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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.

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.

Mikutta R.,Leibniz University of Hanover | Kaiser K.,Martin Luther University of Halle Wittenberg | Dorr N.,Leibniz University of Hanover | Vollmer A.,Bessy Gmbh | And 4 more authors.
Geochimica et Cosmochimica Acta | Year: 2010

Large portions of organic N (ON) in soil exist tightly associated with minerals. Mineral effects on the type of interactions, chemical composition, and stability of ON, however, are poorly understood. We investigated mineral-associated ON along a Hawaiian soil chronosequence (0.3-4100 kyr) formed in basaltic tephra under comparable climatic, topographic, and vegetation conditions. Mineral-organic associations were separated according to density (ρ > 1.6 g/cm3), characterized by X-ray photoelectron spectroscopy (XPS), X-ray absorption near edge fine structure (NEXAFS) and analyzed for amino acid enantiomers and amino sugars. The 14C activity of mineral-bound OC was estimated by accelerator mass spectrometry. The close OC-ON relationship (r = 0.96) and XPS results suggest that ON exists incorporated in bulk mineral-bound OM and likely becomes associated with minerals as part of sorbing OM. The youngest site (0.3 kyr), with soils mainly composed of primary minerals (olivine, pyroxene, feldspar) and with little ON, contained the largest proportion of hydrolyzable amino sugars and amino acids but with a small share of acidic amino acids (aspartic acid, glutamic acid). In soils of the intermediate weathering stage (20-400 kyr), where poorly crystalline minerals and metal(hydroxide)-organic precipitates prevail, more mineral-associated ON was present, containing a smaller proportion of hydrolyzable amino sugars and amino acids due to the preferential accumulation of other OM components such as lignin-derived phenols. Acidic amino acids were more abundant, reflecting the strong association of acidic organic components with metal(hydroxide)-organic precipitates and variable-charge minerals. In the final weathering stage (1400-4100 kyr) with well-crystalline secondary Fe and Al (hydr)oxides and kaolin minerals, mineral-organic associations held less ON and were, relative to lignin phenols, depleted in hydrolyzable amino sugars and amino acids, particularly in acidic amino acids. XPS and NEXAFS analyses showed that the majority (59-78%) of the mineral-associated ON is peptide N while 18-34% was aromatic N. Amino sugar ratios and d-alanine suggest that mineral-associated ON comprises a significant portion of bacterial residues, particularly in the subsoil. With increasing 14C age, a larger portion of peptide N was non-hydrolyzable, suggesting the accumulation of refractory compounds with time. The constant d/l ratios of lysine in topsoils indicate fresh proteinous material, likely due to continuous sorption of or exchange with fresh N-containing compounds. The 14C and the d/l signature revealed a longer turnover of proteinous components strongly bound to minerals (not NaOH-NaF-extractable). This study provides evidence that interactions with minerals are important in the transformation and stabilization of soil ON. Mineral-associated ON in topsoils seems actively involved in the N cycling of the study ecosystems, accentuating N limitation at the 0.3-kyr site but increasing N availability at older sites. © 2010 Elsevier Ltd. 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.

Talyzin A.V.,Umea University | Luzan S.,Umea 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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