Lattice relaxation around arsenic and selenium in CdTe

We have investigated the lattice relaxation around impurity atoms at the anion sublattice in CdTe, such as As acting as acceptor and Se which is isovalent to Te, with fluorescence detected EXAFS. We experimentally verify the lattice relaxation with a bond length being reduced by 8% around the As atom as inferred indirectly from ab-initio calculations of the electric field gradient in comparison with the measured value in a PAC experiment (S. Lany et al., Phys. Rev. B 62, R2259 (2000)). In the case of the isovalent impurity atom Se, the bond length is similarly reduced as determined experimentally by EXAFS and by model calculations with the density functional theory implemented in the WIEN97 program. In contrast to this inward relaxation, preliminary calculations for Br in CdTe, the next element in the series As, Se, and Br, which acts as donor at the Te sublattice, indicate an increase in bond length, an interesting prediction waiting for experimental verification

Metropolis revisited: dialectic of enlightenment, modernity and architectural modernizm

Theodor Adorno ve Max Horkheimer, 'Aydınlanma'nın Diyalektiği: Felsefi Fragmanlar' (1947) adlı yapıtlarında, Aydınlanma projesinin yapısı gereği totaliter olduğunu ve mitolojiyi insan düşüncesinden kovmuş olmasına rağmen kendisinin mite gerilediğini öne sürmektedirler. Aydınlanma paradigmasının ürünü olan birer sanat dalı olarak erken 20. yüzyıl sineması ve mimarlık, Adorno ve Horkheimer'in bu savlarını doğrulamaktadırlar. Fritz Lang'in Metropolis (1927) adlı filmi; bir paradig- ma değişimi olarak Aydınlanma'nın, tarihsel bir dönem olarak Modernite'nin ve bu tarihsel döneme özgü bir üslup olarak Modern Mimari hareketin birbirleri ile ilişkilerinin çözümlenebilmesine olanak sağlayan çok katmanlı bir anlamsal yapı- ya sahiptir. Filmde Aydınlanma-mitoloji ile Modern Mimari-tarihsel içerik diyalektikleri paralel olarak işlenmiştir. Filmdeki, Metropolis'in makine estetiğine dayalı fütüristik ütopik mimarisi ile distopik tekno-totaliter toplumsal düzen arasındaki gerilim, gerçekte tarihsel üsluplardan yararlanmayı reddeden Modern Mimari hareketin ütopik karakteri ile mitoloji olarak tarihsel birikim arasındaki gerilimi yansıtmaktadır. Theodor Adorno and Max Horkheimer asserted that the project of enlightenment which itself is already totalitarian ai- med to overthrow the myths from the human mind and to install human beings as masters reverted to mythology at the end, in their master work 'Dialectic of Enlightment: Philosophical Fragments' (1947). As artistic products of Enlightment Project, cinema and architecture of early twentieth century affirmed Adorno and Horkheimer's thesis. Fritz Lang's Metro- polis (1927)'s multi-layered messages enables us to comprehend the relationships between Enlightment as a paratigmatic change, Modernity as a historical period, Architectural Modernism as an artistic style which is a product of this paradigm and this historical period. In this film, dialectics of Enlightment/mitology and Architectural Modernism/historical content entwined. In reality, the tension between utopian futuristic architecture based on machine aesthetics of Metropolis and its distopian techno-totaliterian social order reflected the tension between utopian characteristic of Modern Avant-garde in architecture who rejects to use historical styles and historical content as mitology

Structural effects and the spin reorientation in Au/Co/Au films

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Lattice dynamics information obtained from EXAFS measurements on Ta

Extended x ray absorption fine structure EXAFS data were measured at three temperatures 20 K, 80 K, and 300 K above the L3 edge of polycrystalline alpha tantalum. The data analysis is based on a recently developed Bayesian approach and uses the FEFF8 code results. Besides the temperature dependence of the lattice constant we obtain a separation of the Debye Waller parameters into structural and thermal contributions. The latter are well described by a force field model with two force parameters. A posteriori errors and cross correlations between the model parameters are calculated, taking the errors of the input EXAFS function as well as systematic uncertainties of the model into account. Lattice dynamical observables determined independently are compared with the results of our force field model using the parameters from the fit of our EXAFS dat

Micromagnetic aspects of magnetoreception of homing pigeons based on iron minerals

The identification of ferrimagnetic iron minerals in the skin of the upper beak of homing pigeons poses fundamental questions on the principles at work in magnetoreception. Aspects concerning the type of mineral, the size, shape and arrangement of the particles are discussed on grounds of micromagnetic simulations

EXAFS study of functionalized nanoclusters and nanocluster assemblies

Extended X-ray absorption fine structure spectroscopy and X-ray diffraction were used to investigate the structure of CdS nanocrystals capped with different ligands. Nanocrystals capped with acetate and thiolate do exhibit the rock-salt structure, a high pressure type phase. These nanocsystals undergo a rock-salt to hawleyite transition after the thermal removal of the ligands at 200°C. Changes in coordination and distances as well as second-neighbor shells in differently capped CdS clusters are discussed in comparison with ZnS-clusters

Development of an online control system for a multi element fluorescence detector

A new control system for fluorescence and EXAFS studies has been developed consisting of Germanium detectors and digital signal processor electronics. Using a standard PC and a new software package leads to a high flexibility regarding application, user interface and use of different synchrotron facilities. The new system achieves spectra with considerable higher quality when compared to a traditional system for fluorescence and EXAFS studies. This allows the investigation of thin films and diluted systems as shown by experiments on a W Nb multilayer system and on FeS2 doped with Z