Rozprawy doktorskie na temat „CUO NANOSTRUCTURES”

Orientador: Marcelo Ornaghi Orlandi
Banca: Anderson Andre Felix
Banca: Valmor Roberto Mastelaro
Banca: Luis Vicente de Andrade Scalvi
Banca: Rosario Elida Suman Bretas
Resumo: Neste trabalho, as propriedades sensoras de gás de nanoestruturas de óxido de estanho puras (SnO2) e híbridas (SnO2-Pt, SnO2-CuO e SnO2-CuO-Pt) foram estudadas na presença de diferentes gases. Os materiais foram sintetizados pelo método de electrospinning seguido por tratamento térmico e, posteriormente, foram caracterizados por termogravimetria (TG), difração de raios X (DRX), microscopia eletrônica de varredura com emissão por campo (MEV-FEG), microscopia eletrônica de transmissão (MET), espectroscopia por dispersão em energia de raios X (EDS), microscopia de força atômica (AFM) e área de superfície específica e porosidade (BET). O foco principal do trabalho foi analisar a resposta dos materiais sintetizados como sensores de gás para a detecção de gases tóxicos e inflamáveis em baixas concentrações e em uma temperatura de operação de 300 °C. Os resultados obtidos a partir das caracterizações estruturais e morfológicas mostraram que o método de electrospinning permite a obtenção de materiais unidimensionais (1D) policristalinos com elevada homogeneidade morfológica e pureza cristalina. Além disso, os elementos químicos presentes nas estruturas de cada material sintetizado foram mapeados e identificados, onde verificou-se que todos os elementos estão homogeneamente distribuídos ao longo da estrutura das fibras. As características superficiais dos materiais, tais como rugosidade e porosidade também foram estudadas e os resultados indicaram que, dependendo da composição química... (Resumo completo, clicar acesso eletrônico abaixo)
Doutor

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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)
Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)
Neste trabalho, as propriedades sensoras de gás de nanoestruturas de óxido de estanho puras (SnO2) e híbridas (SnO2-Pt, SnO2-CuO e SnO2-CuO-Pt) foram estudadas na presença de diferentes gases. Os materiais foram sintetizados pelo método de electrospinning seguido por tratamento térmico e, posteriormente, foram caracterizados por termogravimetria (TG), difração de raios X (DRX), microscopia eletrônica de varredura com emissão por campo (MEV-FEG), microscopia eletrônica de transmissão (MET), espectroscopia por dispersão em energia de raios X (EDS), microscopia de força atômica (AFM) e área de superfície específica e porosidade (BET). O foco principal do trabalho foi analisar a resposta dos materiais sintetizados como sensores de gás para a detecção de gases tóxicos e inflamáveis em baixas concentrações e em uma temperatura de operação de 300 °C. Os resultados obtidos a partir das caracterizações estruturais e morfológicas mostraram que o método de electrospinning permite a obtenção de materiais unidimensionais (1D) policristalinos com elevada homogeneidade morfológica e pureza cristalina. Além disso, os elementos químicos presentes nas estruturas de cada material sintetizado foram mapeados e identificados, onde verificou-se que todos os elementos estão homogeneamente distribuídos ao longo da estrutura das fibras. As características superficiais dos materiais, tais como rugosidade e porosidade também foram estudadas e os resultados indicaram que, dependendo da composição química das fibras, estruturas com diferentes níveis de rugosidade e área superficial podem ser obtidas. Medidas elétricas na presença de NO2, CO, H2, e CH4 mostraram que todos os materiais exibem comportamento de semicondutor do tipo-n e resposta sensora dependente da concentração do gás analito. As fibras de SnO2 e SnO2-Pt exibiram maior resposta sensora para a detecção de NO2 enquanto as fibras de SnO2-CuO e SnO2-CuO-Pt tiveram maior resposta na presença de H2, além de elevada seletividade para H2 em relação ao CH4. Em geral, os resultados obtidos mostram que os materiais produzidos são bastante promissores e têm grande potencial para serem estudados detalhadamente como sensores de gás.
In this work, the gas sensing properties of pure (SnO2) and hybrid (SnO2-Pt, SnO2-CuO and SnO2-CuO-Pt) tin oxide nanostructures were studied in the presence of different analyte gases. Materials were synthesized by electrospinning method followed by thermal treatment and subsequently characterized by thermogravimetry (TG), X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS), atomic force microscopy (AFM) and specific surface area and porosity (BET). The main focus of the work was to analyze the gas sensor response of the synthesized materials for the detection of toxic and flammable gases in low concentrations at 300 °C. The results from the morphological and structural characterizations by XRD, SEM and TEM showed the electrospinning method allows obtaining polycrystalline 1D materials with high morphological homogeneity and crystalline purity. Furthermore, the chemical elements present in the structures of each synthesized material and it was found that all elements are homogeneously distributed throughout the fiber structures. The surface characteristics of materials, such as roughness and porosity were also studied and the results indicated that depending on the chemical composition of the fibers, structures with different levels of roughness and surface area can be obtained. Electrical measurements in the presence of NO2, H2, CO and CH4 were performed in order to verify the gas sensor properties of the nanostructures, and results showed that all materials exhibit n-type semiconducting behavior and the sensor response to be dependent on the analyte gas concentration. The SnO2 and SnO2-Pt fibers showed higher sensor response to NO2 detection while SnO2-CuO and SnO2-CuO-Pt fibers presented greater sensitivity for H2 as well as high selectivity to H2 compared to CH4. In general, the results showed that the produced materials are very promising and have high potential to be studied in detail as gas sensors materials.
FAPESP: 2012/11139-7

One dimensional (1-D), zinc oxide (ZnO) and copper (II) oxide (CuO), nanostructures have great potential for applications in the fields of optoelectronic and sensor devices. Research on nanostructures is a fascinating field that has evolved during the last few years especially after the utilization of the hydrothermal growth method. Using this method variety of nanostructures can be grown from solutions, it is a cheap, easy, and environment friendly approach. These nanostructures can be synthesized on various conventional and nonconventional substrates such as silicon, plastic, fabrics and paper etc. The primary purpose of the work presented in this thesis is to realize controllable growth of ZnO, CuO and nanohybrid ZnO/CuO nanostructures and to process and develop white light emitting diodes and sensor devices from the corresponding nanostructures. The first part of the thesis deals with ZnO nanostructures grown under different hydrothermal conditions in order to gain a better understanding of the growth. Possible parameters affecting the growth such as the pH, the growth temperature, the growth time, and the precursors  concentration which can alter the morphology of the nanostructures were investigated (paper 1). Utilizing the advantage of the low temperature for growth we synthesized ZnO nanostructures on different substrates, specifically on flexible substrates, which are likely to be integrated with flexible organic substrates for future foldable and disposable electronics (paper 2, 3). In the second part of the thesis, using the results and findings from the growth of ZnO nanostructures, it was possible to successfully implement ZnO nanostructures for white light emitting diodes (LEDs) on different flexible substrates (paper 4, 5). In paper 4 we realized a ZnO/polymer LED grown on a paper substrate. In paper 5 we extended the idea to print the ZnO nanorods/polymer hybrid LEDs with potential application to large area flexible displays. In the last part of the thesis, CuO and nanohybrid ZnO/CuO nanostructures were utilized to fabricate Ag+ detection and humidity sensors. In paper 6 we reported Ag+ selective electrochemical sensor based on the use of functionalized CuO nanopetals. To combine the advantages of both oxides nanostructures and to improve the performance we fabricated a pn-heterojuction using intrinsic n-ZnO nanorods and p-CuO nanostructures which were then utilized as an efficient humidity sensor (paper 7).

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

Research on nanomaterials has become increasingly popular because of their unique physical, chemical, optical and catalytic properties compared to their bulk counterparts. Therefore, many efforts have been made to synthesize multidimensional nanostructures for new and efficient nanodevices. Among those materials, zinc oxide (ZnO), has gained substantial attention owing to many outstanding properties. ZnO besides its wide bandgap of 3.34 eV exhibits a relatively large exciton binding energy (60 meV) at room temperature which is attractive for optoelectronic applications. Likewise, cupric oxide (CuO), having a narrow band gap of 1.2 eV and a variety of chemo-physical properties that are attractive in many fields. Moreover, composite nanostructures of these two oxides (CuO/ZnO) may pave the way for various new applications. This thesis can be divided into three parts concerning the synthesis, characterization and applications of ZnO, CuO and their composite nanostructures. In the first part the synthesis, characterization and the fabrication of ZnO nanorods based hybrid light emitting diodes (LEDs) are discussed. The low temperature chemical growth method was used to synthesize ZnO nanorods on different substrates, specifically on flexible non-crystalline substrates. Hybrid LEDs based on ZnO nanorods combined with p-type polymers were fabricated at low temperature to examine the advantage of both materials. A single and blended light emissive polymers layer was studied for controlling the quality of the emitted white light. The second part deals with the synthesis of CuO nanostructures (NSs) which were then used to fabricate pH sensors and exploit these NSs as a catalyst for degradation of organic dyes. The fabricated pH sensor exhibited a linear response and good potential stability. Furthermore, the catalytic properties of petals and flowers like CuO NSs in the degradation of organic dyes were studied. The results showed that the catalytic reactivity of the CuO is strongly depending on its shape. In the third part, an attempt to combine the advantages of both ZnO and CuO NSs was performed by developing a two-step chemical growth method to synthesize the composite NSs. The synthesized CuO/ZnO composite NSs revealed an extended light absorption and enhanced defect related visible emission.

La diminution des dimensions d’un système physique amène l’apparition de nouveaux phénomènes quantiques. C’est pourquoi on retrouve un intérêt croissant, tant dans le domaine fondamental qu’appliqué pour la fabrication de composants de plus en plus petits. Ce travail suit donc cette tendance en présentant une étude des propriétés de transport en fonction de la dimension du système dans le domaine sub-micrométrique d’échantillons de Pr[indice inférieur 2-x]Ce[indice inférieur x]CuO[indice inférieur 4+δ]. On sait déjà que des techniques de nanofabrication de composants électroniques ont été adaptées aux couches minces de matériaux supraconducteurs par plusieurs groupes de recherche. Elles n’ont, par contre, jamais été reproduites sur des couches de cuprates dopés aux électrons dont fait partie le composé Pr[indice inférieur 2-x]Ce[indice inférieur x]CuO[indice inférieur 4+δ]. Nous avons donc repris une technique de nanofabrication éprouvée pour les couches minces d’YBaCuO en espérant qu’elle conviendrait aussi à notre composé. La comparaison des propriétés de transport des systèmes nanométriques avec des échantillons macroscopiques a permis une étude des impacts de cette technique de fabrication sur notre composé. Les étapes de gravure par faisceau d’ions et d’immersion dans un plasma d’oxygène ont été pointées du doigt comme ayant un effet sur les propriétés de transport du composé. On a ainsi mis en évidence que la nanofabrication affectait la stoechiométrie de notre matériau en modifiant sa concentration en oxygène. Outre l’analyse du procédé de nanofabrication, il a été possible d’observer l’incidence qu’a la direction du courant injecté par rapport aux axes cristallins sur certaines propriétés de transport dont la magnétorésistance. De plus, les conséquences de la nanofabrication sur la stoechiométrie du composé ont été analysées par des mesures d’effet Hall.

Всі відомі оксиди в нелегованому стані мають електронний тип провідності, що утруднює створення гетеропереходів на їх основі, які є обов'язковою складовою більшості приладів електроніки. Саме тому важливим є отримання та вивчення властивостей плівок оксидних матеріалів, що мають р-тип провідності, до яких зокрема відноситься оксид міді. У порівнянні з іншими методами отримання плівок оксиду міді, спрей-піроліз не вимагає дорогого вакуумного обладнання, високоякісних підкладок, забезпечує великі швидкості нанесення шарів на підкладках великої площі з різних прекурсорів. Тому, метою роботи стало вивчення властивостей плівок оксиду міді, нанесених методом пульсуючого спрей-піроліза.

100 años después de que el físico holandés Heike Kamerlingh Onnes descubriera que el mercurio tiene una resistencia eléctrica igual a cero, cuando se enfría en el helio líquido, los superconductores son lanzados finalmente para su uso en las redes eléctricas. Los cables superconductores pueden transportar diez veces más energía que el mismo volumen de los cables convencionales de cobre. Aunque parte de esta energía se pierde (pérdidas de corriente alterna) y se necesita usar el nitrógeno líquido para enfriar los cables superconductores y otros dispositivos, tales sistemas de energía son mucho más eficientes que las basadas en cableado de cobre, donde las pérdidas de potencia, alrededor de 7-10%, son en forma de calor. Debido a esto, países como EE.UU., Japón, Corea del Sur, China y Europa han establecido objetivos para las redes "verdes" de electricidad, reduciendo la generación de gases de efecto invernadero (CO2) y construyendo "redes inteligentes" basadas en superconductores más eficientes y robustos. Los cables superconductores de alta temperatura están hechos de un óxido de itrio, bario, cobre (YBCO) que forma parte de la familia de las cerámicas superconductoras de “alta temperatura”, descubiertas por primera vez en 1986. Las perspectivas atractivas ofrecidas por los conductores recubiertos (Coated Conductors), conocidos como la 2 ª generación de superconductores de alta temperatura (2G-HTS), han dado lugar a amplios y fructíferos esfuerzos de investigación y desarrollo para que estos sean preparados para el mercado [2]. Recientemente, LS Cable, una compañía de Corea del Sur con sede en Anyang-si, cerca de Seúl, ha ordenado tres millones de metros de cable superconductor de la firma American Superconductor desde EE.UU., en Devens, Massachusetts, que es el más alto pedido comercial de HTS CC hasta el momento [1] . Los superconductores de alta temperatura (HTS) tienen un enorme potencial para mejorar significativamente los sistemas de energía existentes, tales como cables, motores, transformadores, imanes y generadores, debido a que se puede alcanzar una mayor densidad de energía y se pueden reducir las pérdidas, comparado con los cables de cobre o cables superconductores de baja temperatura [3]. Los materiales superconductores abren tecnologías completamente nuevas en el sector de la energía, tales como limitadores de corriente o de levitación magnética inherentemente estable. Como ejemplos de aplicaciones innovadoras, deben ser mencionados sistemas avanzados de energía para barcos "all-electrical", molinos de viento en la costa y sistemas de transporte. Aunque la investigación sobre materiales HTS ha tenido mucho éxito en el pasado, el desarrollo de materiales superconductores de bajo coste sigue siendo un factor clave de éxito y, a fin de traer estos materiales emergentes en el mercado en un plazo razonable, requiere una investigación de materiales mucho más básica y aplicada. El objetivo principal de esta tesis, es el desarrollo de nuevas arquitecturas simplificadas nanoestructuradas de Coated Conductors, basadas en la deposición de soluciones químicas (CSD). Para ello, el crecimiento y la caracterización de estos Coated Conductors, se ha investigado primero sobre monocristales de YSZ, donde el CeO2 se puede crecer fácilmente como tapa tampón. El conocimiento generado puede ser útil para dos tipos de sustratos metálicos: 1.- sustratos Ni5%W RABiTS con MODLZO como capa tampón; 2.- sustratos policristalinos de Stainless Steel (SS) con ABADYSZ como capa tampón. Teniendo en cuenta la calidad de los sustratos metálicos existentes, esta tesis se ha concentrado en los sustratos policristalinos de Stainless Steel (SS), enviados por la empresa alemana Bruker HTS. El primer paso para obtener arquitecturas simplificadas fue la investigación del oxido de cerio dopado con Gd y Zr que mejor se adapta a los sustratos mencionados. El segundo paso consistió en crecer películas delgadas superconductoras de YBa2Cu3O7-x, con la ruta de los trifluoracetatos. Este trabajo comienza con una breve descripción de la superconductividad, seguido por una breve introducción sobre el compuesto superconductor YBCO y termina con los principales métodos para la obtención de películas de YBCO texturadas de alta calidad. Una caracterización completa de las muestras con diversas técnicas (Microscopía de fuerza atómica (AFM), Difracción de rayos X (DRX), Microscopía Electrónica de Barrido (SEM), Microscopía Electrónica de Transmisión (TEM), Difracción de electrones rasantes (RHEED), Deposición con láser pulsado (PLD), SQUID, Reflectividad de rayos X (XRR) y medidas eléctricas de transporte) es necesaria para comprender el mecanismo complejo de cada superconductor y las interacciones entre las diferentes capas. Han sido investigadas varias películas de óxido de cerio dopado usado como capa tampón superior, preparadas por spin coating. Los requisitos técnicos para obtener Coated Conductors de alta calidad son muy diversos. Para lograr una epitaxia de alta calidad y alta Jc, es necesario llevar a cabo una detallada caracterización morfológica y estructural por medio de SEM y DRX. La microestructura de la capa de YBCO debe estar estrechamente correlacionada con la de la capa tampón. Para estudiar más en detalle las propiedades superconductoras, se han realizado medidas inductivas y de transporte para examinar el flujo de corriente en las películas de YBCO depositadas sobre distintos sustratos. Los resultados obtenidos con las capas de CeO2 crecidas sobre ABADYSZ/SS han sido reportados. La última parte de esta tesis está dedicada al desarrollo de películas delgadas de materiales nanocompuestos de MODBaZrO3-YBa2Cu3O7-x y MODBaCeO3-YBa2Cu3O7-x usando el método químico in-situ. El zirconato de bario (BZO) es el material más atractivo para inducir centros de pinning artificiales en las películas delgadas de YBCO, con el fin de aumentar la densidad de corriente crítica. Una caracterización detallada de los nanocompuestos de BaZrO3 (BZO) crecidos por MOD será presentada a través del SEM, XRD y TEM. Referencias [1] Joseph Milton, "Superconductors come of age," Nature (2010). [2] C. Freyhardt Herbert and et al., "Coated conductors and their applications," Superconductor Science and Technology 23 (1), 010201 (2010). [3] "Nespa - NanoEngineered Superconductors for Power Applications," http://www.ifw-dresden.de/nespa.
100 years after Dutch physicist Heike Kamerlingh Onnes found that mercury has an electrical resistance of zero when cooled in liquid helium, superconductors are finally being rolled out for use in electricity grids. Superconductive wiring carries about ten times as much power as the same volume of conventional copper wiring. Although some of that power is lost (ac losses) and liquid nitrogen must be used to keep cool the superconducting cables or other devices, such power systems are still more efficient than those based on copper wiring, which losses 7-10% of the power it carries as heat. Because of this, several countries, such as USA, Japan, South Korea, China and Europe have established objectives for 'green' electricity networks reducing the greenhouse gas generation (CO2) and build more efficient and robust 'smart grids' based on the superconductors. The high temperature superconducting wires are made based on the ceramic compound yttrium barium copper oxide (YBCO), part of a family of 'high-temperature' superconducting ceramics that were first discovered in 1986. The attractive perspectives offered by coated conductors, known as the 2nd generation of high temperature superconductors (2G-HTS), have triggered broad and fruitful R&D efforts to make them ready for the market place [2]. Recently, LS Cable, a South Korean company based in Anyang-si near Seoul, has ordered three million meters of superconducting wire from the US firm American Superconductor in Devens, Massachusetts, which is the highest commercial order so far of HTS CC [1]. High Temperature Superconductors (HTS) have an enormous potential for significantly improving existing power systems, such as cables, motors, transformers, magnets and generators, because higher power densities and reduced losses can be achieved by replacing copper or low temperature superconductor wires [3]. Superconducting materials will also enable completely new technologies in the power sector, such as fault current limiters or inherently stable magnetic levitation. As examples for innovative applications, advanced energy systems for “all-electrical” ships, off-shore windmills and transportation systems should be mentioned. Although research on the materials aspects of HTS has been highly successful in the past, the development of low cost - high performance HTS materials remains a key factor of success and, in order to bring these emerging materials onto the market in a reasonable time frame, requires significantly more basic and applied materials research. The main objective of this thesis is to develop new simplified nanostructured Coated Conductors architectures based on Chemical Solution Deposition (CSD). For that, the growth and characterization of these Coated Conductors was investigated first on YSZ single crystals where CeO2-derived cap layer can be easily grown. The knowledge generated can be useful for two types of metallic substrates: 1.- MODLZO buffered Ni5%W RABiTS substrates; 2.- ABADYSZ buffered Stainless Steel (SS) polycrystalline substrates. Taking into account the quality of the existing metallic substrates, this thesis has been concentrated on ABADYSZ/SS substrates, provided by Bruker HTS, Germany. The first step for achieving simplified architectures was the investigation of Gd,Zr doped CeO2 which better adapts to the mentioned substrates. The second step consisted in growing YBa2Cu3O7-x superconducting films using the trifluoracetates route. This work starts with a brief description of the superconductivity, followed by a short introduction about the superconductive compound YBCO and ends with the principal methods for obtaining high quality textured YBCO films. A complete characterization of the samples with various techniques (Atomic Force Microscopy (AFM), X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Reflection High-Energy Electron Diffraction (RHEED), Pulsed Laser Deposition (PLD), SQUID, X-ray reflectivity (XRR) and electrical transport measurements) is necessary in order to understand the complex mechanism of each superconductor and the interactions between different layers. Various doped cerium oxide thin films used as cap layer, prepared by spin coating were also investigated. The technical requirements for high quality Coated Conductors are very diverse. To achieve a high quality epitaxy and high Jc, it is necessary to perform a detailed morphological and structural characterization by means of SEM and XRD. This microstructure of the YBCO layer needs to be closely correlated with that of the cap layer. In order to study the superconducting properties in more detail, inductive and transport measurements have been performed to examine current flow in YBCO films deposited on different substrates. The results obtained with CeO2-derived cap layers grown on Alternating Beam Assisted Deposition (ABAD) substrates were also reported. Last part of this thesis is dedicated to the development of BaZrO3-YBa2Cu3O7-x and BaCeO3-YBa2Cu3O7-x nanocomposites thin films by MOD using the in-situ approach. Barium zirconate is the most attractive material to induce artificial pinning centers both in YBCO thin films, in order to increase the critical current density. Detailed characterization by SEM, XRD and TEM of BaZrO3 (BZO) nanocomposite grown by MOD will be presented. References [1] Joseph Milton, "Superconductors come of age," Nature (2010). [2] C. Freyhardt Herbert and et al., "Coated conductors and their applications," Superconductor Science and Technology 23 (1), 010201 (2010). [3] "Nespa - NanoEngineered Superconductors for Power Applications," http://www.ifw-dresden.de/nespa.

Nowadays, everyone feels the impact of nanotechnology in his life. There is a trend that urges people to revisit many research areas with a nano-view, in order to understand how the same thing can work at nano- level. This phenomenon is revolutionizing pharmaceutical sciences and many drugs are being reformulated for possibilities of delivering as a nanosystem. In recent years, a particular attention has been focused on new generations of lipid nanoparticles such as nanostructured lipid carriers (NLC), a second generation of solid lipid nanoparticles (SLN), and monoolein aqueous dispersions (MAD), derived from the mesophases originated from the system monoolein/water/poloxamer. In this thesis different NLC, SLN or MAD formulations were developed as drug delivery systems specifically for antiparkinson or antimycotic drugs, in order to prolong their action and reduce the side effects. Bromocriptine (BC), new synthetized L-DOPA derivatives (Der-A, Der-B, Der-C and Der-D) or Clotrimazole (CLO) have been alternatively chosen as model drugs. Physical and chemical characterizations have been performed on the obtained formulations. In vitro and in vivo studies permitted to obtain release kinetics and evaluate the effectiveness of nanoparticulate systems. BC containing NLC and MAD showed high entrapment efficiency and X-ray diffraction analyses demonstrated that the presence of BC did not affect the scattering profile. In this case, different in vitro experimental approaches were evaluated, showing that the in vitro release of poorly water soluble drugs (as BC) is more affected by the composition of the receiving phase (i.e. in term of presence of water miscible polar organic solvents) rather than by the experi modality adopted for the in vitro determinations. In vivo studies demonstrated that only BC-NLC were able to markedly attenuate motor deficit in 6-OHDA hemilesioned rats, suggesting that NLC represent a more effective carrier to prolong the half-life of BC in vivo. All L-DOPA derivatives were successfully incorporated in NLC. The produced formulations resulted homogeneous in terms of size and remain stable until two months from the preparation. Morphological characterization highlighted that no substantial difference characterized empty and derivatives containing NLC. In vitro kinetics release highlighted that NLC were able to release the contained derivatives in a controlled manner and permit to select Der-A for in vivo tests. In vivo tests demonstrated that the Der-A possess antiparkinson activity. The inclusion of Der-A in SLN, performed using three different concentrations of prodrug, showed different entrapment efficiencies depending on the quantity of active employed. Calorimetric test evidenced an effective interaction between lipid phase and the prodrug. In vitro studies demonstrated a controlled release of Der-A from SLN, also thanks to the extension of the half-life of the prodrug. CLO was incorporated both in MAD and in NLC with high recovery. Shelf life stability evidenced that the solid matrix of NLC enabled to control drug degradation better than MAD. In vitro experiments on candida cells demonstrated that CLO-MAD and CLO-NLC exhibit a higher activity than the free drug. The gelification of CLO containing nanoparticles permitted to obtain formulations able to remain on the mucosa surface. Micro calorimetric assays confirmed that poloxamer formulated gels are able to change their structure, with a rapid passage from liquid to solid (crystalline) form at a temperature lower than vaginal temperature, allowing a selective action in the site of application. Finally it is noteworthy that the production of CLO-NLC poloxamer gel is simple and suitable for industry scaling up.

This work reports the study of semiconductor nanocrystals, also known as quantum dots, focusing specifically on zinc sulfide (ZnS). Two different capping agents were used (glutathione and N-acetyl-L-cysteine) for the preparation of ZnS nanocrystals via aqueous route. The study aimed specifically at evaluating the efficacy of the capping agents in the stabilization of semiconductor nanocrystal suspensions towards coalescence as well as in controlling nanocrystal size and optical properties. In addition the effect of doping the ZnS nanocrystals with transition metal ions (Cu2+ and Co2+) on the photoluminescence properties has also been studied. Finally the possibility of energy transfer between the semiconductor nanocrystals and the safranine dye was also evaluated. Spherical-shaped glutathione and N-acetyl-L-cysteine-capped ZnS nanocrystal were obtained with diameters below 5 nm free from coalescence, showing that both iv capping agents were efficient as stabilizers. Both capping agents lead to the formation of ZnS nancrystals with blue fluorescence, typical of the involvement of surface defect states of ZnS. However, samples prepared with glutathione exhibited higher fluorescence intensities than those obtained with N-acetyl-L-cysteine. Upon doping glutathione-capped ZnS nanocrystals with both copper and cobalt the fluorescence intensities decreased gradually following the increase in nominal concentration of dopants, suggesting that cobalt ions played a similar role as copper. Considering both the effect on the intensities and the absence of d-d metal transitions this study suggests that doping reduced the concentration of cation vacancies as well as the involvement of at least one cobalt state in the transition processes. Changes in emission wavelength with different dopant concentrations were not observed probably owing to lack of influence on the nanocrystal size. Finally the preliminary study of fluorescence quenching of semiconductor nanocrystals by safranine dye indicated that significantly low concentrations were able to quench the emissions. Different components of the emission band were distinctly affected. Data analysis by Stern-Volmer plots suggested the occurrence of more than one transfer processes (energy and/or electron transfer). This study will be refined in future works.
No presente trabalho foram estudados nanocristais semicondutores, tambem conhecidos como pontos quanticos ou quantum dots, selecionando-se especificamente o sulfeto de zinco (ZnS). Foram utilizados ois diferentes agentes estabilizantes (glutationa e N-acetil-L-cisteina) na obtencao de nanocristais de ZnS por via aquosa. Buscou-se avaliar, especificamente, a eficiencia dos agentes tiois na estabilizacao das suspensoes de nanocristais frente a agregacao, no controle e distribuicao de tamanhos das particulas, bem como nas propriedades opticas. Estudou-se, alem disto, o efeito da dopagem com ions de metais de transicao (Cu2+ e Co2+) nas propriedades de fluorescencia. Por fim, foi avaliada a possibilidade de transferencia de energia entre os nanocristais semicondutores dopados e o corante safranina. Os nanocristais semicondutores de ZnS estabilizados por glutationa e por N-acetil-L-cisteina foram obtidos com tamanhos abaixo de 5 nm, formas aproximadamente esfericas e livres de agregacao, evidenciando que ambos agentes ii estabilizantes foram eficientes. Ambos agentes estabilizantes levaram a formacao de nanocristais com emissoes na regiao do azul, caracteristicas do envolvimento de estados de defeito de superficie do ZnS. No entanto, as amostras preparadas com glutationa apresentaram maiores intensidades de fluorescencia, quando comparadas com aquelas preparadas com N-acetil-L-cisteina. A dopagem dos nanocristais semicondutores ZnS/Glu com ions cobre e cobalto teve um efeito de diminuir as intensidades de fluorescencia dependente da concentracao nominal dos dopantes em ambos os casos, sugerindo que o cobalto atua de modo analogo ao cobre. Considerando-se tanto o efeito sobre as intensidades de emissao do ZnS quanto a ausencia de transicoes d-d do metal, o estudo sugeriu que a dopagem reduz a concentracao de vacancias de cations, bem como o envolvimento de pelo menos um dos estados eletronicos do cobalto nos processos de transicao. Nao se observou variacoes nos comprimentos de onda para diferentes concentracoes dos dopantes, provavelmente pela ausencia de interferencia no tamanho dos nanocristais semicondutores formados. Por fim, o estudo preliminar da supressao de fluorescencia dos nanocristais semicondutores pelo efeito de diferentes concentracoes do corante safranina mostrou que concentracoes significativamente baixas do corante foram suficientes para diminuir a intensidade de fluorescencia. Diferentes componentes das bandas de emissao dos nanocristais semicondutores foram influenciados de modo distinto. A analise dos dados pelos graficos de Stern-Volmer sugeriu a ocorrencia de mais de um processo de transferencia (energia e/ou eletrons). Este estudo sera aprofundado nos trabalhos futuros.

Une solution pour limiter les pertes ohmiques résultant de la réduction de la température de fonctionnement des SOFC consiste à élaborer des matériaux d'électrolyte sous forme de couches minces. Dans ce contexte, des couches ultraminces de YSZ et de CGO ont été synthétisées séparément ou sous la forme d'un électrolyte bicouche par dépôt de couches atomiques (ALD) et par pulvérisation cathodique magnétron en condition réactive sur des substrats conducteurs électroniques denses ou poreux. Le dépôt chimique en solution (CBD) a aussi été envisagé comme une technique de dépôt moins onéreuse pour CGO. Les films déposés ont été caractérisés par plusieurs techniques physico-chimiques (microscopie électronique à balayage, diffraction des rayons X, spectrométrie de rayons X à dispersion d'énergie), puis leurs propriétés électriques ont été étudiées par spectroscopie d'impédance. La complexité de l'étude du comportement électrique des couches minces par cette technique a été soulignée. Ces caractérisations ont permis de mettre en évidence et de comparer les principales caractéristiques de ces méthodes d'élaboration et de montrer l'influence du choix de la technique de dépôt sur le comportement électrique des couches minces. Enfin, une étude préliminaire a été menée sur l'élaboration par ALD et les caractérisations physico-chimiques et électriques de couche minces d'oxyde zirconium dopé à l'oxyde d'indium (IDZ).

碩士
國立臺灣大學
物理研究所
95
In the first part of this thesis, we provide an alternative approach that the band edge emission can be greatly enhanced and the defect emission of ZnO nanorods can be reduced by the formations of ZnO/QDs composite. In the photoluminescence (PL) spectra, we observe the strong evidence that the band gap emission enhancement can be as high as 30 times. In the second part, the NiO-Cu¬¬2O superlattices (SLs) and Cu nanotubes were grown based on AAO membranes. We demonstrate the quantum confinement effect in NiO-Cu2O SLs. Finally, we attempt to transform the Cu nanotubes into Cu2O cactus shape nanotubes by using the combination of AAO template and hotplate methods.

碩士
國立中山大學
電機工程學系研究所
107
In this thesis, various copper sulfide (CuS) nanostructures composited with copper oxide (CuO) nanoparticles have been discussed. Nanocomposites are grown on the ITO substrates for non-enzymatic glucose sensing. Different morphologies and thicknesses of the sensing materials have significant effects to the sensitivity and the detection range of the sensors. Various CuS nanostructures are electroplated on the ITO substrate in this study. CuO nanoparticles are decorated on the surface of CuS for modification by RF sputtering system. The CuO/CuS nanocomposites are completed as a double-layered sensing material. By adjusting the concentration of the plating solution and changing the plating time, the morphology and the thickness of CuS can be controlled. We analyze the differences of the sensing material before and after the CuO modification. Sensing performances of the devices to glucose are also been compared. Based on the results, the sensing material CuS has the best performances by fabricating with 0.15M sodium thiosulfate pentahydrate under plating time of 900 s. Its sensitivity is 132.39μAmM-1cm-2. After the CuO modification, the sensitivity is further improved to 139.86μAmM-1cm-2. The results show that the CuO/CuS nanocomposites have higher sensing ability and wider detection range to glucose. It has great potential for biomedical detection.

We report the large scale synthesis of nanostructured copper oxide (CuO) synthesized by cost effective and simple wet chemical route. Nanorods and Nanoflowers and Nanowires have been uniformly grown on Cu foil by the oxidation of Copper. Their growth mechanism has been reported to understand the optimal parameters for controlled growth via a simple coordination self-assembly method on substrates. The composition, morphology and structural identity have been characterized by Scanning Electron Microscope (SEM), X-ray Diffraction (XRD), Energy-Dispersive X-ray spectroscopy (EDX), Fourier Transform Infrared Spectroscopy (FTIR) and Transmission Electron Microscope (TEM). These characterizations clearly show formation of CuO nanorods and nanoflowers having diameter in the range of 16-30 nm. The synthesized structures will have the potential applications as gas sensors, an active electrode material for Li-ion batteries, heterogeneous catalysts, field emission [FE] emitters and solar cells etc.

碩士
國立中山大學
電機工程學系研究所
107
In this study, copper oxide (CuO) nanostructures are prepared on ITO/glass substrate for nitrite (NO2-) sensor. Different CuO nanostructures are synthesized by hydrothermal method firstly. Catalytic ability of various structures is discussed in detail. The CuO nanostructure with highest oxidation peak current to nitrite are stacked on the sputtered CuO thin-film by spin coating, drop coating, and dip coating, respectively. The working electrodes are analyzed for their surface structures and sensing characteristics. According to the results, the sample with nanosheet structure by 15mM precursor solution (mixture of copper nitrate and hexamethylenetetramine) synthesized for 2hr has the largest oxidation peak current of 770.26 μA. Furthermore, the CuO nanosheets are drop coated on the sputtered thin-film to complete the working electrode. It has the sensitivity of 402μAmM-1cm-2. The detection limit is 0.7μM and the linear range is 0.2-1.2mM. Stacked structure in this work has significantly improved the device sensing ability to nitrite. The sensors can be applied to detection of industrial residual and pollutants.

碩士
國立中興大學
材料科學與工程學系所
98
We have successfully synthesized one-dimensional CuO nanowires by thermal oxidation and observed their growth mechanism. The CuO nanowires were adopted to fabricate a simple gas sensor which can be used for detecting low concentration CO. In the atmosphere at temperatures between 300℃ to 600℃, CuO nanowires could be grown. Once the annealing temperature was higher than 700℃or lower than 200℃, no CuO nanowires could be formed. The varieties of synthesis temperature would affect the diameters of CuO nanowires, and the lengths of nanowires would increase with increasing synthesis time. The diameters of CuO nanowires synthesized at 450℃for 6 hours were approximately 130 nm, and the lengths could be up to 15μm or longer. It was found that the number of nanowires synthesized by thermal oxidation would decrease when the substrate was annealed for longer time, which suggests that the CuO nanowires might be grown by the anisotropic atomic diffusion mechanism. The as-synthesized CuO nanowires were indentified as a monoclinic crystal structure and cumulated along with (110) by XRD and TEM analysis. The gas sensor device fabricated by CuO nanowires exhibited good response capacity for detecting low CO concentration at an operating temperature of 300℃. The sensitivity of the gas sensor could be up to 181% at CO concentration of 50ppm, and could still reach 138% even if the CO concentration was as low as 5ppm. At low CO concentration, the response and recovery times for the gas sensor device were on average about 180 seconds and 220 seconds, respectively. Therefore, CuO nanowires have great potential for low- concentration CO gas sensor device.

Nanostructured materials especially, one-dimensional (1D) nanostructures have unique physical, chemical, mechanical properties and are the building blocks for a range of nanoscale devices. The procedure employed for the synthesis of nanostructures involves the use of sophisticated instruments or rigorous chemical reactions. The motivation of our work is to develop a strategy that is simple, cost effective and applicable to a host of oxide materials. Nanostructures of various oxides have been grown from the metal as the source material. 1D ZnO nanostructures have been obtained by simply heating Zn metal in ambient air at temperatures below 600 °C. The nanostructures grow on the surface of the source material and the morphology is controlled by monitoring the curvature of the source material. This technique has an added advantage that neither any catalyst nor any gas flow is required. Tetrapods of ZnO are obtained when Zn is heated above 700 °C in ambient air. It has been shown that the morphology and the aspect ratio (length-to-diameter ratio) of the tetrapods depend on the temperature and the temperature gradient. Photoluminescence studies reveal good optical quality ZnO nanostructures. The technique employed to synthesize 1D ZnO nanostructures has been checked for other oxides. The temperature required for the synthesis of Ga2O3 nanostructures is 1200 °C. Many researchers have shown that Ga2O3 emits in the blue-green region. A red emission is required to get the impression of white light which has been seen for nitrogen doped Ga2O3. As the temperature is very high and Ga is heated in ambient air, unintentional nitrogen doping of 1D Ga2O3 nanostructures is obtained which is the reason for white light emission. The morphology of Ga2O3 nanostructures has been controlled by monitoring the curvature of the starting material as is the case of ZnO. Similar technique has also been employed for the synthesis of CuO nanostructures. The morphology is temperature dependent and 1D CuO nanostructures are obtained when the synthesis temperature is between 400 and 600 C. Possible growth mechanisms have been proposed for all these oxide materials. The entire thesis is based on the results discussed above. It has been organized as follows: Chapter 1 deals with the introduction to nanostructures, importance of 1D nanostructures, the specific applications of different morphologies, materials that are widely explored in the synthesis of nanostructures and different approaches to the synthesis of nanostructures. Growth mechanisms like VLS, VS and SLS are briefly discussed. A brief review on the basic physical properties, applications and different morphologies of ZnO, Ga2O3 and CuO is outlined with emphasis to the various synthesis techniques. Finally the aim and scope of the present work is discussed. Chapter 2 describes the experimental setup used for the synthesis and the basic principles of characterization techniques like x-ray diffraction (XRD), scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), energy dispersive spectrum (EDS), electron energy loss spectroscopy (EELS), photoluminescence (PL), Raman spectroscopy, x-ray photoelectron spectroscopy (XPS), UV-Visible spectroscopy, Fourier Transform Infrared Spectroscopy (FTIR) and thermogravimetric analysis (TGA). Chapter 3 deals with the synthesis of 1D ZnO nanostructures with different morphologies such as nanoneedles, nanorods, nanobelts from Zn powder/granule. The growth process is found to be different from the conventional VS mechanism. The advantage and the versatility of the method is emphasized. In this method, neither a catalyst nor any gas flow is required for the synthesis of oxide nanostructures. Depending upon the Zn powder or Zn granules as the starting material different nanostructures of ZnO have been synthesized. The as-synthesized materials are characterized by XRD, SEM, HRTEM, EDS, TGA and Raman spectroscopy and the results are discussed. Chapter 4 describes the controlled growth of ZnO tetrapods and the influence of temperature and temperature gradient on the growth process. Though there are several methods to synthesize ZnO tetrapods and it has been established that ZnO tetrapods can be synthesized by heating Zn in air, it is advantageous to grow tetrapods of different morphologies with different lengths. The large scale synthesis of ZnO tetrapods by heating Zn in air ambient is discussed in this chapter. The key parameters that control the diameter, length, and morphology of tetrapods are identified. It is shown that the morphology and dimensions of the tetrapods depend not only on the vaporization temperature but also on the temperature gradient of the furnace. The influence of vaporization temperature and growth temperature on the morphology of the tetrapods is discussed elaborately. Chapter 5 explains the one-step synthesis of nitrogen doped Ga2O3 nanostructures of different morphologies and the different growth mechanisms. The experimental method employed for the synthesis of nanostructures is simple and is different from the other reported methods. Neither any catalyst/substrate preparation nor any gas flow is required for the synthesis of Ga2O3 nanostructures. The synthesis involves the heating of molten Ga at high temperatures. Single crystalline monoclinic phase of nitrogen-doped Ga2O3 nanorods, nanobelts and nanoneedles are obtained by this method. The morphology is controlled by monitoring the curvature of the Ga droplet which is achieved by using different substrates. Possible growth processes of different morphology have been proposed. Chapter 6 includes some surprising results on the white light emission of Ga2O3 nanorods. High synthesis temperature generates a high vapor pressure suitable for the growth of Ga2O3 nanorods, creates oxygen vacancy and incorporates nitrogen from the ambient. The oxygen vacancy is responsible for the bluish-green emission, while nitrogen is responsible for the red emission. As a consequence, white light emission is observed from Ga2O3 nanorods when irradiated with UV light. The interesting point is that neither post-treatment of the nanorods nor size control is required for white light emission. Chapter 7 describes the synthesis of CuO nanostructures by heating Cu foil in air ambient. This is an attempt to check whether the synthesis technique employed for ZnO and Ga2O3 is applicable to other oxides. The as-synthesized CuO nanostructures are characterized by XRD, SEM, HRTEM, EDS, TGA, UV-visible, FTIR and the results are discussed. Chapter 8 gives the conclusions and the overall summary of the thesis.

Nanostructured materials especially, one-dimensional (1D) nanostructures have unique physical, chemical, mechanical properties and are the building blocks for a range of nanoscale devices. The procedure employed for the synthesis of nanostructures involves the use of sophisticated instruments or rigorous chemical reactions. The motivation of our work is to develop a strategy that is simple, cost effective and applicable to a host of oxide materials. Nanostructures of various oxides have been grown from the metal as the source material. 1D ZnO nanostructures have been obtained by simply heating Zn metal in ambient air at temperatures below 600 °C. The nanostructures grow on the surface of the source material and the morphology is controlled by monitoring the curvature of the source material. This technique has an added advantage that neither any catalyst nor any gas flow is required. Tetrapods of ZnO are obtained when Zn is heated above 700 °C in ambient air. It has been shown that the morphology and the aspect ratio (length-to-diameter ratio) of the tetrapods depend on the temperature and the temperature gradient. Photoluminescence studies reveal good optical quality ZnO nanostructures. The technique employed to synthesize 1D ZnO nanostructures has been checked for other oxides. The temperature required for the synthesis of Ga2O3 nanostructures is 1200 °C. Many researchers have shown that Ga2O3 emits in the blue-green region. A red emission is required to get the impression of white light which has been seen for nitrogen doped Ga2O3. As the temperature is very high and Ga is heated in ambient air, unintentional nitrogen doping of 1D Ga2O3 nanostructures is obtained which is the reason for white light emission. The morphology of Ga2O3 nanostructures has been controlled by monitoring the curvature of the starting material as is the case of ZnO. Similar technique has also been employed for the synthesis of CuO nanostructures. The morphology is temperature dependent and 1D CuO nanostructures are obtained when the synthesis temperature is between 400 and 600 C. Possible growth mechanisms have been proposed for all these oxide materials. The entire thesis is based on the results discussed above. It has been organized as follows: Chapter 1 deals with the introduction to nanostructures, importance of 1D nanostructures, the specific applications of different morphologies, materials that are widely explored in the synthesis of nanostructures and different approaches to the synthesis of nanostructures. Growth mechanisms like VLS, VS and SLS are briefly discussed. A brief review on the basic physical properties, applications and different morphologies of ZnO, Ga2O3 and CuO is outlined with emphasis to the various synthesis techniques. Finally the aim and scope of the present work is discussed. Chapter 2 describes the experimental setup used for the synthesis and the basic principles of characterization techniques like x-ray diffraction (XRD), scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), energy dispersive spectrum (EDS), electron energy loss spectroscopy (EELS), photoluminescence (PL), Raman spectroscopy, x-ray photoelectron spectroscopy (XPS), UV-Visible spectroscopy, Fourier Transform Infrared Spectroscopy (FTIR) and thermogravimetric analysis (TGA). Chapter 3 deals with the synthesis of 1D ZnO nanostructures with different morphologies such as nanoneedles, nanorods, nanobelts from Zn powder/granule. The growth process is found to be different from the conventional VS mechanism. The advantage and the versatility of the method is emphasized. In this method, neither a catalyst nor any gas flow is required for the synthesis of oxide nanostructures. Depending upon the Zn powder or Zn granules as the starting material different nanostructures of ZnO have been synthesized. The as-synthesized materials are characterized by XRD, SEM, HRTEM, EDS, TGA and Raman spectroscopy and the results are discussed. Chapter 4 describes the controlled growth of ZnO tetrapods and the influence of temperature and temperature gradient on the growth process. Though there are several methods to synthesize ZnO tetrapods and it has been established that ZnO tetrapods can be synthesized by heating Zn in air, it is advantageous to grow tetrapods of different morphologies with different lengths. The large scale synthesis of ZnO tetrapods by heating Zn in air ambient is discussed in this chapter. The key parameters that control the diameter, length, and morphology of tetrapods are identified. It is shown that the morphology and dimensions of the tetrapods depend not only on the vaporization temperature but also on the temperature gradient of the furnace. The influence of vaporization temperature and growth temperature on the morphology of the tetrapods is discussed elaborately. Chapter 5 explains the one-step synthesis of nitrogen doped Ga2O3 nanostructures of different morphologies and the different growth mechanisms. The experimental method employed for the synthesis of nanostructures is simple and is different from the other reported methods. Neither any catalyst/substrate preparation nor any gas flow is required for the synthesis of Ga2O3 nanostructures. The synthesis involves the heating of molten Ga at high temperatures. Single crystalline monoclinic phase of nitrogen-doped Ga2O3 nanorods, nanobelts and nanoneedles are obtained by this method. The morphology is controlled by monitoring the curvature of the Ga droplet which is achieved by using different substrates. Possible growth processes of different morphology have been proposed. Chapter 6 includes some surprising results on the white light emission of Ga2O3 nanorods. High synthesis temperature generates a high vapor pressure suitable for the growth of Ga2O3 nanorods, creates oxygen vacancy and incorporates nitrogen from the ambient. The oxygen vacancy is responsible for the bluish-green emission, while nitrogen is responsible for the red emission. As a consequence, white light emission is observed from Ga2O3 nanorods when irradiated with UV light. The interesting point is that neither post-treatment of the nanorods nor size control is required for white light emission. Chapter 7 describes the synthesis of CuO nanostructures by heating Cu foil in air ambient. This is an attempt to check whether the synthesis technique employed for ZnO and Ga2O3 is applicable to other oxides. The as-synthesized CuO nanostructures are characterized by XRD, SEM, HRTEM, EDS, TGA, UV-visible, FTIR and the results are discussed. Chapter 8 gives the conclusions and the overall summary of the thesis.

碩士
國立臺南大學
電機工程學系碩博士班
106
A large number of factories and vehicles are continuously increasing with the development of industries and cities in the world, and pollutants in the air are also increasing. Vehicle emissions, burning of waste, create construction, agricultural land cultivation and animal husbandry, etc. The main content of this study is the use of copper oxide as a sensing material, applied to MEMS gas sensors, and micro-heaters in MEMS gas sensors to measure various gases including oxidation and reduction gas. In this study, the experimental copper oxide gas sensor is a semiconductor gas sensor type , have various advantages, for example: miniaturized original size (volume reduction elements), low power consumption (energy consumption reduction), low operating temperatures , manufacturing cost is reduced, a high sensitivity. In this study the structure characteristics there of micro electromechanical system sensor element of the gas to be analyzed and measured by SEM, EDX, XRD, XPS. The research themes of this master's thesis include: (1) Copper Oxide Micro-Electro-Mechanical Gas Sensor Process (2.) Analysis of Copper Oxide Thin Films and Characteristics of Copper Oxide Gas Sensors. Keywords: copper oxide; MEMS; gas sensors

碩士
國立臺灣海洋大學
光電科學研究所
103
This study report CuO nanostructures synthesis on copper foil in air by CO2 laser. The crystal structures, morphology, composition, band gap, opto-electronic have been investigated. The crystal structure of the CuO nanostructures were characterized by SEM, TEM, Raman and XRD. The optical properties of the CuO nanostructures were investigated by UV-vis and also opto-electronic response of individual CuO nanowires have been probed. The diameter of CuO nanowires were between 50~100 nm and length is nearly 10μm. The crystal structure of the CuO nanowires were characterized by XRD, Raman and TEM, the lattice spacing of nanowires are 0.235 nm and 0.2531 nm, corresponding to the (111) and (002) crystal planes, and We observed three peaks located at 306, 352 and 637 cm−1 should correspond to monoclinic CuO by Raman spectrum. The band gap of CuO nanowires is determined to be 1.58 eV.

碩士
國立中興大學
物理學系所
105
In this thesis, ZnO nanorods were ALD-deposited at atmospheric pressure in a temperature range of 300 ~ 600°C using diethylzinc (DEZn), and nitrous oxide (N2O) precursors as sources of Zn and O elements in the ZnO nanorods. Then, ZnO nanorods arrays were placed in a breaker containing a CBD solution of copper sulfate , sodium sulfite and a glucose . The solution was heated to 55°C for 10 minutes. This step was repeated three times to complete the deposition of Cu2O nanoparticles on ZnO nanorods. The physical properties of radial ZnO/Cu2O nanostructures were characterized using θ-2θX-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM), and UV-Vis spectrophotometry. It was found that the attached Cu2O nanoparticles appeared as randomly patterns on the edge of the ZnO nanorods. The XRD pattern confirms that the nanoparticles are poly-crystalline cubic structures of Cu2O. Optical transmittance results showed that Cu2O-coated ZnO nanorod arrays reduced the optical transmittance in the visible regime between 400 and 600 nm owing to additional absorption of Cu2O in the ZnO/Cu2O nanostructures.

The basic necessities to sustain life are – air, water and food. Although the harmful effects due to contaminated food or water are dangerous to life, these can be reduced/avoided by controlling the intake. Whereas, in case of air, the same amount of control cannot be exercised as there is very little, one can do in case of inhalation. Maximum damage to life is due to air contamination which can be detected and prevented by using gas sensors. The proper use of these sensors not only save lives, but also minimizes social and financial loss. The objective of this thesis work is to study and explore the use of p-type semiconducting material such as CuO, as a promising gas sensing material for organic compounds (VOCs), compatible with existing silicon fabrication technology. The Thesis consist of 7 chapters: Chapter 1 covers the general introduction about gas sensors, sensor parameters, criteria for the selection of sensing material, suitability of CuO as sensing material and a brief literature survey. The second chapter includes the selection of substrate, cleaning procedures and suitable deposition method. The deposition method used in the present thesis work is DC/RF magnetron sputtering. The reactive magnetron sputtering is employed during the deposition of CuO sensing films. It also includes basic introduction about some of the common material characterization techniques. This is followed by Chapter 3 which includes the optimization of sputtering process parameters such as applied power, working pressure, Ar-O2 ratio and substrate temperature for CuO sensing film and the effect of these on surface morphology. Information on the optimized sputtering parameters for electrode film (silver and gold) deposition has also been included in this chapter. In order to study the sensing behavior of the sensor, suitable testing set-up is necessary. This leads us to Chapter 4 that discusses the development of an in-house built sensor testing setup and its automization using MATLAB. The automated testing set-up facilitates off-time data plotting as well as real-time data plotting during the sensing process. To demonstrate the working of the set-up, some initial results obtained are also included in this chapter. After ascertaining the functioning of the automated gas sensor testing set-up, detailed study on the sensing behavior of nanostructured CuO films was performed. This information along with the necessary details is included in Chapter 5. The sensing response of nanostructured CuO films has been studied for different VOCs such as alcohol, toluene and benzene. The study carried out on the effect of different surface additives like multi-walled carbon nanotubes (MWNTs), gold or platinum on ethanol sensing has also been included in this chapter. During the use of MWNTs as surface additives, different concentrations of MWNTs – 0.01 mg, 0.05 mg and 0.1 mg have been dispersed on the CuO sensing film. The sample with lowest concentration of MWNTs exhibited highest sensitivity and lower response time. It is due to the fact that, higher concentrations of MWNTs do not result into uniform dispersion over the CuO films and cover the sensing film almost completely. Operating temperature is the most important factor affecting the performance of a gas sensor. In order to maintain the operating temperature for the portable sensor, the sensor is usually integrated with a heater. The chapter 6 deals with heater optimization including design, simulation and fabrication. In this chapter, microheater as well as macro-heaters were simulated and fabricated. The fabricated macro-heater is bonded with the sensor by eutectic bonding. One of the bonded samples was studied for its sensing response. The final chapter of the thesis deals with the conclusion of present research work and the possible further work on CuO gas sensor.

The basic necessities to sustain life are – air, water and food. Although the harmful effects due to contaminated food or water are dangerous to life, these can be reduced/avoided by controlling the intake. Whereas, in case of air, the same amount of control cannot be exercised as there is very little, one can do in case of inhalation. Maximum damage to life is due to air contamination which can be detected and prevented by using gas sensors. The proper use of these sensors not only save lives, but also minimizes social and financial loss. The objective of this thesis work is to study and explore the use of p-type semiconducting material such as CuO, as a promising gas sensing material for organic compounds (VOCs), compatible with existing silicon fabrication technology. The Thesis consist of 7 chapters: Chapter 1 covers the general introduction about gas sensors, sensor parameters, criteria for the selection of sensing material, suitability of CuO as sensing material and a brief literature survey. The second chapter includes the selection of substrate, cleaning procedures and suitable deposition method. The deposition method used in the present thesis work is DC/RF magnetron sputtering. The reactive magnetron sputtering is employed during the deposition of CuO sensing films. It also includes basic introduction about some of the common material characterization techniques. This is followed by Chapter 3 which includes the optimization of sputtering process parameters such as applied power, working pressure, Ar-O2 ratio and substrate temperature for CuO sensing film and the effect of these on surface morphology. Information on the optimized sputtering parameters for electrode film (silver and gold) deposition has also been included in this chapter. In order to study the sensing behavior of the sensor, suitable testing set-up is necessary. This leads us to Chapter 4 that discusses the development of an in-house built sensor testing setup and its automization using MATLAB. The automated testing set-up facilitates off-time data plotting as well as real-time data plotting during the sensing process. To demonstrate the working of the set-up, some initial results obtained are also included in this chapter. After ascertaining the functioning of the automated gas sensor testing set-up, detailed study on the sensing behavior of nanostructured CuO films was performed. This information along with the necessary details is included in Chapter 5. The sensing response of nanostructured CuO films has been studied for different VOCs such as alcohol, toluene and benzene. The study carried out on the effect of different surface additives like multi-walled carbon nanotubes (MWNTs), gold or platinum on ethanol sensing has also been included in this chapter. During the use of MWNTs as surface additives, different concentrations of MWNTs – 0.01 mg, 0.05 mg and 0.1 mg have been dispersed on the CuO sensing film. The sample with lowest concentration of MWNTs exhibited highest sensitivity and lower response time. It is due to the fact that, higher concentrations of MWNTs do not result into uniform dispersion over the CuO films and cover the sensing film almost completely. Operating temperature is the most important factor affecting the performance of a gas sensor. In order to maintain the operating temperature for the portable sensor, the sensor is usually integrated with a heater. The chapter 6 deals with heater optimization including design, simulation and fabrication. In this chapter, microheater as well as macro-heaters were simulated and fabricated. The fabricated macro-heater is bonded with the sensor by eutectic bonding. One of the bonded samples was studied for its sensing response. The final chapter of the thesis deals with the conclusion of present research work and the possible further work on CuO gas sensor.

碩士
國立中興大學
材料科學與工程學系所
103
This study mainly uses hydrothermal method to synthesize nanostructured copper oxide (CuO) hollow spheres. In the experimental process, we adopted cupper nitride and urea as the precursor at reaction temperature of 150℃. FE-SEM, XRD, EDS, TEM, BET were used to observe and analyze surface morphology, area, and structure composition of the product, together with exploration of the growth mechanism of the nanostructured hollow spheres. In addition, the nanostructured hollow spheres are also made into a simple gas-sensing element, which can be applied in gas sensing in low concentrations of hydrogen sulfide (H2S). The result shows that the reaction time over 12 hours can synthesize the CuO microspheres. When the reaction time is extended to 24 hours, an opening gradually appears on the nanostructured hollow spheres. The opening is the most obvious when time is extended to 48 hours. Finally, no hollow spheres are produced when heated to 72 hours. In the gas-sensing characteristics, when the CuO specimen obtained from the reaction time of 48 hours is placed in the H2S with the concentration of 30 ppm at an isothermal temperature of 250℃, one can get the best gas-sensing sensitivity (2.78); the shortest response time (21 seconds) and recovery time (236 seconds), respectively, under a soaking temperature of 300℃, and H2S concentration of 30 ppm and 7 ppm. The CuO specimen from the reaction time of 12 hours has the worst sensitivity (1.3) under soaking temperature of 200℃ and H2S concentration of 30 ppm environment. The specific surface area also affects the gas-sensing sensitivity, and the working temperature affects the sensitivity of the response time and recovery time.

碩士
國立東華大學
光電工程學系
101
The hierarchical p-type Cu2O micro/nanostructural film on copper foil is successfully fabricated via a facileand cost-effective template route through transformation of lotus-like CuO/Cu(OH)2 nanosheet/nanowire structure for photoelectrochemical (PEC) hydrogen generation. Various size of Cu2O micro/nanostructuretransfers from CuO nanosheets and Cu(OH)2 nanowires by means of chemically and thermally reducing the oxides from Cu2+ to Cu1+ at temperature of 55oC in solution of ascorbic acid and 500 oC under nitrogen atmosphere, respectively. Regarding the evolution of structure and composition at various reaction temperatures, the results of XRD, Raman, and XPS confirmed the complete transformation of CuO and orthorhombic- phase Cu(OH)2 to cubic-phase Cu2O. Direct band gap of 2.03 eV in Cu2O film is determined via incident photon-to-electron conversion efficiency measurement. Under our best synthesis condition, significantly, this Cu2O hierarchical photocathode exhibits remarkable photocurrent of -2.1 mAcm-2 at a potential of -0.6 V vs. Ag/AgCl, corresponding to the solar conversion efficiency of 2.5 %. These results demonstrate the Cu2O micro/nanostructural film have great potential in solar hydrogen applications.

博士
國立臺灣科技大學
化學工程系
103
Solar hydrogen is known to be a promising energy source to substitute the conventional fossil fuels, as it is sustainable and environmentally friendly. Solar hydrogen can be produced in a number of ways. Photoelectrochemical (PEC) water splitting is one of the most attractive methods for converting solar energy into H2 fuel. A substantial research is being performed in PEC water splitting to improve the materials solar conversion efficiency. In this thesis, Cu2O was investigated for use as photocathode in PEC water splitting for solar hydrogen production. Two major bottlenecks of the application of cuprous oxide to water splitting are its poor stability in aqueous solution and its low photocatalytic efficiency caused by fast electron−hole recombination. The mismatch of the electron diffusion length (20–100 nm) with the light absorption depth near the band gap (~10 μm) also limits the application of Cu2O photoelectrode. The existing literatures dealing with these issues are highly limited by the complexity of the electrode fabrication, low performance, cost of noble metal (Pt) and the availability of rare earth oxides or sulfides as a cocatalyst. Therefore, this thesis focuses on nanostructuring Cu2O, thorough characterization and designing solutions to enhance the photostability and photocurrent density of Cu2O for solar hydrogen production. In the first part of this study, we fabricate a one dimensional (1D) Cu2O straddled with graphene with simple and facile electrodeposition and dip coating, followed by thermal treatment methods. We found that the Cu2O nanowire arrays modified with optimized concentration of graphene lead to significantly enhanced photocurrent density 4.8 mA cm–2, (which is two times that of bare 1D Cu2O, 2.3 mA cm–2), at 0 V vs RHE under AM 1.5 illumination (100 mW cm–2) and a fivefold increased in photostability at the end of 20 minutes measurement (83%). Our detailed characterizations of the photocathode’s after PEC measurement revealed that graphene played a role as a protection layer and is suitable for high-performance and long-term application for PEC water splitting. That is, the high PEC performance of graphene/Cu2O nanocomposite is attributed to the improved crystallinity and the synergetic effect of graphene in absorbing the visible light, suppressing the charge recombination and suppressing photocorrosion of the photoelectrode by preventing direct contact with the electrolyte. In the second part of our work, we report the design, synthesis and characterization of a novel Cu2O/CuO heterojunction decorated with nickel cocatalyst as a highly efficient photocathode for solar hydrogen production. The heterojunction structure was shown and examined by X-ray absorption spectroscopy, X-ray photoelectron spectroscopy (XPS), Raman Spectroscopy and Tip-enhanced Raman spectroscopy (TERS). Due to the heterojunction synergistic effect, the Cu2O/CuO gave a remarkably improved photocurrent density (–2.1 mA/cm2), i.e. 3.1 times higher than a Cu2O photoelectrode. Additionally, the Cu2O/CuO heterojunction, when decorated with nickel cocatalyst, showed six-fold and two-fold increases in photocurrent density (–4.3 mA/cm2) respectively when compared to Cu2O and bare Cu2O/CuO at 0 V vs. RHE under AM 1.5 illumination (100 mW/cm2). Interestingly, the Ni decorated Cu2O/CuO photocathode showed an impressive solar conversion efficiency of 2.71% at –0.4 V vs. Pt, i.e. 467% higher compared to bare Cu2O/CuO. After 20 minutes of standard solar illumination, 87.7% initial photocurrent density was remained for the nickel decorated Cu2O/CuO heterojunction. This is more than 1.5 times that of bare Cu2O/CuO (53.6%), suggesting surface modification with Ni not only effectively promotes water splitting but also stabilizes the photoelectrode. The enhanced photoelectrochemical performance is attributable to the efficient charge transfer and protective role of Ni, the improved crystallinity and the synergistic effect of the heterojunction in light absorption and charge separation. This inexpensive photocathode with increased photocurrent density and photostability offers a higher promise for solar hydrogen production In the final part of this dissertation, we further enhance photocurrent density and photostability of the Cu2O/CuO heterostructure by modifying the surface with CuS as a cocatalyst using a facile SILAR method. The interfacial reaction between CuS and Cu2O/CuO was shown by many experimental evidences, including Raman, XANES/EXFS and XPS. The optimized Cu2O/CuO/CuS photocathode provided remarkably enhanced photocurrent density of – 5.4 mA /cm2 (i.e. > 2.5 times than that of the bare Cu2O/CuO) at 0 V vs. RHE under standard AM 1.5 light illumination. Due to the bicatalytic effects in suppressing the electron- hole recombination, a further increase in photocurrent density, – 5.7 mA/cm2 was noticed after decorating the Cu2O/CuO surface with both CuS and Pt. To the best of our knowledge, this is the highest performance yet reported for a cocatalyst modified Cu2O/CuO photoelectrode for solar water splitting. More importantly, the Cu2O/CuO heterostructure modified with optimum CuS afforded an impressive solar conversion efficiency of ABPE% = 3.6% which is greater than fourfold increase compared with the bare Cu2O/CuO. The stability of the bare Cu2O/CuO photocathode showed about a 44% decrease in initial photocurrent density within 1 h, but the stability was significantly improved i.e. 85% and 92% of the initial photocurrent is maintained after 1 h when the photocathode was modified with CuS and with both CuS and Pt respectively. This highly enhance photoeclrochemical property is due to the fast transfer of photogenerated electrons resulting suppressed electron-hole recombination and synergistic effects of heterojunction in light absorption and charge separation.

碩士
國立成功大學
材料科學及工程學系
105
This study is focused on solid state phase transformation of ZnS to synthesize one-dimensional Cu2-xS nanostructures by using two-step vapor deposition process. One-dimensional ZnS nanostructures are first synthesized using ZnS powders as the source, followed by the growth of Cu2-xS nanostructures through cation exchange reactions using CuCl2 as the source at different temperature. The X-ray diffraction patterns show the presence of Cu1.8S and Cu2S under different conditions. The microstructure and defects of the Cu2-xS nanostructures are analyzed using transmission electron microscopy. At 300℃,the product is meta-stable rhombohedral Cu1.8S with 1-D superlattices and stacking faults. By prolonging the reaction time, the rhombohedral Cu1.8S would transform to cubic Cu1.8S with 3-D superlattices accompanied by zigzag morphology, pores and twins due to stress release. All the superlattices are caused by the ordered arrangement of copper vacancies. We find that while the reactions are controlled by kinetics at 300℃, they are controlled by thermodynamics at higher temperatures. Owing to good electric conductivity and superlattice-induced poor thermal conductivity, Cu1.8S could be a potential thermoelectric material.

碩士
國立成功大學
材料科學及工程學系
102
In this study, Cu2O nanorods were successfully fabricated using a two-step hydrothermal method. In addition, a N2 purging process was used to purify the content of Cu2O. The XRD, SEM, TEM, and UV-VIS characterization tools were applied to check the phases, morphologies, crystallinity, and band gap of Cu2O nanorods, respectively. We found Cu2O nanorods can be applied to various promising applications, including photocatalysis, piezoresistive effects, and photoelectrochemical (PEC) activities. The sample after 30 mins N2 purging showed the best photodegradation efficiency because the highest purity of Cu2O was obtained, which exhibited the property of a direct energy band gap. The I-V characteristics showed the higher current density under higher pressures, indicating the piezoresistive effect. When a visible light was irradiated, the photo-induced piezoresistive effect was observed, which enhanced the photodegradation efficiency. The photocurrent of Cu2O nanorods was measured using a three-electrode configuration of a photoelectrochemical cell. Approximately 3μA/cm2 was observed and the signals were steady after the test of three runs and 8 cycles for each run.

碩士
國立成功大學
材料科學及工程學系
104
ZnS nanostructures with variety morphology such as nanobelts, nanowires, nanosaws and nanocombs have been synthesized via VLS growth mechanism. Structure characterization revealed that nanobelts and nanowires both have Cubic and Hexagonal phases. Nanosaw consists of cubic teeth and hexagonal trunk while the nanocombs have single crystalline Wurtzite (WZ) structure. The positive polar surface of WZ structure causes the second growth on its lateral surface. The nanocomb is transformed from the nanobelts, which is etched along the preferential crystallographic planes in a reactive atmosphere. Cu-doped ZnS nanowires have also been synthesized. The copper-doped nanowires have two morphologies, the straight and the zigzag shape. The copper atoms may cause the lattice distortion in ZnS nanowire and to compensate the energy difference, the nanowire may change growth direction and form the zigzag shape. Finally, we use the ZnS nanowires as template to synthesize the ZnS/Cu2-xS core/shell structures. We also measured the photo response of single ZnS nanowire and ZnS/Cu2-xS nanowire and found that ZnS/Cu2-xS nanowire has high responsivity to UV and 800 nm wavelength light. Moreover, ZnS nanosaw also has enhanced UV light responsivity.

碩士
國立屏東科技大學
機械工程系所
97
Bioactive glasses have attracted much attention because of good biocompatibility and their wide usage as artificial biomaterials in bone repair and replacement. Bioactive glasses are widely used in many tissue engineering applications, such as in dental repairs and orthopedic fixation devices, as well as many others. Mesoporous bioactive glasses materials have received much interest because of their high specific surface area and pore volume, and exhibit better in vitro bone forming bioactivity compared to conventional bioactive glasses. In this study, mesoporous SiO2-CaO-P2O5 bioactive glass was prepared by sol-gel process and the synthesis was accomplished by using triblock copolymer and CTAB as the templates, tetraethyl orthosilicate, calcium nitrate tetrahydrate and triethyl phosphate as the inorganic precursors. The effects of Ca/P ratio of precursors and calcining temperatures on the structure of mesoporous SiO2-CaO-P2O5 bioactive glass were investigated by TGA, XRD, FTIR, SEM, TEM and BET analyses. Using triblock copolymer as the template, mesoporous SiO2-CaO-P2O5 bioactive glasses with the amorphous phase were obtained at 400~700°C for Ca/P ratio of 2:2, 3:2, 4:2 and 5:2. Using CTAB as the template and the samples calcined at 400~700°C were composed of amorphous phase for Ca/P ratio of 2:2, but apatite phase were formed as the calcining temperatures were 400~700°C for Ca/P ratio of 3:2, 4:2 and 5:2. The mesoporous SiO2-CaO-P2O5 bioactive glass is shown to have a large pore size of 400.29 Å for Ca/P ratio of 2:2 and using triblock copolymer as template after being calcined at 400℃. In addition, the mesoporous SiO2-CaO-P2O5 bioactive glass III also showed a high specific surface area of 706.16 m2/g at 600 ºC calcination for Ca/P ratio of 3:2 and using CTAB as template.

碩士
國立成功大學
材料科學及工程學系
102
One-dimensional ZnO nanowires (NWs), nanotubes (NTs) and Cu/Cu2O NWs electrodeposited via high aspect ratio anodic alumina oxide (AAO) template assistance. An AAO template was fabricated by two-step anodization process. The morphologies of the ZnO nanostructures synthesized under H2O2 with various electrolyte concentrations of ZnSO4 were NTs and NWs. Cu/Cu2O nanostructures were synthesized under CuSO4 and lactic acid electrolyte. The Cu in Cu/Cu2O compound nanowire will change with different deposition current density. They all have ability for water splitting.

博士
國立臺灣科技大學
光電工程研究所
106
Cuprous oxide (Cu2O) is a promising semiconductor material for photo-voltaic(PV), photoelectrochemical cells (PEC) and other optoelectronic applications. The aim of this thesis was to deposit and characterize high quality Cu2O nano-structures for these and other applications. In this study, well-structured Cu2O nano-rods, truncated nano-cubes, and nano-pyramids were successfully fabricated using ion beam sputter deposition (IBSD) in which the Cu2O samples were grown on quartz and silicon substrates with a substrate temperature of 450°C and a base pressure of 4.5 x 10-5 Torr using metallic copper as a target material. In the first part of this thesis, we studied the growth of different Cu2O nano-structures deposited on quartz substrates. The results show that by changing the argon/oxygen flow rates starting from 6:1 to 14:1, Cu2O thin film (Ar:O2=3.6:0.6), Cu2O nano-rods of length 1-2 µm (Ar:O2=4.5:0.5, 6:0.5, and 7:0.5) were grown on quartz substrates. In addition to the Cu2O thin film and Cu2O nano-rods grown on quartz substrates, triangular pyramids (Ar:O2=3.6:0.4), and Cu2O truncated nano-cubes (Ar:O2=4.4:0.4) were grown on Si/SiO2 substrates. The structural characterizations were done employing XRD and FE-SEM. The results show that all the samples are poly-crystalline structures Cu2O and the preferable growth direction was to the (111) crystal plane. All the samples were also investigated by Micro Raman spectra and the results indicate all the Raman bands are typical characteristic of the phonon modes of Cu2O phases. The temperature dependent PL measurements have been done for the samples and the results show Cu2O samples deposited with low oxygen flow rates (Ar:O2=4.5:0.5, 6.0:0.5, 4.4:0.4 and 7.0:0.5), have PL emission peak centered at ~720 nm which is attributed due to doubly oxygen vacancy induced luminescence at a temperature of 12 to 100 K. While the sample deposited with Ar:O2=3.6:0.6 shows no PL emissions which indicates that Cu2O nanostructures are prone to enhance the PL emissions. Among the different Cu2O nanostructures, Cu2O triangular nanopyramids interestingly shows a strong green exciton PL emission centered at 509 nm resulted due to radiative recombination of photogenerated electrons at room temperature. The PL measurements show that no PL emission as a result of copper vacancy defects showing the carrier types are of n-type. Furthermore, all the samples have been investigated using XPS and the results show the Cu2O Cu 2p core level binding energies centered at 932.4 eV, and 952.4 eV were observed. Moreover, the O 1s spectra at 530.5 eV shows additional confirmation of the surface composition and phase purity of Cu2O samples. Optical transmittance measurements also have been done and the results show that transmittance value is lower for Cu2O thin film and higher for Cu2O nanorods. The highest transmittance value is obtained for the sample with argon/oxygen flow rate of 9:1 which is ~79%. The Tauc's plots of all the samples show also that the band gap shifts from 2.5 eV to 2.3 eV as the oxygen flow rates drops. The photoelectrochemical characterizations also show all the samples deposited with low oxygen flow rates show n-type carrier and p-type for samples deposited at high oxygen flow rates. The stability of the photocurrent values generated by Cu2O photoelectrodes were excellent (~95%). The photocurrent measurements show that the sample with argon/oxygen flow rate of 9:1 shows a significantly enhanced anodic photocurrent density of ~2.2 mA/cm2. The Mott-Schottky plots of the samples except the one with higher oxygen flow rate (Ar:O2=6:1) (which shows a negative value of the slope), show positive values of the slopes which are additional confirmations of the n-type carriers. The calculations of the carrier densities from the Mott Schottky plots shows that the highest values is obtained for the sample with argon/oxygen flow rate of 9:1 which has a value of and the smaller value of the acceptor densities is for the p-type sample which is . We also demonstrated the application of the Cu2O photo-electrodes for water reduction and oxidation by studying the band edge positions of the semiconductors with respect to both normal hydrogen electrode and vacuum energy levels and the samples are promising for use as photo-electrode materials.

碩士
國立清華大學
化學系
104
This study examines the facet-dependent optical properties of size-tunable Ag–Cu2O core–shell nanocrystals with 38, 42, and 50 nm cubic Ag cores. The Ag cores were prepared from octahedral Au seeds. The Cu2O shells are single-crystalline. In the case of Au@Ag–Cu2O nanocrystals with 42 nm Ag cores, the Ag surface plasmon resonance (SPR) absorption band at 485 nm has been widely red-shifted to 730, 755, and 775 nm for rhombic dodecahedra, truncated octahedra, and cuboctahedra, respectively, after forming the Cu2O shells. The Ag SPR band positions are mostly fixed despite large changes in the shell thickness, showing the presence of facet-dependent optical properties. Due to the strong Ag SPR band absorption, all samples exhibit a better photothermal activity than that of Au–Cu2O nanocrystals. Facet-dependent heat transmission may be present for particles with Ag SPR band much deviated from the laser wavelength, but this phenomenon is lost for particles with SPR band approaching the excitation wavelength as the particles become highly photothermally efficient to give solution temperatures of 80–95 ºC within 3 min of laser irradiation.