Caractérisation des contraintes résiduelles dans les substrats de silicium cristallin pour le photovoltaïque

Le silicium obtenu par croissance cristalline de lingots massifs est la matière la plus utilisée dans l'industrie du photovoltaïque (PV). Outre les contraintes thermiques apparaissant durant la croissance, les techniques de mise en forme des lingots en substrats induisent des contraintes résiduelles faibles mais néfastes lors de la fabrication des cellules solaires. Le but de l'étude est de caractériser ces contraintes résiduelles afin d'améliorer le procédé de fabrication des substrats. La photoélasticimétrie infrarouge apparaît comme une méthode puissante pour la mesure de ces champs de contraintes faibles (quelques MPa) de façon non-destructive, sans contact et in-situ à l'échelle du substrat. Un banc de mesure a été mis en place afin de mener à bien l'étude. Les origines des contraintes résiduelles ont été dissociées et différents procédés de découpes ont été comparés

Drying nano particles solution on an oscillating tip at an air liquid interface: what we can learn, what we can do

Evaporation of fluid at micro and nanometer scale may be used to self-assemble nanometre-sized particles in suspension. Evaporating process can be used to gently control flow in micro and nanofluidics, thus providing a potential mean to design a fine pattern onto a surface or to functionalize a nanoprobe tip. In this paper, we present an original experimental approach to explore this open and rather virgin domain. We use an oscillating tip at an air liquid interface with a controlled dipping depth of the tip within the range of the micrometer. Also, very small dipping depths of a few ten nanometers were achieved with multi walls carbon nanotubes glued at the tip apex. The liquid is an aqueous solution of functionalized nanoparticles diluted in water. Evaporation of water is the driving force determining the arrangement of nanoparticles on the tip. The results show various nanoparticles deposition patterns, from which the deposits can be classified in two categories. The type of deposit is shown to be strongly dependent on whether or not the triple line is pinned and of the peptide coating of the gold nanoparticle. In order to assess the classification, companion dynamical studies of nanomeniscus and related dissipation processes involved with thinning effects are presented

Catalyst preparation for CMOS-compatible silicon nanowire synthesis

Metallic contamination was key to the discovery of semiconductor nanowires, but today it stands in the way of their adoption by the semiconductor industry. This is because many of the metallic catalysts required for nanowire growth are not compatible with standard CMOS (complementary metal oxide semiconductor) fabrication processes. Nanowire synthesis with those metals which are CMOS compatible, such as aluminium and copper, necessitate temperatures higher than 450 C, which is the maximum temperature allowed in CMOS processing. Here, we demonstrate that the synthesis temperature of silicon nanowires using copper based catalysts is limited by catalyst preparation. We show that the appropriate catalyst can be produced by chemical means at temperatures as low as 400 C. This is achieved by oxidizing the catalyst precursor, contradicting the accepted wisdom that oxygen prevents metal-catalyzed nanowire growth. By simultaneously solving material compatibility and temperature issues, this catalyst synthesis could represent an important step towards real-world applications of semiconductor nanowires.Comment: Supplementary video can be downloaded on Nature Nanotechnology websit

Uncertainty calculation of indoor and outdoor performance measurements for PV modules

Since uncertainties are often overlooked, this analysis highlights why considering uncertainties on PV power or efficiency values is crucial in order to compare published values for different PV technologies. Following the International Energy Agency Report on “Uncertainties in PV System Yield predictions and Assessments” and European FP7 Sophia project, the state of the art of outdoor and indoor uncertainty calculations on PV modules performances is reviewed. Calculation tools are compared and discussed in order to identify the most relevant one. Indoor measurements are based on instantaneous measurements with a dedicated set up: a solar simulator, called “flash-test”. The simulated conditions are close to the standard tests conditions with a stable irradiance, AMG1.5 spectrum and at 25 °C ± 1 °C, which are more stable than outdoor tests. Outdoor measurements are taken performed on variable time periods. Variations over months are commonly observed within ± 5 % that is why averaging on long periods looks relevant to reduce the standard deviation down to 1.3 %. Outdoor measurements are performed close to Chambery in France, under a soft alpine climate, with current-voltage curve tracers. Indoor and outdoor values are finally compared and discussed

Mechanical stirring: novel engineering approach for in situ spectroscopic analysis of melt at high temperature

International audienceThis paper proposes a novel engineering approach to control molten metals at high temperatures considering the industrial environment of such materials. To reduce analysis time and cost, in-line analysis techniques are more advantageous as they provide real-time information about melt composition. For this reason, recent research works focus on the development of new devices based on LIBS (Laser Induced Breakdown Spectroscopy). These devices allowed for analyzing impurities inside molten metals with great performance. However, improvements related to the immersion probe conception are still required. Indeed, the previous design used bubbling inside the melt, leading to spatial instabilities of the surface analyzed by LIBS. The solution presented here is mechanical stirring by innovative rotary blades which will be a part of an immersion LIBS probe. Their rotation will generate a representative, renewed, and stable surface that will be targeted by spectroscopic techniques in general and particularly by LIBS laser for molten metal monitoring at high temperatures. This solution was validated using experimental tests based on particle imaging velocimetry (PIV) in water at room temperature and then applied to silicon melt at high temperatures. To do so, it was necessary to design a system that allows the introduction of the blade in the melt and controls its rotation

Z-contrast cryo-electron tomography probes shell porosity in multi-shell nanocomposites

International audienceStructures of nanoparticles are becoming increasingly complex as they keep acquiring multi-functionality. These nanoparticles often adopt a core–shell structure and comprise different types of materials. Their outer shell forms the interface between the particle core and the environment. and its porosity governs any material exchange. Current techniques for measuring porosity exist for microscopic samples but techniques adapted to nanoscale samples are wanting. We probed indirectly the porosity of an outer silica shell grown over silica nanospheres by means of metal-chelating agents located in the interior of the nanospheres. Using a high-tilt cryo-holder, we performed electron tomography with a high-angle annular dark field detector to determine the 3D structure of these multi-shell nanocomposites. Contamination was significantly reduced at 104 K. Tomographic reconstructions revealed the distribution of functional domains binding metal ions that had penetrated the porous silica shell around the core particle

Comparative analysis of mechanical strength of diamond-sawn silicon wafers depending on saw mark orientation, crystalline nature and thickness

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