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Marzegalli A.,University of Milan Bicocca | Isa F.,Polytechnic of Milan | Groiss H.,Johannes Kepler University | Muller E.,ETH Zurich | And 8 more authors.
Advanced Materials | Year: 2013

An innovative strategy in dislocation analysis, based on comparison between continuous and tessellated film, demonstrates that vertical dislocations, extending straight up to the surface, easily dominate in thick Ge layers on Si(001) substrates. The complete elimination of dislocations is achieved by growing self-aligned and self-limited Ge microcrystals with fully faceted growth fronts, as demonstrated by AFM extensive etch-pit counts. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

Hannesschlager C.,Upper Austria University of Applied Sciences | Revol V.,Center Suisse dElectronique et Microtechnique | Plank B.,Upper Austria University of Applied Sciences | Salaberger D.,Upper Austria University of Applied Sciences | Kastner J.,Upper Austria University of Applied Sciences
Case Studies in Nondestructive Testing and Evaluation | Year: 2015

X-ray scatter dark field imaging (SDFI) tomography was used to investigate the glass fibre orientation of short fibre-reinforced polymers (SFRPs). The fibre orientation of fibre-reinforced polymers is decisive for the mechanical strength of injection-moulded parts. For this paper four different positions, with volumes along the melt flow and with weld lines, of an injection-moulded part were investigated with SDFI computed tomography with a voxel size of (43 μm)3 and absorption-based high resolution X-ray computed tomography (XCT) with a voxel size of (6.5 μm)3. The results of the SDFI computed tomography are compared with the fibre orientation to investigate the dependence of the SDFI signal on fibre orientation. The exact fibre orientation was determined by evaluation of the high resolution absorption XCT data. In particular, it is shown that the weld line and areas with different fibre orientations can be characterised by SDFI even at a voxel size of (43 μm)3 and that fibre orientation properties can be detected. © 2015 The Authors. Published by Elsevier Ltd. Source

Meduna M.,Masaryk University | Falu C.V.,Masaryk University | Falu C.V.,ETH Zurich | Isa F.,ETH Zurich | And 8 more authors.
Journal of Applied Crystallography | Year: 2016

Extending the functionality of ubiquitous Si-based microelectronic devices often requires combining materials with different lattice parameters and thermal expansion coefficients. In this paper, scanning X-ray nanodiffraction is used to map the lattice bending produced by thermal strain relaxation in heteroepitaxial Ge microcrystals of various heights grown on high aspect ratio Si pillars. The local crystal lattice tilt and curvature are obtained from experimental threedimensional reciprocal space maps and compared with diffraction patterns simulated by means of the finite element method. The simulations are in good agreement with the experimental data for various positions of the focused X-ray beam inside a Ge microcrystal. Both experiment and simulations reveal that the crystal lattice bending induced by thermal strain relaxation vanishes with increasing Ge crystal height. © 2016 International Union of Crystallography. Source

Ranieri J.,Ecole Polytechnique Federale de Lausanne | Vincenzi A.,Ecole Polytechnique Federale de Lausanne | Chebira A.,Center Suisse dElectronique et Microtechnique | Atienza D.,Ecole Polytechnique Federale de Lausanne | Vetterli M.,Ecole Polytechnique Federale de Lausanne
IEEE Transactions on Computers | Year: 2015

Chip designers place on-chip thermal sensors to measure local temperatures, thus preventing thermal runaway situations in many-core processing architectures. However, the quality of the thermal reconstruction is directly dependent on the number of placed sensors, which should be minimized, while guaranteeing full detection of all the worst case temperature gradient. In this paper, we present an entire framework for the thermal management of complex many-core architectures, such that we can precisely recover the thermal distribution from a minimal number of sensors. The proposed sensor placement algorithm is guaranteed to reduce the impact of noisy measurements on the reconstructed thermal distribution. We achieve significant improvements compared to the state of the art, in terms of both computational complexity and reconstruction precision. For example, if we consider a 64 cores systems-on-chip with 64 noisy sensors (σ2 = 4), we achieve an average reconstruction error of 1.5 °C, that is less than half of what previous state-of-the-art methods achieve. We also study the practical limits of the proposed method and show that we do not need realistic workloads to learn the model and efficiently place the sensors. In fact, we show that the reconstruction error is not significantly increased if we randomly generate the power-traces of the components or if we have just a part of the correct workload. © 2015 IEEE. Source

Taboada A.G.,ETH Zurich | Kreiliger T.,ETH Zurich | Falub C.V.,ETH Zurich | Isa F.,Polytechnic of Milan | And 13 more authors.
Applied Physics Letters | Year: 2014

We report on the mask-less integration of GaAs crystals several microns in size on patterned Si substrates by metal organic vapor phase epitaxy. The lattice parameter mismatch is bridged by first growing 2-μm-tall intermediate Ge mesas on 8-μm-tall Si pillars by low-energy plasma enhanced chemical vapor deposition. We investigate the morphological evolution of the GaAs crystals towards full pyramids exhibiting energetically stable {111} facets with decreasing Si pillar size. The release of the strain induced by the mismatch of thermal expansion coefficients in the GaAs crystals has been studied by X-ray diffraction and photoluminescence measurements. The strain release mechanism is discussed within the framework of linear elasticity theory by Finite Element Method simulations, based on realistic geometries extracted from scanning electron microscopy images. © 2014 AIP Publishing LLC. Source

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