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Lorenzo F.,Ecole Polytechnique Federale de Lausanne | Aebersold A.B.,Ecole Polytechnique Federale de Lausanne | Morales-Masis M.,Ecole Polytechnique Federale de Lausanne | Ledinsky M.,ASCR Institute of Physics Prague | And 9 more authors.
ACS Applied Materials and Interfaces | Year: 2017

Two fundamental requirements of transparent conductive oxides are high conductivity and low optical absorptance, properties strongly dependent on the free-carrier concentration of the film. The free-carrier concentration is usually tuned by the addition of dopant atoms; which are commonly assumed to be uniformly distributed in the films or partially segregated at grain boundaries. Here, the combination of secondary ion mass spectroscopy at the nanometric scale (NanoSIMS) and Kelvin probe force microscopy (KPFM) allows direct imaging of boron-dopant distribution in polycrystalline zinc oxide (ZnO) films. This work demonstrates that the boron atoms have a bimodal spatial distribution within each grain of the ZnO films. NanoSIMS analysis shows that boron atoms are preferentially incorporated into one of the two sides of each ZnO grain. KPFM measurements confirm that boron atoms are electrically active, locally increasing the free-carrier concentration in the film. The proposed cause of this nonuniform dopant distribution is the different sticking coefficient of Zn adatoms on the two distinct surface terminations of the ZnO grains. The higher sticking coefficient of Zn on the c+ surface restricts the boron incorporation on this side of the grains, resulting in preferential boron incorporation on the c- side and causing the bimodal distribution. © 2017 American Chemical Society.

Kreiliger T.,ETH Zurich | Falub C.V.,ETH Zurich | Taboada A.G.,ETH Zurich | Isa F.,Polytechnic of Milan | And 9 more authors.
Physica Status Solidi (A) Applications and Materials Science | Year: 2014

Monolithic integration of absorber layer and readout electronics is expected to greatly improve spatial resolution and sensitivity of X-ray imaging detectors. It requires, however, heteroepitaxial growth of thick, lattice, and thermally mismatched absorber layers on a Si substrate. Wafer bowing and layer cracks induced by temperature changes have so far appeared to be insurmountable obstacles in the way of realizing such a device. Here we present first results on a detector concept which does not suffer from such shortcomings. The absorber consists of closely spaced, tall Ge crystals, typically a few microns in width, each forming a heterojunction diode with the Si substrate. Electrical measurements on such diodes reveal reverse dark currents of the order of 1 mA/cm2, low enough for detector fabrication. We present a preliminary version of such a detector, where the pixel size is determined by the CMOS circuits rather than individual Ge crystals. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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.

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.

Curone D.,European Center for Training and Research in Earthquake Engineering | Secco E.L.,European Center for Training and Research in Earthquake Engineering | Tognetti A.,University of Pisa | Loriga G.,D'Appolonia S.p.A. | And 7 more authors.
IEEE Transactions on Information Technology in Biomedicine | Year: 2010

Financed by the EuropeanCommission, a consortium of 23 European partners, consisting of universities, research institutions, industries, and organizations operating in the field of emergency management, is developing a new generation of "smart" garments for emergency-disaster personnel. Garments integrate newly developed wearable and textile solutions, such as commercial portable sensors and devices, in order to continuously monitor risks endangering rescuers' lives. The system enables detection of health-state parameters of the users (heart rate, breathing rate, body temperature, blood oxygen saturation, position, activity, and posture) and environmental variables (external temperature, presence of toxic gases, and heat flux passing through the garments), to process data and remotely transmit useful information to the operation manager. The European-integrated project, called Proe- TEX (Protection e-Textiles: Micro-Nano-Structured fiber systems for Emergency-DisasterWear) started on February, 2006 and will end on July, 2010. During this 4.5 years period, three subsequent generations of sensorized garments are being released. This paper proposes an overview of the project and gives a description of the second-generation prototypes, delivered at the end of 2008. © 2006 IEEE.

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.

Bandi T.,Center Suisse dElectronique et Microtechnique | Bandi T.,Ecole Polytechnique Federale de Lausanne | Polido-Gomes J.,Ecole Polytechnique Federale de Lausanne | Neels A.,Center Suisse dElectronique et Microtechnique | And 2 more authors.
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2013

We report on the susceptibility of structural MEMS materials to proton radiation damage. Radiation tests at space relevant doses were conducted on MEMS resonators. The two materials examined were single crystal silicon and SU-8, which are both in widespread use in microsystems. The resonance frequency was monitored for measuring minute changes of the Young's modulus. No radiation-induced changes of the elasticity were observed in the silicon devices up to fluences of 1013 cm-2, corresponding to a total ionizing dose (TID) of over 5.5 MRad for 10 MeV protons. The SU-8 resonators showed a variation of less than ±5.5% at doses of up to 1.4 Mrad (TID). Chemical and structural analyses of the polymer were performed using infrared absorption spectroscopy and x-ray diffraction methods. We discuss possible mechanisms for the observed changes of the elasticity of SU-8. © 2013 Copyright SPIE.

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.

Revol V.,Center Suisse dElectronique et Microtechnique | Plank B.,Upper Austria University of Applied Sciences | Kaufmann R.,Center Suisse dElectronique et Microtechnique | Kastner J.,Upper Austria University of Applied Sciences | And 2 more authors.
NDT and E International | Year: 2013

X-ray scatter dark field imaging (SDFI) using a Talbot-Lau grating interferometer has recently attracted growing interest for the non-destructive testing and evaluation of light materials. In this work, we developed the method further for the characterisation of the laminate structure of carbon fibre reinforced polymers. In particular, we used the anisotropic properties of the small angle scattering signal to image the fibre bundles running in different directions independently with excellent contrast. The results obtained for four different woven carbon fibre reinforced polymer samples were compared to high resolution X-ray computed tomography results. We found that SDFI allows for the visualisation of the weave pattern structure and analysis of the size of the carbon fibre bundle in three dimensions, even if the individual fibres cannot be separated or the absorption contrast between the carbon fibres and the epoxy matrix is very low. © 2013 Elsevier Ltd.

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.

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