Ce travail de thèse porte sur la caractérisation à l'échelle du fil unique des propriétés de fils GaN de taille micronique (µfil), en vue du développement d'une technologie de diodes électroluminescentes (LEDs) à base d'une assemblée de µfils GaN crûs par épitaxie en phase vapeur aux organométalliques. Chaque µfil est lui-même une LED constituée d'un cœur de type n et d'une coquille de type p, entre lesquels est insérée une zone active composée de multi-puits quantiques InGaN/GaN. En premier lieu, les propriétés électriques des différentes régions du cœur de type n ont été analysées par des mesures de résistivité à l'échelle du fil unique. Le µfil GaN:Si fortement dopé possède une conductivité électrique jamais rapportée dans le cas de couches planaires comparables. Une approche originale combinant une mesure de résistivité et de propriétés thermoélectriques a alors été développée pour séparer les contributions de la densité d'électrons et de leur mobilité à température ambiante dans ces µfils. Des mesures optiques résolues spatialement de cathodoluminescence (CL) et µRaman confirment ces valeurs de densités d'électrons. Une seconde partie détaille une étude résolue spatialement des jonctions p-n cœur-coquille par des techniques à base d'un faisceau électronique. Sur un µfil clivé, la jonction tridimensionnelle (axiale et radiale) existante dans ces structures est mise en évidence par une cartographie du champ électrique (courant induit par faisceau électronique, EBIC) ou du potentiel électrostatique (contraste de tension des électrons secondaires). Ces techniques renseignent alors sur les niveaux de dopage donneur et accepteur et les longueurs de diffusion des porteurs minoritaires à proximité de la jonction. La cartographie EBIC décrit également l'état d'activation des dopants Mg dans la coquille p-GaN:Mg. Finalement, la combinaison de mesures EBIC et CL avec une étude des propriétés électro-optiques d'un µfil LED, fournit des voies d'optimisation pour la réalisation de LEDs à base de µfils plus efficaces. / This thesis deals with the characterization of GaN microwires (µwires) at the single wire level,toward the development of a light-emitting diode (LED) technology based on an ensemble of standing GaN µwires grown by metal organic vapour phase epitaxy. Each µwire is actually an LED consisting of an n-type core and a p-type shell, between which an InGaN/GaN multiquantum well active region is inserted. First, the electrical properties of the different parts of the n-type core were determined using resistivity measurements at the single wire level. The GaN:Si µwire exhibits conductivity values never reported by the planar layer counterparts. An original technique combining resistivity and thermoelectric measurements was developed to infer the electron density and mobility in these µwires. Spatially resolved optical measurements such as cathodoluminescence (CL) and µRaman confirmed the electron density values. The second part describes a spatially resolved study of the core-shell p-n junction using electron beam probing techniques. On a cleaved wire, the tridimensional (axial and radial) junction was highlighted by mapping the electric field (electron beam induced current, EBIC) or the electrostatic potential (secondary electron voltage contrast). These techniques yielded the donor and acceptor doping levels as well as the minority carriers diffusion lengths in the vicinity of the junction. EBIC mapping also provided the activation state of Mg dopants in the p-GaN:Mg shell. Finally, a study of the electro-optical properties of a single µwire LED, combined with EBIC and CL measurements, paves the way to the fabrication of more efficient µwire-based LED.

Phosphorus plays a crucial role in modern p-block chemistry.1 One reason for that is the diagonal relationship between phosphorus and carbon.2 Comparable to carbon and its chemistry, phosphorus tends to form homoatomic bonds, which is explainable by the relatively high P–P single bond energy (ca. 200 kJ/mol).3 Thus, a plethora of poly-phosphorus compounds are reported in the last decades comprising of fascinating bonding motifs4 and interesting applications in coordination5-7 and synthetic8-11 chemistry, as well as in ligand design.12,13 A crucial point in the chemistry of polyphosphanes is of course the formation of P–P bonds. Numerous synthetic procedures are established and reviewed including salt metathesis,4a,14 dehalosilylation15 and dehalostannylation16 reactions, base promoted dehydrohalogenation reactions17 and dehydrogenative coupling reactions mediated by main group compounds18 or catalysis by transition metals.5,19 Moreover, dialkylamino-substituted phosphanes are used in condensation reactions to form P–P bonds since the early 1960’s. Yet these reactions need elevated temperatures, somewhat limiting the formation of polyphosphorus compounds as stated by the few examples reported.17d,20 The application of pyrazolyl-substituted phosphanes in P–P bond formation reactions is a relatively young field of research.21 Their synthesis and general chemical behavior as well as advantages in comparison to dialkylamino-substituted phosphanes is discussed in the following chapter.

Carbon based nanostructures, such as fullerenes, carbon nanotubes and graphene showed a high potential for a vast of electronic and energy applications. However, properties of such materials in pristine forms can be insufficient to satisfy diverse specific demands, and tailoring their intrinsic properties is of increasing importance. In this work, different types of single-walled carbon nanotubes (SWCNTs) with controlled semiconducting fractions are p-/n-type doped by chemical doping in an attempt to tailor physical properties of the SWCNTs for the use in flexible thermoelectric (TE) devices and thermoplastic polymer-based conducting composites. Several p-/n-type doping schemes and an electronic type separation strategy have been developed to fulfill the task. A complete solution for efficient and scalable production of doped SWCNTs for the fabrication of flexible thermoelectric components is developed in this work. For p-type doping, a combined experimental and theoretical work demonstrates that boron atomic doping is an efficient way to simultaneously improve Seebeck coefficient (S) and electrical conductivity (σ) of SWCNT films, showing an increased thermoelectric power factor (S2σ) up to 255 μW/mK2 by a factor of 2.5 comparing to the pristine SWCNTs. For n-type doping, treatment of SWCNTs with potassium oxide and crown ether solution lead to a negative Seebeck coefficient of -30 μV/K and a promising S2σ up to 50 μW/mK2. A gel chromatography method has been developed to separate large-diameter (1.2-1.8nm) SWCNTs by electronic properties and to increase the purity of the sorted semiconducting carbon nanotubes (sc-SWCNTs) up to 95%. Effects of p-/n-type doping induced by different plasma treatments on the thermoelectric properties have been investigated for thin films made of sorted sc-SWCNTs. The high-purity sc-SWCNTs show significantly improved S of 125 μV/K. As the effects of p-type doping, air plasma treatments with proper duration (40s) lead to the increase of S, σ and thus S2σ up to 190 μW/mK2. The n-type doping for the SWCNT films have been performed via ammonia plasma treatment, and a negative S value of -80 μV/K has been achieved in air at 110oC, which is one of the best values ever reported for n-type carbon nanotube films. A flexible thermoelectric module was fabricated by printing ink made of the prepared boron doped SWCNTs and an organic solvent as an example for producing efficient all-carbon thermoelectric generators. At a temperature difference ΔT=60 K, the output voltage reaches 20 mV and the power output of 400 nW is obtained, although no “n”-legs are used in this module. At last, a work has been done on the development of melt mixed composites as TE materials, in which polypropylene is used as the matrix and boron-doped SWCNTs are used as conducting fillers. A percolation threshold lower than 0.25wt. % and a maximum conductivity up to 125 S/m at 5wt. % of SWCNT load have been achieved. The maximum conductivity is more than two times higher than that of the composites made with pristine SWCNTs as fillers.

[pt] Heteroestruturas sensíveis à luz solar possuem grande potencial em diferentes aplicações direcionadas a um futuro limpo e sustentável, como a fotoprodução de hidrogênio (H2) e a remediação ambiental. No contexto da fotocatálise, o dióxido de titânio (TiO2) desempenha um papel crucial devido à sua ampla gama de aplicações, excelente estabilidade química, baixa toxicidade e custo relativamente baixo. No entanto, o TiO2 puro possui algumas desvantagens, como uma alta taxa de recombinação e baixa sensibilidade à luz solar, o que limita sua eficiência em aplicações fotocatalíticas. Portanto, o desenvolvimento contínuo de novos materiais com o objetivo de superar essas desvantagens é obrigatório. Entre as abordagens reportadas para superar as deficiências do TiO2 puro está a formação de heterojunções com outros semicondutores, melhorando a separação de cargas e, portanto, a eficiência fotocatalítica. Óxidos de níquel e óxidos de cobre são relatados como alternativas promissoras para a formação de heterojunções com TiO2, melhorando a transferência de carga e aumentando a absorção de luz no espectro visível do TiO2 puro. Esta tese apresenta diferentes estudos voltados para a síntese e caracterização de novos nanomateriais heteroestruturados eficientes para geração fotocatalítica de hidrogênio e degradação de poluentes perigosos. No primeiro estudo, foi relatada uma heterojunção p-n de NiO/TiO2 obtida via mecanoquímica, que apresentou uma taxa elevada de fotoprodução pelo sol de H2 em comparação com o TiO2 puro (8.85 mmol h-1 g-1 vs. 0.73 mmol h-1 g-1). Em todos os casos, a adição de NiO suportado em TiO2 reduziu a taxa de recombinação e aumentou a absorção de luz visível. Estudos de TEM, XPS e XAS demonstraram que uma dispersão homogênea e uma configuração de spin favorável dos pequenos aglomerados de NiO suportados em TiO2 foram responsáveis pela eficiência superior exibida pela amostra preparada via mecanoquímica, denominada NiO/P90- BM. Notavelmente, testes de ciclagem, de longo prazo e de envelhecimento mostraram que o fotocatalisador relatado é eficiente após vários ciclos, para uso prolongado e após longos períodos de armazenamento. Além disso, foram realizados estudos combinando EPR e a técnica de captura de spin para aprofundar na produção de superóxido e hidroxila pelas heterojunções de NiO/TiO2. Esses estudos forneceram insights sobre a aplicação potencial das heterojunções de NiO/TiO2 para a degradação fotocatalítica de poluentes gasosos e aquosos. Os resultados de EPR lançaram luz sobre a amostra de NiO/P90-BM como a mais eficiente na fotogeração de ROS, revelando que a síntese mecanoquímica resultou em uma arquitetura mais eficiente para a geração de radicais superóxido e hidroxila. Finalmente, foi relatada uma rota simples de química branda para preparar uma heteroestrutura de nanocubos de óxido cúprico (Cu2O NCs) e TiO2, denominada Cu2O NCs/TiO2, como um adsorvente eficiente para a tetraciclina (TC), que é um antibiótico de amplo espectro. FTIR e TGA foram realizados antes e após o processo de adsorção para demonstrar a adsorção de TC pela heteroestrutura Cu2O NCs/TiO2. Além disso, foram realizados testes com irradiação de luz visível para distinguir entre os processos de remoção por adsorção e fotocatalítica. Além disso, foram realizadas medições de EPR usando captura de spin para investigar a fotoprodução de ROS. Curiosamente, não houve fotoprodução de ROS detectável pela heteroestrutura Cu2O NCs/TiO2, demonstrando que a remoção de TC é exclusivamente devido à adsorção. Estes resultados contribuem para esclarecer uma discrepância na literatura quanto à atividade fotocatalítica dos Cu2O NCs sob luz visível. Coletivamente, esta pesquisa avançou o entendimento dos mecanismos fotocatalíticos e relatou novos nanomateriais heteroestruturados, destacando seu potencial para aplicações sustentáveis em diversos contextos relacionados ao meio ambiente e transição energética. / [en] Solar light-responsive heterostructures hold great potential in different applications toward a clean and sustainable future, such as hydrogen (H2) photoproduction and environmental remediation. In the context of photocatalysis, titanium dioxide (TiO2) plays a crucial role due to its wide range of applications, excellent chemical stability, low toxicity, and relatively low cost. However, neat TiO2 has some shortfalls, such as a high recombination rate and low sensitivity to solar light, which limits its efficiency in photocatalytic applications in general. Therefore, the continuous development of new materials aimed at improving these limitations is mandatory. Among the approaches to overcome the neat TiO2 shortfalls is the formation of heterojunctions with suitable semiconductors, improving charge separation and, therefore, photocatalytic efficiency. Nickel oxides and copper oxides are reported as promising alternatives for forming heterojunctions with TiO2, enhancing the charge transfer and broadening the light absorption in the visible spectrum. This thesis presents different studies aimed at the synthesis and characterization of new efficient heterostructured nanomaterials for photocatalytic hydrogen generation and hazardous pollutants abatement. In the first study, a NiO/TiO2 p-n heterojunction obtained via mechanochemistry was reported, which exhibited an improved solar-driven H2 photoproduction rate compared to neat TiO2 (8.85 mmol h-1g-1vs. 0.73 mmol h-1g-1). In all cases, the addition of NiO supported on TiO2 reduced the recombination rate and enhanced the visible light absorption. TEM, XPS, and XAS studies demonstrated that a homogenous dispersion and a favorable spin configuration of NiO clusters supported on TiO2 were responsible for the superior efficiency exhibited by the sample prepared via mechanochemistry, labeled as NiO/P90-BM. Noticeably, cycling, long-term, and aging tests have shown that the reported photocatalyst is efficient after several cycles, prolonged use, and after long periods of storage. Furthermore, studies combining EPR and the spin trapping technique were carried out to delve into the production of superoxide and hydroxyl by NiO/TiO2 heterojunctions. These studies provided insights into the potential application of the NiO/TiO2 heterojunctions for the photocatalytic degradation of gaseous and aqueous pollutants. The EPR results shed light on the NiO/P90-BM sample as the most efficient in ROS photogeneration, revealing that mechanochemical synthesis resulted in a more efficient architecture for generating superoxide and hydroxyl radicals. Besides, a simple soft chemistry route was reported to prepare a heterostructure of cuprous oxide nanocubes (Cu2O NCs) and TiO2, labeled as Cu2O NCs/TiO2, as an efficient adsorbent for tetracycline (TC), which is a broad-spectrum antibiotic. FTIR and TGA were carried out before and after the adsorption process to demonstrate the adsorption of TC by the Cu2O NCs/TiO2 heterostructure. Additionally, tests with visible light irradiation were performed to distinguish between adsorption and photocatalytic removal processes. In addition, EPR measurements were also carried out using spin trapping to investigate the ROS photoproduction. Interestingly, there was no detectable ROS photoproduction by the Cu2O NCs/TiO2 heterostructure, demonstrating that TC removal is solely due to adsorption. These results contribute to clarifying a discrepancy in the literature regarding the photocatalytic activity of Cu2O NCs under visible light. Collectively, this research has advanced the understanding of photocatalytic mechanisms and reported new heterostructured nanomaterials, while highlighting their potential for sustainable applications in diverse environmental and energy transition related contexts.

Experimental studies presented in this thesis have shown the first realisation of resonant tunnelling transport through two impurities in a vertical double-barrier tunnelling diode; have proved the chiral nature of charge carriers in graphene by studying ballistic transport through graphene $p$-$n$ junctions; have demonstrated significant differences of $1/f$ noise in graphene compared with conventional two-dimensional systems. Magnetic field parallel to the current has been used to investigate resonant tunnelling through a double impurity in a vertical double-barrier resonant tunnelling diode, by measuring the current-voltage and differential conductance-voltage characteristics of the structure. It is shown that such experiments allow one to obtain the energy levels, the effective electron mass and spatial positions of the impurities. The chiral nature of the carriers in graphene has been demonstrated by comparing measurements of the conductance of a graphene $p$-$n$-$p$ structure with the predictions of diffusive models. This allowed us to find, unambiguously, the contribution of ballistic resistance of graphene $p$-$n$ junctions to the total resistance of the $p$-$n$-$p$ structure. In order to do this, the band profile of the $p$-$n$-$p$ structure has been calculated using the realistic density of states in graphene. It has been shown that the developed models of diffusive transport can be applied to explain the main features of the magnetoresistance of $p$-$n$-$p$ structures. It was shown that $1/f$ noise in graphene has much more complicated concentration and temperature dependences near the Dirac point than in usual metallic systems, possibly due to the existence of the electron-hole puddles in the electro-neutrality region. In the regions of high carrier concentration where no inhomogeneity is expected, the noise has an inverse square root dependence on the concentration, which is also in contradiction with the Hooge relation.

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

The aim of this thesis is to answer whether a group of databases dedicated to selling books or a group of databases dedicated to lending books is more efficient. The measurements used to determine the efficiency of the two kinds of databases are Cumulated Gain and precision in modified versions. The inquiry has been conducted thus that the same 18 queries have been put forth to six databases and these results have consequently been judged according to relevance on a 4-graded scale by five respondents. The rankinglevels have then been merged to one average value per respondent and ranking. These values have then been used to determine CG/iCG/nCG and P@n per query, rank 1-10, per database and per group (the groups being STORE (BUTIK) and LIBRARY (BIBLIOTEK). To measure precision the relevance rankings were merged into binary values representing not relevant and relevant. These ones and zeros have then been used to judge precision per rank 1-10, per database and per group. The precision values regarding individual databases have been calculated for comparison against the average values of the entire groups BUTIK & BIBLIOTEK.No significant differences in efficiency between STORE and LIBRARY were observed at DCV=10 although differences were obvious at positions 1-10 and between individual databases. The method is unsuccessful in answering whether the purpose of a database is a factor in how well it performs in regards to efficiency / Program: Bibliotekarie

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Chiral pyridines as organocatalysts have been used in asymmetric organic synthesis in recent years. The asymmetric synthesis of camphor fused pyridine type novel organocatalysts were perfomed starting from cheap and easily available natural (+)-camphor. Using camphor fused pyridine skeleton, six organocatalysts 29, 32, 33, 38, 40, and 41were successfully synthesized. The first four nucleophilic and Lewis base catalysts 29, 32, and 33 are different P-oxides and P,N-dioxides which were tested in allylation of aldehydes via allyltrichlorosilane. L-proline amide 38 and D-proline amide 40 can be named as secondary amine catalyst. They were tested in direct aldol reaction between acetone and aromatic aldehydes in aqueous medium. Final group of catalyst is hydrogen bonding type catalyst which is thiourea based 41.

O conhecimento da física de semicondutores foi usado para desenvolver e otimizar um sensor ótico de silício capaz de determinar com precisão a posição bidimensional de incidência de um feixe de luz em sua superfície. O sensor usa o efeito de fototensão lateral para gerar um sinal elétrico de saída que é função da posição de incidência da luz. Tecnologia planar do silício foi usada na fabricação do dispositivo, incluindo implantação iônica, difusão, fotolitografia, deposição de filmes metálicos e crescimento de dielétricos. A caracterização elétrica do sensor inclui medidas estáticas, com a distribuição de portadores em regime estacionário, medidas dinâmicas, onde é analisado o transiente do sinal elétrico e medidas espectroscópicas para analisar a resposta do sensor em função do comprimento de onda da luz incidente. Simulações dos processos de fabricação, parâmetros dos passos tecnológicos, distribuição dos portadores e do potencial elétrico bidimensional no sensor foram usadas para a otimização das características do sensor.