Buried screen-printed contacts for silicon solar cells

A Simple way to improve solar cell efficiency is to enhance the absorption of light and reduce the shading losses. One of the main objectives for the photovoltaic roadmap is the reduction of metalized area on the front side of solar cell by fin lines. Industrial solar cell production uses screen-printing of metal pastes with a limit in line width of 70-80 μm. This paper will show a combination of the technique of laser grooved buried contact (LGBC) and Screen-printing is able to improve in fine lines and higher aspect ratio. Laser grooving is a technique to bury the contact into the surface of silicon wafer. Metallization is normally done with electroless or electrolytic plating method, which a high cost. To decrease the relative cost, more complex manufacturing process was needed, therefore in this project the standard process of buried contact solar cells has been optimized in order to gain a laser grooved buried contact solar cell concept with less processing steps. The laser scribing process is set at the first step on raw mono-crystalline silicon wafer. And then the texturing etch; phosphorus diffusion and SiNx passivation process was needed once. While simultaneously optimizing the laser scribing process did to get better results on screen-printing process with fewer difficulties to fill the laser groove. This project has been done to make the whole production of buried contact solar cell with fewer steps and could present a cost effective opportunity to solar cell industries.

Mechanical and tribological properties of PVD-coated cemented carbide as evaluated by a new multi-pass scratch testing method

A new test method based on multipass scratch testing has been developed for evaluating the mechanical and tribological properties of thin, hard coatings. The proposed test method uses a pin-on-disc tribometer and during testing a Rockwell C diamond stylus is used as the “pin” and loaded against the rotating coated sample. The influence of normal load on the number of cycles to coating damage is investigated and the resulting coating damage mechanisms are evaluated by posttest scanning electron microscopy. The present study presents the test method by evaluating the performance of Ti0.86Si0.14N, Ti0.34Al0.66N, and (Al0.7Cr0.3)2O3 coatings deposited by cathodic arc evaporation on cemented carbide inserts. The results show that the test method is quick, simple, and reproducible and can preferably be used to obtain relevant data concerning the fatigue, wear, chipping, and spalling characteristics of different coating-substrate composites. The test method can be used as a virtually nondestructive test and, for example, be used to evaluate the fatigue and wear resistance as well as the cohesive and adhesive interfacial strength of coated cemented carbide inserts prior to cutting tests.

Estudo exploratório da deposição de filmes de diamante em alguns substratos cerâmicos

o presente trabalho é um estudo exploratório a respeito da síntese de filmes de diamante via deposiçãoquímica a vapor (CVD) sobre alguns substratos cerâmicos: diboreto de titânio (TiB2), ítria (Y20a), zircão (ZrSi04), zircônia parcialmente e totalmente estabilizada com ítria (Zr02), pirofilita ( Al2Si4OlO(OHh), .alumina (Al2Oa) e nitreto de boro hexagonal (h-BN). Estes substratos foram produzidos, em sua maioria, a partir da sinterização de pós micrométricos em altas temperaturas. Além do estudo em relação a possíveis candidatos alternativos ao tradicional silício para o crescimento de filmes auto-sustentáveis, procuramos encontrar substratos onde o filme aderisse bem e cujas propriedades tribológicas pudessem ser melhoradas com o recobrimento com filme de diamante.Dentre os materiais selecionados, constatamos que a topografia da superfície relacionada à densidade de contornos de grão, desempenha um papel relevante na nucleação do diamante. Além disso, os materiais que favorecem a formação de carbonetos conduziram a melhores resultados na nucleação e crescimento do filme, indicando que a ação da atmosfera reativa do CVD com o substrato também contribui decisivamente para o processo de nucleação. A partir dos resultados obtidos, concluímos que a aderência do filme de diamante ao zircão é excelente, assim como a qualidade do filme, o que pode serexplorado convenientemente caso as propriedades mecânicas do sinterizado de zircão sejam adequadas. No caso da zircônia parcialmente estabilizada, os resultados obtidos foram surpreendentes e este material poderia substituir o convencional substrato de silício para a deposição de filmes auto-sustentados de diamante, com inúmeras vantagens, dentre elas o fato de ser reutilizável e de não ser necessário ataque com ácidos para remoção do substrato, o que evita a geração de resíduos químicos.

Posicionamento estratégico : o caso da Union Carbide do Brasil

Análise das possíveis estratégias a serem adotadas pela Union Carbide do Brasil. Parte da premissa da decisão da empresa em não expandir seus negócios no Brasil. Considera que a estratégia de posicionamento é a mais adequada levando-se em conta as características da empresa, do mercado e as opções possíveis

Estudo da sinterização do aço inox 316L reforçado com 3% Carbeto de Tântalo - TaC

The present work shows a contribution to the studies of development and solid sinterization of a metallic matrix composite MMC that has as starter materials 316L stainless steel atomized with water, and two different Tantalum Carbide TaC powders, with averages crystallite sizes of 13.78 nm and 40.66 nm. Aiming the metallic matrix s density and hardness increase was added different nanometric sizes of TaC by dispersion. The 316L stainless steel is an alloy largely used because it s high resistance to corrosion property. Although, its application is limited by the low wear resistance, consequence of its low hardness. Besides this, it shows low sinterability and it cannot be hardened by thermal treatments traditional methods because of the austenitic structure, face centered cubic, stabilized mainly in nickel presence. Steel samples added with TaC 3% wt (each sample with different type of carbide), following a mechanical milling route using conventional mill for 24 hours. Each one of the resulted samples, as well as the pure steel sample, were compacted at 700 MPa, room temperature, without any addictive, uniaxial tension, using a 5 mm diameter cylindrical mold, and quantity calculated to obtain compacted final average height of 5 mm. Subsequently, were sintered in vacuum atmosphere, temperature of 1290ºC, heating rate of 20ºC/min, using different soaking times of 30 and 60 min and cooled at room temperature. The sintered samples were submitted to density and micro-hardness analysis. The TaC reforced samples showed higher density values and an expressive hardness increase. The complementary analysis in optical microscope, scanning electronic microscope and X ray diffractometer, showed that the TaC, processed form, contributed with the hardness increase, by densification, itself hardness and grains growth control at the metallic matrix, segregating itself to the grain boarders

Simulação computacional de medidas estereológicas em estruturas de metal duro (WC-Co)

This work focuses on the creation and applications of a dynamic simulation software in order to study the hard metal structure (WC-Co). The technological ground used to increase the GPU hardware capacity was Geforce 9600 GT along with the PhysX chip created to make games more realistic. The software simulates the three-dimensional carbide structure to the shape of a cubic box where tungsten carbide (WC) are modeled as triangular prisms and truncated triangular prisms. The program was proven effective regarding checking testes, ranging from calculations of parameter measures such as the capacity to increase the number of particles simulated dynamically. It was possible to make an investigation of both the mean parameters and distributions stereological parameters used to characterize the carbide structure through cutting plans. Grounded on the cutting plans concerning the analyzed structures, we have investigated the linear intercepts, the intercepts to the area, and the perimeter section of the intercepted grains as well as the binder phase to the structure by calculating the mean value and distribution of the free path. As literature shows almost consensually that the distribution of the linear intercepts is lognormal, this suggests that the grain distribution is also lognormal. Thus, a routine was developed regarding the program which made possible a more detailed research on this issue. We have observed that it is possible, under certain values for the parameters which define the shape and size of the Prismatic grain to find out the distribution to the linear intercepts that approach the lognormal shape. Regarding a number of developed simulations, we have observed that the distribution curves of the linear and area intercepts as well as the perimeter section are consistent with studies on static computer simulation to these parameters.

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

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, although the latter has been formed in lesser amounts

Estudo da molhabilidade de ligas de adição à base de prata sobre insertos cerâmicos para aplicação em brocas perfuração de poços de petróleo

Metal-ceramic interfaces are present in tricone drill bits with hard ceramic inserts for oil well drilling operations. The combination of actions of cutting, crushing and breaking up of rocks results in the degradation of tricone drill bits by wear, total or partial rupture of the drill bit body or the ceramic inserts, thermal shock and corrosion. Also the improper pressfitting of the ceramic inserts on the bit body may cause its total detachment, and promote serious damages to the drill bit. The improvement on the production process of metal-ceramic interfaces can eliminate or minimize some of above-mentioned failures presented in tricone drill bits, optimizing their lifetime and so reducing drilling metric cost. Brazing is a widely established technique to join metal-ceramic materials, and may be an excellent alternative to the common mechanical press fitting process of hard ceramic inserts on the steel bit body for tricone drill bit. Wetting phenomena plays an essential role in the production of metal/ceramic interfaces when a liquid phase is present in the process. In this work, 72Silver-28Copper eutectic based brazing alloys were melted onto zirconia, silicon nitride and tungsten carbide/Co substrates under high vacuum. Contact angle evolution was measured and graphically plotted, and the interfaces produced were analysed by SEM-EDX. The AgCu eutectic alloy did not wet any ceramic substrates, showing high contact angles, and so without chemical interaction between the materials. Better results were found for the systemns containing 3%wt of titanium in the AgCu alloy. The presence os titanium as a solute in the alloy produces wettable cand termodinamically stable compounds, increasing the ceramics wetting beahviour

Síntese e caracterização de CuNb2O6 e CuNbC através de reação sólido- sólido e gás- sólido a baixa temperatura

The refractory metal carbides have proven important in the development of engineering materials due to their properties such as high hardness, high melting point, high thermal conductivity and high chemical stability. The niobium carbide presents these characteristics. The compounds of niobium impregnated with copper also have excellent dielectric and magnetic properties, and furthermore, the Cu doping increases the catalytic activity in the oxidation processes of hydrogen. This study aimed to the synthesis of nanostructured materials CuNbC and niobium and copper oxide from precursor tris(oxalate) oxiniobate ammonium hydrate through gas-solid and solid-solid reaction, respectively. Both reactions were carried out at low temperature (1000°C) and short reaction time (2 hours). The niobium carbide was produced with 5 % and 11% of copper, and the niobium oxide with 5% of copper. The materials were characterized by X-Ray Diffraction (XRD), Rietveld refinement, Scanning Electron Microscopy (SEM), X-Ray Fluorescence Spectroscopy (XRF), infrared spectroscopy (IR), thermogravimetric (TG) and differential thermal analysis (DTA , BET and particle size Laser. From the XRD analysis and Rietveld refinement of CuNbC with S = 1.23, we observed the formation of niobium carbide and metallic copper with cubic structure. For the synthesis of mixed oxide made of niobium and copper, the formation of two distinct phases was observed: CuNb2O6 and Nb2O5, although the latter was present in small amounts

Effects of Silicon and Drought Stress on Tuber Yield and Leaf Biochemical Characteristics in Potato

Silicon has beneficial effects on many crops, mainly under biotic and abiotic stresses. Silicon can affect biochemical, physiological, and photosynthetic processes and, consequently, alleviates drought stress. However, the effects of Si on potato (Solanum tuberosum L.) plants under drought stress are still unknown. The objective of this study was to evaluate the effect of Si supply on some biochemical characteristics and yield of potato tubers, either exposed or not exposed to drought stress. The experiment was conducted in pots containing 50 dm(3) of a Typic Acrortox soil (33% clay, 4% silt, and 63% sand). The treatments consisted of the absence or presence of Si application (0 and 284.4 mg dm(-3)), through soil amelioration with dolomitic lime and Ca and Mg silicate, and in the absence or presence of water deficit (-0.020 MPa and -0.050 MPa soil water potential, respectively), with eight replications. Silicon application and water deficit resulted in the greatest Si concentration in potato leaves. Proline concentrations increased under lower water availability and higher Si availability in the soil, which indicates that Si may be associated with plant osmotic adjustment. Water deficit and Si application decreased total sugars and soluble proteins concentrations in the leaves. Silicon application reduced stalk lodging and increased mean tuber weight and, consequently, tuber yield, especially in the absence of water stress.

Nitrogen and silicon fertilization of upland rice

O silício não é considerado um elemento essencial para o crescimento e desenvolvimento das plantas, entretanto, sua absorção traz inúmeros benefícios, principalmente ao arroz, como aumento da espessura da parede celular, conferindo resistência mecânica a penetração de fungos, melhora o ângulo de abertura das folhas tornando-as mais eretas, diminuindo o auto-sombreamento e aumentando a resistência ao acamamento, especialmente sob altas doses de nitrogênio. O presente trabalho teve por objetivo avaliar os efeitos da adubação nitrogenada e silicatada nos componentes vegetativos, nos componentes da produção, na altura da planta e na produtividade da cultivar de arroz IAC 202. O experimento foi constituído da combinação de três doses de nitrogênio (5, 75 e 150 mg de N kg-1 de solo) aplicado na forma de uréia e quatro doses de silício (0, 200, 400 e 600 mg de SiO2 kg-1 de solo), aplicado na forma de silicato de cálcio. O delineamento experimental utilizado foi o inteiramente casualizado em esquema fatorial 3 ´ 4 (N = 5). A adubação nitrogenada aumentou o número de colmos e panículas por metro quadrado e o número total de espiguetas, refletindo na produtividade de grãos. O perfilhamento excessivo causado pela adubação nitrogenada inadequada causou redução na porcentagem de colmos férteis, na fertilidade das espiguetas e da massa de grãos. A adubação silicatada reduziu o número de espiguetas chochas por panícula e aumentou a massa de grãos sem, contudo, refletir na produtividade de grãos.

Silicon leaf application and physiological quality of white oat and wheat seeds

Plant nutrition can positively influence quality of seeds by improving plant tolerance to adverse climate. In this context, silicon is currently considered a micronutrient and it is beneficial to plant growth, especially Poaceaes such as white oat and wheat, thereby improving physiological quality of seeds. This study had the objective of evaluating the effects of silicon leaf application on plant tillering, silicon levels and physiological quality of white oat and wheat seeds besides establishing correlations between them. Two experiments were carried out in winter with white oat and wheat. The experimental design was the completely randomized block with eight replications. Treatments consisted of foliar application of silicon (0.8% of soluble silicon, as stabilized orthosilicic acid) and a control (with no application). Silicon levels in leaves were determined at flowering whereas the number of plants and panicles/spikes per area was counted right before harvest. Seed quality was evaluated right after harvest through mass, germination and vigor tests. Data was submitted to variance analysis and means were compared by the Tukey test at a probability level of 5%. Person's linear correlation test was performed among silicon level in plants, tillering and seed quality data. Silicon leaf application increases root and total length of white oat seedlings as an effect of higher Si level in leaves. Silicon leaf application increases mass of wheat seeds without affecting germination or vigor.

Seed germination and seedling development of white oat affected by silicon and phosphorus fertilization

Os fertilizantes silicatados tem sido cada vez mais usados na agricultura devido a inúmeros benefícios, tais como correção da acidez de solos tropicais e efeitos positivos no desenvolvimento de gramíneas. A disponibilidade de nutrientes e a nutrição de plantas desempenham papel importante na produção de sementes e podem influenciar a qualidade fisiológica de sementes de aveia-branca (Avena sativa L.). Avaliou-se a germinação de sementes e o desenvolvimento de plântulas de aveia-branca em função da adubação com silício e fósforo. O delineamento experimental foi inteiramente casualizado, em esquema fatorial 2 x 4, com seis repetições. Os tratamentos consistiram de 20 e 200 mg dm-3 de P2O5, aplicados na forma de superfosfato triplo, combinados com 0, 150, 300 e 450 mg dm-3 de Si na forma de silicato de potássio. O experimento foi realizado em casa de vegetação, conduzindo-se sete plantas por vaso, com capacidade para 15 L de terra. As panículas foram colhidas e debulhadas manualmente e, as sementes, armazenadas em sacos de papel em condições normais de ambiente. As sementes foram avaliadas quanto ao teor de água, massa de sementes, germinação, condutividade elétrica, comprimento e massa da matéria seca de plântulas. Sementes de aveia-branca com qualidade superior são produzidas com 20 mg dm-3 de P2O5, independente da dose de Si. Sementes com maior germinação e vigor são obtidas com 300 e 450 mg dm-3 de K2SiO3, respectivamente. Os comprimentos da raiz e total das plântulas foram inferiores nas doses de Si até 300 kg ha-1, porém a dose de fósforo somente afetou o desenvolvimento das plântulas de maneira distinta quando aplicada junto com a maior dose de silício.

DYNAMICS AT INFINITY of A CUBIC CHUA'S SYSTEM

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)