Laser applications in thin-film photovoltaics

We review laser applications in thin-film photovoltaics (thin-film Si, CdTe, and Cu(In,Ga)Se2 solar cells). Lasers are applied in this growing field to manufacture modules, to monitor Si deposition processes, and to characterize opto-electrical properties of thin films. Unlike traditional panels based on crystalline silicon wafers, the individual cells of a thin-film photovoltaic module can be serially interconnected by laser scribing during fabrication. Laser scribing applications are described in detail, while other laser-based fabrication processes, such as laser-induced crystallization and pulsed laser deposition, are briefly reviewed. Lasers are also integrated into various diagnostic tools to analyze the composition of chemical vapors during deposition of Si thin films. Silane (SiH4), silane radicals (SiH3, SiH2, SiH, Si), and Si nanoparticles have all been monitored inside chemical vapor deposition systems. Finally, we review various thin-film characterization methods, in which lasers are implemente

Optical emission spectroscopy to diagnose powder formation in SiH4-H2 discharges

Silane and hydrogen discharges are widely used for the deposition of silicon thin film solar cells in large area plasmaenhanced chemical vapor deposition reactors. In the case of microcrystalline silicon thin film solar cells, it is of crucial importance to increase the deposition rate in order to reduce the manufacturing costs. This can be performed by using high silane concentration, and usually high RF power and high pressure, all favorable to powder formation in the discharge that generally reduces the deposition rate as well as the deposited material quality. This work presents a study of powder formation using time-resolved optical emission spectroscopy. It is shown that this technique is suitable to detect different regimes in powder formation ranging from powder free discharge to discharge producing large dust particles. Intermediate powder formation regimes include the formation of small silicon clusters at plasma ignition as well as cycle of powder growth and ejection out of the discharge, and both are observable by this low-cost and experimentally simple technique

Laser applications in thin-film photovoltaics

We review laser applications in thin-film photovoltaics (thin-film Si, CdTe, and Cu(In,Ga)Se2 solar cells). Lasers are applied in this growing field to manufacture modules, to monitor Si deposition processes, and to characterize opto-electrical properties of thin films. Unlike traditional panels based on crystalline silicon wafers, the individual cells of a thin-film photovoltaic module can be serially interconnected by laser scribing during fabrication. Laser scribing applications are described in detail, while other laserbased fabrication processes, such as laser-induced crystallization and pulsed laser deposition, are briefly reviewed. Lasers are also integrated into various diagnostic tools to analyze the composition of chemical vapors during deposition of Si thin films. Silane (SiH4), silane radicals (SiH3, SiH2, SiH, Si), and Si nanoparticles have all been monitored inside chemical vapor deposition systems. Finally, we review various thin-film characterization methods, in which lasers are implemented

Modeling enteric methane emission from beef cattle in Brazil: a proposed equation performed by principal component analysis and mixed modeling multiple regression.

Brazil has the largest commercial beef cattle herd in the world but does not have its own model to predict methane (CH4 ) emission. The aim of this study was to create the first empirical enteric CH4 emission equation from variables that describe the animal diet using a meta-analytical data from Brazilian scientific publications (n = 50, published from 2003 to 2012)

Impact of secondary gas-phase reactions on microcrystalline silicon solar cells deposited at high rate

The role of secondary gas-phase reactions during plasma-enhanced chemical vapor deposition of microcrystalline silicon is a controversial subject. In this paper, we show that the enhancement of such reactions is associated with the improvement of material properties of absorber layers deposited at high constant rate. We detect powder, a product of secondary gas-phase reactions, via infrared laser absorption spectroscopy, laser light scattering, and optical emission spectroscopy. As the powder formation is increased, we measure a systematic improvement of device performance. This demonstrates that secondary gas-phase reactions are not detrimental to the material quality of microcrystalline silicon deposited at high rate. © 2010 American Institute of Physics

Equipamentos, instalações e protocolos de mensuração de consumo de matéria seca em bovinos

Data of dry matter intake (DMI) individually measured in animals are critical to the feed efficiency (FE) indexes. This information guide the decisions made in breeding programs. Here, the objective was describes the technologies and protocols available to measure the DMI in cattle and the use of these information on genetic evaluations. The electronic identification by radio frequency when coupled with weighing bunks (plus storage of data) can be used for monitoring the DMI throughout the day. When performed at individual pens, the cattle feedlot may change the behavior, performance and, consequently, the FE. Thus, the relevance of data at these housing types can be questioned. Calan-gate is an alternative system for collective pens, however, dominant animals can get access to food of subordinates. In the GrowSafe System it is possible obtained data of DMI plus the time (duration) and frequency (bunk attendance). Studies indicate that changes in DMI are due to interactions and behavior of animals in collective pens. In the context of genetic evaluation, although individual pens (IP) are useful for measuring DMI, this condition is not representative. Data from IP can negatively impact on estimates of heritability for DMI and FE. Several studies have shown that there is moderate to strong genetic correlation between the DMI data and FE indexes, showing considerable variation exists among animals. Thus, genetic selection using these features greatly increase profitability in the beef cattle production system. Additionally, the accuracy and precision in the measurement of DMI are critical in this process.Dados de consumo de matéria seca (CMS) são fundamentais para o cálculo dos índices de eficiência alimentar, os quais norteiam as tomadas de decisões nos programas de seleção genética. Objetivou-se abordar as tecnologias disponíveis para medir o CMS em bovinos, os protocolos de mensuração de consumo, bem como a utilização destes nas avaliações genéticas. Entre as tecnologias, a identificação eletrônica por rádio frequência, acoplada a cochos com pesagem e armazenamento dos dados pode ser usada para o monitoramento do CMS ao longo do dia. Quando feito em baias individuais, o confinamento pode alterar o comportamento, desempenho e eficiência alimentar, e, consequentemente, a relevância dos dados nessas instalações pode ser questionada. O Calan-gate é um equipamento alternativo para baias coletivas, contudo animais dominantes podem conseguir acesso ao alimento dos subordinados. Já o GrowSafe, além de registrar o CMS de cada animal, efetua a medição do tempo (duração) e frequência (quantas vezes o animal frequenta o cocho). Visando qualidade dos dados de CMS e eficiência alimentar, os testes de desempenho devem ter duração mínima de 70 dias, contudo esse tempo pode variar de acordo com as diferenças biológicas entre os animais e variabilidade associada ao erro de medição. Vários trabalhos demonstram que existe de moderada a forte correlação genética entre os dados de CMS e os índices de eficiência alimentar, mostrando que considerável variação para esta característica existe entre os animais. Com isso, a seleção genética utilizando essas características aumentaria consideravelmente a rentabilidade no sistema de produção de bovinos de corte, sendo que a acurácia e precisão na mensuração do CMS são fundamentais nesse processo

Measuring sub-mm structural displacements using QDaedalus: a digital clip-on measuring system developed for total stations

The monitoring of rigid structures of modal frequencies greater than 5 Hz and sub-mm displacement is mainly based so far on relative quantities from accelerometers, strain gauges etc. Additionally geodetic techniques such as GPS and Robotic Total Stations (RTS) are constrained by their low accuracy (few mm) and their low sampling rates. In this study the application of QDaedalus is presented, which constitutes a measuring system developed at the Geodesy and Geodynamics Lab, ETH Zurich and consists of a small CCD camera and Total Station, for the monitoring of the oscillations of a rigid structure. In collaboration with the Institute of Structural Engineering of ETH Zurich and EMPA, the QDaedalus system was used for monitoring of the sub-mm displacement of a rigid prototype beam and the estimation of its modal frequencies up to 30 Hz. The results of the QDaedalus data analysis were compared to those of accelerometers and proved to hold sufficient accuracy and suitably supplementing the existing monitoring techniques