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Schumann M.F.,Karlsruhe Institute of Technology | Wiesendanger S.,Friedrich - Schiller University of Jena | Goldschmidt J.C.,Fraunhofer Institute for Solar Energy Systems | Blasi B.,Fraunhofer Institute for Solar Energy Systems | And 7 more authors.
Optica | Year: 2015

Nontransparent contact fingers on the sun-facing side of solar cells represent optically dead regions which reduce the energy conversion per area. We consider two approaches for guiding the incident light around the contacts onto the active area. The first approach uses graded-index metamaterials designed by two-dimensional Schwarz–Christoffel conformal maps, and the second uses freeform surfaces designed by one-dimensional coordinate transformations of a point to an interval. We provide proof-of-principle demonstrators using direct laser writing of polymer structures on silicon wafers with opaque contacts. Freeform surfaces are amenable to mass fabrication and allow for complete recovery of the shadowing effect for all relevant incidence angles. © 2015 Optical Society of America.


PubMed | University of Helsinki, University of Tennessee at Knoxville, BG Klinikum Bergmannstrost Halle gGmbH, Fraunhofer Institute for Microstructure of Materials and Systems IMWS and Friedrich - Schiller University of Jena
Type: | Journal: Micron (Oxford, England : 1993) | Year: 2016

Degeneration of intervertebral disc (IVD) tissue is characterized by several structural changes that result in variations in disc physiology and loss of biomechanical function. The complex process of degeneration exhibits highly intercorrelated biomechanical, biochemical, and cellular interactions. There is currently some understanding of the cellular changes in degenerated intervertebral disc tissue, but microstructural changes and deterioration of the tissue matrix has previously been rarely explored. In this work, sequestered IVD tissue was successfully characterized using histology, light microscopy, and scanning electron microscopy (SEM) to quantitatively evaluate parameters of interest for intervertebral disc degeneration (IDD) such as delamination of the collagenous matrix, cell density, cell size, and extra cellular matrix (ECM) thickness. Additional qualitative parameters investigated included matrix fibration and irregularity, neovascularization of the IVD, granular inclusions in the matrix, and cell cluster formation. The results of this study corroborated several previously published findings, including those positively correlating female gender and IVD cell density, age and cell size, and female gender and ECM thickness. Additionally, an array of quantitative and qualitative investigations of IVD degeneration could be successfully evaluated using the given methodology, resin-embedded SEM in particular. SEM is especially practical for studying micromorphological changes in tissue, as other microscopy methods can cause artificial tissue damage due to the preparation method. Investigation of the microstructural changes occurring in degenerated tissue provides a greater understanding of the complex process of disc degeneration as a whole. Developing a more complete picture of the degenerative changes taking place in the intervertebral disc is crucial for the advancement and application of regenerative therapies based on the pathology of intervertebral disc degeneration.


Klehm J.,Fraunhofer Institute for Microstructure of Materials and Systems IMWS | Henning S.,Fraunhofer Institute for Microstructure of Materials and Systems IMWS | Adhikari R.,Tribhuvan University | Brandt J.,Universitatsklinikum Halle Saale
Macromolecular Symposia | Year: 2016

Based on electron microscopic investigations, initial stages of microcrack formation and growth in bone are described as craze-like phenomena. The comparison of micro- and nanoscopic processes of deformation and fracture induced under different experimental conditions give rise to the conclusion that crazing is a fundamental micromechanical process during bone damage and fracture. Although there are striking similarities to crazes in polymeric materials, craze formation and growth in bone is strongly influenced by the morphology of the main building blocks of the bone matrix, i.e., the mineralized collagen fibrils, as well as by the significant anisotropy of bone architecture. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim


Mora Huertas A.C.,Martin Luther University of Halle Wittenberg | Schmelzer C.E.H.,Martin Luther University of Halle Wittenberg | Schmelzer C.E.H.,Fraunhofer Institute for Microstructure of Materials and Systems IMWS | Hoehenwarter W.,Leibniz Institute of Plant Biochemistry | And 2 more authors.
Biochimie | Year: 2016

Skin aging is characterized by different features including wrinkling, atrophy of the dermis and loss of elasticity associated with damage to the extracellular matrix protein elastin. The aim of this study was to investigate the aging process of skin elastin at the molecular level by evaluating the influence of intrinsic (chronological aging) and extrinsic factors (sun exposure) on the morphology and susceptibility of elastin towards enzymatic degradation. Elastin was isolated from biopsies derived from sun-protected or sun-exposed skin of differently aged individuals. The morphology of the elastin fibers was characterized by scanning electron microscopy. Mass spectrometric analysis and label-free quantification allowed identifying differences in the cleavage patterns of the elastin samples after enzymatic digestion. Principal component analysis and hierarchical cluster analysis were used to visualize differences between the samples and to determine the contribution of extrinsic and intrinsic aging to the proteolytic susceptibility of elastin. Moreover, the release of potentially bioactive peptides was studied. Skin aging is associated with the decomposition of elastin fibers, which is more pronounced in sun-exposed tissue. Marker peptides were identified, which showed an age-related increase or decrease in their abundances and provide insights into the progression of the aging process of elastin fibers. Strong age-related cleavage occurs in hydrophobic tropoelastin domains 18, 20, 24 and 26. Photoaging makes the N-terminal and central parts of the tropoelastin molecules more susceptible towards enzymatic cleavage and, hence, accelerates the age-related degradation of elastin. © 2016 Elsevier B.V. and Société Française de Biochimie et Biologie Moléculaire (SFBBM)


De Pablos-Martin A.,Fraunhofer Institute for Microstructure of Materials and Systems IMWS | Grosse C.,Fraunhofer Institute for Microstructure of Materials and Systems IMWS | Cismak A.,Fraunhofer Institute for Microstructure of Materials and Systems IMWS | Hoche T.,Fraunhofer Institute for Microstructure of Materials and Systems IMWS
Acta Metallurgica Sinica (English Letters) | Year: 2016

A nanosecond pulsed laser was used to weld stainless steel foils of 10 lm thickness to the sapphire substrates. The microstructure of the bonded interface was studied. Both materials were partially ablated under the influence of the laser beam. An inhomogeneous distribution of the steel and sapphire along the bonded interface is observed. The electrical resistance of the steel foil was measured before and after laser welding, showing that the weld slightly increases the electrical resistance but still keeps the values acceptable for electrical contacts. © The Chinese Society for Metals and Springer-Verlag Berlin Heidelberg 2016.


Simon-Najasek M.,Fraunhofer Institute for Microstructure of Materials and Systems IMWS | Lorenz G.,Fraunhofer Institute for Microstructure of Materials and Systems IMWS | Lindner A.,Micronas GmbH Freiburg | Altmann F.,Fraunhofer Institute for Microstructure of Materials and Systems IMWS
Microelectronics Reliability | Year: 2016

Semiconductor devices used in automotive applications undergo numerous stress situations depending on their particular application. Corrosion, as one main crucial failure mechanisms, can affect the lifetime of electronic components on system, device or even die level. In this paper, a novel corrosion mechanism on HALL sensor devices is investigated and clarified. This corrosion is only occurring under complex conditions like layout aspects, ionic impurities combined with humidity penetration and thermo-mechanical strain due to packaging and additional mechanical load from further over moulding. It is shown how advanced physical and chemical analysis can be combined with finite element simulation to ascertain a chemical degradation running on silicon, silicon dioxide and metallisation level to derive the complete chemical reaction mechanism for the observed corrosion defects. To verify the new failure mode, experiments to recreate this type of corrosion were carried out. Finally, conclusions are drawn on how failure modes can be prevented and how the robustness of the HALL devices under harsh environments can be increased. © 2016 Elsevier Ltd


Brand S.,Fraunhofer Institute for Microstructure of Materials and Systems IMWS | Simon-Najasek M.,Fraunhofer Institute for Microstructure of Materials and Systems IMWS | Kogel M.,Fraunhofer Institute for Microstructure of Materials and Systems IMWS | Jatzkowski J.,Fraunhofer Institute for Microstructure of Materials and Systems IMWS | And 2 more authors.
Microelectronics Reliability | Year: 2016

The formation of voids in metal layers upon stress-induced migration is a well-known defect mechanism in integrated circuits. This phenomenon largely accelerates with increasing ambient temperature. Consequently, the occurrence and the growth of voids result in an increased electrical resistivity which once more leads to an acceleration of the growth rate highly impacting the reliability and the life span of the device. Technological improvements aim at the minimization of stress induced voiding. However, for understanding and optimization of process related factors non-destructive methods for screening and systematic monitoring of the void formation e.g. during stepwise reliability testing are required. In the current paper, the formation of voids induced by repetitive thermal loads has been assessed and evaluated semi-destructively by employing Scanning Acoustic GHz-Microscopy. Prior to the acoustic inspection, sophisticated semi-destructive preparation was required to provide access to the region of interest. Voids with sizes below the acoustic resolution limit have been detected. The relative number and the size of appearance have been analysed using a custom made analysis software tool. © 2016 Elsevier Ltd


Kogel M.,Fraunhofer Institute for Microstructure of Materials and Systems IMWS | Altmann F.,Fraunhofer Institute for Microstructure of Materials and Systems IMWS | Tismer S.,Fraunhofer Institute for Microstructure of Materials and Systems IMWS | Brand S.,Fraunhofer Institute for Microstructure of Materials and Systems IMWS
Microelectronics Reliability | Year: 2016

In the current paper the application of a custom developed 2-dimenional scanning magnetic field microscope based on tunnel-magnetoresistive sensors and subsequent qualitative and quantitative analysis is described. To improve sensitivity and to enable the detection and evaluation of phase deviations, an off-line lock-in approach was employed by driving the samples under test with an injected current at a fixed signal frequency. Amplitude and phase evaluation was based on simultaneous acquisition of the reference and the measurement signal obtained from the magnetic field sensor. This off-line lock-in approach enables not just the detection but also the estimation of changes in signal phase caused by capacitive, inductive or ohmic coupling of the induced currents. Furthermore assessed magnetic fields were converted into the current density by solving the inverse magnetic problem and post processing of the acquired signals. For verification of the developed set-up the current density distribution was computed from experimentally acquired magnetic fields for a two-wire test structure. In addition quantitative values of the current density were derived for a calibration pattern containing defined structures. Finally, to evaluate the practical relevance a power MOSFET with unknown defect was analysed and an area of unexpectedly increased magnetic field intensity was observed. © 2016


Naumann F.,Fraunhofer Institute for Microstructure of Materials and Systems IMWS | Brand S.,Fraunhofer Institute for Microstructure of Materials and Systems IMWS
2016 17th International Conference on Thermal, Mechanical and Multi-Physics Simulation and Experiments in Microelectronics and Microsystems, EuroSimE 2016 | Year: 2016

The excitation and propagation of acoustic waves as employed in scanning acoustic microscopy follows highly complex phenomena which commonly cannot be visualized experimentally. The current paper describes the application of modelling and numerical simulation of these phenomena in structures like complex microelectronic samples or acoustic lenses. The design of acoustic lenses and their active elements have been optimized based on the numerical studies performed here. Simulation based visualization of the wave propagation and energy conversion in a Through Silicon Via with different defects at 1 GHz acoustic frequency supported the understanding and interpretation of the received acoustic signals. © 2016 IEEE.


PubMed | Max Planck Institute of Microstructure Physics, Fraunhofer Institute for Microstructure of Materials and Systems IMWS and Max Planck Institute for Chemical Physics of Solids
Type: Journal Article | Journal: Advanced materials (Deerfield Beach, Fla.) | Year: 2016

Fully compensated ferrimagnets with tetragonal crystal structure have the potential for large spin-polarization and strong out-of-plane magnetic anisotropy; hence, they are ideal candidates for high-density-memory applications. Tetragonal Heusler thin films with compensated magnetic state are realized by substitution of Pt in Mn

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