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Core-shell Type Nanocrystalline Fto Photoanodes For Dye Sensitized Solar CellsIcli, Kerem Cagatay 01 September 2010 (has links) (PDF)
Aim of this work is to construct dye sensitized solar cells employing core shell type nanocrystalline FTO/TiO2 photoanodes. Fluorine doped tin dioxide (FTO) nanoparticles were synthesized under hydrothermal conditions. Homogeneously precipitated SnO2 nanoparticles were dispersed in aqueous solutions containing NH4F as fluorine source and heat treated at 180oC for 24 hours. X-Ray analysis revealed that particles show rutile type cassiterite structure. Particles had 50 m2/g specific surface area measured by BET. Particle size was around 15-20 nm verified by XRD, BET and SEM analysis. Electrical resistivity of the powders measured with four point probe technique was around 770 ohm.cm for an F/Sn atomic ratio of 5, which showed no further decrease upon increasing the fluorine content of solutions. Thick films were deposited by screen printing technique and SEM studies revealed that agglomeration was present in the films which decreased the visible light transmission measured by UV-Visible spectrophotometry. TiO2 shell coating was deposited by hydrolysis of ammonium hexafluorotitanate and TiCl4 aqueous solutions. Efficiency of FTO nanoparticles was enhanced upon surface treatment where best result was 4.61 % for cells treated with TiCl4. Obtained photocurrent of 22.8 mA/cm2 was considered to be very promising for the future work. Enhancement
v
in efficiency was mostly attributed to suppressed recombination of photoelectrons and it is concluded that improved efficiencies can be obtained after successful synthesis of FTO nanoparticles having lower resistivity values and deposition of homogeneous shell coatings.
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Nanocrystal Silicon Based Visible Light Emitting Pin DiodesAnutgan, Mustafa 01 December 2010 (has links) (PDF)
The production of low cost, large area display systems requires a light emitting material
compatible with the standard silicon (Si) based complementary metal oxide semiconductor
(CMOS) technology. The crystalline bulk Si is an indirect band semiconductor with very
poor optical properties. On the other hand, hydrogenated amorphous Si (a-Si:H) based wide
gap alloys exhibit strong visible photoluminescence (PL) at room temperature, owing to the
release of the momentum conservation law. Still, the electroluminescence (EL) intensity from
the diodes based on these alloys is weak due to the limitation of the current transport by the
localized states.
In the frame of this work, first, the luminescent properties of amorphous silicon nitride
(a-SiNx:H) thin films grown in a plasma enhanced chemical vapor deposition (PECVD) system
were analyzed with respect to the nitrogen content. Then, the doping effciency of p- and
n-type hydrogenated nanocrystalline Si (nc-Si:H) films was optimized via adjusting the deposition
conditions. Next, the junction quality of these doped layers was checked and further
improved in a homojunction pin diode.
Heterojunction pin light emitting diodes (LEDs) were fabricated with a-SiNx:H as the
luminescent active layer. The EL effciency of the fresh diodes was very low, as expected.
As a solution, the diodes were electro-formed under high electric field leading to nanocrystallization
accompanied by a strong visible light emission from the whole diode area. The
current-voltage (I-V) and EL properties of these transformed diodes were investigated in detail.
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Aplicações do método interação de configuraçäes ao estudo de espectroscopia eletrônica, fotoeletrônica e ressonância quadrupolar nuclear / Applications of Multireference Configuration Interaction Method to Electronic, Photoelectronic, and Nuclear Quadrupole Ressonance SpectroscopiesBorin, Antonio Carlos 10 December 1993 (has links)
Esta tese tem como objetivo central a descrição teórica rigorosa da estrutura, de propriedades e da espectroscopia de alguns sistemas diatômicos. Como abordagem de cálculo ela se serve da metodologia interação de configurações na sua forma conhecida como excitações simples e duplas a partir de um conjunto de múltiplas referências (MRSD-CI), além de conjuntos base relativamente extensos de funções Gaussianas Cartesianas contraídas. Ela propõe a existência de duas novas espécies moleculares, BeC e BeC+, para as quais um total de 20 estados eletrônicos (13 para o BeC e 7 para o BeC+) foram caracterizados através de suas curvas de potencial e de seus respectivos estados vibro-rotacionais. Constantes espectroscópicas para cada estado foram calculadas e os momentos elétricos das transições eletrônicas mais relevantes foram também estudados. Essas transições foram analisadas tanto em termos de probabilidades de transição calculadas via momento de transição como por meio de fatores de Franck-Condon. Transições vibro-rotacionais dentro de um mesmo estado eletrônico foram ainda examinadas. Para esses vários estados, tempos de vida radiativa foram também calculados. Complementando essa descrição espectroscópica, uma discussão sobre a natureza da ligação química nesses sistemas foi ainda apresentada. Conjugando os resultados obtidos para essas duas espécies, o espectro fotoeletrônico da molécula BeC foi simulado servindo-se da aproximação de Franck-Condon para estimar as intensidades das linhas de cada banda. Além de propriedades eletrônicas como o momento de dipolo, cálculos de gradiente de campo elétrico no átomo de berílio em função da distância internuclear foram também realizados com o propósito de fornecer dados teóricos confiáveis que permitam a determinação experimental do momento quadrupolar do núcleo de 9Be sobre o qual existe certa controvérsia na literatura. Tais cálculos, realizados para os sitemas BeH+ e BeC, além de incluirem o efeito da vibração molecular no gradiente de campo elétrico na forma de uma média vibracional, mostraram que a aproximação de Buckingham usada por alguns grupos não é apropriada para descrever tal efeito. / The aim of this thesis is to describe theoretically the structure, properties, and the spectroscopy of some diatomic species using the multirefence single and double excitations configuration interaction approach, and an extensive atomic basis set of contracted Cartesian Gaussian orbitals. Two new diatomic species are proposed, BeC and BeC+, for which twenty electronic states have been characterized (13 for BeC, and 7 for BeC+) by means of their potential energy curves and vibro-rotational states. Spectroscopic constants for both of them have been computed, as well as electric moments of the most relevant electronic transitions. The transitions have been described by using either transitions probabilities computed with the aid of the theoretical transition moment functions, or by Franck-Condon factors. Vibro-rotational transitions within the same electronic state have also been described. Radiative lifetimes have been computed for several states. Complementing the spectroscopic description, a descussion on the nature of the chemical bonding has also been presented. A combination of the results for the neutral and ionic species allowed the calculation of the vertical and adiabatic ionization potentials and the Franck-Condon distribution spectrum for transitions from the ground state of BeC to selected bound states of BeC+. Besides the electronic properties, as dipole moment, the electric field gradient at the 9Be nucleus has also been computed as a function of the internuclear distance with the purpose of providing reliable theoretical results to help in the spectroscopic determination of the nuclear quadrupole moment of 9Be, since the data reported to date do not seem to be so conclusive. This kind of analysis has been carried out for the species BeH+ and BeC. By taking into account the nuclear motion effects on the electric field gradient as an average over the vibrational wavefunction, it was possible to show that the commom practice of using the Buckingham\'s expression to compute such correction is not recornrnended.
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Pumping Chamber Design In Diode-pumped Solid-state Lasers For Maximum System Efficiency And Minimum Optical DistortionSezgin, Kubilay 01 January 2013 (has links) (PDF)
The beam quality and the system efficiency of a diode-pumped solid-state laser source are directly
related to the thermal profile inside the laser crystal. The thermal profile in a laser crystal should be
made uniform in order to reduce the negative effects of the thermal lens. However, the absorbed pump
profile that forms a uniform thermal profile inside the gain medium may adversely affect the system
efficiency. In this thesis, a computational and empirical method was developed for designing pumping
chambers that results in a suitable thermal profile inside the gain medium, and thus desired laser beam
quality was achieved while keeping the system efficiency at an acceptable level. Accomplishment of
this thesis work will lead to the design of pumping chambers and resonators in high power laser
systems operating at even higher thermal loads.
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The Effects Of Post-annealing Process On The Physical Properties Of Silver-indium-selenium Ternary Semiconductor Thin Films Deposited By Electron Beam TechniqueColakoglu, Tahir 01 August 2009 (has links) (PDF)
Ternary chalcopyrite compounds are the semiconductors with suitable properties
to be used as absorber materials in thin film solar cells. AgInSe2 is a promising
candidate with its several advantages over the widely used CuInSe2. The purpose of this study was to optimize the physical properties of the Ag-In-Se (AIS)
thin films that were deposited by e-beam evaporation of Ag3In5Se9 single crystal powder for solar cell applications by means of post-annealing process under
nitrogen atmosphere. The as-grown AIS thin films were annealed at 200, 300 and 400oC and their structural, optical, electrical and photoelectrical properties were examined to
observe the effects of post-annealing process. Structural characterization of the films was performed by X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) analyses. Optical properties of the films were investigated by optical transmittance measurements. Electrical and photoelectrical properties of the films were examined by temperature dependent conductivity, photoconductivity under different illumination intensities and spectral photoresponse measurements.
It was discovered that the annealing of AIS thin films at 200oC resulted in the best physical properties for solar cell applications. The obtained films were polycrystalline with mixed binary and ternary crystalline phases, such as
Ag3In5Se9, AgInSe2 and InSe, and showed n-type conductivity with room temperature conductivity value of 2.3x10-6 (Ohm­ / cm)-1. The band gap energy of the
200oC-annealed films was determined as 1.68 eV from spectral photoresponse measurements.
The results of the study revealed that the inadequate Ag incorporation and segregation and/or reevaporation of Se atoms at high annealing temperatures were the major problems encountered in producing single phase polycrystalline
AgInSe2 thin films. The required stoichiometry of thin films should be maintained during the growth of the films by means of an alternative deposition procedure and the films should be selenized during post-annealing process.
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Aplicações do método interação de configuraçäes ao estudo de espectroscopia eletrônica, fotoeletrônica e ressonância quadrupolar nuclear / Applications of Multireference Configuration Interaction Method to Electronic, Photoelectronic, and Nuclear Quadrupole Ressonance SpectroscopiesAntonio Carlos Borin 10 December 1993 (has links)
Esta tese tem como objetivo central a descrição teórica rigorosa da estrutura, de propriedades e da espectroscopia de alguns sistemas diatômicos. Como abordagem de cálculo ela se serve da metodologia interação de configurações na sua forma conhecida como excitações simples e duplas a partir de um conjunto de múltiplas referências (MRSD-CI), além de conjuntos base relativamente extensos de funções Gaussianas Cartesianas contraídas. Ela propõe a existência de duas novas espécies moleculares, BeC e BeC+, para as quais um total de 20 estados eletrônicos (13 para o BeC e 7 para o BeC+) foram caracterizados através de suas curvas de potencial e de seus respectivos estados vibro-rotacionais. Constantes espectroscópicas para cada estado foram calculadas e os momentos elétricos das transições eletrônicas mais relevantes foram também estudados. Essas transições foram analisadas tanto em termos de probabilidades de transição calculadas via momento de transição como por meio de fatores de Franck-Condon. Transições vibro-rotacionais dentro de um mesmo estado eletrônico foram ainda examinadas. Para esses vários estados, tempos de vida radiativa foram também calculados. Complementando essa descrição espectroscópica, uma discussão sobre a natureza da ligação química nesses sistemas foi ainda apresentada. Conjugando os resultados obtidos para essas duas espécies, o espectro fotoeletrônico da molécula BeC foi simulado servindo-se da aproximação de Franck-Condon para estimar as intensidades das linhas de cada banda. Além de propriedades eletrônicas como o momento de dipolo, cálculos de gradiente de campo elétrico no átomo de berílio em função da distância internuclear foram também realizados com o propósito de fornecer dados teóricos confiáveis que permitam a determinação experimental do momento quadrupolar do núcleo de 9Be sobre o qual existe certa controvérsia na literatura. Tais cálculos, realizados para os sitemas BeH+ e BeC, além de incluirem o efeito da vibração molecular no gradiente de campo elétrico na forma de uma média vibracional, mostraram que a aproximação de Buckingham usada por alguns grupos não é apropriada para descrever tal efeito. / The aim of this thesis is to describe theoretically the structure, properties, and the spectroscopy of some diatomic species using the multirefence single and double excitations configuration interaction approach, and an extensive atomic basis set of contracted Cartesian Gaussian orbitals. Two new diatomic species are proposed, BeC and BeC+, for which twenty electronic states have been characterized (13 for BeC, and 7 for BeC+) by means of their potential energy curves and vibro-rotational states. Spectroscopic constants for both of them have been computed, as well as electric moments of the most relevant electronic transitions. The transitions have been described by using either transitions probabilities computed with the aid of the theoretical transition moment functions, or by Franck-Condon factors. Vibro-rotational transitions within the same electronic state have also been described. Radiative lifetimes have been computed for several states. Complementing the spectroscopic description, a descussion on the nature of the chemical bonding has also been presented. A combination of the results for the neutral and ionic species allowed the calculation of the vertical and adiabatic ionization potentials and the Franck-Condon distribution spectrum for transitions from the ground state of BeC to selected bound states of BeC+. Besides the electronic properties, as dipole moment, the electric field gradient at the 9Be nucleus has also been computed as a function of the internuclear distance with the purpose of providing reliable theoretical results to help in the spectroscopic determination of the nuclear quadrupole moment of 9Be, since the data reported to date do not seem to be so conclusive. This kind of analysis has been carried out for the species BeH+ and BeC. By taking into account the nuclear motion effects on the electric field gradient as an average over the vibrational wavefunction, it was possible to show that the commom practice of using the Buckingham\'s expression to compute such correction is not recornrnended.
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