Multi-functional properties of CaCu3Ti4O12 thin films

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Evaluation of shear bond strength at the interface of two porcelains and pure titanium injected into the casting mold at three different temperatures

Statement of problem. Titanium has physical and mechanical properties, which have led to its increased use in dental prostheses despite casting difficulties due to high melting point and formation of oxide layers which affect the metal-ceramic bond strength.Purpose. This in vitro study evaluated the shear bond strength of the interface of 2 dental porcelains and pure titanium injected into a mold at 3 different temperatures.Material and methods. Using commercially pure (cp) titanium bars (Titanium, Grade I) melted at 1668degreesC and cast at mold temperatures of 430degreesC, 700degreesC or 900degreesC, 60 specimens were machined to 4 x 4 mm, with a base of 5 x 1 mm. The 4-mm surfaces were airborne-particle abraded with 100 mum aluminum oxide before applying and firing the bonding agent and evaluating the 2 porcelains (Triceram/Triline ti and Vita Titankeramik). Ten specimens were prepared for each temperature and porcelain combination Shear bond testing was performed in a universal testing machine, with a 500-kg load cell and crosshead speed of 0.5 mm/min. The specimens were loaded until failure. The interfaces of representative fractured specimens of each temperature were examined with a scanning electron microscope (SEM) and energy dispersive spectrometer (EDS). Data for shear bond strength (MPa) were statistically analyzed by 2-way ANOVA and the Tukey test (alpha = .05).Results. The results showed significant differences for the metal/porcelain interaction effect (P = .0464). There were no significant differences for the 2 porcelains (P = .4250). The Tukey test showed a significant difference between the pair cp Ti 430degreesC Triceram and cp Ti 900degreesC Triceram, with respective mean values and SDs of 59.74 +/- 11.62 and 34.03 +/- 10.35 MPa.Conclusion. Triceram porcelain showed a bond strength decrease with an increase in the mold temperature for casting titanium. The highest bond strength for Vita porcelain and the best metal-ceramic interface observed with the SEM were found with the mold temperature of 700degreesC.

Energy transfer and frequency upconversion in Yb3+-Er3+-doped PbO-GeO2 glass containing silver nanoparticles

We report the infrared-to-visible frequency upconversion in Er3+-Yb3+-codoped PbO-GeO2 glass containing silver nanoparticles (NPs). The optical excitation is made with a laser at 980 nm in resonance with the F-2(5/2)-> F-2(7/2) transition of Yb3+ ions. Intense emission bands centered at 525, 550, and 662 nm were observed corresponding to Er3+ transitions. The simultaneous influence of the Yb3+-> Er3+ energy transfer and the contribution of the intensified local field effect due to the silver NPs give origin to the enhancement of the whole frequency upconversion spectra.

Optically anisotropic and photoconducting Langmuir-Blodgett films of neat poly(3-hexylthiophene)

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Portadores quentes: modelo browniano

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Investigação de contatos elétricos e propriedades de filmes finos de SnO2 dopados com os íons terras raras Eu3+ e Ce3+

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Técnicas avançadas para caracterização de processos de transporte dependente do Spin

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Investigação das características I x V e C x V de NCPS puro, com nitrogênio substitucional carregado (-1 e +1) e com grupos doador (NO2)-aceitador (NH2) através de métodos derivados de hartree-fock

Neste trabalho, fizemos uma investigação sobre o estudo teórico das características I x V e C x V de Nanotubo Carbono de Parede Simples (NCPS) puro, com Nitrogênio substitucional carregado com cargas -1 (caracterizando um indicativo de dopagem tipo n) e +1 (caracterizando um indicativo de dopagem tipo p) e na presença de grupos doador (NO₂)-aceitador (NH₂), através da simulação computacional do estado fundamental de NCPS, bem como de sua estrutura eletrônica e propriedades ópticas, utilizando parametrizações semi-empíricas AM1 (Austin Mudel 1) e ZINDO/S-ClS (Zerner´s lntermediate Neglect of Differential Orbital/Spectroscopic - Cunfiguration lnteraction Single) derivadas da Teoria de Hartree-Fock baseada em técnicas de química quântica. Por meio deste modelo teórico analisamos as propriedades ópticas e eletrônicas, de maior interesse para esses materiais, a fim de se entender a melhor forma de interação desses materiais na fabricação de dispositivos eletrônicos, tais como TECs (Transistores de Efeito de Campo) ou em aplicações em optoeletrônica tais como DEL (Dispositivo Emissor de Luz). Observamos que NCPS com Nitrogênio substitucional apresentam defeitos conformacionais do tipo polarônico. Fizemos as curvas dos espectros UV-visível de Absorção para NCPS armchair e zigzag puro, com Nitrogênio substitucional carregado com cargas (-1 e +1) e na presença de grupos doador (NO₂)-aceitador (NH₂), quando perturbados por intensidades diferentes de campo elétrico. Verificamos que em NCPS zigzag ao aumentarmos a intensidade do campo elétrico, suas curvas sofrem grandes perturbações. Obtivemos as curvas p x E, I x V e C x V para esses NCPS, concluímos que NCPS armchair possui comportamento resistor, pois suas curvas são lineares e zigzag possui comportamento semelhante ao dos dispositivos eletrônicos importantes para o avanço tecnológico. Assim, nossos resultados estão de bom acordo com os resultados experimentais e teóricos de NCPS puro e com Nitrogênio encontrados na literatura.

Propriedades multifuncionais do CaCu3Ti4O12: estudo dos mecanismos e suas aplicações

Pós-graduação em Ciência e Tecnologia de Materiais - FC

Caracterização e aplicação da Blenda PEDOT : PSS/PVA na construção de eletrodos transparentes e dispositivos eletroluminescentes

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Desenvolvimento de sensor baseado em polímeros molecularmente impressos para determinação de álcoois superiores em óleo fúsel

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Liquid crystalline hexabenzocoronenes as organic molecular materials - synthesis, characterization and application

Die vorliegende Arbeit 'Liquid Crystalline Hexabenzocoronenes as Organic Molecular Materials - Synthesis, Characterization and Application' war durch drei Schwerpunkte definiert:1. Verbesserung der Synthese von Hexabenzocoronen Derivaten mit sechsfacher Alkyl-Substitution,2. Entwicklung von molekularen Materialien mit verbesserten Eigenschaften wie zum Beispiel Löslichkeit und Verarbeitbarkeit,3. Einsatz der entwickelten Moleküle in optoelektronischen Bauteilen wie zum Beispiel organischen Solarzellen und Feld-Effekt-Transistoren.Mit Hilfe einer neuen Syntheseroute ist es gelungen Aryl-Aryl und Aryl-Alkyl Kupplungen sehr spät in der Reaktionssequenz von Hexabenzocoronenen einzusetzen. Dies führte zu einer Vielzahl substituierter HBC Derivate. Die Einführung eines Phenyl Spacers zwischen den HBC Kern und die äußeren Alkylketten, wie zum Beispiel in HBC-PhC12, hatte eine Vielzahl positiver Effekte wie dramatisch verbesserte Löslichkeit und Flüssigkristallinität bei Raumtemperatur zur Folge. Die Kombination dieser Phänomene ermöglichte die Bildung hochgeordneter Filme, welche sehr wichtig für den Einsatz in organischen Bauelementen sind. Mit Hilfe von STM Techniken an der Fest-Flüssig Phasengrenze wurden hochgeordnete 2-D Strukturen der HBC Moleküle gefunden. Die Kombination von extrem hoher kolumnarer Ordnung, bestimmt mit Hilfe der Festkörper NMR Spektroskopie, mit einer konstant hohen Ladungsträgerbeweglichkeit, führte zu dem sehr erfolgreichen Einsatz von HBC-PhC12 in organischen Solarzellen.

Control of the long-range self-organization of polycyclic aromatic hydrocarbons for device applications

Electronic devices based on organic semiconductors have gained increased attention in nanotechnology, especially applicable to the field of field-effect transistors and photovoltaic. A promising class of materials in this reseach field are polycyclic aromatic hydrocarbons (PAHs). Alkyl substitution of these graphenes results in the selforganization into one-dimensional columnar superstructures and provides solubility and processibility. The nano-phase separation between the π-stacking aromatic cores and the disordered peripheral alkyl chains leads to the formation of thermotropic mesophases. Hexa-peri-hexabenzocoronenes (HBC), as an example for a PAH, exhibits some of the highest values for the charge carrier mobility for mesogens, which makes them promising candidates for electronic devices. Prerequisites for efficient charge carrier transport between electrodes are a high purity of the material to reduce possible trapping sites for charge carriers and a pronounced and defect-free, long-range order. Appropriate processing techniques are required to induce a high degree of aligned structures in the discotic material over macroscopic dimensions. Highly-ordered supramolecular structures of different discotics, in particular, of HBC derivatives have been obtained by solution processing using the zone-casting technique, zone-melting or simple extrusion. Simplicity and fabrication of highly oriented columnar structures over long-range are the most essential advantages of these zone-processing methods. A close relation between the molecular design, self-aggregation and the processing conditions has been revealed. The long-range order achieved by the zone-casting proved to be suitable for field effect transistors (FET).

Electronic energy transfer processes and charge carrier transport in pi-conjugated polymers

Conjugated polymers have attracted tremendous academical and industrial research interest over the past decades due to the appealing advantages that organic / polymeric materials offer for electronic applications and devices such as organic light emitting diodes (OLED), organic field effect transistors (OFET), organic solar cells (OSC), photodiodes and plastic lasers. The optimization of organic materials for applications in optoelectronic devices requires detailed knowledge of their photophysical properties, for instance energy levels of excited singlet and triplet states, excited state decay mechanisms and charge carrier mobilities. In the present work a variety of different conjugated (co)polymers, mainly polyspirobifluorene- and polyfluorene-type materials, was investigated using time-resolved photoluminescence spectroscopy in the picosecond to second time domain to study their elementary photophysical properties and to get a deeper insight into structure-property relationships. The experiments cover fluorescence spectroscopy using Streak Camera techniques as well as time-delayed gated detection techniques for the investigation of delayed fluorescence and phosphorescence. All measurements were performed on the solid state, i.e. thin polymer films and on diluted solutions. Starting from the elementary photophysical properties of conjugated polymers the experiments were extended to studies of singlet and triplet energy transfer processes in polymer blends, polymer-triplet emitter blends and copolymers. The phenomenon of photonenergy upconversion was investigated in blue light-emitting polymer matrices doped with metallated porphyrin derivatives supposing an bimolecular annihilation upconversion mechanism which could be experimentally verified on a series of copolymers. This mechanism allows for more efficient photonenergy upconversion than previously reported for polyfluorene derivatives. In addition to the above described spectroscopical experiments, amplified spontaneous emission (ASE) in thin film polymer waveguides was studied employing a fully-arylated poly(indenofluorene) as the gain medium. It was found that the material exhibits a very low threshold value for amplification of blue light combined with an excellent oxidative stability, which makes it interesting as active material for organic solid state lasers. Apart from spectroscopical experiments, transient photocurrent measurements on conjugated polymers were performed as well to elucidate the charge carrier mobility in the solid state, which is an important material parameter for device applications. A modified time-of-flight (TOF) technique using a charge carrier generation layer allowed to study hole transport in a series of spirobifluorene copolymers to unravel the structure-mobility relationship by comparison with the homopolymer. Not only the charge carrier mobility could be determined for the series of polymers but also field- and temperature-dependent measurements analyzed in the framework of the Gaussian disorder model showed that results coincide very well with the predictions of the model. Thus, the validity of the disorder concept for charge carrier transport in amorphous glassy materials could be verified for the investigated series of copolymers.

Thiophene- Based Materials for Photovoltaic Applications

Thiophene oligomers (OTs) and polymers (PTs) are currently attracting remarkable attention as organic materials showing semiconducting, fluorescent, nonlinear optical and liquid crystalline properties. All these properties can be fine-tuned through minor structural modifications. As a consequence, thiophene oligomers and polymers are among the most investigated compounds for applications in organic electronics, optoelectronics and thin film devices such as field effect transistors (FETs), light emitting diodes (LEDs) and photovoltaic devices (PVDs). Our research aims to explore the self-assembly features and the optical, electrical and photovoltaic properties of a class of thiophene based materials so far scarcely investigated, namely that of oligo- and polythiophenes head-to-head substituted with alkyl or S-alkyl chains. In particular, we synthesized these compounds in short reaction times, high yields, high purity and environmentally friendly procedures taking advantage of ultrasound (US) and microwave (MW) enabling technologies in Suzuki-Miyaura cross-couplings.