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Nievendick J.,Fraunhofer Institute for Solar Energy Systems | Kwapil W.,FMF Freiburger Materialforschungszentrum | Rentsch J.,Fraunhofer Institute for Solar Energy Systems
Conference Record of the IEEE Photovoltaic Specialists Conference | Year: 2011

Preferred grain boundary etching during acidic texturization of mc-Si wafers causes the formation of deep and sharp trench structures. This paper shows that their depth and sharpness directly influence the breakdown voltage at critical locations. This finding can be explained by the electric field enhancement at the curved tip of the etch pits, superposing the strong electric field surrounding the metal precipitates which are due to Schottky contact formation. This paper shows that it is possible to engineer the breakdown behavior in critical material by choosing an appropriate texturization method. © 2011 IEEE. Source

Blum K.,University Hospital Freiburg | Wiest W.,University of Wurzburg | Fella C.,University of Wurzburg | Balles A.,University of Wurzburg | And 8 more authors.
Dental Materials | Year: 2015

Objectives Based on the current lack of data and understanding of the wear behavior of dental two-piece implants, this study aims for evaluating the microgap formation and wear pattern of different implants in the course of cyclic loading. Methods Several implant systems with different conical implant-abutment interfaces were purchased. The implants were first evaluated using synchrotron X-ray high-resolution radiography (SRX) and scanning electron microscopy (SEM). The implant-abutment assemblies were then subjected to cyclic loading at 98 N and their microgap was evaluated after 100,000, 200,000 and 1 million cycles using SRX, synchrotron micro-tomography (μCT). Wear mechanisms of the implant-abutment connection (IAC) after 200,000 cycles and 1 million cycles were further characterized using SEM. Results All implants exhibit a microgap between the implant and abutment prior to loading. The gap size increased with cyclic loading with its changes being significantly higher within the first 200,000 cycles. Wear was seen in all implants regardless of their interface design. The wear pattern comprised adhesive wear and fretting. Wear behavior changed when a different mounting medium was used (brass vs. polymer). Significance A micromotion of the abutment during cyclic loading can induce wear and wear particles in conical dental implant systems. This feature accompanied with the formation of a microgap at the IAC is highly relevant for the longevity of the implants. © 2015 Academy of Dental Materials. Source

Heikkinen H.,VTT Technical Research Center of Finland | Gadda A.,VTT Technical Research Center of Finland | Vahanen S.,VTT Technical Research Center of Finland | Salonen J.,VTT Technical Research Center of Finland | And 4 more authors.
IEEE Nuclear Science Symposium Conference Record | Year: 2012

The article describes a low temperature bump bonding process to flip chip bond CdTe sensors on Timepix readout chips with two separate pixel pitches: 55 μm and 110 μm. Because the sensor properties of CdTe start to degrade around 150°C, InSn (48-52) solder joints were used. The solder bumping process flow and flip chip bonding routine are described, and leakage currents and radiation images are compared at different pitches. The results show low leakage currents and a good bump bonding yield with both pitches. © 2011 IEEE. Source

Alaribe L.,FMF Freiburger Materialforschungszentrum | Disch C.,FMF Freiburger Materialforschungszentrum | Fauler A.,FMF Freiburger Materialforschungszentrum | Engels R.,Julich Research Center | And 6 more authors.
IEEE Transactions on Nuclear Science | Year: 2012

Much work is going on presently to improve the crystal growth and packaging of the Eu 2+ activated SrI 2 scintillator, thanks to its excellent scintillation properties like high light yield and good energy resolution. Larger crystals are needed for spectroscopic applications, and proper packaging is important for long-time field use and application in other areas due to its hygroscopic nature. In this paper, we report on the successful growth of a SrI 2Eu[6mol%] single crystal in silica ampoule to prevent melt hydration and oxygen contamination using the vertical Bridgman technique. The scintillation properties of a 0.314 cm 3SrI 2:Eu sample are presented, showing a light output of ∼ 80000 ph/MeV. A 360 μm sample was investigated for X-ray imaging applications; we also show how the sample was prepared for the measurement and the result of this preliminary investigation. © 2012 IEEE. Source

Zang A.,Erlangen Center for Astroparticle Physics | Pelzer G.,Erlangen Center for Astroparticle Physics | Anton G.,Erlangen Center for Astroparticle Physics | Ballabriga Sune R.,CERN | And 11 more authors.
Progress in Biomedical Optics and Imaging - Proceedings of SPIE | Year: 2014

Photon-counting detectors in medical x-ray imaging provide a higher dose efficiency than integrating detectors. Even further possibilities for imaging applications arise, if the energy of each photon counted is measured, as for example K-edge-imaging or optimizing image quality by applying energy weighting factors. In this contribution, we show results of the characterization of the Dosepix detector. This hybrid photon- counting pixel detector allows energy resolved measurements with a novel concept of energy binning included in the pixel electronics. Based on ideas of the Medipix detector family, it provides three different modes of operation: An integration mode, a photon-counting mode, and an energy-binning mode. In energy-binning mode, it is possible to set 16 energy thresholds in each pixel individually to derive a binned energy spectrum in every pixel in one acquisition. The hybrid setup allows using different sensor materials. For the measurements 300 μm Si and 1 mm CdTe were used. The detector matrix consists of 16 x 16 square pixels for CdTe (16 x 12 for Si) with a pixel pitch of 220 μm. The Dosepix was originally intended for applications in the field of radiation measurement. Therefore it is not optimized towards medical imaging. The detector concept itself still promises potential as an imaging detector. We present spectra measured in one single pixel as well as in the whole pixel matrix in energy-binning mode with a conventional x-ray tube. In addition, results concerning the count rate linearity for the different sensor materials are shown as well as measurements regarding energy resolution. © 2014 SPIE. Source

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