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Ayala P.,University of Vienna | Kitaura R.,Nagoya University | Nakanishi R.,Nagoya University | Shiozawa H.,University of Surrey | And 4 more authors.
Physical Review B - Condensed Matter and Materials Physics | Year: 2011

Here we report on controlling the effective hybridization and charge transfer of rare-earth elements inside a carbon nanotube (CNT) nanoreactor. The tubular space inside CNTs can encapsulate one-dimensional (1D) crystals such as ErCl3, which we have used as a starting material. Applying a thermochemical reaction in ultrahigh vacuum, we obtain elemental Er nanowires still encapsulated in the CNTs. The hybridization degree and the effective charge changes were directly accessed across the Er 4d and 3d edges by high-energy spectroscopy. It was found that Er is trivalent but the effective valence is reduced for the Er-filled tube, which strongly suggests an increased hybridization between the nanotube π states and the Er 5d orbitals. This was also evidenced by the conduction band response determined in C1s-x-ray absorption spectroscopy (XAS). These results have significant implications for the 1D electronic and magnetic properties of these and similar rare-earth nanowire hybrids. © 2011 American Physical Society.

Chkhalo N.I.,RAS Institute for Physics of Microstructures | Kunstner S.,Bessy Gmbh | Polkovnikov V.N.,RAS Institute for Physics of Microstructures | Salashchenko N.N.,RAS Institute for Physics of Microstructures | And 2 more authors.
Applied Physics Letters | Year: 2013

Results on optimization and manufacturing of La/B4C multilayers are reported. Such mirrors are promising optical elements for the development of the next generation of nano-lithography at an operation wavelength of 6.7 nm. A near-normal incidence reflectivity of up to 58.6% has been measured at the BESSY-II soft x-ray reflectometer beamline. This is the highest reflectivity measured so far at this wavelength. The potential to further increase the reflectivity of the multilayers is discussed. © 2013 American Institute of Physics.

Carley R.,Max Born Institute for Nonlinear Optics and Short Pulse Spectroscopy | Carley R.,Free University of Berlin | Dobrich K.,Max Born Institute for Nonlinear Optics and Short Pulse Spectroscopy | Frietsch B.,Max Born Institute for Nonlinear Optics and Short Pulse Spectroscopy | And 7 more authors.
Physical Review Letters | Year: 2012

The temporal evolution of the exchange-split Δ 2-like Σ valence bands of the 4f-ferromagnet gadolinium after femtosecond laser excitation has been studied using angle-resolved photoelectron spectroscopy based on high-order harmonic generation. The ultrafast drop of the exchange splitting reflects the magnetic response seen in femtosecond magnetic dichroism experiments. However, while the minority valence band reacts immediately, the response of the majority counterpart is delayed by 1 picosecond and is only half as fast. These findings demonstrate that laser excitation drives the valence band structure out of magnetic equilibrium. © 2012 American Physical Society.

Flak D.,AGH University of Science and Technology | Flak D.,Empa - Swiss Federal Laboratories for Materials Science and Technology | Braun A.,Empa - Swiss Federal Laboratories for Materials Science and Technology | Vollmer A.,Bessy Gmbh | Rekas M.,AGH University of Science and Technology
Sensors and Actuators, B: Chemical | Year: 2013

Substitution of Fe2O3 with 5-20mol%TiO2 by flame spray synthesis (FSS) forms solid solutions of single crystal nanoparticles as small as 15.5 nm with a correspondingly high specific surface area (95 m2/g), as confirmed with X-ray diffraction and transmission electron microscopy. Their electronic structure and microstructure lends the solid solution a characteristic which can be exploited for H2 sensing, more so than with pure α-Fe2O3. With a combination of near edge X-ray absorption fine structure spectroscopy, and with electrochemical impedance analysis, that we apply under realistic sensor operation conditions, we are able to qualitatively probe the electronic structure and describe the mechanisms of hydrogen sensing at the molecular scale and correlate the hydrogen sensing property with charge transfer and valence band characteristics. © 2012 Elsevier B.V. All rights reserved.

Uschakow S.,Bessy Gmbh | Gaupp A.,Bessy Gmbh | MacDonald M.,Canadian Light Source Inc. | Schafers F.,Bessy Gmbh
Journal of Physics: Conference Series | Year: 2013

We investigate polarisation properties of a reflective Mo/Si multilayer system in the EUV range using polarized synchrotron radiation at BESSY-II. The characterization involves reflectivity measurements with s- and p-polarized light as a function of the wavelength for three different angles near normal incidence. The phase retardance is determined near normal incidence for one fixed angle of incidence as a function of the wavelength. As an additional spin-off of the polarimetry measurement the Stokes parameters of the beamline could be determined. With the 8-axis UHV-polarimeter we have measured the complex reflection coefficients for the first time and establish this ellipsometry technique as an additional sensitive probe to characterize and model multilayer optical elements.

Neumann A.,Bessy Gmbh | Anders W.,Bessy Gmbh | Kugeler O.,Bessy Gmbh | Knobloch J.,Bessy Gmbh
Physical Review Special Topics - Accelerators and Beams | Year: 2010

Many proposals for next generation light sources based on single pass free electron lasers or energy recovery linac facilities require a continuous wave (cw) driven superconducting linac. The effective beam loading in such machines is very small and in principle the cavities can be operated at a bandwidth of a few Hz and with less than a few kW of rf power. However, a power reserve is required to ensure field stability. A major error source is the mechanical microphonics detuning of the niobium cavities. To understand the influence of cavity detuning on longitudinal beam stability, a measurement program has been started at the horizontal cavity test facility HoBiCaT at HZB to study TESLA-type cavities. The microphonics detuning spectral content, peak detuning values, and the driving terms for these mechanical oscillations have been analyzed. In combination with the characterization of cw-adapted fast tuning systems based on the piezoelectric effect this information has been used to design a detuning compensation algorithm. It has been shown that a compensation factor between 2-7 is achievable, reducing the typical detuning of 2-3 Hz rms to below 0.5 Hz rms. These results were included in rf-control simulations of the cavities, and it was demonstrated that a phase stability below 0.02° can be achieved. © 2010 The American Physical Society.

Massee F.,University of Amsterdam | De Jong S.,University of Amsterdam | Huang Y.,University of Amsterdam | Siu W.K.,University of Amsterdam | And 10 more authors.
Nature Physics | Year: 2011

The origin of colossal magnetoresistance (CMR) in manganese oxides is among the most challenging problems in condensed-matter physics today. The true nature of the low-temperature electronic phase of these materials is heavily debated. By combining photoemission and tunnelling data, we show that in the archetypal bilayer system La 2 '2x Sr 1+2x Mn 2 O 7, polaronic degrees of freedom win out across the CMR region of the phase diagram. This means that the generic ground state of bilayer manganites supports a vanishing coherent quasi-particle spectral weight at the Fermi level throughout k-space. The incoherence of the charge carriers, resulting from strong electron-lattice interactions and the accompanying orbital physics, offers a unifying explanation for the anomalous charge-carrier dynamics seen in transport, optics and electron spectroscopies. The stacking number N is the key factor for true metallic behaviour, as an intergrowth-driven breakdown of the polaronic domination to give a metal possessing a traditional Fermi surface is seen in this system. © 2011 Macmillan Publishers Limited. All rights reserved.

Jung C.,Bessy Gmbh
Synchrotron Radiation News | Year: 2016

In the framework of the International Year of Light and Light-Based Technologies, a global initiative of the United Nations, the National Research Nuclear University MEPhI in Moscow dedicated one of the meetings of the series Advanced Accelerator and Radiation Physics (AARP) to “Ancient Radiations: New Physics and High-Tech Applications.” Chaired by M. N. Strikhanov and S. B. Dabagov, the AARP series of international meetings is dedicated to frontier topics in fundamental and applied research associated with new techniques of beam acceleration, novel powerful radiation sources, and applications based on radiation physics. Previous events were held at NRNU MEPhI, at the National Laboratories of Frascati (LNF-INFN), at CERN, at the Naples' Institute of Engines (IM CNR), the CEA Cadarache Research Center, and at Adyge State University in Maykop. They were dedicated to novel techniques for electron beam acceleration, to advanced methods for free electron lasing, to Compton scattering of relativistic electrons in a strong laser field, to the plasma Wakefield acceleration technique, advanced X-ray optical solutions for studying both fundamental and applied physics (e.g., incoherent and coherent X-ray imaging by tabletop facilities), novel X-ray spectroscopy instrumentation, powerful X-ray source studies by means of polycapillary optics, etc., as well as research performed in the framework of collaborations among LNF-INFN and MEPhI, the Tomsk Politechnic University, the Lebedev Physical Institute of the Russian Academy of Sciences, the CNR, and the CEA. © , Copyright Helmholtz-Zentrum Berlin für Materialien und Energie.

Krug M.,University of Konstanz | Krug M.,Bessy Gmbh | Lee S.-J.,University of Konstanz | Lee S.-J.,Kyung Hee University | And 3 more authors.
Protein Science | Year: 2013

TrmB is a repressor that binds maltose, maltotriose, and sucrose, as well as other a-glucosides. It recognizes two different operator sequences controlling the TM (Trehalose/Maltose) and the MD (Maltodextrin) operon encoding the respective ABC transporters and sugardegrading enzymes. Binding of maltose to TrmB abrogates repression of the TM operon but maintains the repression of the MD operon. On the other hand, binding of sucrose abrogates repression of the MD operon but maintains repression of the TM operon. The three-dimensional structure of TrmB in complex with sucrose was solved and refined to a resolution of 3.0 Å . The structure shows the N-terminal DNA binding domain containing a winged-helix-turn-helix (wHTH) domain followed by an amphipathic helix with a coiled-coil motif. The latter promotes dimerization and places the symmetry mates of the putative recognition helix in the wHTH motif about 30 Å apart suggesting a canonical binding to two successive major grooves of duplex palindromic DNA. This suggests that the structure resembles the conformation of TrmB recognizing the pseudopalindromic TM promoter but not the conformation recognizing the nonpalindromic MD promoter. © 2013 The Protein Society.

Talyzin A.V.,Umeå University | Luzan S.,Umeå University | Anoshkin I.V.,Aalto University | Nasibulin A.G.,Aalto University | And 6 more authors.
ACS Nano | Year: 2011

Reaction of single-walled carbon nanotubes (SWNTs) with hydrogen gas was studied in a temperature interval of 400-550 °C and at hydrogen pressure of 50 bar. Hydrogenation of nanotubes was observed for samples treated at 400-450 °C with about 1/3 of carbon atoms forming covalent C-H bonds, whereas hydrogen treatment at higher temperatures (550 °C) occurs as an etching. Unzipping of some SWNTs into graphene nanoribbons is observed as a result of hydrogenation at 400-550 °C. Annealing in hydrogen gas at elevated conditions for prolonged periods of time (72 h) is demonstrated to result also in nanotube opening, purification of nanotubes from amorphous carbon, and removal of carbon coatings from Fe catalyst particles, which allows their complete elimination by acid treatment. © 2011 American Chemical Society.

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