@article{LomadzeKopyshevBargheeretal.2017, author = {Lomadze, Nino and Kopyshev, Alexey and Bargheer, Matias and Wollgarten, Markus and Santer, Svetlana}, title = {Mass production of polymer nano-wires filled with metal nano-particles}, series = {Scientific reports}, volume = {7}, journal = {Scientific reports}, publisher = {Nature Publ. Group}, address = {London}, issn = {2045-2322}, doi = {10.1038/s41598-017-08153-0}, pages = {3759 -- 3764}, year = {2017}, abstract = {Despite the ongoing progress in nanotechnology and its applications, the development of strategies for connecting nano-scale systems to micro-or macroscale elements is hampered by the lack of structural components that have both, nano-and macroscale dimensions. The production of nano-scale wires with macroscale length is one of the most interesting challenges here. There are a lot of strategies to fabricate long nanoscopic stripes made of metals, polymers or ceramics but none is suitable for mass production of ordered and dense arrangements of wires at large numbers. In this paper, we report on a technique for producing arrays of ordered, flexible and free-standing polymer nano-wires filled with different types of nano-particles. The process utilizes the strong response of photosensitive polymer brushes to irradiation with UV-interference patterns, resulting in a substantial mass redistribution of the polymer material along with local rupturing of polymer chains. The chains can wind up in wires of nano-scale thickness and a length of up to several centimeters. When dispersing nano-particles within the film, the final arrangement is similar to a core-shell geometry with mainly nano-particles found in the core region and the polymer forming a dielectric jacket.}, language = {en} } @article{YinInhesterVeeduetal.2017, author = {Yin, Zhong and Inhester, Ludger and Veedu, Sreevidya Thekku and Quevedo, Wilson and Pietzsch, Annette and Wernet, Philippe and Groenhof, Gerrit and F{\"o}hlisch, Alexander and Grubmueller, Helmut and Techert, Simone}, title = {Cationic and Anionic Impact on the Electronic Structure of Liquid Water}, series = {The journal of physical chemistry letters}, volume = {8}, journal = {The journal of physical chemistry letters}, publisher = {American Chemical Society}, address = {Washington}, issn = {1948-7185}, doi = {10.1021/acs.jpclett.7b01392}, pages = {3759 -- 3764}, year = {2017}, abstract = {Hydration shells around ions are crucial for many fundamental biological and chemical processes. Their local physicochemical properties are quite different from those of bulk water and hard to probe experimentally. We address this problem by combining soft X-ray spectroscopy using a liquid jet and molecular dynamics (MD) simulations together with ab initio electronic structure calculations to elucidate the water ion interaction in a MgCl2 solution at the molecular level. Our results reveal that salt ions mainly affect the electronic properties of water molecules in close vicinity and that the oxygen K-edge X-ray emission spectrum of water molecules in the first solvation shell differs significantly from that of bulk water. Ion-specific effects are identified by fingerprint features in the water X-ray emission spectra. While Mg2+ ions cause a bathochromic shift of the water lone pair orbital, the 3p orbital of the Cl- ions causes an additional peak in the water emission spectrum at around 528 eV.}, language = {en} } @article{SanderHerzogPudelletal.2017, author = {Sander, Mathias and Herzog, Marc and Pudell, Jan-Etienne and Bargheer, Matias and Weinkauf, N. and Pedersen, M. and Newby, G. and Sellmann, J. and Schwarzkopf, J. and Besse, V. and Temnov, V. V. and Gaal, P.}, title = {Spatiotemporal Coherent Control of Thermal Excitations in Solids}, series = {Physical review letters}, volume = {119}, journal = {Physical review letters}, publisher = {American Physical Society}, address = {College Park}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.119.075901}, pages = {102 -- 110}, year = {2017}, abstract = {X-ray reflectivity measurements of femtosecond laser-induced transient gratings (TG) are applied to demonstrate the spatiotemporal coherent control of thermally induced surface deformations on ultrafast time scales. Using grazing incidence x-ray diffraction we unambiguously measure the amplitude of transient surface deformations with sub-angstrom resolution. Understanding the dynamics of femtosecond TG excitations in terms of superposition of acoustic and thermal gratings makes it possible to develop new ways of coherent control in x-ray diffraction experiments. Being the dominant source of TG signal, the long-living thermal grating with spatial period. can be canceled by a second, time-delayed TG excitation shifted by Lambda/2. The ultimate speed limits of such an ultrafast x-ray shutter are inferred from the detailed analysis of thermal and acoustic dynamics in TG experiments.}, language = {en} } @article{MorHerzogGolezetal.2017, author = {Mor, Selene and Herzog, Marc and Golez, Denis and Werner, Philipp and Eckstein, Martin and Katayama, Naoyuki and Nohara, Minoru and Takagi, Hide and Mizokawa, Takashi and Monney, Claude and Staehler, Julia}, title = {Ultrafast Electronic Band Gap Control in an Excitonic Insulator}, series = {Physical review letters}, volume = {119}, journal = {Physical review letters}, publisher = {American Physical Society}, address = {College Park}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.119.086401}, pages = {11559 -- 11567}, year = {2017}, abstract = {We report on the nonequilibrium dynamics of the electronic structure of the layered semiconductor Ta2NiSe5 investigated by time-and angle-resolved photoelectron spectroscopy. We show that below the critical excitation density of F-C = 0.2 mJ cm(-2), the band gap narrows transiently, while it is enhanced above FC. Hartree-Fock calculations reveal that this effect can be explained by the presence of the low-temperature excitonic insulator phase of Ta2NiSe5, whose order parameter is connected to the gap size. This work demonstrates the ability to manipulate the band gap of Ta2NiSe5 with light on the femtosecond time scale.}, language = {en} } @article{AroraMawassSandigetal.2017, author = {Arora, Ashima and Mawass, Mohamad-Assaad and Sandig, Oliver and Luo, Chen and Uenal, Ahmet A. and Radu, Florin and Valencia, Sergio and Kronast, Florian}, title = {Spatially resolved investigation of all optical magnetization switching in TbFe alloys}, series = {Scientific reports}, volume = {7}, journal = {Scientific reports}, publisher = {Nature Publ. Group}, address = {London}, issn = {2045-2322}, doi = {10.1038/s41598-017-09615-1}, pages = {9}, year = {2017}, abstract = {Optical control of magnetization using femtosecond laser without applying any external magnetic field offers the advantage of switching magnetic states at ultrashort time scales. Recently, all-optical helicity-dependent switching (AO-HDS) has drawn a significant attention for potential information and data storage device applications. In this work, we employ element and magnetization sensitive photoemission electron microscopy (PEEM) to investigate the role of heating in AO-HDS for thin films of the rare-earth transition-metal alloy TbFe. Spatially resolved measurements in a 3-5\&\#8201;\&\#956;m sized stationary laser spot demonstrate that AO-HDS is a local phenomenon in the vicinity of thermal demagnetization in a 'ring' shaped region. The efficiency of AO-HDS further depends on a local temperature profile around the demagnetized region and thermally activated domain wall motion. We also demonstrate that the thickness of the film determines the preferential switching direction for a particular helicity.}, language = {en} } @article{ChenSavateevPronkinetal.2017, author = {Chen, Zupeng and Savateev, Aleksandr and Pronkin, Sergey and Papaefthimiou, Vasiliki and Wolff, Christian Michael and Willinger, Marc Georg and Willinger, Elena and Neher, Dieter and Antonietti, Markus and Dontsova, Dariya}, title = {"The Easier the Better" Preparation of Efficient Photocatalysts-Metastable Poly(heptazine imide) Salts}, series = {Advanced materials}, volume = {29}, journal = {Advanced materials}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {0935-9648}, doi = {10.1002/adma.201700555}, pages = {21800 -- 21806}, year = {2017}, abstract = {Cost-efficient, visible-light-driven hydrogen production from water is an attractive potential source of clean, sustainable fuel. Here, it is shown that thermal solid state reactions of traditional carbon nitride precursors (cyanamide, melamine) with NaCl, KCl, or CsCl are a cheap and straightforward way to prepare poly(heptazine imide) alkali metal salts, whose thermodynamic stability decreases upon the increase of the metal atom size. The chemical structure of the prepared salts is confirmed by the results of X-ray photoelectron and infrared spectroscopies, powder X-ray diffraction and electron microscopy studies, and, in the case of sodium poly(heptazine imide), additionally by atomic pair distribution function analysis and 2D powder X-ray diffraction pattern simulations. In contrast, reactions with LiCl yield thermodynamically stable poly(triazine imides). Owing to the metastability and high structural order, the obtained heptazine imide salts are found to be highly active photo-catalysts in Rhodamine B and 4-chlorophenol degradation, and Pt-assisted sacrificial water reduction reactions under visible light irradiation. The measured hydrogen evolution rates are up to four times higher than those provided by a benchmark photocatalyst, mesoporous graphitic carbon nitride. Moreover, the products are able to photocatalytically reduce water with considerable reaction rates, even when glycerol is used as a sacrificial hole scavenger.}, language = {en} } @article{MiedemaMitznerGanschowetal.2017, author = {Miedema, P. S. and Mitzner, Rolf and Ganschow, S. and F{\"o}hlisch, Alexander and Beye, Martin}, title = {X-ray spectroscopy on the active ion in laser crystals}, series = {Physical chemistry, chemical physics : a journal of European Chemical Societies}, volume = {19}, journal = {Physical chemistry, chemical physics : a journal of European Chemical Societies}, publisher = {Royal Society of Chemistry}, address = {Cambridge}, issn = {1463-9076}, doi = {10.1039/c7cp03026f}, pages = {21800 -- 21806}, year = {2017}, abstract = {The active ions in typical laser crystals were studied with Resonant Inelastic X-ray Scattering (RIXS) and Partial Fluorescence Yield X-ray Absorption (PFY-XAS) spectroscopies as solid state model systems for dilute active centers. We analyzed Ti3+ and Cr3+ in alpha-Al2O3:Ti3+ and LiCaAlF6:Cr3+, respectively. The comparison of experimental data with semi-empirical multiplet calculations provides insights into the electronic structure and shows how measured crystal field energies are related across different spectroscopies.}, language = {en} } @article{KretschmerRungeCoumou2017, author = {Kretschmer, Marlene and Runge, Jakob and Coumou, Dim}, title = {Early prediction of extreme stratospheric polar vortex states based on causal precursors}, series = {Geophysical research letters}, volume = {44}, journal = {Geophysical research letters}, publisher = {American Geophysical Union}, address = {Washington}, issn = {0094-8276}, doi = {10.1002/2017GL074696}, pages = {8592 -- 8600}, year = {2017}, abstract = {Variability in the stratospheric polar vortex (SPV) can influence the tropospheric circulation and thereby winter weather. Early predictions of extreme SPV states are thus important to improve forecasts of winter weather including cold spells. However, dynamical models are usually restricted in lead time because they poorly capture low-frequency processes. Empirical models often suffer from overfitting problems as the relevant physical processes and time lags are often not well understood. Here we introduce a novel empirical prediction method by uniting a response-guided community detection scheme with a causal discovery algorithm. This way, we objectively identify causal precursors of the SPV at subseasonal lead times and find them to be in good agreement with known physical drivers. A linear regression prediction model based on the causal precursors can explain most SPV variability (r(2)=0.58), and our scheme correctly predicts 58\% (46\%) of extremely weak SPV states for lead times of 1-15 (16-30)days with false-alarm rates of only approximately 5\%. Our method can be applied to any variable relevant for (sub)seasonal weather forecasts and could thus help improving long-lead predictions.}, language = {en} } @article{CabezaMishurovaGarcesetal.2017, author = {Cabeza, Sandra and Mishurova, Tatiana and Garc{\´e}s, Gonzales and Sevostianov, Igor and Requena, Guillermo and Bruno, Giovanni}, title = {Stress-induced damage evolution in cast AlSi12CuMgNi alloy with one- and two-ceramic reinforcements}, series = {Journal of materials science}, volume = {52}, journal = {Journal of materials science}, publisher = {Springer}, address = {New York}, issn = {0022-2461}, doi = {10.1007/s10853-017-1182-7}, pages = {10198 -- 10216}, year = {2017}, abstract = {Two composites, consisting of an as-cast AlSi12CuMgNi alloy reinforced with 15 vol\% Al2O3 short fibres and with 7 vol\% Al2O3 short fibres + 15 vol\% SiC particles, were studied. Synchrotron computed tomography disclosed distribution, orientation, and volume fraction of the different phases. In-situ compression tests during neutron diffraction in direction parallel to the fibres plane revealed the load partition between phases. Internal damage (fragmentation) of the Si phase and Al2O3 fibres was directly observed in CT reconstructions. Significant debonding between Al matrix and SiC particles was also found. Finally, based on the Maxwell scheme, a micromechanical model was utilized for the new composite with two-ceramic reinforcements; it rationalizes the experimental data and predicts the evolution of all internal stress components in each phase.}, language = {en} } @article{YoonLopezVafinetal.2017, author = {Yoon, P. H. and Lopez, R. A. and Vafin, Sergei and Kim, S. and Schlickeiser, R.}, title = {Spontaneous emission of Alfvenic fluctuations}, series = {Plasma physics and controlled fusion}, volume = {59}, journal = {Plasma physics and controlled fusion}, publisher = {IOP Publ. Ltd.}, address = {Bristol}, issn = {0741-3335}, doi = {10.1088/1361-6587/aa77c3}, pages = {8}, year = {2017}, abstract = {Low-frequency fluctuations are pervasively observed in the solar wind. The present paper theoretically calculates the steady state spectra of low-frequency electromagnetic (EM) fluctuations of the Alfvenic type for thermal equilibrium plasma. The analysis is based upon a recently formulated theory of spontaneously emitted EM fluctuations in magnetized thermal plasmas. It is found that the fluctuations in the magnetosonic mode branch is constant, while the kinetic Alfvenic mode spectrum is dependent on a form factor that is a function of perpendicular wave number. Potential applicability of the present work in the wider context of heliospheric research is also discussed.}, language = {en} }