Cuprous oxide (Cu2O) was first investigated in the 1920s as a semiconductor material with Eg~2.17 eV. It is ideal for applications in solar cells, electrochromic devices, oxygen and humidity sensors because of its high optical absorption coefficient, non-toxic nature, abundant availability and low cost for production. Many groups have tried different ways to grow the cuprous oxide by, for instance, sputtering, CVD, PLD, MBE, and electro-deposition etc. Among them, the sputtering method is probably the most cost-effective and easy to operate. In this work, the cuprous oxide thin films were grown on R-Al2O3 and (110)-MgO substrates by DC reactive magnetron sputtering. Thin films grown at different temperatures under various oxygen partial pressures were studied by X-ray diffraction (XRD) to test their structural perfections. Samples with the Cu2O on Al2O3(1012) and MgO(110) were studied via measurement of cathodoluminescence(CL) spectroscopy, photoluminescence (PL) spectroscopy, transmission spectroscopy and magneto transport behaviors. The correlation of growth condition and physical properties are discussed.

Metal and metal oxides are widely used in industry, and to optimize their performance their surfaces are commonly functionalized by the formation of thin films. Self-assembled monolayers (SAMs) are deposited on metals or metal oxides either from solution or by gas deposition. Thiols with polar terminal groups are utilized for creating the responsive surfaces which can interact electrostatically with other adsorbates. Surface charge effects wetting and adhesion, and many other surface properties. Polar terminal groups in thiols could be used to modify these factors. Mixed SAMs can provide more flexible surfaces, and could change the resulting surface properties under the influence of factors such as pH, temperature, and photo-illumination. Therefore, in order to control these phenomena by mixed polar-terminated thiols, it is necessary to understand the composition and conformation of the mixed SAMs and their response to these factors. In this work, mixtures of thiols with carboxylic and amino terminal groups were studied. Carboxylic and amino terminal groups of thiol interact with each other via hydrogen bonding in solution and form a complex. Complexes adsorb to the surface in non-conventional orientations. Unmixed SAMs from each type, either carboxylic terminated thiols or amino terminated thiols are in standing up orientation while SAMs from complexes are in an axially in-plane orientation. Selenol is an alternative to replace thiols for particular applications such as contact with biological matter which has a better compatibility with selenol than sulfur. However, the    Se-C bond is weaker than the S-C bond which limits the application of selenol. Understanding the selenol adsorption mechanism on gold surfaces could shed some light on Se-C cleavage and so is investigated in this work. Se-C cleavage happens in the low coverage areas on the step since atoms at steps have lower coordination making them more reactive than atoms on the terraces.  Another area where the self-assembly of molecules is of importance is for dye sensitized solar cells, which are based on the adsorption of the dye onto metal oxides surfaces such as TiO2.The interface between the SAM of dye and the substrate is an important factor to consider when designing dyes and surfaces in dye sensitized solar cells (DSSCs). The quality of the self-assembled monolayers of the dye on the TiO2 surface has a critical influence on the efficiency of the DSSCs.  Creation of just a monolayer of dye on the surface could lead to an efficient current of photo-excited electrons to the TiO2 and degeneration of the dye by redox. This work, T-PAC dye showed island growth with some ad-layer that is not in contact with the surface, whereas the MP13 dye adsorption is laminar growth.  Cuprite (Cu2O) is the initial and most common corrosion product for copper under atmospheric conditions. Copper could be a good replacement for noble metal as catalysts for methanol dehydrogenation. Knowledge about the structure of Cu2O(100) and Cu2O(111) surfaces could be used to obtain a deeper understanding of methanol dehydrogenation mechanisms with respect to adsorption sites on the surfaces. In this work, a detailed study was done of Cu2O(100) surface which revealed the possible surface structures as the result of different preparation conditions. Studies of the structure of Cu2O(100) and Cu2O(111) surfaces show that Cu2O(100) has a comparatively stable surface and reduces surface reactivity. As a consequence, dehydrogenation of methanol is more efficient on the Cu2O(111) surface. The hydrogen produced from methanol dehydrogenation is stored in oxygen adatom sites on both surfaces. / <p>QC 20161107</p>

La détermination des distributions de contrainte et de déformation dans des matériaux opaques est une question clé pour évaluer leur comportement sous des conditions de chargement souvent complexes. La plupart des méthodes expérimentales utilisées aujourd’hui pour traiter ce problème sont des méthodes invasives ou bien inefficaces pour les matériaux opaques. Dans ce contexte nous proposons d’utiliser le signal de Résonance Quadripolaire Nucléaire (RQN) de petits cristaux, utilisés comme charge, dans des matériaux peu ou pas conducteurs. Les contraintes transmissent par la matrice au cristal induisent une déformation de son réseau cristallin qui à son tour induit une modification de sa fréquence RQN. La RQN est, par conséquent, sensible aux déformations induites par une contrainte mécanique externe et le cristal agit comme une jauge de contrainte à l’échelle du micron. Nous appelons cette méthode la piézospectroscopie RQN.L’objectif de cette étude est de prouver que l’on peut utiliser la piézospectroscopie RQN pour mesurer des contraintes au sein de matériaux opaques et plus précisément au sein d’élastomères. Le lien fondamental entre la variation de fréquence RQN et le tenseur de contrainte appliqué au cristal a été étudié. Pour cela nous avons choisi le 63Cu dans la cuprite comme sonde RQN. Expérimentalement, la dépendance à la contrainte de la fréquence RQN est mesurée en utilisant différentes sollicitations mécaniques générées par des montages originaux intégrant mesure de contrainte et de RQN. Les résultats ainsi obtenus sont discuté en regard de calculs quantiques basés sur la DFT.En outre, comme preuve de concept de la piézospetroscopie RQN, nous avons réalisé des expériences supplémentaires en utilisant des conditions de chargement qui nous ont permis de démontrer, sans faire d’hypothèses sur les propriétés mécaniques du Cu2O, que la variation de fréquence RQN est représentative de la composante hydrostatique du champ de contrainte interne de l’élastomère. Nous avons ensuite étudié la capacité de cette méthode à cartographier un champ de contrainte hétérogène. / The determination of stress and strain distributions in opaque materials is a key issue to evaluate their mechanical behavior. However, most of the methods used today to measure stress are either extremely invasive or ineffective for opaque materials. Within this context, we propose to use the Nuclear Quadrupolar Resonance (NQR) signal of small crystals, embedded within non, or poorly, conductive materials. Stresses transferred by the matrix to the crystal induce a deformation of its lattice which in turn results in a modification of the Electric Field Gradient (EFG) at the nucleus of interest. NQR is, as a consequence, sensitive to deformations induced by external mechanical stress and the crystals act as local stress gauges at the micron-scale. We call this method NQR piezospectroscopy.The objective of this study is to prove that NQR piezospectroscopy can be used to measure stress within opaque materials and more precisely within elastomer. The fundamental link between the NQR frequency variation and the stress tensor applied to the crystal has been studied. For that purpose, 63Cu in cuprite has been selected as a NQR probe. The stress dependence of its NQR frequency is investigated experimentally using different mechanical loadings generated within an original integrated NQR – stress device and discussed in the light of DFT ab-initio calculations.In addition, as proof-of-concept of NQR piezospectroscopy, additional experiments were carried out using loading conditions proving, without hypothesis on cuprite’s mechanical properties, that its NQR frequency shift is representative of the hydrostatic component of the elastomer inner stress field. We then investigated the ability of this method to map an heterogeneous stress field.

Le travail présenté dans cette thèse porte sur la synthèse et les caractérisations thermiques et rhéologiques d’un nouveau type de nanofluide : le système Cu2O/Glycérol. La caractérisation est faite en fonction de la taille des particules mises en suspension, de la température et de la fraction volumique solide. Ce travail a nécessité la synthèse des nanoparticules et des nanofluides par la méthode de décomposition thermique des précuseurs organométalliques, qui présente un bon rendement en quantité de nanoparticules (17%). Et le montage d’un dispositif de caractérisation thermique utilisant la méthode 3ω. Finalement, nous avons passé à la caractérisation rhéologique et thermique de ces échantillons. Les résultats obtenus avec ce nouveau système sont intéressants, car l’augmentation de la conductivité thermique atteint des valeurs importantes : 120% et 35% respectivement pour des fractions volumiques aussi faibles que 0,625% et 0,078% de nanoparticules de 7 nm de diamètre, sans influence notable sur la viscosité du fluide hôte, permettant une bonne amélioration du bilan énergétique total. Nous avons observé que la concentration et la taille (surface) des nanoparticules sont des paramètres clefs du comportement de la conductivité thermique effective du nanofluide Cu2O/Glycérol. Nos mesures nous ont permis de déduire la prédominance des modifications de la surface des nanoparticules (par fonctionnalisation ou par réaction chimique secondaire) sur le mouvement brownien dans les transferts thermiques nanoparticules/ fluide hôte. / The work presented in this thesis involves the synthesis and thermal and rheological characterization of a new type of nanofluid : the Cu2O/glycerol system. The characterization was carried out as a function of the size of the particles in suspension, the temperature and the volume fraction of nanoparticles. The nanoparticles and nanofluids were synthesised by the thermal decomposition method, providing a good yield of nanoparticles (17%). Apparatus for thermal measurements using the 3ω method was constructed, and rheological and thermal characterization was carried out. Significant increases in thermal conductivity were observed : 120% and 35% for volume fractions as low as 0.625% and 0.078%, respectively, of 7-nm-diameter nanoparticles, without noticeable effect on the viscosity of the host fluid, leading to a considerable improvement in the energy content.We found that the concentration and surface area of the nanoparticles are key parameters influencing the behaviour of the effective thermal conductivity of the nanofluid. Surface modification of the nanoparticles by functionalization or secondary chemical reactions has a profound effect on the Brownian motion in the heat transfer between nanoparticles and fluid host.

Doctor of Philosophy / Antimicrobial coatings can inhibit the spread, via surfaces, of various diseases that infect humans. Antimicrobial coatings are useful because they can continue to kill pathogens (germs) for a long time after the surface is coated. This is a big improvement over use of common disinfectants that must be applied continuously. The main goal of this dissertation research is to develop various surface coatings that are antimicrobial and can provide a rapid killing of germs. We demonstrate 6 different antimicrobial coatings that rapidly inactivate a wide variety of pathogens, such as the most recent coronavirus, drug-resistant bacteria, or fungi. The antimicrobial coatings were composed of a variety of adhesives and active antimicrobial ingredients. Traditional adhesives and recently-invented adhesives were incorporated into the coatings, and active ingredients included copper, copper oxide, or zinc oxide. In short, our coatings provide a short killing period of a few minutes to one hour. Additionally, we investigated the mechanism of action of copper oxide surface coatings, and determined that the proximity of microbial cells to an antimicrobial surface is the key to inactivation or killing of the pathogen. Also, we measured the transfer of the most recent coronavirus from solid surfaces to skin under various conditions. We found that a substantial quantity of the virus is transferred to skin. More specifically, when the virus-infected droplet is still wet, a higher percentage is transferred from the solid to skin. In addition, we composed a review of the scientific literature on antimicrobial coatings with a focus on coatings and methods that inactivate the coronavirus.

Na constante busca de novas estratégias para melhorar a atividade catalítica, foi que a começos do século passado, a síntese de nanopartículas de formato controlado, tornou-se em um dos acontecimentos que revolucionaram a abordagem catalítica da Química, criando assim a linha da nanociência, onde com a síntese de nanopartículas de formato ao nível nano, é possível controlar as propriedades catalíticas dos materiais a nível macroscópico. O presente trabalho apresenta, a síntese de nanopartículas de óxido cuproso (NPs-Cu2O) com faces cristalográficas controladas. Foi possível sintetizar estruturas cúbicas, esféricas, e octaédricas, sendo os cubos e octaedros os que possuem faces cristalográficas de tipo (100) e (111), respectivamente. Entretanto, as esferas possuem uma mistura entre ambas das faces. As propriedades catalíticas das NPs-Cu2O foram testadas eletroquimicamente mediante uma reação modelo de detecção de glicose. As NPs-Cu2O, foram sintetizadas em médio básico com cloreto de cobre (CuC12) como percursor, posteriormente com concentrações diferentes de cloridrato de hidroxilamina (NH2OHoHCI) foram obtidas NPs-Cu2O com estrutura cúbica, octaédrica e esférica. Posteriormente, foram imobilizadas numa superfície de eletrodo de carbono vítreo, mediante a técnica de casting. A oxidação catalítica da glicose, permitiu observar que o desempenho da estrutura cúbica fossesuperior, com uma sensibilidade de 442 ± 7 &#181;A mM-1 cm-2, enquanto as estruturas esféricas e octaédricas foram de 165 ± 3 &#181;A mM-1 cm-2 e 38 ± 1 &#181;A mM-1 cm-2, respectivamente. Seguido as NPs-Cu2O, foram testadas na presença de Ácido Ascórbico (AA) e Ácido Úrico (UA), foi observado que os cubos possuem uma seletividade única, comparada com as outras estruturas. Dito comportamento foi estudado com Analise computacional (DFT), onde foi possível de observar que a distribuição entre átomos de Cobre e Oxigênio, determina a seletividade do material. Numa segunda etapa, para entender a importância da conservação estrutural e integridade morfológica, foram testadas as NPs-Cu2O, aos diferentes dias após de ser sintetizadas, observando claramente uma relação entre estrutura e atividade catalítico. Foi observado que nas estruturas cúbicas o deterioro foi maior em comparação com as outras estruturas, isto acompanhado mediante DFT, foi determinado que estrutura cúbica apresenta uma maior interação com o oxigênio, provocando assim, que a rápida transformação de Cu(I) para Cu(II), como CuO. Por último as NPs-Cu2O, foram testadas por espectroscopia de fotoelétrons excitados por raios X (XPS), este analise ajudou a compreender que o desempenho catalítico, não estava relacionado com a formação de Cu (III). Estes resultados foram apoiados pelos resultados obtidos pela espectroscopia de infravermelho in situ (FTIR), já que nessa análise foi possível de observar como o estabilizante (SDS), foi determinante em cada estrutura. / In the constant search for new strategies by advance of catalytic activities, was that at the beginning of the last century the synthesis of nanoparticles in a controlled format, became one of the events that revolutionized the catalytic approach of Chemistry, thus creating a line of nanoscience, where with the synthesis of nanoparticles of format at the nano level, it is possible to control catalytic properties of materiais at the macroscopic level. Consequently, the present work the synthesis of cuprous oxide nanoparticles (Cu2O-NPs), with crystallography faces welldefined. It was possible synthesize cubic, spherical and octahedral structure, the cubes and octahedrons being those having crystallographic faces of type (100) and (111), respectively. Meanwhile, the spheres have a mixture between both faces. The catalytic properties of Cu2O-NPs were electrochemically tested by a model glucose detection reaction. The Cu2O-NPs were synthetized in basic solution with cooper chlorate (CuCl2) like precursor, after with different concentration of hydroxylamine hydrochloride (NH2OH&#183; HCl) were obtain cubic, spheres and octahedral structure. Posteriorly, were immobilized in a glassy carbon surface, through the technique of casting. The catalyst oxidation of glucose allowed observe that the performance of cubic structure was superior, with a sensibility of 442 ± 7 &#181;A mM-1 cm-2, while the spheres and octahedral structure were 165 ± 3 &#181;A mM-1 cm-2 e 38 ± 1 &#181;A mM-1 cm-2, respectively. Following the Cu2O-NPs, they were tested in the presence of Ascorbic Acid (AA) and Uric Acid (UA), it was observed that the cubes have a unique selectivity compared to the other Cu2O-NPs structure. This behavior was studies with com putational analysis (DFT), where it was possible to observed that the distribution between copper and oxygen atoms determines the selectivity of material. In a second step, to understand the importance of structure conservation and morphological integrity, Cu2O-NPs were tested at different days after being synthesized, noting clearly a relation between structure and catalytic activity. It was observed that cubic structure the deterioration was greater in comparation with the other structures, this being accompanied by DFT, it was determinate that cubic structure show a greater interaction with the oxygen, thus provoking that rapid transformation of Cu (I) to Cu(II), like CuO. Finally, the Cu2O-NPs were tested by x-ray excited photoelectron spectroscopy (XPS), this analysis helped to understand the catalytic activity was not related to Cu (III) formation. These results were supported by those obtained by in situ (FTIR), since in this analysis it was possible to observe how the stabilizer (SDS) was determinant in each structure.

Na constante busca de novas estratégias para melhorar a atividade catalítica, foi que a começos do século passado, a síntese de nanopartículas de formato controlado, tornou-se em um dos acontecimentos que revolucionaram a abordagem catalítica da Química, criando assim a linha da nanociência, onde com a síntese de nanopartículas de formato ao nível nano, é possível controlar as propriedades catalíticas dos materiais a nível macroscópico. O presente trabalho apresenta, a síntese de nanopartículas de óxido cuproso (NPs-Cu2O) com faces cristalográficas controladas. Foi possível sintetizar estruturas cúbicas, esféricas, e octaédricas, sendo os cubos e octaedros os que possuem faces cristalográficas de tipo (100) e (111), respectivamente. Entretanto, as esferas possuem uma mistura entre ambas das faces. As propriedades catalíticas das NPs-Cu2O foram testadas eletroquimicamente mediante uma reação modelo de detecção de glicose. As NPs-Cu2O, foram sintetizadas em médio básico com cloreto de cobre (CuC12) como percursor, posteriormente com concentrações diferentes de cloridrato de hidroxilamina (NH2OHoHCI) foram obtidas NPs-Cu2O com estrutura cúbica, octaédrica e esférica. Posteriormente, foram imobilizadas numa superfície de eletrodo de carbono vítreo, mediante a técnica de casting. A oxidação catalítica da glicose, permitiu observar que o desempenho da estrutura cúbica fossesuperior, com uma sensibilidade de 442 ± 7 &#181;A mM-1 cm-2, enquanto as estruturas esféricas e octaédricas foram de 165 ± 3 &#181;A mM-1 cm-2 e 38 ± 1 &#181;A mM-1 cm-2, respectivamente. Seguido as NPs-Cu2O, foram testadas na presença de Ácido Ascórbico (AA) e Ácido Úrico (UA), foi observado que os cubos possuem uma seletividade única, comparada com as outras estruturas. Dito comportamento foi estudado com Analise computacional (DFT), onde foi possível de observar que a distribuição entre átomos de Cobre e Oxigênio, determina a seletividade do material. Numa segunda etapa, para entender a importância da conservação estrutural e integridade morfológica, foram testadas as NPs-Cu2O, aos diferentes dias após de ser sintetizadas, observando claramente uma relação entre estrutura e atividade catalítico. Foi observado que nas estruturas cúbicas o deterioro foi maior em comparação com as outras estruturas, isto acompanhado mediante DFT, foi determinado que estrutura cúbica apresenta uma maior interação com o oxigênio, provocando assim, que a rápida transformação de Cu(I) para Cu(II), como CuO. Por último as NPs-Cu2O, foram testadas por espectroscopia de fotoelétrons excitados por raios X (XPS), este analise ajudou a compreender que o desempenho catalítico, não estava relacionado com a formação de Cu (III). Estes resultados foram apoiados pelos resultados obtidos pela espectroscopia de infravermelho in situ (FTIR), já que nessa análise foi possível de observar como o estabilizante (SDS), foi determinante em cada estrutura. / In the constant search for new strategies by advance of catalytic activities, was that at the beginning of the last century the synthesis of nanoparticles in a controlled format, became one of the events that revolutionized the catalytic approach of Chemistry, thus creating a line of nanoscience, where with the synthesis of nanoparticles of format at the nano level, it is possible to control catalytic properties of materiais at the macroscopic level. Consequently, the present work the synthesis of cuprous oxide nanoparticles (Cu2O-NPs), with crystallography faces welldefined. It was possible synthesize cubic, spherical and octahedral structure, the cubes and octahedrons being those having crystallographic faces of type (100) and (111), respectively. Meanwhile, the spheres have a mixture between both faces. The catalytic properties of Cu2O-NPs were electrochemically tested by a model glucose detection reaction. The Cu2O-NPs were synthetized in basic solution with cooper chlorate (CuCl2) like precursor, after with different concentration of hydroxylamine hydrochloride (NH2OH&#183; HCl) were obtain cubic, spheres and octahedral structure. Posteriorly, were immobilized in a glassy carbon surface, through the technique of casting. The catalyst oxidation of glucose allowed observe that the performance of cubic structure was superior, with a sensibility of 442 ± 7 &#181;A mM-1 cm-2, while the spheres and octahedral structure were 165 ± 3 &#181;A mM-1 cm-2 e 38 ± 1 &#181;A mM-1 cm-2, respectively. Following the Cu2O-NPs, they were tested in the presence of Ascorbic Acid (AA) and Uric Acid (UA), it was observed that the cubes have a unique selectivity compared to the other Cu2O-NPs structure. This behavior was studies with com putational analysis (DFT), where it was possible to observed that the distribution between copper and oxygen atoms determines the selectivity of material. In a second step, to understand the importance of structure conservation and morphological integrity, Cu2O-NPs were tested at different days after being synthesized, noting clearly a relation between structure and catalytic activity. It was observed that cubic structure the deterioration was greater in comparation with the other structures, this being accompanied by DFT, it was determinate that cubic structure show a greater interaction with the oxygen, thus provoking that rapid transformation of Cu (I) to Cu(II), like CuO. Finally, the Cu2O-NPs were tested by x-ray excited photoelectron spectroscopy (XPS), this analysis helped to understand the catalytic activity was not related to Cu (III) formation. These results were supported by those obtained by in situ (FTIR), since in this analysis it was possible to observe how the stabilizer (SDS) was determinant in each structure.

L'électronique transparente est actuellement limitée par la difficulté de construire une jonction p-n transparente, en raison du manque d'oxyde transparent conducteur (TCO) de type p réellement performant. L'oxyde cuivreux Cu2O est un TCO de type p prometteur, mais sa bande interdite relativement étroite pour un TCO (2,1 eV), limite sa transmittance dans le domaine visible. Dans le cadre de cette thèse, nous cherchons à augmenter cette valeur. Pour cela, nous explorons la méthode MOCVD comme technique de dépôt pour le dopage au strontium et au calcium de l’oxyde cuivreux. Ce dopage est supposé élargir la bande interdite du Cu2O d'après des calculs ab initio effectués à l'institut Tyndall, à Cork. Dans le chapitre I, nous présentons le contexte de cette thèse. Après avoir expliqué les conditions que doit remplir un matériau pour être un TCO de type p, nous présentons l'état de l'art concernant le Cu2O. Dans le chapitre II, nous présentons l'ensemble des techniques utilisées dans le cadre de cette thèse, de l'élaboration (MOCVD, recuits thermiques) à la caractérisation (MEB, MET, AFM, DRX, spectroscopie FTIR, spectroscopie Raman, XPS, spectroscopie UV-vis-NIR, mesures 4 pointes et mesures d'effet Hall). Au cours du chapitre III, l'influence des paramètres de la MOCVD sur la composition et la morphologie a été analysée pour l’élaboration de couches de Cu2O pures, non dopées en vue d'établir les conditions optimales de dépôt. Nous obtenons des couches continues sur substrat de Si/SiO2, alors qu'elles sont systématiquement hétérogènes avec des zones sans dépôt sur silicium. En outre, nous mettons en évidence le risque d'obtenir la phase cuivre métallique lorsque la concentration de précurseur est élevée, la pression partielle d'oxygène faible et/ou la température élevée. Partant de ces conditions optimales, nous étudions dans le chapitre IV l'influence du dopage au strontium sur les propriétés fonctionnelles des couches (résistivité, largeur de bande interdite et transmittance dans le visible). Une chute de la résistivité a été observée lors du dopage au strontium. Les couches non dopées ont des résistivités de l'ordre de 103 Ω.cm ou plus, contre 10 Ω.cm pour les couches contenant entre 6 et 15% de strontium. La conductivité est bien de type p avec une mobilité de l’ordre de 10 cm2.V-1.s-1 et une densité de porteur de quelques 1016 cm-3. L’écart très grand entre cette densité de porteur et la teneur globale en Sr est lié à la présence d’une contamination des couches par du carbonate et du fluorure de strontium mis en évidence par FTIR et XPS. L’influence réelle de ces impuretés n’a pu être déterminée. Enfin il n'a pas été constaté de variation significative des propriétés optiques, la bande interdite restant large d'environ 2,4 eV et la transmittance moyenne entre 500 et 1000 nm de l'ordre de 55%. Des tendances similaires sont observées dans le chapitre V qui aborde le dopage au calcium, avec comme particularité le fait pour un fort taux de dopage et sous assistance UV, d'aboutir à la présence d'espaces vides localisés à l'interface substrat/Cu2O qui pourrait être lié à la décomposition du carbonate de calcium. Finalement, nous procédons à des recuits thermiques des couches, dopées ou non, dans le chapitre VI. Pour les couches non dopées, cela permet de diminuer la résistivité jusqu’à des valeurs de 10-100 Ω.cm. Pour les couches dopées, cela permet aux couches ayant une résistivité initiale de 10 Ω.cm de descendre jusqu'à 1 Ω.cm. Au cours de cette thèse, nous avons établi les effets du dopage au Sr ou Ca qui conduisent à une forte chute de résistivité sans impact sur les propriétés optiques à la différence des résultats prévus par les calculs ab initio. Nous sommes ainsi parvenus à améliorer les propriétés des couches Cu2O transparentes de type p. / Transparent electronic is currently limited by the lack of a really performant p-type transparent conducting oxide (TCO), which makes the elaboration of a transparent p-n junction challenging. Cuprous oxide Cu2O is a promising p-type TCO, but its optical transmittance in the visible spectrum is limited by its relatively low band gap (2.1 eV). In this thesis, we aim at increasing this value. To achieve that, we explore MOCVD as the growth method for strontium and calcium doping of cuprous oxide. According to ab-initio calculations performed at Tyndall Institute in Cork, doping with these elements is supposed to increase the band gap of Cu2O. In chapter I, we introduce the context of this thesis. After explaining the required conditions that a material must fulfil to be a p-type TCO, we present the state of the art of Cu2O. In chapter II, we present all the techniques used in this work, from the elaboration (MOCVD, thermal annealing) to characterization (SEM, TEM, AFM, XRD, FTIR, Raman spectroscopy, XPS, UV-vis-NIR spectroscopy, 4 point probe and Hall effect measurement). In chapter III, our objective is to synthesize pure, undoped Cu2O thin films. We explore the influence of the MOCVD parameters on the films composition and morphology. We get homogenous films on Si/SiO2 substrates, while we get heterogeneous films with un-deposited parts on silicon substrate. In addition, we show the risk to get the metallic copper phase when precursor concentration is high, oxygen partial pressure is low, and/or temperature is high. This enables us to determine the optimal deposition conditions. Starting from those optimal conditions, we study the influence of strontium doping on the functional properties of the films (resistivity, band gap and visible light transmittance) in chapter IV. A decrease of resistivity was observed with strontium doping. While undoped films show resistivity values of 103 Ω.cm or more, films doped from 6 to 15% strontium show resistivity values of about 10 Ω.cm. P-type conductivity was confirmed through Hall effect measurements, with a mobility close to 10 cm2.V-1.s-1 and a charge carrier density of about 1016 cm-3. The large difference between this carrier density and the Sr concentration can be linked with the presence of a strontium carbonate and fluoride contamination that was detected by FTIR and XPS. The exact influence of those impurities is not well known. In addition, no significant variation of optical properties was observed, the band gap remained close to 2.4 eV and average transmittance in the 500-1000 nm range was about 55%. Similar tendencies were observed for calcium doping, addressed in chapter V. Calcium doping showed the particularity of leading to the presence of cavities localized at the substrate/Cu2O interface, for a high dopant concentration and under UV assistance. Eventually, we performed thermal annealing on some samples, doped and undoped, in chapter VI. For undoped samples, it allowed to decrease resistivity in the 10-100 Ω.cm range. For doped samples, it allows samples showing initial resistivity of about 10 Ω.cm to decrease it to 1 Ω.cm. No impact of thermal annealing on sample morphology or composition was observed. In this thesis, we successfully established the effects of Sr or Ca doping, which lead to a significant decrease of the resistivity without impact on the optical properties, unlike what was predicted by the ab initio calculations. We were thus able to improve the p-type transparent Cu2O thin films properties.

L'électronique transparente est actuellement limitée par la difficulté de construire une jonction p-n transparente, en raison du manque d'oxyde transparent conducteur (TCO) de type p réellement performant. L'oxyde cuivreux Cu2O est un TCO de type p prometteur, mais sa bande interdite relativement étroite pour un TCO (2,1 eV), limite sa transmittance dans le domaine visible. Dans le cadre de cette thèse, nous cherchons à augmenter cette valeur. Pour cela, nous explorons la méthode MOCVD comme technique de dépôt pour le dopage au strontium et au calcium de l’oxyde cuivreux. Ce dopage est supposé élargir la bande interdite du Cu2O d'après des calculs ab initio effectués à l'institut Tyndall, à Cork. Dans le chapitre I, nous présentons le contexte de cette thèse. Après avoir expliqué les conditions que doit remplir un matériau pour être un TCO de type p, nous présentons l'état de l'art concernant le Cu2O. Dans le chapitre II, nous présentons l'ensemble des techniques utilisées dans le cadre de cette thèse, de l'élaboration (MOCVD, recuits thermiques) à la caractérisation (MEB, MET, AFM, DRX, spectroscopie FTIR, spectroscopie Raman, XPS, spectroscopie UV-vis-NIR, mesures 4 pointes et mesures d'effet Hall). Au cours du chapitre III, l'influence des paramètres de la MOCVD sur la composition et la morphologie a été analysée pour l’élaboration de couches de Cu2O pures, non dopées en vue d'établir les conditions optimales de dépôt. Nous obtenons des couches continues sur substrat de Si/SiO2, alors qu'elles sont systématiquement hétérogènes avec des zones sans dépôt sur silicium. En outre, nous mettons en évidence le risque d'obtenir la phase cuivre métallique lorsque la concentration de précurseur est élevée, la pression partielle d'oxygène faible et/ou la température élevée. Partant de ces conditions optimales, nous étudions dans le chapitre IV l'influence du dopage au strontium sur les propriétés fonctionnelles des couches (résistivité, largeur de bande interdite et transmittance dans le visible). Une chute de la résistivité a été observée lors du dopage au strontium. Les couches non dopées ont des résistivités de l'ordre de 103 Ω.cm ou plus, contre 10 Ω.cm pour les couches contenant entre 6 et 15% de strontium. La conductivité est bien de type p avec une mobilité de l’ordre de 10 cm2.V-1.s-1 et une densité de porteur de quelques 1016 cm-3. L’écart très grand entre cette densité de porteur et la teneur globale en Sr est lié à la présence d’une contamination des couches par du carbonate et du fluorure de strontium mis en évidence par FTIR et XPS. L’influence réelle de ces impuretés n’a pu être déterminée. Enfin il n'a pas été constaté de variation significative des propriétés optiques, la bande interdite restant large d'environ 2,4 eV et la transmittance moyenne entre 500 et 1000 nm de l'ordre de 55%. Des tendances similaires sont observées dans le chapitre V qui aborde le dopage au calcium, avec comme particularité le fait pour un fort taux de dopage et sous assistance UV, d'aboutir à la présence d'espaces vides localisés à l'interface substrat/Cu2O qui pourrait être lié à la décomposition du carbonate de calcium. Finalement, nous procédons à des recuits thermiques des couches, dopées ou non, dans le chapitre VI. Pour les couches non dopées, cela permet de diminuer la résistivité jusqu’à des valeurs de 10-100 Ω.cm. Pour les couches dopées, cela permet aux couches ayant une résistivité initiale de 10 Ω.cm de descendre jusqu'à 1 Ω.cm. Au cours de cette thèse, nous avons établi les effets du dopage au Sr ou Ca qui conduisent à une forte chute de résistivité sans impact sur les propriétés optiques à la différence des résultats prévus par les calculs ab initio. Nous sommes ainsi parvenus à améliorer les propriétés des couches Cu2O transparentes de type p. / Transparent electronic is currently limited by the lack of a really performant p-type transparent conducting oxide (TCO), which makes the elaboration of a transparent p-n junction challenging. Cuprous oxide Cu2O is a promising p-type TCO, but its optical transmittance in the visible spectrum is limited by its relatively low band gap (2.1 eV). In this thesis, we aim at increasing this value. To achieve that, we explore MOCVD as the growth method for strontium and calcium doping of cuprous oxide. According to ab-initio calculations performed at Tyndall Institute in Cork, doping with these elements is supposed to increase the band gap of Cu2O. In chapter I, we introduce the context of this thesis. After explaining the required conditions that a material must fulfil to be a p-type TCO, we present the state of the art of Cu2O. In chapter II, we present all the techniques used in this work, from the elaboration (MOCVD, thermal annealing) to characterization (SEM, TEM, AFM, XRD, FTIR, Raman spectroscopy, XPS, UV-vis-NIR spectroscopy, 4 point probe and Hall effect measurement). In chapter III, our objective is to synthesize pure, undoped Cu2O thin films. We explore the influence of the MOCVD parameters on the films composition and morphology. We get homogenous films on Si/SiO2 substrates, while we get heterogeneous films with un-deposited parts on silicon substrate. In addition, we show the risk to get the metallic copper phase when precursor concentration is high, oxygen partial pressure is low, and/or temperature is high. This enables us to determine the optimal deposition conditions. Starting from those optimal conditions, we study the influence of strontium doping on the functional properties of the films (resistivity, band gap and visible light transmittance) in chapter IV. A decrease of resistivity was observed with strontium doping. While undoped films show resistivity values of 103 Ω.cm or more, films doped from 6 to 15% strontium show resistivity values of about 10 Ω.cm. P-type conductivity was confirmed through Hall effect measurements, with a mobility close to 10 cm2.V-1.s-1 and a charge carrier density of about 1016 cm-3. The large difference between this carrier density and the Sr concentration can be linked with the presence of a strontium carbonate and fluoride contamination that was detected by FTIR and XPS. The exact influence of those impurities is not well known. In addition, no significant variation of optical properties was observed, the band gap remained close to 2.4 eV and average transmittance in the 500-1000 nm range was about 55%. Similar tendencies were observed for calcium doping, addressed in chapter V. Calcium doping showed the particularity of leading to the presence of cavities localized at the substrate/Cu2O interface, for a high dopant concentration and under UV assistance. Eventually, we performed thermal annealing on some samples, doped and undoped, in chapter VI. For undoped samples, it allowed to decrease resistivity in the 10-100 Ω.cm range. For doped samples, it allows samples showing initial resistivity of about 10 Ω.cm to decrease it to 1 Ω.cm. No impact of thermal annealing on sample morphology or composition was observed. In this thesis, we successfully established the effects of Sr or Ca doping, which lead to a significant decrease of the resistivity without impact on the optical properties, unlike what was predicted by the ab initio calculations. We were thus able to improve the p-type transparent Cu2O thin films properties.

Une opportunité attrayante consisterait à utiliser l'énergie solaire, abondante et (quasi)inépuisable, pour valoriser le CO2 en carburants. Ceci permettrait de répondre à une double préoccupation : le dérèglement climatique imputable à l’augmentation de la concentration de gaz à effet de serre dans l’atmosphère d’une part, et d’autre part la raréfaction annoncée des ressources en énergie. Les végétaux sont capables de réduire le dioxyde de carbone en composés hydrogénocarbonés et d’oxyder simultanément l’eau en dioxygène par photosynthèse. Cette étude se propose d’élaborer des matériaux capables d’absorber la lumière et d’imiter le processus naturel, notamment son schéma énergétique en Z. La création de systèmes inorganiques comportant des hétérojonctions SCp (cathode) - Métal - SCn (anode) a été envisagée pour répondre à la problématique. Deux stratégies de synthèse ont alors été mises au point afin d’élaborer différents photocatalyseurs composite SCp@M/SCn notamment Cu2O@Pt/TiO2. L’évaluation des performances photocatalytiques a permis de révéler les bénéfices apportés par la présence d’hétérojunctions en termes de séparation des charges photogénérées et de sélectivité quant à la production de composés hydrogénocarbonés par photocatalyse. Ces travaux apportent une pierre importante à l’édifice d’un procédé de « photosynthèse artificielle » / An enticing opportunity would consist in using abundant and inexhaustible solar energy to valorise CO2 into fuels. That might answer in an elegant way to environmental and energetic concerns: the global warming due to atmospheric CO2 concentration increase and the dreaded shortage of energy resources. Green plants are able to reduce carbon dioxide into hydrocarbonated compounds and to oxidise simultaneously water into dioxygen by using photosynthesis. This study will focus on the design of materials able to absorb light and to imitate this natural process and more particularly its typical energetic Z-scheme. The chosen strategy is the creation of inorganic systems with SC-p (cathode) - Metal - SC-n (anode) heterojunctions. Two synthesis strategies were elaborated to obtain composite photocatalysts SCp@M/SCn, and more particularly Cu2O@Pt/TiO2. The evaluation of photocatalytic performances reveals heterojunctions benefits in term of charge separation and selectivity for photocatalytic hydrocarbonated compounds production. This study seems to do its bit towards “artificial photosynthesis” process