentation du taux de mortalité. La pathophysiologie du DAFK n’est pas parfaitement comprise. Par exemple, la cause de l’accélération de la perte de la fonction pulmonaire, qui débute des années avant l’apparition du DAFK, n'est pas élucidée. Tous les patients atteints de la FK, même ceux sans le DAFK, présentent de l’hyperglycémie et des fluctuations glycémiques. D’ailleurs, une étude a démontré que la réactivité immunitaire est affectée par l’hyperglycémie dans un modèle animal de la FK et il y a des évidences que les lymphocytes sans CFTR fonctionnel ou en présence d’un excès de glucose ont des réactions inflammatoires anormales. Donc, nous avons émis l’hypothèse que les patients atteints de la FK, surtout ceux non-diabétiques et pré-diabétiques, auront une plus grande proportion de lymphocytes Th17 et Treg produisant la cytokine pro-inflammatoire IL-17A comparativement aux sujets sains et que l’augmentation de cette cytokine pourrait influencer la chute accélérée des fonctions pulmonaires avant l’apparition du DAFK. Des niveaux élevés d’IL-17A sont retrouvés dans les poumons des patients atteints de la FK et dans le sang périphérique des patients avec le diabète de type 1 (DT1) et de type 2 (DT2). L’IL-17A peut aussi être produite par les lymphocytes Treg dysfonctionnels. Habituellement, ces lymphocytes atténuent les réponses inflammatoires excessives, mais lorsqu’ils sont dysfonctionnels, ils peuvent produire de l’IL-17A, contribuant ainsi à l’état inflammatoire. De plus, nous avons supposé que les proportions de Th17 et Treg produisant de l’IL-17A seront associées aux fonctions pulmonaires des patients atteints de la FK et que l’alimentation, l’activité physique et la composition corporelle influenceraient ces relations. Les résultats de cette thèse ont montré que, malgré une association entre la proportion de lymphocytes dans le sang périphérique et les indices de fluctuations glycémiques, celles-ci n’influençaient pas les proportions de lymphocytes Th17 et Treg produisant de l’IL-17A lorsqu’ils étaient mis en culture pour 24 ou 48 heures dans des milieux contenant soit 5 mM ou 25 mM de glucose et stimulés par le phorbol 12-myristate 13-acetate (PMA) et le phytohemagglutinine (PHA) ou, encore, non stimulés. De plus, ces proportions étaient semblables entre les patients atteints de la FK et les individus en santé. Toutefois, les proportions de lymphocytes Treg stimulés produisant de l’IL-17A des sujets sains étaient plus élevées que les proportions de lymphocytes Treg non stimulés de tous les participants (patients atteints de la FK et individus en santé). Tout ceci suggérant donc que les Treg des sujets sains et atteints de la FK ne réagissaient pas de la même façon à la stimulation. D’ailleurs, la durée d’incubation affectait les proportions de Th17 produisant de l’IL-17A, mais elle n’avait aucun effet sur les proportions de Treg produisant cette cytokine. Donc, ces types cellulaires réagissaient différemment dans les mêmes milieux de culture. De plus, nous avons observé que seulement l’énergie provenant des glucides affectait modestement les indices de fluctuations glycémiques et que les proportions de Th17 et Treg produisant de l’IL-17A n’étaient pas associées aux fonctions pulmonaires des patients atteints de la FK. En conclusion, les patients atteints de la FK avaient plus d’hyperglycémie et de fluctuations glycémiques, mais elles n’influençaient pas les proportions de lymphocytes Th17 et Treg produisant de l’IL-17A ex vivo. Dans des études futures, il faudrait étudier le rôle de l’IL-17A dans les poumons des patients avec et sans le DAFK et réaliser une étude prospective pour déterminer si une augmentation des niveaux d’IL-17A chez les patients sans le DAFK se traduit par une chute accélérée des fonctions pulmonaires avant l’apparition de cette complication.
Cystic fibrosis (CF) is the most common autosomal recessive genetic disease among Caucasians and it is cause by a mutation in the Cystic Fibrosis Transmembrane Regulator (CFTR) gene. With the emergence of more aggressive therapies to treat CF, the median life expectancy of patients with CF has increased and new complications, such as CF-related diabetes (CFRD), have emerged. CFRD is associated with increased mortality. The physiopathology of this complication is not fully understood. For instance, the reason why people with CF have an accelerated decline in lung functions years before the diagnosis of CFRD is not known. Patients with CF, even those without CFRD, have increased hyperglycemia and glucose fluctuations. In addition, a study has reported that hyperglycemia affected immune reactivity in a mouse model of the disease. Furthermore, studies have shown that lymphocytes without a functional CFTR or that have increased uptake of glucose have abnormal immune responses. Therefore, we hypothesized that patients with CF, specifically those with normal and impaired glucose tolerance, would have increased proportions of Th17 and Treg lymphocytes producing the pro-inflammatory cytokine IL-17A and that the increase in IL-17A levels would contribute to the accelerated decline of lung functions before the onset of CFRD. Increased levels of IL-17A have been found in the lungs of patients with CF and the peripheral blood of patients with type 1 (T1D) and 2 diabetes (T2D). Dysfunctional Treg lymphocytes can also produce IL-17A. These lymphocytes usually attenuate excessive immune responses but, in certain cases, can be dysfunctional and produce the pro-inflammatory cytokine IL-17A. Moreover, we hypothesized that the proportions of these cells producing IL-17A would be associated to lung functions in patients with CF and that nutrition, physical activity and body composition could influence the relationship between inflammation and glucose fluctuations. Although an association between the proportion of lymphocytes in the peripheral blood of participants and glucose fluctuations was observed, glucose fluctuations did not affect the proportions of Th17 and Treg lymphocytes producing IL-17A stimulated with PHA and PMA or not stimulated in media containing either 5 or 25 mM of glucose for 24 or 48 hours. Furthermore, these proportions were similar between healthy individuals and patients with CF with the exception of the proportion of stimulated Treg lymphocytes producing IL-17A of healthy individuals that was greater than the proportions of non-stimulated Treg lymphocytes producing IL-17A of all participants (patients with CF and healthy individuals). This suggests that Treg lymphocytes of healthy individuals and CF patients do not respond in the same manner to stimulation by phorbol 12-myristate 13-acetate (PMA) and phytohemagglutinin (PHA). Also, the duration of incubation affected the proportions of Th17 cells producing IL-17A but did not affect the proportion of Treg producing this cytokine. Therefore, these two types of lymphocytes are differently affected in the same culture media. Also, only the proportion of calories from carbohydrates affected modestly glucose fluctuations and the proportions of Th17 and Treg lymphocytes producing IL-17A were not associated to lung functions in CF patients. To conclude, patients with CF had increased hyperglycemia and glucose flucutations when compared to healthy individuals but this glucose variability did not affect the proportions of Th17 and Treg lymphocytes producing IL-17A ex vivo. Future studies are needed to explore the role of IL-17A in the lungs of patients with CFRD and a prospective study would be important in order to determine if an increase in IL-17A in patients without CFRD is associated to an accelerated decrease in lung functions before the onset of this complication.

碩士
國立臺東大學
生命科學系碩士班
96
The aim of this research is to study species compositions and population fluctuations of Heptageniidae between fast and slow sites at Danan Stream. Three sampling sites which included fast and slow areas were set up at midstream of Danan stream. Five stones were taken at each slow and fast area respectively monthly from April 2007 to May 2008. The specimen were preserved in 75

碩士
國立中興大學
園藝學系所
94
Leaf analysis was used to determine the seasonal changes of mineral elements of‘King’guava. Results showed that the microelement changed very little except for iron, which increased rapidly after September. The macronutrient concentrations remained rather stable during the period of July to September. Likewise the trend was the same for the months of January to March. By contrast, the calcium concentration dropped rapidly from April to August. It is concluded that July to September are the proper time to collect samples for leaf analysis according to the stable condition of the elements in the leaves. The range of variation of mineral elements of‘King’guava in summer and winter are as follows, and can be used as a guide for the diagnosis of mineral disorders in guava: N：1.86-2.11%；P：0.14-0.16%；K：1.18-1.31%；Ca：1.05-1.78%；Mg：0.33-0.34%；Fe：74-106ppm；Mn：63-69ppm；Zn：18-24ppm；Cu：15-29pp for the summer crop. Leaf mineral elements in winter crop (January to March)：N：1.23-1.60%；P：0.17-0.28%；K：1.23-1.60%；Ca：1.25-1.71%；Mg：0.16-0.22%；Fe：139-302ppm；Mn：86-104ppm；Zn：23-33ppm；Cu：18-48ppm. Change in the respiration rate and ethylene production of‘King’guava at different developmental stages was also investigated. The‘King’guava fruit with a 2cm diameter was found to have a relatively high respiration rate on the day of sampling, which dropped gradually, rose again after day 4, and at the same time the fruit showed sign of browning. The respiration rate of middle-sized fruit with a diameter of 5cm to 7cm was relatively low, and the ethylene production rate from‘King’guava was also maintained at very low and steady states. No ethylene production was detected as the developmental stage advanced still further. The‘King’guava with propylene treatment was found to have no capacity of autocatalytic ethylene synthesis. It is likely to be non-climacteric as evidenced by the fruit firmness, total soluble solids and change of peel color of the guava. Effects of low temperature storage on the fruit quality of summer and winter crops stored at 1、5、10℃ were investigated. Samples were taken every week. The fruit firmness decreased with increased time of storing, and was found to be less firm at 5℃. The total soluble solids were higher in the winter fruit than those of the summer fruit. The ascorbic acid was found increased in summer crop while fruits were stored at 1℃ and 5℃. Soluble titratable acidity had no obvious change. No significant change was observed in appearance after the low temperature storage of guava, but browning symptom was found after it was returned to 25℃ for 3 days, especially those stored at 10℃ for 4 weeks. Fruit decay and hypha growth on the skin appeared to be apparent after being stored for 5 week and then returned to room temperature for 3 days. Our results showed that 1℃ seems to be the most suitable temperature for guava storage. The vapor heat treatment was an effective means of controlling the oriental fruit fly in guava fruits. The treatment temperature was 46.5℃ for 15 or 35 minutes but over 40 minutes caused heat injury. Transportation at 1℃ for 7 days could keep the fruit quality. This finding may serve as a reference for transport and quarantine when exporting guava fruits.

Understanding the drivers of microbiome variation in corals is crucial to better predict the effects of environmental pressures on coral holobionts and coral reef ecosystems. However, much remains to be understood about corals and the interactions they establish with microorganisms. My hypothesis is that the microbiome of the surface mucus layer (SML) is mainly influenced by environmental parameters due to its direct contact with the environment, whereas the tissue microbiome is more driven by the physiology of the coral host. Therefore, the aim of the present work is to distinguish the effect of the host’s intrinsic and environmental factors on the microbiome composition in different coral compartments (SML and tissue), and to identify possible overarching trends in the environmental sensitivity of distinct microbiomes within a coral holobiont. Using next-generation amplicon-sequencing of the 16S rRNA gene, the analyses showed that microbiomes of Acropora spp. differed significantly between compartments (SML versus tissue) and species (A. tenuis versus A. millepora), but also among sampling location and season. Seawater samples were characterized by dominance of members of the Synechococcaceae and Pelagibacteraceae. In Acropora spp., mucus microbiome was dominated by members of Flavobacteriaceae, Synechococcaceae, Rhodobacteraceae and Pelagibacteraceae families, while the tissue microbiome was dominated by the Endozoicimonaceae family. SML microbiomes of both coral hosts correlated best with environmental parameters as ammonium, total suspended solids, particulate organic carbon, number of raindays and nitrate/nitrite. However, the amount of influence from environmental parameters on the mucus (explaining 12-15% of variation) is relatively low as compared with the influence of those parameters on the seawater microbiome (explaining 49% of variation). In contrast, the tissue microbiomes of the two Acropora species showed distinct and species-specific responses to environmental and physiological parameters, suggesting host-specific modulation of the environmental drivers of the tissue microbiome.
Os corais são considerados organismos holobiontes, uma unidade viva composta pelo hospedeiro e seu microbioma associado. Os corais, por exemplo, podem estar associados a eucariontes dinoflagelados (família Symbiodiniaceae), procariontes (Bacteria e Archaea) e/ou fungos. Os microrganismos associados aos corais estão envolvidos em diversas funções para o bom funcionamento dos processos fisiológicos do hospedeiro. Por exemplo, podem atuar como mediadores nos ciclos biogeoquímicos e na nutrição do hospedeiro, como também na defesa do mesmo contra agentes patogénicos. Portanto, são essenciais para a manutenção do estado saudável dos corais. Além disso, o microbioma dos corais está sob constante influência de flutuações dos fatores ambientais e fisiológicos dos seus hospedeiros. Compreender os fatores que influenciam a composição e funcionamento do microbioma é crucial para criar estratégias de conservação dos corais e, consequentemente, protegê-los dos efeitos das alterações globais, por exemplo. No entanto, ainda há muito a descobrir sobre a interação simbiótica em corais. O foco da presente tese é a comunidade de procariontes associados, que podem ser referenciados também como comunidades microbianas ou microbiomas ao longo da tese (conforme encontrado na literatura). As comunidades microbianas podem estar associadas a diferentes partes ou “compartimentos” do pólipo do coral. Os compartimentos incluem o muco superficial, tecido, esqueleto e a cavidade gástrovascular. Cada compartimento possui características únicas e, devido a isto, abriga microbiomas específicos, podendo variar tanto em abundância como em diversidade taxonómica. Por exemplo, estudos revelam que o microbioma do muco superficial de pólipos de corais é mais abundante e mais diverso que o tecido interno dos corais. A camada do muco apresenta-se como uma interface entre o epitélio dos pólipos e a coluna de água. Por isso põe-se a hipótese que a sua comunidade microbiana inclui não só os membros já residentes do muco, como também transientes originários de outras fontes (tais como a coluna de água, sedimentos em suspensão e/ou organismos bentónicos). Pelo contrário, as camada de tecido (epiderme e gastroderme) dos corais são dominadas principalmente por bactérias do género Endozoicomonas e também por microalgas fotossintéticas (da família Symbiodinaceae), extremamente importantes para a sobrevivência dos corais. Portanto, o estudo específico do microhabitat que o microbioma habita é crucial para o estudo geral de microbiomas de corais. No entanto, atualmente, estudos que englobam fatores que podem influenciar os microbiomas não se focam em diferentes compartimentos, mas apenas num só compartimento (geralmente o tecido). As primeiras descobertas neste tema mostraram que as comunidades microbianas específicas de corais são relativamente estáveis numa escala espacio-temporal. Estudos mais recentes propõem inúmeros fatores, para além da especificidade, que podem afetar a estrutura e a abundância relativa de membros dos microbiomas de corais. Por exemplo, diferenças geográficas, mudanças sazonais, poluição ou o estado fisiológico do hospedeiro. Porém, este tópico ainda é considerado bastante limitado e controverso, e mais estudos são necessários neste contexto.. O principal objetivo deste estudo é distinguir os efeitos de fatores ambientais e fisiológicos do hospedeiros na variação da composição das comunidades microbianas de diferentes compartimentos nos pólipos de corais (muco e tecido), e também, identificar possíveis tendências da sensibilidade ambiental dos microbiomas identificados. A minha hipótese é que o microbioma do muco é principalmente influenciado por parametros ambientais, devido ao seu contato mais direto com o ambiente, enquanto que o microbioma do tecido responde mais às mudanças fisiológicas do hospedeiro. Para testar esta hipótese, dados de Sequenciamento de Nova Geração (NGS) do gene 16S do RNA ribossomal dos microbiomas de diferentes compartimentos (muco e tecido) e espécies de coral (A. tenuis e A. millepora) foram usados em conjunto com dados de fatores ambientais e fisiológicos dos hospedeiros. O microbioma da coluna de água foi usado como referência no estudo. Em geral, os resultados mostraram que os microbiomas da Acropora diferiram significativamente entre os compartimentos e espécies, e também foram influenciados temporalmente e espacialmente. A riqueza de zOTU (“zero-radius OTU” ou unidade taxonómica operacional, a qual é designada como a menor entidade taxonómica existente) entre os microbiomas analisados diferiu significativamente entre o microbioma do muco, tecido e coluna de água, e também entre as espécies de Acropora. A riqueza de zOTU não diferiu entre estações ou local de coleta. O microbioma da coluna de água abrigou a comunidade mais rica, seguido da do muco e da comunidade do tecido. A diversidade alfa baseada no índex de Shannon também diferiu significativamente entre os microbiomas do muco, tecido e coluna de água, porém não diferiu entre espécies de corais, estação e local de coleta. A diversidade de zOTU foi significativamente maior no microbioma do muco em relação ao microbioma da coluna de água, enquanto que o microbioma do tecido foi o menos diverso entre todos. As amostras da coluna de água foram caracterizadas pela dominância de membros de Synechococcaceae e Pelagibacteraceae. Membros pertencentes às famílias Flavobacteriaceae, Synechococcaceae, Rhodobacteraceae e Pelagibacteraceae foram dominantes no microbioma do muco das espécies de Acropora, e membros da família Endozoicimonaceae foram dominantes no microbioma do tecidos de ambas as espécies. Os microbiomas do muco de ambas espécies de Acropora apresentaram maior influência de parâmetros ambientais como amónia, sólidos suspensos totais, carbono orgânico particulado, número de dias chuvosos e nitritos/nitratos. No entanto, a quantidade de influência dos parâmetros ambientais no muco (explicando 12-15% da variação) é relativamente baixa em comparação com a influência desses parametros no microbioma da água do mar (explicando 49% da variação). Por outro lado, os microbiomas do tecido apresentaram respostas distintas entre as espécies de Acropora nos parâmetros ambientais e fisiológicos, sugerindo modulação específica do hospedeiro aos fatores ambientais do microbioma do tecido. Em conclusão, o presente estudo revela que microbiomas presentes em compartimentos fisicamente distintos respondem diferentemente a fatores ambientais e fisiológicos, o que é uma novidade para os estudos de microbiomas de corais e sua dinâmica. Portanto, este estudo esclarece parte do conhecimento limitado e controverso neste contexto, e também estimula o uso de abordagens metodológicas mais holísticas sobre o tema. Sugestões para estudos futuros podem incluir o uso de outras espécies, diferentes das usadas no presente trabalho, e também testes experimentais (não só baseado em correlações) para o fornecimento de uma compreensão mais ampla da variação de microbiomas em corais.

碩士
國立交通大學
電子物理系所
99
In this study, the nitrogen (N) composition fluctuation effect of a high nitrogen incorporation into self-assemble InAs quantum dots (QDs) grown on GaAs substrate by molecular beam epitaxy (MBE) on S-K mode is investigated by using current-voltage measurement (I-V), capacitance-voltage (C-V), and photoluminescence measurement. Incorporating nitrogen into InAs extend the 2D critical thickness to 3D growth. We observe a decrease in PL intensity and a broadening of the PL emission with incorporating N, the emission include a nitrogen-contain InAsN wetting layer and a InAsN QDs with nitrogen composition fluctuation. The N distribution of InAsN QDs can be estimated by theory calculation on C-V profiling. After annealing process, the density of InAsN QDs decreases and the nitrogen composition fluctuation is reduced. The excitation of the electron-hole pairs in the QDs by illumination on the QDs is also studied. The electron-hole pairs can lead to the photoluminescence, photocurrent and photocapacitance by mechanisms of carrier recombination and emission. Furthermore, we analyze temperature and energy dependences of photocurrent and photocapacitance on samples of before and after annealing. Comparing with the electron and hole emission rates from the InAsN quantum state, photocapacitance is obviously found as the difference of electron and hole emission rate enhance. On the photocurrent analysis, electron escape process is thermal emission from the quantum state to the GaAs band edge on the sample before anneling, and the electron escape process is the phonon-assisted tunneling from quantum state via the InGaAs capping layer state to the GaAs conduction band edge on the sample after annealing. A theory model by a simple rate equation can explain the mechanisms of illumination on QDs, estimate the hole emission rate, and the conduction-band offset ratio is roughly 60% (6：4) for the InAsN/GaAs material system.