III-V semiconductor nanowires (NWs) are often referred to as one-dimensional (1-D) materials because of their high aspect ratios and excellent quantum confinement properties. Spacing between NWs in a NW array is on the order of ~102 nm, which is close to the wavelength of visible light. These properties make NWs have excellent light trapping effects and suitability for optoelectronic applications, such as solar cells and photodetectors. Gallium arsenide (GaAs) has high electron mobility and a band gap of 1.424 eV, which makes it an ideal material for solar cells. Since GaAs NWs can be grown on either GaAs substrates or foreign substrates such as silicon (Si) substrates without lattice mismatch issues, they are being widely studied for photovoltaic applications. GaAs NWs could be achieved by the vapor-liquid-solid (VLS) method in molecular beam epitaxy (MBE), or etching a GaAs substrate by inductively coupled plasma reactive ion etching (ICP-RIE). Cyclotene was used as the filling material in gaps between NWs to support a low sheet resistance front contact and prevent shunts. An In/ITO contact was developed to achieve a lower contact resistance to n-GaAs NWs than an ITO contact, while it had a similar transmittance as ITO. A crack test also showed that insertion of a thin indium layer between ITO and GaAs NWs solved the ITO crack issue during heating that resulted from a large difference in coefficients of thermal expansion (CTE) between ITO and cyclotene. Energy dispersive x-ray spectrometry (EDS) was used to determine indium diffusion into NWs, and it showed that indium diffusion was not so significant to damage the features in NWs. A novel method to achieve substrate-free NW arrays by combining ICP-RIE and selective chemical etching together was also introduced. This method made it possible to measure the transmittance of NW arrays and contact layers for the first time. Absorption of GaAs NW arrays with various NW diameters and periods were also determined experimentally. / Thesis / Master of Applied Science (MASc)

A study of thermal, structural, electrical and optical characteristics of molybdenum black surface coatings on various substrates has been made. The suitability of these coatings for use as selective absorbers for solar collector applications has been assessed. Molybdenum black (Mo black) coatings were prepared by electrodeposition (on aluminium) and a chemcial conversion method (on zinc and electroplated cobalt on nickel plated copper substrates). The solar absorptancer (αs) and thermal emittances (εth) of the coatings were determined from room temperature spectral reflectance measurements in the solar (0.3 to 2.5μm) and infrared regions (2.5 to 50 μm) respectively. The effect of different preparation parameters and substrate pretreatments on the spectral selectivity has been investigated in order to optimize the thermal performance. The spectral selectivity is related to the Mo-black coating thickness and surface roughness together with the microstructure, of the substrate and the intermediate layer. Dip coatings on polished zinc have significant selectivity (αs/ εth = 8.4 when αs = 0.76). The absorptance of the dip coatings is increased to 0.87 with εth = 0.13 by chemical etching of zinc prior to coating deposition. For coatings on electroplated cobalt on nickel plated copper (cobalt (NC) substrate), an absorptance as high as 0.94 has been obtained with an emittance value 0.3. By using an addition agent in the plating solution of cobalt the high emittance can be reduced to 0.1 with αs = 0.91 giving a coating with a relatively high efficiency (82.5%) for photo-thermal energy conversion. A study of the surface composition and microstructure of the coatings has been made using scanning and transmission electron microscopy together with electron diffraction, X-ray diffraction and X-ray photoelectron spectroscopy. The structural investigations indicate that Mo-black coatings contain polycrystals of orthorhombic Mo4O11 with a small proportion of Ni(OH)2. Presence of water and also Mo4O11 in the coatings are evident from IR spectroscopy study. The bandgap of the coating has been determined from optical transmission spectra (1.66 eV) and also from reflectance spectra (0.85 eV). The discrepancy between these two values has been discussed. The refractive indices of the coatings have also been estimated. The band gaps and refractive indices are found to be related to the spectral selectivity of the coatings. The durability test of the coatings shows that the coatings on etched zinc are more resistant to heat treatment than the coatings on unetched zinc. The coatings on cobalt (NC) substrates also show good stability for relatively short periods at temperatures ~400ºC. A study of the electrical properties of Mo-black coatings suggests that at electrical field strengths (greater than 106v/m the dominant conduction process is of the Poole-Frenkel type. The activation energy of the conduction process has been estimated to be -0.56 eV at higher temperatures. The effect of heat treatment on the electrical properties of the coatings has been examined. The dielectric constant of Mo-black has been estimated from A. C. measurements. At high frequency (20 kHz) the value of the dielectric constant is about 4.0.

Orientador: Mauricio Roriz / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Civil, Arquitetura e Urbanismo / Made available in DSpace on 2018-08-11T13:02:36Z (GMT). No. of bitstreams: 1 Dornelles_KelenAlmeida_D.pdf: 6559934 bytes, checksum: 3966f1604b84180c07c07723d60bf746 (MD5) Previous issue date: 2008 / Resumo: A radiação solar é responsável por importante parcela da carga térmica dos edifícios e seu impacto sobre esta carga depende, principalmente, da absortância solar do envelope construtivo. A falta de dados precisos e atualizados de absortância solar para superfícies opacas faz com que pesquisadores e especialistas utilizem a percepção visual ou adotem tabelas baseadas em cores, consagrando-se o conceito de que a absortância seria crescente na medida em que as cores fossem mais escuras. Para comprovar que a visão humana não é instrumento adequado para indicar o quanto uma superfície absorve de energia solar, este trabalho apresenta dados de absortância solar para diferentes cores e tipos de tintas utilizadas em superfícies opacas de edificações no Brasil, a partir de medições de refletância em espectrofotômetro. Com base nesses dados, são propostos métodos de determinação da absortância solar de superfícies opacas, que podem ser utilizados por projetistas, pesquisadores e especialistas. Além do espectrofotômetro, apresenta-se um método que se baseia na digitalização de amostras em scanner comum e posterior classificação de suas cores a partir dos sistemas cromáticos digitais RGB e HSL. O segundo método utiliza dados de refletância obtidos através do espectrômetro ALTA II e o terceiro método baseia-se em medidas de temperaturas superficiais das amostras, a partir de absortâncias medidas para amostras de cores branca e preta, adotadas como referência. Os dados de absortância solar obtidos com o espectrofotômetro foram ajustados ao espectro solar padrão, considerando-se que a energia solar não é constante ao longo do espectro. Este ajuste indicou que a absortância diminui quando submetida às diferentes intensidades da radiação solar. Finalmente, analisou-se o efeito da rugosidade superficial sobre a absortância solar de amostras pintadas com diferentes cores de tintas, cujos resultados indicaram que a rugosidade aumenta linearmente a absortância das superfícies. As diversas análises e discussões apresentadas neste trabalho comprovam que apenas a cor não é fator determinante da absortância de uma superfície opaca. Além disso, os métodos propostos para sua quantificação são bastante precisos e confiáveis, cujos valores estimados através dos métodos do scanner, ALTA II e medida de temperaturas superficiais apresentaram diferenças inferiores a 10%, 6,8% e 3,7%, respectivamente, quando comparados com as absortâncias medidas em espectrofotômetro / Abstract: Solar radiation is the main responsible factor for the thermal load of buildings, and its impact over this load depends, mainly, on the solar absorptance of the building envelope. The lack of reliable and current data implies that researchers and specialists use visual perception or adopt tables based on surface colors to quantify the solar absorptance, which enhances the concept that absorptance increases as much as colors are darker. In order to show that the human eye is not reliable indicator of how much solar energy a surface absorbs, this work presents solar absorptance data for different paint colors, which are commonly used in Brazilian façades, measured with a spectrophotometer. Based on these data, determination methods of solar absorptance are proposed and can be used by designers, researchers, and specialists. Besides the spectrophotometer, it is presented a method based on samples digital images through a scanner, in which samples were classified according to the RGB and HSL digital chromatic systems. The second method uses the reflectances of samples measured with the ALTA II spectrometer, and the third method is based on the samples surface temperatures and the absorptances of black and white reference samples. Solar absorptance data measured with the spectrophotometer were adjusted to the standard solar spectrum, because the solar energy is not constant along the solar spectrum. This correction indicated solar absorptance diminishes when submitted to different solar radiation intensities. Finally, the influence of roughness on the solar absorptance was analyzed, whose results indicated roughness linearly increases surfaces solar absorptance. The several analysis and discussions presented in this work prove that only color is not a determinant factor of the solar absorptance. Furthermore, proposed methods are very reliable to identify the solar absorptance of opaque surfaces, whose estimated values with scanner, ALTA II, and surface temperature methods presented differences under 10%, 6,8%, and 3,7%, respectively, when compared to the absorptances measured with the spectrophotometer / Doutorado / Arquitetura e Construção / Doutor em Engenharia Civil

<p>The optical efficiency of a commercially available sputter deposited spectrally selective solar absorber was improved. The main purposes were to decrease the thermal emittance, increase the solar absorbtance of the absorber and to protect the substrate from degradation due to environmental influence. The adhesion properties between the corrosion-protecting barrier and the substrate were also studied. This project was focused on process improvements that are realistic to implement in industrial production.</p><p>The thermal emittance of the absorber was decreased from 0.12 to 0.06 by changing the material of the corrosion-protecting layer from nickel-chromium to copper-nickel. Copper-nickel was less sensitive to variations in the sputter parameters than nickel-chromium. A novel method that could simplify the search for alternative corrosion resistant materials with a low thermal emittance has been purposed. Since resistivity data usually exist or can easily be measured and infrared measurements require more sophisticated measurements, the Hagen-Rubens relation was investigated for copper-nickel and nickel-chromium alloys. The dc-resistivity was found to be related to the infrared emittance or the integrated thermal emittance for alloys in their solid soluble fcc phase.</p><p>The solar absorbtance was increased when a graded index absorbing coating was tailored for a crossover of the reflectance from low to high reflectance at about 2.5 µm. The solar absorber graded index coating was optimized for nickel metal content in nickel oxide and a solar absorptance of 0.89-0.91 was achieved. The solar absorptance was further increased to 0.97 when an antireflection coating was added on top of the absorbing layer.</p><p>Finally, extrapolation algorithms were developed to assure correct determination of the thermal emittance for coatings on glass since modern spectrometers that do not cover the complete wavelength interval required to calculate the thermal emittance of surfaces at room temperatures accurately. The error arising from the extrapolation algorithms were smaller than the noise from the optical measurements. Similar strategies can be used for other surfaces.</p>

The optical efficiency of a commercially available sputter deposited spectrally selective solar absorber was improved. The main purposes were to decrease the thermal emittance, increase the solar absorbtance of the absorber and to protect the substrate from degradation due to environmental influence. The adhesion properties between the corrosion-protecting barrier and the substrate were also studied. This project was focused on process improvements that are realistic to implement in industrial production. The thermal emittance of the absorber was decreased from 0.12 to 0.06 by changing the material of the corrosion-protecting layer from nickel-chromium to copper-nickel. Copper-nickel was less sensitive to variations in the sputter parameters than nickel-chromium. A novel method that could simplify the search for alternative corrosion resistant materials with a low thermal emittance has been purposed. Since resistivity data usually exist or can easily be measured and infrared measurements require more sophisticated measurements, the Hagen-Rubens relation was investigated for copper-nickel and nickel-chromium alloys. The dc-resistivity was found to be related to the infrared emittance or the integrated thermal emittance for alloys in their solid soluble fcc phase. The solar absorbtance was increased when a graded index absorbing coating was tailored for a crossover of the reflectance from low to high reflectance at about 2.5 µm. The solar absorber graded index coating was optimized for nickel metal content in nickel oxide and a solar absorptance of 0.89-0.91 was achieved. The solar absorptance was further increased to 0.97 when an antireflection coating was added on top of the absorbing layer. Finally, extrapolation algorithms were developed to assure correct determination of the thermal emittance for coatings on glass since modern spectrometers that do not cover the complete wavelength interval required to calculate the thermal emittance of surfaces at room temperatures accurately. The error arising from the extrapolation algorithms were smaller than the noise from the optical measurements. Similar strategies can be used for other surfaces.

A building constructed according to the climatic characteristics in where it is inserted is important condition to reach thermal comfort and energy saving. However, into the brasilian s housing production predomine standardized architecture models all over the country, wich does not distinct the different local climates, producting, many times, environments without thermal comfort. Factors as the building arrangement, the glazed oppening s dimensions, its exposition to the sun and the thermal properties of the construction materials that compound the buildings envelope are points that define a better thermalenergetic performance. Therefore, this work evaluated the influence of the envelope shading and absorptance to the thermal performance and the energetic consumption of multiple housing buildings situated in Meceió AL having as studing object a model that represents a tipical vertial building tipology developed by PAR Programa de Arrendamento Residencial (Housing Leasehold Program). The methodology is based on parametric analisis in order to compare the reference model to some proposed parameters (solar protection devices, the surroundings and the external walls absorptance), using computer simulation by the EnergyPlus 4.0 software (Energyplus, 2009). To reach the proposed aims there werw vary a parameter by turn, maintaining the other several characteristics of the reference model. The results indicated that the use of solar protection devices and the profit of the building arragement morphology contributed to a better thermal and energetic performance of the building. The predominance of light colors on the external walls was a positive aspect to get fortunate thermal results, thus, is recomended that this characteristic be kept on the city housing programs of Maceio, because it contributed to the energy consumption reduction. / Fundação de Amparo a Pesquisa do Estado de Alagoas / Uma edificação construída de acordo com as características climáticas de onde está inserida é condição importante para a obtenção do conforto térmico e economia energética. Todavia, observa-se que no âmbito da produção habitacional brasileira há a predominância de modelos arquitetônicos padronizados em todo o país, sem distinção quanto às diversidades climáticas locais, produzindo-se muitas vezes ambientes com ausência de conforto térmico. Fatores como a disposição do arranjo construtivo, a dimensão e exposição solar das aberturas envidraçadas e as propriedades dos materiais construtivos que compõem a envoltória são pontos definidores para um melhor desempenho termoenergético de um edifício. Sendo assim, o presente trabalho avaliou a influência do sombreamento e da absortância da envoltória no desempenho térmico e consumo energético em edifícios residenciais multifamiliares localizados em Maceió AL, tendo como objeto de estudo um modelo que representa a tipologia típica de edifício vertical desenvolvido pelo Programa de Arrendamento Residencial PAR. A metodologia fundamentou-se em análises paramétricas visando à comparação entre o modelo de referência e alguns parâmetros propostos (dispositivo de proteção solar, o entorno e a absortância das paredes externas), através de simulações computacionais utilizando o programa EnergyPlus 4.0 (Energyplus, 2009). Para o alcance dos objetivos propostos foi variado um parâmetro por vez, preservando-se as demais características do modelo de referência. Os resultados obtidos indicaram que a utilização de protetor solar e o aproveitamento da morfologia do arranjo construtivo contribuíram para um melhor desempenho termoenergético do edifício. A consideração da predominância da cor clara na textura das paredes externas também foi um aspecto considerado positivo para a obtenção de resultados térmicos favoráveis e que se recomenda que seja mantida nos programas habitacionais para a cidade de Maceió, pois também implicou redução no consumo energético.

Philosophiae Doctor - PhD / The limited supply of fossil hydrocarbon resources and the negative impact of CO2 emission on the global environment dictate the increasing usage of renewable energy sources. Concentrating solar power (CSP) systems are the most likely candidate for providing the majority of the renewable energy. For efficient photo-thermal conversion, these systems require spectrally selective solar absorber surfaces with high solar absorbance in the solar spectrum region and low thermal emittance in the infrared region. In this thesis, a spectrally selective AlxOy/Pt/AlxOy multilayer solar absorber was designed and deposited onto copper substrate using electron beam evaporation at room temperature. The employment of ellipsometric measurements and optical simulation was proposed as an effective method to optimize and deposit the multilayer solar absorber coatings. The optical constants measured using spectroscopic ellipsometry, showed that both AlxOy layers, which used in the coatings, were dielectric in nature and the Pt layer was semi-transparent. The optimized multilayer coatings exhibited high solar absorptance ~ 0.94±0.01 and low thermal emittance ~ 0.06 ± 0.01 at 82oC.The structural and optical properties of the coatings were investigated. It was found that the stratification of the coatings consists of a semitransparent middle Pt layer sandwiched between two layers of AlxOy. The top and bottom AlxOy layers were nonstoichiometric with no crystalline phases present. The Pt layer is in the fcc crystalline phase with a broad size distribution and spheroidal shape in and between the rims of AlxOy. The surface roughness of the stack was found to be comparable to the inter-particle distance. To study the thermal stability of the multilayer solar absorber coatings, the samples were annealed at different temperatures for different duration in air. The results showed changes in morphology, structure, composition, and optical properties depend on both temperature and duration of annealing. The XRD pattern showed that the intensity of Pt decreased with increasing annealing temperature and therefore, disappeared at high temperature. With increasing annealing temperature, an increase in the size of Pt particles was observed from SEM. The AlxOy/Pt/AlxOy multilayer solar absorber coatings deposited onto Cu substrate were found to be thermally stable up to 500oC in air for 2 h with good spectral selectivity of 0.951/0.09. At 600oC and 700oC, the spectral selectivity decreased to 0.92/0.10 and 0.846/0.11 respectively, which is attributed to the diffusion of Cu and formation of CuO and Cu2O phases. Long term thermal stability study showed that the coatings were thermally stable in air up to 450oC for 24 h. To elucidate the degradation mechanism beyond 500oC, HI-ERDA has been used to study depth-dependent atomic concentration profiles. These measurements revealed outward diffusion of the copper substrate towards the surface and therefore, the decrease in the constituents of the coating. Hence, to prevent copper from diffusing towards the coatings, a thin Tantalum (Ta) layer was deposited between the base AlxOy layer and the copper substrate.The effect of a thin Ta layer on the thermal stability of AlxOy/Pt/AlxOy multilayer solar absorber coatings was investigated. The Cu/Ta/AlxOy/Pt/AlxOy multilayer solar absorber coatings were found to be thermally stable up to 700oC in air for 2 h with good spectral selectivity of 0.937/0.10. At 800oC, the spectral selectivity decreased to 0.870/0.12, which is attributed to the diffusion of Cu and formation of CuO phase. The formation of CuO phase was confirmed by XRD, EDS and Raman spectroscopy. Long term thermal stability study showed that the coatings were thermally stable in air up to 550oC for 24 h. Therefore, the Cu/Ta/AlxOy/Pt/AlxOy spectrally selective solar absorber coatings can be used for high temperature solar-thermal applications.

Made available in DSpace on 2015-05-14T12:09:28Z (GMT). No. of bitstreams: 1 arquivototal.pdf: 11490325 bytes, checksum: c5db739b54c8a079086312556753c528 (MD5) Previous issue date: 2013-09-30 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / Given the importance of adaptation of the building to the climate in search of more thermally and energy efficient buildings, this study evaluates the influence of shading devices and solar absorption coefficient of the envelope in the thermal and energy performance of residential buildings located in the Manaíra, João Pessoa-PB , through computer simulations, using the DesignBuilder program. The work involved the development of a methodology for the identification of the main characteristics of residential buildings in urban cutout study. Were analyzed 25 buildings with respect to: frequency of occurrence of numbers of floors, terrain and edification shape, area of apartments, percentage area of window and of wall in the facades, facade orientation, existence of elements of sun protection and constructive characteristics general. Based on the data collected, a representative model of constructive reality was elaborated, called predominant typology and used as the base case in the simulations. One set of typologies was simulated, determined from alterations constructive variables such as solar protection and absorption coefficient of the envelope, as well as, the urban variable surroundings obstruction. The analysis variables considered were the temperature of the internal air, solar gain through opaque and transparent closings and load required for cooling. Was observed that the shading caused in the area around contributes to a reduction in internal temperature and solar gain, but the balance is not always favorable, some models analyzed presented an increase in solar gain by opaque closings. Just like the density of surrounding area can elevate the air temperature and energy consumption in domestic environments. The use of the shutter openings resulted in better thermal and energy performance, higher than the adoption of low absorption coefficient ( = 0.20). / Diante da importância da adequação da edificação ao clima em busca de edificações mais eficientes termicamente e energeticamente, este trabalho avalia a influência dos dispositivos de sombreamento e do coeficiente de absorção solar da envoltória no desempenho térmico e energético de edifícios residenciais multipavimentos localizados no bairro de Manaíra, município de João Pessoa-PB, através de simulações computacionais, utilizando o programa DesignBuilder. O trabalho compreendeu o desenvolvimento de uma metodologia para o levantamento das principais características de edifícios residenciais multipavimentos no recorte urbano em estudo. Foram analisados 25 edifícios com relação à: frequência de ocorrência de números de pavimentos, forma do terreno e da edificação, área dos apartamentos tipo, percentual de área de janela e de parede nas fachadas, orientação das fachadas, existência de elementos de proteção solar e características construtivas gerais. Com base nos dados levantados, um modelo representativo da realidade construtiva foi elaborado, denominada de tipologia predominante e utilizada como caso base das simulações. Um conjunto de tipologias foi simulado, determinado a partir de alterações de variáveis construtivas, como proteção solar e coeficiente de absorção da envoltória, assim como, a variável urbana obstrução do entorno. As variáveis de análise consideradas foram a temperatura do ar interna, o ganho solar através dos fechamentos opacos e transparentes e a carga necessária para resfriamento. Observou-se que o sombreamento provocado pelo entorno contribui para a redução da temperatura interna e ganho de calor, porém nem sempre o balanço é favorável, alguns modelos analisados apresentaram um aumento no ganho solar pelos fechamentos opacos. Assim como, o adensamento do entorno, pode elevar a temperatura do ar e o consumo de energia nos ambientes internos. O uso da veneziana nas aberturas resultou no melhor desempenho térmico e energético, superior à adoção de baixo coeficiente de absorção (=0,20).

In the past few years, studies regarding new bio-based materials have led to an increased attention in the nanoscale product of cellulose, called nanocellulose. This biodegradable and renewable material has interesting physical, optical and thermal properties. The optical properties could be affected by tuning the nanostructure of the material, which makes it interesting for further investigation. The promising properties of nanocellulose can be useful in many different applications. The aim of this work was therefore to study the optical properties of nanocellulose, and to examine if the material is suitable for spectral design of camouflage or in passive cooling applications. The optical properties of a nanocellulose, specifically cellulose nanofiber (CNF), have been studied. Freestanding CNF films and CNF films deposited on glass substrates were made and characterized by spectroscopy, ellipsometry, BRDF measurements, and optical microscopy. The freestanding samples were examined with different CNF concentrations of 0.52% and 1.0%, and different thicknesses. The samples on glass substrates all had a concentration of 1.0% CNF, but with different amount deposited solution which was either drop or spin coated. The freestanding CNF samples show high transmission in the visual region and relatively high emissivity in the atmospheric windows. This implies that it can be used as an effective material for passive radiative cooling. A thicker sample could also be used to increase the emissivity in the atmospheric windows and improve the ability for passive cooling. The low reflectance, and high emissivity in the atmospheric windows can be promising for use in camouflage applications, according to earlier studies. However, the suitable properties are very dependent on the spectral response of the background. Additional measurements need to be performed and more specified scenarios are necessary to draw any further conclusions.

Absolicon is a pioneering solar technology development company specializing in the manufacturing and selling of advanced solar energy systems engineered to generate renewable energy for diverse use. Comprising essential components such as reflectors (mirrors) and a solar receiver tube, these solar energy systems are equipped to efficiently capture and convert solar irradiation into usable thermal energy. As an integral facet of an ongoing research, this project will contribute to optimize the reflection and absorption capacity in receiver tubes of Absolicon's solar collectors. The aim is to investigate optically selective plasmonic coatings intended as an undercoating in the solar selective surfaces. The main coating material that will be used and analysed is gold due to its plasmonic properties and inert nature as well as its low toxicity. The gold will be coated on stainless steel using physical vapor deposition (PVD) and then annealed at mid-to-high temperatures to produce a plasmonic surface. The effect of Au thicknesses, annealing times/temperature and will be investigated to optimize the coating with regards to optical properties based on a systematic method called Design of Experiments (DoE). The goal for the gold coating is to increase the reflectance in the infrared region while generating a plasmonic absorption peak in the visible region (the position and width will be optimized), making it a more beneficial surface to coat a solar selective surface than the original stainless steel (SS). It was found that the size and inter-particle distance of GNPs depend on the temperature and annealing time for different thickness. The surface analysis from SEM-images and AFM-topographs provided that samples with smaller grains are more likely to exhibit significant plasmonic effects compared to larger grains. According to the surface characterization, either thinner gold coating exposed to high temperature for short annealing time or thicker gold coating with longer annealing time provide plasmonic absorption peak in visible light region.