Low dimensional nanostructures of zinc oxide (ZnO), cupric oxide (CuO), and their composite nanostructures possess remarkable physical and chemical properties. Fundamental understanding and manipulation of these unique properties are crucial for all potential applications. Integration of nanostructured ZnO and CuO and their hybrid composites may play a significant role in the existing technology while paving the way for new exciting areas. Solution based low temperature synthesis of ZnO and CuO nanostructures have attracted extensive research efforts during the last decade. These efforts resulted in a plenteous number of nanostructures ranging from quantum dots into very complex three dimensional nanomaterials. Among the various low temperature synthesis methods the hydrothermal technique became one of the most popular approaches. The use of hydrothermal approach enabled the synthesis of diversity of nanomaterials on conventional and nonconventional substrates such as metals, glass, plastic and paper etc. The primary objectives of this thesis are to study and understand the characteristics of nanostructured ZnO, CuO, and their hybrid composites synthesized at low temperature. Likewise, the hybrid composites were successfully utilized to fabricate light emitting diodes and sensors. This thesis is organized into three major parts. In the beginning the synthesis and characterization of nanostructured ZnO, CuO, and their composite nanostructures are elaborated. Efforts have been made to understand the selective assembly of hierarchical CuO nanostructures on ZnO nanorods and to correlate it to the observed unique properties of the CuO/ZnO composite nanostructures. In the second part of the thesis fabrication, characterization, and device application of ZnO/p-polymer hybrid light emitting diode (HyLEDs) on flexible substrates are presented. In particular single and blended p-type light emissive polymers were controllably developed for potential greener and cheaper white light emitters. It was found that the HyLEDs exhibited rectifying diode characteristics together with white light emission covering the entire visible range. In the third part, pH and relative humidity sensing applications of CuO nanoflowers, and CuO/ZnO nanocorals, respectively, are described. A pH sensor based on CuO nanoflowers demonstrated good sensitivity and reproducibility over a wide range of pH. By taking the advantages of the selective growth of CuO nanostructures on ZnO nanorods and their naturally formed p-n heterojunction the realization of high sensitivity humidity sensor was achieved. The humidity sensor fabricated from the CuO/ZnO nanocorals displayed the highest sensitivity factor reported so far for its constituent materials; along with reasonably fast dynamic responses. A brief outlook into future challenges and opportunities are also presented in the last part of the thesis. / Nanophotonics

Zinc Oxide (ZnO) is one of the most extensively studied semiconductors because of its unique properties, namely, its wide band gap (3.37 eV) and high excitation binding energy (60 meV). These properties make ZnO a promising material for uses in a broad range of applications including sensors, catalysis and optoelectronic devices. The presented research covers a broad spectrum of these interesting nanomaterials, from their synthesis and characterization to their use as photocatalyts. A new synthetic approach for producing morphology controlled ZnO nanostructures was developed using microwave irradiation (MWI). The rapid decomposition of zinc acetate in the presence of a mixture of oleic acid (OAC) and oleylamine (OAM) results in the formation of hexagonal ZnO nanopyramids and ZnO rods of varying aspect ratios. The factors that influence the morphology of these ZnO nanostructures were investigated. Using ligand exchange, the ZnO nanostructures can be dispersed in aqueous medium, thus allowing their use as photocatalysts for the degradation of malachite green dye in water. Photocatalytic activity is studied as a function of morphology; and, the ZnO nanorods show enhanced photocatalytic activity for the degradation of the dye compared to hexagonal ZnO nanopyramids. After demonstrating the catalytic activity of these ZnO nanostructures, various ways to enhance photocatalytic activity were studied by modification of this MWI method. Photocatalytic activity is enhanced through band gap modulation and the reduction of electron-hole recombination. Several approaches were studied, which included the incorporation of Au nanoparticles, N-doping of ZnO, supporting ZnO nanostructures on reduced graphene oxide (RGO), and supporting N-doped ZnO on N-doped RGO. ZnO-based nanostructures were studied systematically through the entire process from synthesis and characterization to their use as photocatalysis. This allows for a thorough understanding of the parameters that impact these processes and their unique photocatalytic properties.

Ce travail concerne l'intégration, par épitaxie sous jets moléculaires (EJM), de matériaux nitrures d’éléments III (en particulier GaN) sur des substrats et couches tremplins à base d’oxyde de zinc (ZnO). L’objectif était la réalisation et l’étude d’hétérostructures nitrures de type puits quantiques (PQs) (Al,Ga)N/GaN et (In,Ga)N/GaN, en vue d’évaluer leurs potentialités pour la réalisation de diodes électroluminescentes (LEDs). En particulier, deux orientations cristallographiques ont été étudiées : le plan « polaire » (0001) (dit plan C) et le plan « non polaire » (11-20) (dit plan A). Les couches de GaN orientées suivant le plan A (11-20), « a-GaN », ont été épitaxiées sur des tremplins de (Zn, Mg)O (11-20) / saphir (10-12) réalisés par EJM. L’anisotropie de la morphologie de surface, de la microstructure cristalline, ainsi que de l'émission optique des couches de a-GaN, a été mise en évidence. Une série d'échantillons de PQs de a-(GaN/Al0.2Ga0.8N) avec des épaisseurs de puits différentes a été fabriquée, et l'absence d’effet Stark quantique confiné dans ces hétérostructures a été établie. Des procédés de croissance de GaN sur des substrats de ZnO massifs d’orientation A, « a-ZnO », et C, « c-ZnO », ont également été développés. En particulier, des couches de GaN (0001), « c-GaN », avec une polarité Ga- ou N- ont été épitaxiées sur la face O de substrats c-ZnO. Les mécanismes de détermination de la polarité ont été analysés. Des LEDs bleues contenant une zone active constituée de PQs (In, Ga)N / GaN ont été réalisées sur des substrats c-ZnO. Des puissances de sortie atteignant 40 µW à 20 mA et 0,1 mW à 60 mA ont été mesurées. Enfin, des PQs (In, Ga)N / GaN ont été fabriqués sur substrats a-ZnO et comparés à des PQs fabriqués sur c-ZnO avec des conditions de croissance équivalentes. Les résultats indiquent une concentration en In plus importante dans le cas des PQs épitaxiés sur c-ZnO et une polarisation de l’émission de PL suivant la direction <1-100> dans le cas des PQs épitaxiés sur a-ZnO. / This work focus on the integration of III-nitride materials, by molecular beam epitaxy (MBE), on ZnO based templates and substrates. The objective is to explore the potential of (Al,Ga)N/GaN and (In,Ga)N/GaN multi-quantum wells (MQWs) grown on ZnO for the fabrication of light emitting diodes (LEDs). In particular, two crystal orientations are studied: the polar (0001) plane (c-plane) and the nonpolar (11-20) plane (a-plane). The structural and optical properties of epitaxial layers are mainly characterized by AFM, SEM, XRD, TEM and PL. A-plane (11-20) GaN layers have been grown on a-(Zn,Mg)O/r-sapphire templates by MBE. The surface morphology, the crystal microstructure, as well as the optical emission of a-GaN layers show strong anisotropic properties. A series of a-plane Al0.2Ga0.8N/GaN MQWs with different well thicknesses have been fabricated and the absence of quantum confined Stark effect in these nonopolar heterostructures has been evidenced. Processes of growing GaN on both c- and a- plane bulk ZnO substrates have been developed. In particular, GaN layers with either Ga- or N- polarities have been grown on O face ZnO, and their polarity determination mechanisms have been analyzed. (In,Ga)N/GaN MQWs based blue LEDs have been demonstrated on c- ZnO substrates. Output powers of 40 µW at 20 mA and 0.1 mW at 60 mA have been measured. Finally, a-plane (In,Ga)N/GaN MQWs are fabricated on bulk a-ZnO substrates and compared with c-plane MQWs grown under similar conditions. PL measurements indicate that a-plane MQWs exhibit a lower In incorporation efficiency and a polarized emission along <1-100> direction.

La pollution actuelle des effluents hospitaliers par des médicaments, nécessite le développement de nouvelles techniques de traitement, la photocatalyse étant l’une des plus efficaces pour remédier à ce type de pollution. Cependant, les oxydes métalliques utilisés pour la photocatalyse (TiO2, ZnO, …) ne sont activables que sous irradiation UV. L’association de ces oxydes à des Quantum Dots (QDs), crée une hétérojonction qui étend la zone d’activation du photocatalyseur vers les rayonnements visibles et diminue les recombinaisons des porteurs de charges. La première partie de ce travail décrit le développement d’un photocatalyseur activable sous irradiation solaire pour la dégradation du colorant Orange II. Nous avons d’abord caractérisé l’hétérojonction créée entre ZnO et les QDs CuInS2/ZnS (ZCIS) puis étudié leur efficacité photocatalytique, en regardant notamment leurs capacités à générer des espèces réactives de l’oxygène. Dans la seconde partie, nous avons évalué la photodégradation d’un agent anticancéreux, l’Ifosfamide, présent dans les effluents hospitaliers. Pour cela, des réacteurs fermés agités et des microréacteurs ont été utilisés. Dans les deux cas, l’Ifosfamide, ainsi que ses intermédiaires de dégradation, sont photodégradés efficacement par le catalyseur ZnO/ZCIS sous une irradiation solaire de faible intensité (5 mW/cm2). Dans le cas des microréacteurs, le dépôt du catalyseur dans le microcanal a été optimisé et sa stabilité évaluée. Les résultats montrent que le catalyseur ZnO/ZCIS est réutilisable cinq fois sans perte d’activité, témoignant d’une bonne recyclabilité, ce qui en fait un bon candidat pour des applications photocatalytiques / The pollution of hospital effluents by pharmaceutical drugs, requires the development of new treatment techniques. Among these processes, photocatalysis is one of the most efficient one and allows the remediation of this kind of pollution. However, metal oxides used for photocatalysis (TiO2, ZnO, …) can only be activated by UV light. The association of these oxides with quantum dots (QDs) creates an heterojunction, which not only allows to extend the activation spectrum of the photocatalyst to the visible region but also decreases the charge carriers recombinations. The first part of this work describes the development of a catalyst responding to solar light irradiation for the degradation of the Orange II dye. First, we characterized the heterojunction created between ZnO and the CuInS2/ZnS (ZCIS) QDs and evaluated their photocatalytic efficiency. This work was undertaken by evaluating the capacity of the ZnO/ZCIS catalyst to produce reactive oxygen species (ROS). In the second part, we studied the photodegradation of the antineoplastic agent Ifosfamide commonly found in hospital effluents. For this purpose, closed and agitated reactors but also microreactors were used. In both cases, Ifosfamide, and the compounds originating from its degradation, can be fully photodegraded under simulated light of weak intensity (5 mW/cm2) using the ZnO/ZCIS catalyst. In the case of microreactors, the deposition of the catalyst was optimized and its stability evaluated. Results obtained demonstrate that the ZnO/ZCIS catalyst can be reused, at least five times, without significant loss in activity, thus demonstrating its ability to be used in real photocatalytic applications

A utilização descontrolada de pesticidas tem provocado no decorrer dos anos a intoxicação de milhares de pessoas no mundo, uma vez que, seus resíduos têm sido depositados em alimentos, em solos e em ambientes aquáticos. Assim, a construção de duas novas plataformas sensoras para a detecção de pesticidas é o objetivo desse trabalho. Na primeira plataforma foi utilizado o polieletrólito catiônico polietilenoimina (PEI) em conjunto com o polissacarídeo extracelular algal (PSE) produzido pela microalga criptofícea Cryptomonas tetrapirenoidosa preparados através da técnica de deposição \"spin-coating\". E a segunda plataforma foi produzida por eletrodeposição pulsada, entre um potencial de redução e um de oxidação, utilizando nanoestruturas de óxido de zinco (ZnO). Para caracterizar as plataformas, foram utilizadas as técnicas de microscopia eletrônica de varredura com fonte de emissão de campo (FEG-SEM), difração de raios X (XRD), espectroscopia de absorção ultravioleta-visível (UV-Vis), microscopia de força atômica (AFM) e espectroscopia de reflexão-absorção no Infravermelho com modulação da polarização (PM-IRRAS). Através da imobilização da enzima polifenol oxidase na forma de extrato bruto em sua fonte natural (fruto abacate), as plataformas de PEI/PSE e ZnO, foram avaliadas como biossensores de catecol e do inseticida carbaril. De modo comparativo, as plataformas de PEI/PSE sem a presença imobilizada da enzima também foram estudadas para a detecção do catecol e do carbaril. A simplicidade na formação e na construção dessas plataformas vem qualificá-las como viáveis a serem produzidas em escala industrial e com baixo custo de processamento. E diante dos resultados obtidos no desenvolvimento desses biossensores destaca-se a eficiência e a rapidez de detecção, o que os tornam economicamente promissores e competitivos em termos de aplicações ambientais. / The uncontrolled use of pesticides has resulted over the years the intoxication of thousands of people in the world, since their waste has been deposited in food, in soil and aquatic environments. Thus, the construction of two new sensors platforms for pesticide detection is the objective of this work. At first platform was used cationic polyelectrolyte polyethyleneimine (PEI) along with the extracellular algal polysaccharide (EPS) produced by microalgae criptofícea Cryptomonas tetrapirenoidosa prepared by deposition technique \"spin-coating\". The second platform was produced by pulsed electrodeposition between a reduction and an oxidation potential using nanostructures zinc oxide (ZnO). To characterize the platforms, we used the techniques of field emission gun scanning electron microscopy (FEG-SEM), X-ray diffraction (XRD), ultraviolet visible absorption spectroscopy (UV-Vis), atomic force microscopy (AFM), and polarization modulation infrared reflection-absorption spectroscopy (PM-IRRAS). By immobilization of the polyphenol oxidase enzyme as a crude extract in their natural source (avocado fruit), platforms PEI/PSE and ZnO, they were evaluated as catechol and carbaryl insecticide biosensors. In a comparative way, the platforms PEI/PSE without the presence of immobilized enzyme were also studied for detection of catechol and carbaryl. The simplicity in the formation and construction of these platforms comes qualify them as viable to be produced on an industrial scale and low cost processing. And on the results obtained in the development of such biosensors stand out the efficiency and speed of detection, which make them economically promising and competitive in terms of environmental applications.

Depuis le début des années 2000, une vaste classe de nanofils de nitrures d’éléments III et de ZnO peut être synthétisée avec un excellent contrôle des propriétés de dopage et de composition. La géométrie spécifique de ces nanofils permet de faire croître des hétérostructures radiales et axiales qui ont des propriétés optiques et de transport très avantageuses par rapport aux couches minces. Ces propriétés en font des candidats prometteurs pour la réalisation d’une nouvelle génération de dispositifs plus efficaces (LEDs, photodétecteurs,…). Pour cela, il est indispensable de comprendre les nouveaux effets induits par la géométrie particulière de ces nanostructures : c’est l’objet de cette thèse. Dans une première partie, je présente une étude des propriétés optiques de nanofils de semiconducteurs à grande énergie de bande interdite. J’analyse d’abord l’effet de la contrainte sur les propriétés d’émission des nanofils cœur-coquille GaN/AlGaN. En particulier, je mets en évidence le croisement des bandes de valence et son influence sur les propriétés optiques des nanofils. Ensuite, je me focalise sur l’effet du confinement quantique et les propriétés de polarisation dans les nanofils hétérostructurés de nitrures d’éléments III. Dans une seconde partie, je m’intéresse à la réalisation et à la caractérisation de dispositifs à base de nanofils de nitrures d’éléments III et de ZnO. J’expose tout d’abord la modélisation et l’étude expérimentale de photodétecteurs à ensemble de nanofils en mettant en avant l’influence des états de surface sur leur réponse. Je m’intéresse ensuite aux propriétés de transport dans des nanofils uniques de nitrures d’éléments III hétérostructurés. Je montre, en particulier, que ces hétérostructures sont le siège d’une résistance différentielle négative. Enfin, je présente la réalisation et la caractérisation de photodétecteurs et de LEDs utilisant des nanofils uniques InGaN/GaN cœur-coquille. Un modèle électrique équivalent permet de rendre compte du comportement observé. / Since the early 2000s, a large class of wide bandgap nanowires can be grown with an excellent control of doping and composition. The specific geometry of the nanowires leads to radial or axial heterostructures with better optical and transport properties compared to thin films. Due to these properties, they are promising candidates for a new generation of more efficient devices (LEDs, photodetectors, etc.). It is essential to understand the new effects induced by the particular geometry of these nanostructures.In the first part, I deal with the optical properties of wide bandgap semiconductor nanowires. First, I analyze the effect of the stress on the emission properties of core-shell GaN/AlGaN nanowires. I highlight the intersection of valence bands and its influence on the optical properties of nanowires. Then, I focus on the effect of quantum confinement and on the polarization properties of III-nitride heterostructured nanowires.In the second part, I describe the fabrication and characterization of III-nitride and ZnO nanowire-based devices. I first model and study photodetectors based on ensemble of nanowires. Then, I focus on the transport properties of single heterostructured nanowires of III-nitride heterostructures. I show in particular that these heterostructures exhibit a negative differential resistance. Finally, I present characterization of photodetectors and LEDs using single core-shell InGaN/GaN nanowires. An equivalent electrical circuit explains the observed behavior

Dans les microcavités semiconductrices, les polaritons excitoniques sont obtenus à partir du couplage fort entre l'exciton et le photon. Le régime de laser à polaritons à température ambiante, première étape vers le condensat de Bose-Einstein (BEC), a été atteint dans des microcavités ZnO et nous avons dans cette thèse étudié les propriétés des condensats de polaritons. Nous avons réalisé la spectroscopie linéaire et déterminé les propriétés spatiales de nouvelles microcavités ZnO sur substrat Si structuré en mesa, de haut facteur de qualité Q. Plusieurs géométries de génération de condensats de polariton ont été mises en oeuvre et comparées. Nous avons également mesuré, au travers d'expériences d'imagerie 2D en champ proche et en champ lointain, et modélisé, en résolvant l'équation de Gross-Pitaevskii, la propagation des condensats. Nous avons ainsi pu décrire les phénomènes mis en jeu dans la propagation des condensats à 80 et 300K pour une excitation fortement focalisée par rapport à une excitation étendue à 2D. Ces travaux posent les bases de dispositifs polaritoniques à 300K dans lesquels les condensats seront façonnés et contrôlés. / In semiconductors microcavities, exciton-polaritons arise from the strong coupling between excitons and photons. The polariton laser at room temperature, which is the first step to Bose-Einstein condensation (BEC), has been achieved in ZnO microcavities and the study of polariton condensates is the main issue of this work. We have studied the linear spectroscopy and measured the spatial properties of new high-Q ZnO microcavities grown on a patterned Si-substrate. Many generation geometries have been set up and compared to control the shape of polariton condensates. We have also measured and simulated polariton condensates propagation, using respectively 2D imaging experiments in near-field and far-field and by resolving the Gross-Pitaevskii equation. Then we were able to describe the variety of phenomena involved in the condensates propagation at 80 and 300 K for a tightly focused excitation compared to a wide 2D excitation. Those experiments pave the way for the development of polariton devices operating at 300 K in which polariton condensates can be patterned and controlled.

Ce travail porte sur l'élaboration de cellules solaires CuInSe2 (CIS) en couches minces. Différentes techniques de croissance ont été mises en œuvre pour concevoir les matériaux composant la structure photovoltaïque. Ainsi, l'absorbeur CuInSe2 a été déposé par coévaporation sous vide (PVD) sur un substrat de verre recouvert de molybdène. Un système de détection de la lumière diffusée (SLS) par l'échantillon a été développé pour permettre le suivi in situ des transitions de phases pauvres/riches en cuivre. Cela a permis la croissance de couches de CuInSe2 à larges grains ainsi que le contrôle de leurs propriétés électro-optiques. La couche tampon de CdS a été obtenue par bain chimique (CBD) et son épaiseur optimisée par un procédé original où le substrat est directement chauffé par conduction. Enfin, la couche fenêtre de ZnO a été élaborée par divers procédés de croissance tels que l'électrodéposition (ED) et le dépôt par couches atomiques (ALD). Les propriétés structurales, optiques et électriques des différentes couches minces sont étudiées et mises en relation avec les performances photovoltaïques des cellules élaborées. / The aim of this work is the design of thin film CuInSe2 solar cells. Different growth techniques have been used to elaborate the layers involved in this photovoltaic stack. Thus, the absorber CuInSe2 has been deposited by coevaporation under vacuum (PVD) onto a molybdenum coated glass substrate. A scattered light monitoring system (SLS) has been designed in order to follow in situ the copper poor/rich phases transitions. It has led to the growth of CuInSe2 layers made of large crystalline grains with both high optical and electrical properties. The CdS buffer layer has been elaborated by chemical bath deposition (CBD) and its thickness has been tuned by an original process involving a conduction heated holder. Finally, the ZnO window layer has been grown by various techniques such as electrodeposition (ED) and atomic layer deposition (ALD). Structural, optical and electrical properties of all these thin films have been studied and correlated with the photovoltaic parameters of the solar cells elaborated.

La biodisponibilité d'un composé minéral dépend de sa solubilité in vivo contrôlée par ses propriétés physicochimiques. Cependant, les caractéristiques physicochimiques qui influencent la solubilité et la biodisponibilité des produits utilisés en nutrition animale ne sont pas clairement connues. L'oxyde de zinc (ZnO) est un additif alimentaire couramment utilisé pour satisfaire le besoin en zinc (Zn) des animaux monogastriques. L'objectif de ce projet était de caractériser plusieurs types de ZnO utilisés en nutrition animale pour mieux appréhender leur devenir dans le tractus digestif et leur biodisponibilité. Les différentes sources de ZnO ont des propriétés physicochimiques variables qui influencent leurs cinétiques de dissolution. Une quarantaine d'échantillons de ZnO collectés à travers le monde auprès d'industries de la nutrition animale ont été caractérisés en termes de densité, densité tassée, taille de particules, forme, aire spécifique et cinétiques de dissolution. Une analyse en composantes principales (ACP) a été réalisée pour identifier les caractéristiques les plus pertinentes et classer les échantillons par familles. La nature des paramètres les plus pertinents suggère un mécanisme en deux étapes : dissolution de ZnO en ions Zn2+ à la surface des particules, suivie d'une diffusion vers la solution. La vitesse de dissolution détermine probablement le devenir de ZnO dans le tractus gastro-intestinal et pourrait donc expliquer les différences de performances. Une étude in vivo de produits représentatifs de chaque famille a permis de déterminer les effets des caractéristiques physicochimiques sur la biodisponibilité. Une étude dose-réponse a été réalisée sur des poulets Cobb en croissance (8 à 23 jours d'âge) soumis à un régime de base contenant 23 ppm de zinc ou à 14 régimes supplémentés à raison de 6 ou 12 ppm de ZnO (6 sources différentes) ou de sulfate de Zn. La teneur en zinc du tibia a été utilisée pour estimer la biodisponibilité relative des différentes sources de ZnO par rapport au sulfate de Zn utilisé comme référence (100%). La biodisponibilité des différentes sources variait entre 49% à 160%. La taille des agrégats et la surface spécifique expliquent une large part de la variabilité sur la biodisponibilité. En conclusion, les propriétés physicochimiques de ZnO permettent d'expliquer partiellement la variabilité observée des biodisponibilités du zinc car la complexité des phénomènes physiologiques rend difficile une telle prédiction / The bioavailability of a trace mineral source is related to its in vivo solubility, which in turn is determined by its physicochemical properties. It is still not clear which characteristics are more relevant in affecting solubility and bioavailability of feed compounds. Zinc Oxide (ZnO) is a common feed additive used to supplement zinc in the diet of monogastrics animals. However, different sources have shown different responses in animal bioavailability. This project aims to characterize different feed grade ZnO to better clarify their fate in the digestive tract and explain differences in bioavailability. It was hypothesized that the different sources of feed grade ZnO have various physicochemical properties that lead to distinct dissolution kinetics. Over 40 samples of ZnO have been collected from the feed industry worldwide. Samples were analyzed for density, tapped density, particle size, shape, specific area and dissolution kinetics. A principal component analysis (PCA) was performed to define the most relevant characteristics and categorize the samples into groups. The results showed that there is not only one variable influencing the kinetics of dissolution. It suggests a dissolution mechanism in 2 steps, in which there is the dissolution of ZnO into Zn ions in the surface of the particle, followed by a diffusion to the bulk solution. The speed of dissolution can determine the fate of zinc oxide products in the gastrointestinal tract and therefore may explain the different results in animal performance. Representative products from each family were selected for an in vivo trial to measure the effect of their characteristics on the zinc bioavailability. Male Cobb broilers were used in a dose-response experiment from 8 to 23 days of age. Treatments consisted of a basal diet with 23 ppm of zinc and 14 diets supplemented with 6 or 12 ppm of Zn in the form of different oxides or sulfate. Bone zinc was used to determine zinc bioavailability. The bioavailability of the different sources varied from 49 to 160% considering zinc sulfate as the reference. Aggregate size and specific surface area explain a large part of the variability observed on values of bioavailability. In conclusion, physicochemical properties of ZnO can partly explain the variability observed in terms of Zn biological value. However, the complexity of physiological processes makes difficult the prediction of Zn bioavailability based only on these characteristics

Semiconductor-based gas sensors have been used for a wide range of applications over the last few decades. In this thesis, sensing properties of pure ZnO and Ga doped ZnO are investigated. There are three types of tested gas species, H2, O2 and NO, and three test temperatures, 300oC, 400oC and 500oC. After measurements of response to exposure to H2 and O2, it is concluded that Ga doped ZnO and ZnO are both n-type metal oxides. In measurements of NO, two test conditions were considered, the case with background O2 (10%) in the gas flow and the case without background O2. NO can be oxidized to NO2 or reduced to N2 and O2. The resistance of Ga doped ZnO and ZnO sensors always decreases for all exposures to NO except for the case in which the Ga doped ZnO sensor was exposed to NO in a background of O2 at 500 oC. In this special case, the resistance of Ga doped ZnO actually increases during exposure to low concentrations of NO (&lt; 30 ppm). It is not clear whether the change in response direction is due to an n-p transition or different reactions between gas molecules and Ga doped ZnO. Work function measurements were therefore conducted to understand more about the electron transfer during gas exposure. The work function measurements suggest that there are probably several stages of interactions between gas molecules and Ga doped ZnO during each gas pulse exposure.