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On the template synthesis of nanostructured inorganic/organic hybrid films

GONCALES, V. R.; SALVADOR, R. P.; ALCANTARA, M. R.; TORRESI, S. I. Cordoba de
Fonte: ELECTROCHEMICAL SOC INC Publicador: ELECTROCHEMICAL SOC INC
Tipo: Artigo de Revista Científica
ENG
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Prussian Blue has been introduced as a mediator to achieve stable, sensitive, reproducible, and interference-free biosensors. However, Na(+), Li(+), H(+), and all group II cations are capable to block the activity of Prussian Blue and, because Na(+) can be found in most human fluids, Prussian Blue analogs have already been developed to overcome this problem. These analogs, such as copper hexacyanoferrate, have also been introduced in a conducting polypyrrole matrix to create hybrid materials (copper hexacyanoferrate/polypyrrole, CuHCNFe/Ppy) with improved mechanical and electrochemical characteristics. Nowadays, the challenges in amperometric enzymatic biosensors consist of improving the enzyme immobilization and in making the chemical signal transduction more efficient. The incorporation of nanostructured materials in biosensors can optimize both steps and a nanostructured hybrid CuHCNFe/Ppy mediator has been developed using a template of colloidal polystyrene particles. The nanostructured material has achieved sensitivities 7.6 times higher than the bulk film during H(2)O(2) detection and it has also presented better results in other analytical parameters such as time response and detection limit. Besides, the nanostructured mediator was successfully applied at glucose biosensing in electrolytes containing Prussian Blue blocking cations. (C) 2008 The Electrochemical Society.

Preparação de hidróxidos mistos nanoestruturados de níquel/cobalto e desenvolvimento de sensores FIA amperométricos; Preparation of nanostructured nickel/cobalt mixed hydroxides and development of FIA amperometric sensors

Martins, Paulo Roberto
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 21/03/2012 PT
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Nesta tese foram desenvolvidos sensores amperométricos baseados em porfirinas supramoleculares e hidróxido de níquel nanoestruturado e estabilizado na fase alfa, bem como novos materiais baseados em hidróxidos mistos de níquel e cobalto nanoetruturados e estabilizados na fase alfa. Também, um analisador FIA amperométrico, foi desenvolvido em colaboração com o Laboratório de Instrumentação Analítica do IQ-USP, para a determinação e quantificação de SO2 livre em amostras reais, como vinhos, águas de coco e sucos de frutas. Os sensores amperométricos baseados em porfirinas supramoleculares foram empregados na determinação de SO2 livre, presente em sucos de frutas e águas de coco, utilizando um sistema FIA amperométrico. O sistema FIA amperométrico foi constituído de um injetor manual, uma cela amperométrica em fluxo integrada a uma unidade de difusão de gases e um fluxo de uma solução de ácido sulfúrico e de uma solução de eletrólito. Possíveis interferentes como ácido ascórbico, catecol, glicose e benzoato de sódio foram avaliados antes de iniciar as análises das amostras reais. Os resultados das análises foram comparados com o método oficial Monier-Williams. Os níveis de SO2 livre encontrados nas amostras estavam de acordo com o que é preconizado pela Legislação Brasileira. Os eletrodos de FTO...

Nanostructured films of perylene derivatives: High performance materials for taste sensor applications

Constantino, C. J L; Antunes, P. A.; Venancio, E. C.; Consolin, N.; Fonseca, F. J.; Mattoso, L. H C; Aroca, R. F.; Oliveira, O. N.; Riul, A.
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Artigo de Revista Científica Formato: 95-101
ENG
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47.9564%
Four perylene derivatives (PTCD) have been used as transducing materials in taste sensors fabricated with nanostructured Langmuir-Blodgett (LB) films deposited onto interdigitated gold electrodes. The Langmuir monolayers of PTCDs display considerable collapse pressures, with areas per molecule indicative of an edge-on or head-on arrangement for the molecules at the air/water interface. The sensing units for the electronic tongue were produced from 5-layer LB films of the four PTCDs, whose electrical response was characterized with impedance spectroscopy. The distinct responses of the PTCDs, attributed to differences in their molecular structures, allowed one to obtain a finger printing system that was able to distinguish tastes (salty, sweet, bitter and sour) at 1 μM concentrations, which, in some cases, are three orders of magnitude below the human threshold. Using Principal Component Analysis (PCA) data analysis, the electronic tongue also detected trace amounts of a pesticide and could distinguish among samples of ultrapure, distilled and tap water, and two brands of mineral water. © 2004 by American Scientific Publishers. All rights reserved.

Nanostructured Composites Based on Carbon Nanotubes and Epoxy Resin for Use as Radar Absorbing Materials

Silva, Valdirene Aparecida; Folgueras, Luiza de Castro; Candido, Geraldo Mauricio; Paula, Adriano Luiz de; Rezende, Mirabel Cerqueira; Costa, Michelle Leali
Fonte: Univ Fed Sao Carlos, Dept Engenharia Materials Publicador: Univ Fed Sao Carlos, Dept Engenharia Materials
Tipo: Artigo de Revista Científica Formato: 1299-1308
ENG
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47.90322%
Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq); Nanostructured polymer composites have opened up new perspectives for multifunctional materials. In particular, carbon nanotubes (CNTs) present potential applications in order to improve mechanical and electrical performance in composites with aerospace application. The combination of epoxy resin with multiwalled carbon nanotubes results in a new functional material with enhanced electromagnetic properties. The objective of this work was the processing of radar absorbing materials based on formulations containing different quantities of carbon nanotubes in an epoxy resin matrix. To reach this objective the adequate concentration of CNTs in the resin matrix was determined. The processed structures were characterized by scanning electron microscopy, rheology, thermal and reflectivity in the frequency range of 8.2 to 12.4 GHz analyses. The microwave attenuation was up to 99.7%, using only 0.5% (w/w) of CNT, showing that these materials present advantages in performance associated with low additive concentrations.

Charge transport and recombination of dye sensitized 1D nanostructured-TiO2 films prepared by reactive sputtering

Sequeira, S.; Lobato, K.; Torres, Erica; Brites, Maria João; Barreiros, Maria Alexandra; Mascarenhas, João
Fonte: Laboratório Nacional de Energia e Geologia Publicador: Laboratório Nacional de Energia e Geologia
Tipo: Conferência ou Objeto de Conferência
Publicado em //2014 ENG
Relevância na Pesquisa
58.050054%
Dye sensitized solar cells (DSCs) are governed by light absorption, charge injection, electron transport and recombination and electrolyte diffusion. One way to improve the efficiency of these devices is by the design of highly ordered nanostructured semiconductor materials.The advantages can be two-fold: Firstly charge transport within the metal-oxide can be enhanced and hence thicker films can be employed and secondly, the complete permeation with a solid-state hole-transport medium of the sensitized metal-oxide can be facilitated. Nanostructured materials should promote vectorial electron diffusion and have as few recombination sights as possible so as to further enhance electron lifetimes and electron collection efficiencies. These materials should also have a high surface area so as to allow for efficient dye-loading and hence light absorption. Highly ordered TiO2 nanostructured films were prepared by reactive sputtering and their charge transport characteristics evaluated in DSCs. These were compared to DSCs employing mesoporous TiO2 films prepared by doctor blade technique using commercial paste. Charge transport characteristics were evaluated by impedance spectroscopy (IS), incident photon to current conversion efficiencies (IPCE) and current-voltage (iV) curves under simulated AM1.5G irradiation. Film morphology and structural properties were evaluated by scanning electron microscopy (SEM) and X-ray diffraction (XRD)...

Synchrotron SAXS Studies of Nanostructured Materials and Colloidal Solutions: A Review

Craievich,A.F.
Fonte: ABM, ABC, ABPol Publicador: ABM, ABC, ABPol
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/03/2002 EN
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Structural characterisations using the SAXS technique in a number of nanoheterogeneous materials and liquid solutions are reviewed. The studied systems are protein (lysozyme)/water solutions, colloidal ZnO particles/water sols, nanoporous NiO-based xerogels, hybrid organic-inorganic siloxane-PEG and PPG nanocomposites and PbTe semiconductor nanocrystals embedded in a glass matrix. These investigations also focus on the transformations of time-varying structures and on structural changes related to variations in temperature and composition. The reviewed investigations aim at explaining the unusual and often interesting properties of nanostructured materials and solutions. Most of the reported studies were carried out using the SAXS beamline at the National Synchrotron Light Laboratory (LNLS), Campinas, Brazil.

Synthesis and characterization of nanostructured ceramics powders for biomedical applications

Camargo,Nelson Heriberto de Almeida; Bellini,O. J.; Gemelli,Enori; Tomiyama,M.
Fonte: Rede Latino-Americana de Materiais Publicador: Rede Latino-Americana de Materiais
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/12/2007 EN
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Nanostructured materials have been largely studied in the last few years because they have a great potential to applications in different fields like physics, chemistry, biology, mechanic and medicine. Synthesis and characterization of nanostructured materials is a subject of great interest involving science, market, politicians, government and society. The nanostructured materials are in demand in biomedical area, mainly the bioceramics composed of calcium phosphates (Ca/P), which have an excellent biocompatibility and mineralogical characteristics similar to those of bones. The aim of this work was to optimize the method of powder synthesis of nanostructured calcium phosphate and of nanocomposites composed of calcium phosphate//SiO2n, containing 5, 10 and 15% (in volume) of nanometric silica (SiO2n). The results are expressed according to the method of synthesis, mineralogical and morphological characterization, and thermal behavior for the different compositions of the nanostructured powder synthesized.

Síntese e caracterização de TaC e óxido misto de tântalo e cobre nanoestruturados a partir do precursor oxálico de tântalo através de reações gás-sólido e sólido-sólido a baixa temperatura; Synthesis and characterization of TaC and Mixed Oxide Nanostructured Tantalum and Copper From The Precursor Oxalic Tantalum Through Reactions Gas-Solid and Solid-Solid Low Temperature

Lima, Maria José Santos
Fonte: Universidade Federal do Rio Grande do Norte; BR; UFRN; Programa de Pós-Graduação em Ciência e Engenharia de Materiais; Processamento de Materiais a partir do Pó; Polímeros e Compósitos; Processamento de Materiais a part Publicador: Universidade Federal do Rio Grande do Norte; BR; UFRN; Programa de Pós-Graduação em Ciência e Engenharia de Materiais; Processamento de Materiais a partir do Pó; Polímeros e Compósitos; Processamento de Materiais a part
Tipo: Dissertação Formato: application/pdf
POR
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The research and development of nanostructured materials have been growing significantly in the last years. These materials have properties that were significantly modified as compared to conventional materials due to the extremely small dimensions of the crystallites. The tantalum carbide (TaC) is an extremely hard material that has high hardness, high melting point, high chemical stability, good resistance to chemical attack and thermal shock and excellent resistance to oxidation and corrosion. The Compounds of Tantalum impregnated with copper also have excellent dielectric and magnetic properties. Therefore, this study aimed to obtain TaC and mixed tantalum oxide and nanostructured copper from the precursor of tris (oxalate) hydrate ammonium oxitantalato, through gas-solid reaction and solid-solid respectively at low temperature (1000 ° C) and short reaction time. The materials obtained were characterized by X-ray diffraction (XRD), Rietveld refinement, Scanning Electron Microscopy (SEM), Spectroscopy X-Ray Fluorescence (XRF), infrared spectroscopy (IR), thermogravimetric (TG), thermal analysis (DTA) and BET. Through the XRD analyses and the Reitiveld refinement of the TaC with S = 1.1584, we observed the formation of pure tantalum carbide and cubic structure with average crystallite size on the order of 12.5 nanometers. From the synthesis made of mixed oxide of tantalum and copper were formed two distinct phases: CuTa10O26 and Ta2O5...

Procedure for Synthesis of nanostructured materials with improved functional and/or structural properties via aerosol methods (Spray pyrolysis)

Rabanal Jiménez, Mª Eugenia
Fonte: Universidade Carlos III de Madrid Publicador: Universidade Carlos III de Madrid
Tipo: Relatório Formato: application/pdf
Publicado em 24/11/2008 ENG
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The Spanish University Carlos III de Madrid has developed a new method in order to obtain nanostructured particles (ceramic, metallic and composite) with improved functional and structural properties. Spray pyrolysis is a way in order to obtain nanostructured particles. Optimization of synthesis process, evaluating the experimental parameter as pH, concentration and chemical nature of precursor solution, density, viscosity, carrier gas, temperature of reactor, etc. allow us to synthesize materials with improved properties. The group is looking for technical cooperation with companies.

Processing and properties of high performance 7075 Al and AZ91 Mg powder metallurgy alloys

Jabbari Taleghani, Mohammad Ali
Fonte: Universidade Carlos III de Madrid Publicador: Universidade Carlos III de Madrid
Tipo: Tese de Doutorado
ENG
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48.08955%
Aluminum (Al) and magnesium (Mg) alloys have received considerable attention over the past decades as potential materials of choice to achieve significant weight savings. Although the market for Al and Mg products continues to grow, many opportunities remain untapped because of the low stiffness and strength of Al and Mg alloys in comparison with ferrous alloys and some other structural materials. On the other hand, grain refinement is considered an effective way to increase the strength of metallic materials. In recent years, high-energy milling has been widely exploited for the production of nanostructured materials, and grain sizes with nanometer dimensions have been observed in almost all high-energy milled pure metals, metallic alloys, and intermetallic compounds. Although the processing and characterization of nanostructured Al alloys and composites by mechanical alloying has been the subject of many studies, studies on the high-energy milling of Mg alloys are scarce. It should also be considered that to be suitable for structural applications, the nanocrystalline Al and Mg powders produced by mechanical alloying should then be consolidated to bulk materials. The consolidation route can have significant effects on the microstructure and mechanical properties of the processed bulk product. However...

Nanostructured Few-Layer Graphene with Superior Optical Limiting Properties Fabricated by a Catalytic Steam Etching Process

Sun, Zhenyu; Dong, Ningning; Xie, Kunpen; Xia, Wei; König, Dennis; Tharamani, Chikka Nagaiah; Sanchez, Miguel Dario; Ebbinghaus, Petra; Erbe, Andreas; Zhang, Xiaoyan; Ludwig, Alfred; Schuhmann, Wolfgang; Wang, Jun; Muhler, Martin
Fonte: American Chemical Society Publicador: American Chemical Society
Tipo: info:eu-repo/semantics/article; info:ar-repo/semantics/artículo; info:eu-repo/semantics/publishedVersion Formato: application/pdf
ENG
Relevância na Pesquisa
48.1621%
Tailoring the morphology and structure of graphene can result in novel properties for advanced applications. Here, we demonstrate the fabrication of nanostructured few-layer graphene through a mild etching process via catalytic steam gasification of carbon by Fe nanoparticles (NPs). Controlling the reaction temperature, steam concentration, and the loading density of the NPs enables the finetuning of the etching level of graphene. Well-defined nanotrenches with a width of less than 25 nm were formed by channeling of the catalytic NPs. Etching caves and  quasisemicircular etched edges were observed as well. The nonlinear optical properties of the resulting nanostructured graphene were studied under a 532 nm nanosecond pulse laser through an open-aperture apparatus. At the same level of the linear extinction coefficient, it exhibits superior optical limiting performance in comparison with pristine graphene and C60, showing a large potential in nanophotonic devices. This enhancement is ascribed to the defects formed by etching resulting in a finite band gap in nanostructured graphene.; Fil: Sun, Zhenyu. Ruhr-University Bochum. Laboratory of Industrial Chemistry; Alemania;; Fil: Dong, Ningning. Chinese Academy of Sciences. Shanghai Institute of Optics and Fine Mechanics. Key Laboratory of Materials for High-Power Laser; China;; Fil: Xie...

Organometallic derivatives of polyphosphazenes as precursors for metallic nanostructured materials

Valenzuela, María Luisa; Díaz, Carlos
Fonte: SPRINGER Publicador: SPRINGER
Tipo: Artículo de revista
EN
Relevância na Pesquisa
47.9564%
Co-polyphosphazenes containing anchored organometallic fragments are useful precursors for nanostructured metallic materials. Pyrolysis in air at 800 degrees yields metallic nanoparticles of the type, M degrees/M (x) O (y) /M (z) (P (x) O (y) )/P4O7, depending on the metal used; i.e., M degrees when the metal is a noble metal, metal oxide when the metal is Cr, W and Ru, metallic pyrophosphate when M = Mn and Fe. The organic spacer of the polyphosphazene influences strongly the morphology of the pyrolytic product. The mechanism of formation of the nanostructured materials involves carbonization of the organic matter, which produces holes where the nanoparticles are grown. Reaction of the phosphorus polymeric chain with O-2 yield phosphorus oxide units, which act as a P4O7 matrix to stabilize the nanoparticles and/orP(x)O(y)(-n) for the formation of metallic pyrophosphates. The method appears to be a general and versatile new route to metallic nanostructured materials.

The role of electromagnetic trapped modes in extraordinary transmission in nanostructured materials

Borisov, A. G.; de Abajo, F. J. García; Shabanov, S. V.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
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We assert that the physics underlying the extraordinary light transmission (reflection) in nanostructured materials can be understood from rather general principles based on the formal scattering theory developed in quantum mechanics. The Maxwell equations in passive (dispersive and absorptive) linear media are written in the form of the Schr\"{o}dinger equation to which the quantum mechanical resonant scattering theory (the Lippmann-Schwinger formalism) is applied. It is demonstrated that the existence of long-lived quasistationary eigenstates of the effective Hamiltonian for the Maxwell theory naturally explains the extraordinary transmission properties observed in various nanostructured materials. Such states correspond to quasistationary electromagnetic modes trapped in the scattering structure. Our general approach is also illustrated with an example of the zero-order transmission of the TE-polarized light through a metal-dielectric grating structure. Here a direct on-the-grid solution of the time-dependent Maxwell equations demonstrates the significance of resonances (or trapped modes) for extraordinary light transmissio; Comment: 14 pages, 6 figures; Discussion in Section 4 expanded; typos corrected; a reference added; Figure 4 revised

Morphological, structural and electrochemical properties of lithium iron phosphates synthesized by Spray Pyrolysis

Martín Hernández, María Isabel; Gómez, L. S.; Meatza, I. de; Bengoechea, M.; Cantero, I.; Rabanal, M. Eugenia
Fonte: Elsevier Publicador: Elsevier
Tipo: Artículo Formato: 1403281 bytes; application/pdf
ENG
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Article in Press, Accepted Manuscript.; In the field of materials for Lithium ion batteries, the lithium iron phosphate LiFePO4 has been proven for use as a positive electrode due to its good resistance to thermal degradation and overcharge, safety and low cost. The use of nanostructured materials would improve its efficiency. This work shows the results of the synthesis of nanostructured materials with functional properties for Lithium batteries through aerosol techniques. The Spray Pyrolysis method allows synthesizing nanostructured particles with spherical geometry, not agglomerates, with narrow distribution of particle size and homogeneous composition in respect to a precursor solution. Experimental techniques were focused on the morphological (SEM and TEM), structural (XRD and HRTEM-SAED), chemical (EDS) and electrochemical characterization.; The authors gratefully appreciate the financial support of the Ministry for Education and Science of Spain in the project “Advanced materials for Lithium batteries through alternative synthesis” (PIROLION project-PROFIT 2007-2008), MAT2007-64486-C07-05 (FEDER) and the Juan de la Cierva program JCI-2005-1892-13 (M.I. Martín). We thank I. Boyano for helpful discussions and A. Lago for experimental aid. The assistance in TEM characterization of the Electron Microscopy and Citometry Center...

Nanostructured micromaterials and devices for sensing and removing of chemical contaminants

López Marzo, Adaris María
Fonte: [Barcelona] : Universitat Autònoma de Barcelona, Publicador: [Barcelona] : Universitat Autònoma de Barcelona,
Tipo: Tesis i dissertacions electròniques; info:eu-repo/semantics/doctoralThesis Formato: application/pdf
Publicado em //2013 ENG; ENG
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This PhD thesis is related to the study and development of innovative nanostructured materials and devices join to strategies with interest for pollutants detection and removal being in line with the nowadays challenges of environmental technologies. The sensing and removing of chemical contaminants continues to be a research topic with an increasing interest for the scientific community. The development of novel nanostructured materials based on a CaCO3-polymer composite with different morphologies and polymorphs constitutes large part of this thesis. Material based on CaCO3-PEI from vaterite or calcite phase with spheric/ellipsoidic or rod shapes, respectively, have been synthesized. Several syntheses strategies modifying various reaction conditions were carried out up to finding of a new procedure, able to provide vaterite-PEI microspheres with controlled size and complete polymorph discrimination. In the new synthesis, CaCl2 and NaCO3 are mixing under 45 min of sonication, using 8 mg/mL poly(ethyleneimine) (PEI) as a crystal growth modifier (CGM) in the mixed water–organic solvent (H2O/EtOH). These hybrid nanostructured CaCO3(vaterite)-PEI material presents a high functionalizing capacity for biomolecules and an increase of the negative superficial charge. These properties make it suitable for electrochemical biosensor applications as demonstrated in collaborative works that appear in the annexes of this thesis. On the other hand...

Biocompatible Ti-based metallic glasses and nanocomposite materials

Hynowska, Anna
Fonte: [Barcelona] : Universitat Autònoma de Barcelona, Publicador: [Barcelona] : Universitat Autònoma de Barcelona,
Tipo: Tesis i dissertacions electròniques; info:eu-repo/semantics/doctoralThesis; info:eu-repo/semantics/publishedVersion Formato: application/pdf
Publicado em //2014 ENG
Relevância na Pesquisa
47.9513%
Aquesta Tesi comprèn la síntesi i caracterització d'aliatges de base Ti amorfs i nanoestructurats. Així, s'han estudiat diversos aliatges amb composició Ti-44.3Nb- 8.7Zr12.3Ta, Ti-31.0Fe-9.0Sn, Ti40Zr20Hf20Fe20, Ti45Zr15Pd35-xSi5Nbx (x = 0, 5%) com a exemples d'aliatges de base Ti nanoestructurats, i el vidre amorf massís Ti40Zr10Cu38Pd12. Aquests materials es van escollir tenint en compte les seves potencials aplicacions com a implants ortopèdics. La primera part d'aquesta Tesi va consistir en la síntesi i caracterització d'aquests aliatges bo i fent especial èmfasi en les correlacions existents en el triangle microestructura – comportament mecànic – biocompatibilitat. En la segona part es van dur a terme tractaments d'irradiació amb feixos d'ions del vidre amorf com a estratègia per modificar les seves propietats superficials i, de retruc, incrementar-ne la compatibilitat biomecànica. Totes les mostres es van sintetitzar per fusió d'arc i posterior emmotllament. Es va dur a terme una caracterització exhaustiva de tipus tèrmic i estructural de les mostres anteriorment mencionades mitjançant calorimetria diferencial d'escombrat (DSC), difracció de raigs X (XRD) i microscòpia electrònica de rastreig i transmissió (SEM...

Synthesis of nanoparticles and nanostructured materials by self-sssembly

Varón Izquierdo, Miriam
Fonte: [Barcelona] : Universitat Autònoma de Barcelona, Publicador: [Barcelona] : Universitat Autònoma de Barcelona,
Tipo: Tesis i dissertacions electròniques; info:eu-repo/semantics/doctoralThesis Formato: application/pdf
Publicado em //2012 ENG; ENG
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57.75755%
L'aparició de noves propietats químiques i físiques dins l'escala nanomètrica és un dels motius principals que fa necessari l'estudi de nanopartícules de diferents metalls, del seus òxids i dels seus aliatges, pel disseny de les seves futures aplicabilitats. Aquesta tesi estudia dos blocs temàtics: i) la síntesi i ii) l'autoensamblatge de nanopartícules metàl·liques. En el primer bloc, s'estudien els aspectes més rellevants de la preparació de nanopartícules metàl·liques (constituïdes per un o dos metalls diferents) de mida i forma controlada. Es desenvolupa les síntesis de diferents partícules magnètiques, i s'obtenen dispersions col·loïdals de nanopartícules de cobalt (Co) i alguns del seus òxids, així com d' or (Au), platí (Pt) i alguns dels seus aliatges. Les nanopartícules de Co estan rebent un interès creixent degut a les propietats magnètiques que presenta el material, la qual cosa les fa molt interessants per a un nombre elevat d'aplicacions tecnològiques. Però la sensibilitat del material en front l'oxidació (la qual produeix canvis en les seves propietats magnètiques) requereix que es faci un estudi profund d'aquests processos. En aquest treball, s'han sintetitzat nanopartícules de Co de diferents mides i s'han estudiat els paràmetres que afecten les seves propietats magnètiques. A més...

Preparation and characterization of bulk nanostructures Cu-Co magnetic alloys

Gartley, Michael
Fonte: Rochester Instituto de Tecnologia Publicador: Rochester Instituto de Tecnologia
Tipo: Tese de Doutorado
EN_US
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48.04147%
With new fabrication and measurement technologies now readily available, much attention has been focused on nanostructured materials. The sub-micron scale features of these materials gives them unique physical properties. To understand these properties, conventional methods of materials characterization are not always applicable. Therefore, new methods of characterization are needed for these nanostructured materials. In this project, we have developed nanostructured Cu-Co alloys. Alloys contain 0.3-5.0 wt% cobalt. Alloys are solution-annealed such that the cobalt dissolves in the solid copper phase. By subsequently aging the solid solutions with 1.5% Co at lower temperatures, the cobalt precipitates out of solution and forms precipitate particles with sizes ranging from 0-3 00A. The growth rate of these particles is a function of the aging temperature. These sub-micron sized cobalt particles possess interesting and useful magnetic properties. It was found that the Cu-Co solid solutions behave paramagnetically, with their initial susceptibility being proportional to the square of the cobalt content. For the aged alloys, magnetic methods are used to characterize the material. Using vibrating sample magnetometry, we measured saturation magnetization and coercivity. The saturation magnetization is a function of amount of cobalt that has precipitated out of solid solution. Cobalt concentration in solid solution was also obtained from x-ray diffraction analysis. The coercivity is a function of cobalt particle size and shape distribution. These magnetic particles were also characterized by magnetic force microscopy.

Energy transfer in nanostructured materials

Haughn, Chelsea
Fonte: University of Delaware Publicador: University of Delaware
Tipo: Tese de Doutorado
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68.1621%
Doty, Matthew; Energy transport and loss are critical to the performance of optoelectronic devices such as photovoltaics and terahertz imaging devices. Nanostructured materials provide many opportunities to tailor transport and loss parameters for specific device applications. However, it has been very difficult to correlate specific nanoscale structural parameters with changes in these performance metrics. I report the development of new ways of using time-resolved photoluminescence (TRPL) to probe charge and energy transport and loss dynamics. These techniques are applied to several types of nanostructured materials, including bulk semiconductors with defects, self-assembled quantum dots and colloidal quantum dots. First, GaAs/InP double heterostructures grown via metal organic chemical vapor deposition (MOCVD) were characterized with TRPL. TRPL is typically used to extract minority carrier lifetimes, but we discovered that the measured lifetime depended critically on the intensity of the exciting laser. We developed a Shockley-Read-Hall model to extract trap state densities from intensity-dependent TRPL measurements. Second, we characterized energy and charge transfer between InAs quantum dots and ErAs nanoinclusions within III-V heterostructures. Using intensity- and temperature-dependent TRPL...

Nanostructured photovoltaic materials using block polymer assemblies

Mastroianni, Sarah Elizabeth
Fonte: University of Delaware Publicador: University of Delaware
Tipo: Tese de Doutorado
Relevância na Pesquisa
47.982207%
Epps, Thomas H., III; Despite its potential as an abundant, sustainable alternative to non-renewable energy sources, solar energy currently is underutilized. Photovoltaics, which convert energy from sunlight into electricity, commonly are made from inorganic semiconductor materials that require expensive manufacturing and processing techniques. Alternatively, organic materials can be used to produce flexible and lightweight organic photovoltaic (OPV) devices, which can be prepared using solution-based processing techniques. However, OPV devices are limited by low efficiencies and short lifetimes compared to their inorganic counterparts. In OPV systems, charge carriers are generated in the active layer via the separation of excitons (electron-hole pairs) at interfaces between donor and acceptor materials. Because excitons have a limited diffusion length (???10 nm), they may recombine before reaching a donor-acceptor interface if domain sizes are large. This exciton recombination can limit device efficiency; thus, the design parameters for improved active layer morphologies include large interfacial areas, small size scales, and continuous conducting pathways. Currently, most OPV devices are prepared by blending donor and acceptor materials in bulk heterojunction (BHJ) devices...