Browsing by Author "Fischer, P."

Muscular dystrophies (MD) are inherited disorders and characterized by progressive muscle weakness. The majority of cases are caused by defects of the muscle membrane, mostly affecting transmembraneous proteins, the extracellular matrix, and components of the subsarkolemmal cytoskeleton. Additionally, sarcomer-associated proteins and parts of the nuclear membrane are also affected. Diagnosis is based on muscle biopsy, except in dystrophinopathies, which are preferentially diagnosed by molecular genetics. Muscle biopsy may be replaced by less invasive techniques in Emerin and Merosin (alpha(2)-Laminin) deficiency. Using highly specific monoclonal antibodies, differential diagnosis of MD can be established by immunohistochemistry and Western blotting. Only in cases locking a definite result, sequencing of the appropriate gene should be performed. Nevertheless, some cases remain undiagnosed.

The high-voltage (NV-) CMOS pixel sensors offer several good properties: a fast charge collection by drift, the possibility to implement relatively complex CMOS in-pixel electronics and the compatibility with commercial processes. The sensor element is a deep n-well diode in a p-type substrate. The n-well contains CMOS pixel electronics. The main charge collection mechanism is drift in a shallow, high held region, which leads to a fast charge collection and a high radiation tolerance. We are currently evaluating the use of the high-voltage detectors implemented in 180 nm I-IV-CMOS technology for the highluminosity ATLAS upgrade. Our approach is replacing the existing pixel and strip sensors with the CMOS sensors while keeping the presently used readout ASICs. By intelligence we mean the ability of the sensor to recognize a particle hit and generate the address information. In this way we could benefit from the advantages of the NV sensor technology such as lower cost, lower mass, lower operating voltage, smaller pitch, smaller clusters at high incidence angles. Additionally we expect to achieve a radiation hardness necessary for ATLAS upgrade. In order to test the concept we have designed two I-IVCMOS prototypes that can be readout in two ways: using pixel and strip readout chips. In the case of the pixel readout, the connection between 1-1V-CIV1OS sensor and the readout AMC can be established capacitively. (C) 2014 Elsevier B.V. All rights reserved

In order to study sub-100-nm domains in magnetic multilayers a combination of three high-resolution imaging techniques has been applied to the same samples for the first time: magnetic force microscopy (MFM), Lorentz microscopy with a transmission electron microscope, and magnetic transmission x-ray microscopy (MTXM). The samples-atomically stacked [Fe(001)/Au(001)](n) multilayers with an approximate L1(0)-lattice-were prepared by molecular beam epitaxy (MBE) on a GaAs(001) substrate which was then locally removed by laser-induced wet etching to create a window that is transparent for 200 keV electrons and soft x-rays. Magnetization curves with perpendicular and in-plane applied field indicate a spontaneous perpendicular magnetization with an equilibrium domain pattern in small fields and reversible wall motion. About 60 nm wide domains could be observed with MFM and MTXM, respectively. Lorentz images did not show any in-plane magnetic contrast, but the domain pattern appeared when the sample was tilted. This indicates that the magnetization is indeed strictly perpendicular. (C) 2000 American Institute of Physics. [S0021-8979(00)80208-X].

The magnetization reversal of an array of 1 mum squared FeGd dots has been studied by magnetic transmission x-ray microscopy (MTXM). A (4 Angstrom Fe/4 Angstrom Gd) x 75 multilayered FeGd system has been prepared on a 30 nm thin Si3N4 membrane by sputtering and structured by optical lithography and ion beam etching techniques. Both the domain structure within each single dot and the collective switching behavior could be observed with MTXM. A large variation in the nucleation field of the dots was found and can be attributed to the shape of the dots. A correlation between the nucleation field and the perimeter of each dot could be deduced. Hysteresis loops of individual dots are derived, taking into account the proportionality of the dichroic contrast to the magnetization of the sample. The stepped profile of the magnetization loop of a single dot is found to be clearly distinct from a continuous film. The high lateral resolution and the possibility to record the images in varying external magnetic fields proves that MTXM is a highly adapted tool to investigate nanostructured magnetic systems. (C) 2001 American Institute of Physics.

Transmission x-ray microscopy with the x-ray magnetic circular dichroism as a contrast mechanism was used to image the field dependent evolution of magnetic domains in artificially nanostructured strips of a multilayered Fe/Gd system. A diversity of domain configurations have been imaged for different strengths of the applied magnetic field and different widths of the strips, varying between 100 nm, and 1 mum. Undulating domain patterns, analogous to those observed in other condensed matter systems could be found.

A multilayered FeGd system sputtered on a Si3N4-membrane was used to demonstrate that magnetic transmission x-ray microscopy enables the imaging of the domain structure with high resolution in a quantitative way and in varying external magnetic fields. The field-dependent evolution of sub-100 nm out-of-plane magnetized domains, i.e., the transition from stripe into bubble domains, could be observed in detail. It has been shown that critical fields like the bubble collapse field can be described by a wall energy model. Contrary to the assumption of the theory, the magnetization does not remain perpendicular to the film plane in all cases. This is only true inside the bubbles. In the stripe domains the magnetic moments rotate. Their angle could be measured as a function of the external applied field. Internal stray fields can cause a rotation of moments leading to a contrast at the edges of stripe domains. The results indicate that the magnetization reversal in 3d/4f multilayers is not only determined by wall motions and is therefore more complex than previously assumed. (C) 2000 American Institute of Physics. [S0021-8979(00)80108-5].

The combination of high-resolution chemically sensitive soft X-ray microscopy with stereo imaging and processing techniques presented here forms a novel tool for the investigation of aqueous colloidal systems. Information about the spatial distribution within the sample is provided with small calculation effort processing just a pair of stereo micrographs. Thus, the extension towards investigation of dynamical behaviour is possible on the part of the experiment as well as of the processing. The potential of this technique is demonstrated with applications in aqueous soil and clay samples. Within these samples, haematite particles are identified taking advantage of the elemental contrast at the Fe-L edge around E = 707 eV. In combination with stereo microscopy, information about spatial arrangements are revealed and correlated to electrostatic interactions of the different mixtures, addressing to an actual question of soil scientists. The technique allows in-situ sample manipulation, which is demonstrated by a test specimen where particles were added during imaging.

The first transmission x-ray microscope, dedicated for magnetic imaging is currently being built at the beamline ID-10 at BESSY II in Berlin using a helical undulator which provides photons with circular-, horizontal-, vertical. and linear polarization under various angles in the energy range between 0.2 and 2 keV. The microscope will use the x-ray circular and the x-ray linear magnetic dichroism as a magnetic contrast to study ferromagnetic and antiferromagnetic domains. A condenser with dynamical aperture synthesis will produce a reduced, spatially fixed, incoherent, and vertically dispersed image of the source, which will be matched to the aperture of the micro zone plate (MZP). In an object field of 15 mum by 15 mum a monochromaticity of E/DeltaE = 1700 will be obtained, which is sufficient for magnetic spectromicroscopy, enabling us to investigate lateral distributions of magnetic moments separated by different elements, chemical shifts and even by spin and orbital contributions. A solenoid and/or lithographically patterned microcoils will allow studying magnetization reversal processes on different time scales, down to a sub-nanoseconds level where precessional switching and damping mechanisms occur.

X-ray magnetic circular dichroism (X-MCD) was used as a large, element-specific and quantitative magnetic contrast mechanism in the soft X-ray microscopes at BESSY I (Berlin) and the ALS (Berkeley). The present state and potential of magnetic transmission X-ray microscopy (MTXM) is outlined. The possibility to record images in varying magnetic fields and the high spatial resolution down to 25 nm were used to image out-of-plane magnetized (4 Angstrom Fe / 4 Angstrom Gd) x 75 systems. Magnetic domains could be studied in arrays of circular and square dots with lateral dimensions down to 180 nm. Hysteresis loops of individual dots were deduced using the direct proportionality of the X-MCD contrast to the sample magnetization. Images of a 3 nm Cr / 50 nm Fe / 6 nm Cr film demonstrate for the first time that MTXM is also able to observe in-plane magnetized domains. In the future the possible applications of MTXM will be extended with regard to the strength of the external field, the available energy range and the sample conditions by building a dedicated transmission X-ray microscope for magnetic imaging at BESSY II.

Undulation instabilities of magnetic domains have been observed in nanostructured strips of a ferromagnetic Fe/Gd multilayer. The novel technique of magnetic transmission x-ray microscopy, which is based on the x-ray magnetic circular dichroism, was used for imaging. Below a critical magnetic field, sinus-like modulations of the magnetic domains could be observed. At a higher rate of field induced strain rectangular patterns occur. They seem to be characteristic for the reduced lateral width of the magnetic system and are in contrast to chevron patterns observed in extended systems. The domain morphologies found in different magnetic fields H, and in nanowires of various widths L-z, have been summarized in a H-L-z "phase" diagram. An analogy with theoretical predictions for extended systems could be found. (C) 2002 American Institute of Physics.

The here presented combination of stereo imaging and elemental mapping with soft X-ray microscopy reveals the spatial arrangement of naturally aqueous colloidal systems, e.g. iron oxides in soil colloid clusters. Changes in the spatial arrangement can be induced by manipulating the sample in-situ and thus be investigated directly and as a function of time.