TY - JOUR A1 - Szczerba, Wojciech A1 - Costo, R. A1 - Veintemillas-Verdaguer, S. A1 - del Puerto Morales, M. A1 - Thünemann, Andreas T1 - SAXS analysis of single- and multi-core iron oxide magnetic nanoparticles N2 - This article reports on the characterization of four superparamagnetic iron oxide nanoparticles stabilized with dimercaptosuccinic acid, which are suitable candidates for reference materials for magnetic properties. Particles p1 and p2 are single-core particles, while p3 and p4 are multi-core particles. Small-angle X-ray scattering analysis reveals a lognormal type of size distribution for the iron oxide cores of the particles. Their mean radii are 6.9 nm (p1), 10.6 nm (p2), 5.5 nm (p3) and 4.1 nm (p4), with narrow relative distribution widths of 0.08, 0.13, 0.08 and 0.12. The cores are arranged as a clustered network in the form of dense mass fractals with a fractal dimension of 2.9 in the multi-core particles p3 and p4, but the cores are well separated from each other by a protecting organic shell. The radii of gyration of the mass fractals are 48 and 44 nm, and each network contains 117 and 186 primary particles, respectively. The radius distributions of the primary particle were confirmed with transmission electron microscopy. All particles contain purely maghemite, as shown by X-ray absorption fine structure spectroscopy KW - Superparamagnetic nanoparticles KW - Iron oxide KW - Reference materials KW - SAXS KW - Small-angle x-ray scattering KW - XANES KW - X-ray absorption near-edge structure KW - X-ray absorption fine structure PY - 2017 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-395948 DO - https://doi.org/10.1107/S1600576717002370 SN - 1600-5767 VL - 50 IS - Part 2 SP - 481 EP - 488 PB - (IUCr) International Union of Crystallography AN - OPUS4-39594 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Brieger, C. A1 - Melke, J. A1 - van der Bosch, N. A1 - Reinholz, Uwe A1 - Riesemeier, Heinrich A1 - de Oliveira Guilherme Buzanich, Ana A1 - Krishna Kayarkatte, M. A1 - Derr, I. A1 - Schökel, A. A1 - Roth, C. ED - de Oliveira Guilherme Buzanich, Ana T1 - A combined in-situ XAS–DRIFTS study unraveling adsorbate induced changes on Pt nanoparticle structure N2 - The adsorption behavior of Platinum nanoparticles was studied for the as-received catalyst (under inert gas), under hydrogen and CO atmosphere using our newly designed in-situ cell. X-ray Absorption Spectroscopy (XAS) and Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) experiments were performed simultaneously with high data quality. Structural information and the type of adsorbate could be revealed via Extended X-ray Absorption Fine Structure (EXAFS) analysis, Δμ X-ray Absorption Near Edge Structure analysis (Δμ XANES) and in-situ DRIFTS. The as-received catalyst showed sub-surface oxygen and O(n-fold). Under CO atmosphere only CO(atop) was found. Reversible adsorbate induced changes of the Pt nanoparticle structure were derived from changes in the Pt-Pt coordination number and the corresponding bond distance. Under reducing conditions (H2, CO) a significant increase in both values occurred. Temperature dependent desorption of CO revealed a gradual shift from Pt-CO to Pt-O. Reoxidation was clearly assigned to strong metal support interaction from the SiO2 support. KW - X-ray absorption spectroscopy KW - DRIFTS KW - XANES KW - CO adsoprtion KW - Platinum KW - String metal support interaction KW - Silica support KW - Adsorbates KW - Infrared spectroscopy PY - 2016 DO - https://doi.org/10.1016/j.jcat.2016.03.034 SN - 0021-9517 VL - 339 SP - 57 EP - 67 PB - Elsevier AN - OPUS4-38367 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Brieger, C. A1 - Melke, J. A1 - van der Bosch, N. A1 - Reinholz, Uwe A1 - Riesemeier, Heinrich A1 - de Oliveira Guilherme Buzanich, Ana A1 - Krishna Kayarkatte, M. A1 - Schoeckel, A. A1 - Roth, C. T1 - A combined in-situ XAS-DRIFTS study unraveling adsorbate induced changes on the Pt nanoparticle structure N2 - The adsorption behavior of Platinum nanoparticles was studied for the as-received catalyst (under inert gas), under hydrogen and CO atmosphere using our newly designed in-situ cell. X-ray Absorption Spectroscopy (XAS) and Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) experiments were performed simultaneously with high data quality. Structural information and the type of adsorbate could be revealed via Extended X-ray Absorption Fine Structure (EXAFS) analysis, Dl X-ray Absorption Near Edge Structure analysis (Dl XANES) and in-situ DRIFTS. The as-received catalyst showed sub-surface oxygen and O(n-fold). Under CO atmosphere only CO(atop) was found. Reversible adsorbate induced changes of the Pt nanoparticle structure were derived from changes in the PtAPt coordination number and the corresponding bond distance. Under reducing conditions (H2, CO) a significant increase in both values occurred. Temperature dependent desorption of CO revealed a gradual shift from PtACO to PtAO. Reoxidation was clearly assigned to strong metal support interaction from the SiO2 support. KW - X-ray absorption spectroscopy KW - DRIFTS KW - XANES KW - CO adsorption KW - Platinum KW - Strong metal support interaction KW - Silica support KW - Adsorbates KW - Infrared spectroscopy PY - 2016 DO - https://doi.org/10.1016/j.jcat.2016.03.034 IS - 339 SP - 57 EP - 67 PB - Elsevier Inc. CY - Philadelphia, Pennsylvania, USA AN - OPUS4-35815 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Girod, Matthias A1 - Vogel, Stefanie A1 - Szczerba, Wojciech A1 - Thünemann, Andreas T1 - How temperature determines formation of maghemite nanoparticles N2 - We report on the formation of polymer-stabilized superparamagnetic single-core and multi-core maghemite nanoparticles. The particle formation was carried out by coprecipitation of Fe(II) and Fe(III) sulfate in a continuous aqueous process using a micromixer system. Aggregates containing 50 primary particles with sizes of 2 nm were formed at a reaction temperature of 30 °C. These particles aggregated further with time and were not stable. In contrast, stable single-core particles with a diameter of 7 nm were formed at 80 °C as revealed by small-angle X-ray scattering (SAXS) coupled in-line with the micromixer for particle characterization. X-ray diffraction and TEM confirmed the SAXS results. X-ray absorption near-edge structure spectroscopy (XANES) identified the iron oxide phase as maghemite. KW - Iron Oxide Nanoparticles KW - Micromixer KW - SAXS KW - XANES KW - Carboxydextran KW - Nanotechnology PY - 2015 DO - https://doi.org/10.1016/j.jmmm.2014.09.057 SN - 0304-8853 VL - 380 SP - 163 EP - 167 PB - Elsevier B.V. CY - Amsterdam AN - OPUS4-32564 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Szczerba, Wojciech A1 - Schott, M. A1 - Riesemeier, Heinrich A1 - Thünemann, Andreas A1 - Kurth, D.G. T1 - Thermally induced structural rearrangement of the Fe(II) coordination geometry in metallo-supramolecular polyelectrolytes N2 - Rigid rod-type metallo-supramolecular coordination polyelectrolytes with Fe(II) centres (Fe-MEPEs) are produced via the self-assembly of the ditopic ligand 1,4-bis(2,2':6',2''-terpyridine-4'-yl)benzene (tpy-ph-tpy) and Fe(II) acetate. Fe-MEPEs exhibit remarkable electrochromic properties; they change colour from blue to transparent when an electric potential is applied. This electrochemical process is generally reversible. The blue colour in the ground state is a result of a metal-to-ligand charge transfer at the Fe(II) centre ion in a quasi-octahedral geometry. When annealed at temperatures above 100 °C, the blue colour turns into green and the formerly reversible electrochromic properties are lost, even after cooling down to room temperature. The thermally induced changes in the Fe(II) coordination sphere are investigated in situ during annealing of a solid Fe-MEPE using X-ray absorption fine structure (XAFS) spectroscopy. The study reveals that the thermally induced transition is not accompanied by a redox process at the Fe(II) centre. From the detailed analysis of the XAFS spectra, the changes are attributed to structural changes in the coordination sphere of the Fe(II) site. In the low temperature state, the Fe(II) ion rests in a quasi-octahedral coordination environment surrounded by six nitrogen atoms of the pyridine rings. The axial Fe–N bond length is 1.94 Å, while the equatorial bond length amounts to 1.98 Å. In the high temperature state, the FeN6-site exhibits a distortion with the axial Fe–N bonds being shortened to 1.88 Å and the equatorial Fe–N bonds being elongated to 2.01 Å. KW - Metallo-supramolecular polyelectrolytes KW - Electrochromism KW - XANES KW - EXAFS KW - Local structure KW - Thermal stability PY - 2014 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-317331 DO - https://doi.org/10.1039/c4cp01187b SN - 1463-9076 SN - 1463-9084 VL - 16 IS - 36 SP - 19694 EP - 19701 PB - The Royal Soc. of Chemistry CY - Cambridge AN - OPUS4-31733 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Grehn, M. A1 - Seuthe, T. A1 - Reinhardt, F. A1 - Höfner, M. A1 - Griga, N. A1 - Eberstein, M. A1 - Bonse, Jörn T1 - Debris of potassium-magnesium silicate glass generated by femtosecond laser-induced ablation in air: An analysis by near edge X-ray absorption spectroscopy, micro Raman and energy dispersive X-ray spectroscopy N2 - The redeposited material (debris) resulting from ablation of a potassium–magnesium silicate glass upon scanning femtosecond laser pulse irradiation (130 fs, 800 nm) in air environment is investigated by means of three complementary surface analytical methods. Changes in the electronic band structure of the glass constituent Magnesium (Mg) were identified by X-ray Absorption Near Edge Structure spectroscopy (XANES) using synchrotron radiation. An up-shift of ≈0.8 eV of a specific Magnesium Κ-edge absorption peak in the spectrum of the redeposited material along with a significant change in its leading edge position was detected. In contrast, the surface left after laser ablation exhibits a downshift of the peak position by ≈0.9 eV. Both observations may be related to a change of the Mg coordinative state of the laser modified/redeposited glass material. The presence of carbon in the debris is revealed by micro Raman spectroscopy (µ-RS) and was confirmed by energy dispersive X-ray spectroscopy (EDX). These observations are attributed to structural changes and chemical reactions taking place during the ablation process. KW - Femtosecond laser ablation KW - Potassium-magnesium silicate glass KW - Debris KW - XANES KW - EDX KW - Raman spectroscopy PY - 2014 DO - https://doi.org/10.1016/j.apsusc.2013.10.028 SN - 0169-4332 SN - 1873-5584 VL - 302 SP - 286 EP - 290 PB - Elsevier B.V. CY - Amsterdam AN - OPUS4-30454 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Hennig, C. A1 - Ikeda-Ohno, A. A1 - Kraus, Werner A1 - Weiss, S. A1 - Pattison, P. A1 - Emerich, H. A1 - Abdala, P. M. A1 - Scheinost, A.C. T1 - Crystal structure and solution species of Ce(III) and Ce(IV) formates: From mononuclear to hexanuclear complexes N2 - Cerium(III) and cerium(IV) both form formate complexes. However, their species in aqueous solution and the solid-state structures are surprisingly different. The species in aqueous solutions were investigated with Ce K-edge EXAFS spectroscopy. Ce(III) formate shows only mononuclear complexes, which is in agreement with the predicted mononuclear species of Ce(HCOO)2+ and Ce(HCOO)2+. In contrast, Ce(IV) formate forms in aqueous solution a stable hexanuclear complex of [Ce6(µ3-O)4(µ3-OH)4(HCOO)x(NO3)y]12–x-y. The structural differences reflect the different influence of hydrolysis, which is weak for Ce(III) and strong for Ce(IV). Hydrolysis of Ce(IV) ions causes initial polymerization while complexation through HCOO– results in 12 chelate rings stabilizing the hexanuclear Ce(IV) complex. Crystals were grown from the above-mentioned solutions. Two crystal structures of Ce(IV) formate were determined. Both form a hexanuclear complex with a [Ce6(µ3-O)4(µ3-OH)4]12+ core in aqueous HNO3/HCOOH solution. The pH titration with NaOH resulted in a structure with the composition [Ce6(µ3-O)4(µ3-OH)4(HCOO)10(NO3)2(H2O)3]·(H2O)9.5, while the pH adjustment with NH3 resulted in [Ce6(µ3-O)4(µ3-OH)4(HCOO)10(NO3)4]·(NO3)3(NH4)5(H2O)5. Furthermore, the crystal structure of Ce(III) formate, Ce(HCOO)3, was determined. The coordination polyhedron is a tricapped trigonal prism which is formed exclusively by nine HCOO– ligands. The hexanuclear Ce(IV) formate species from aqueous solution is widely preserved in the crystal structure, whereas the mononuclear solution species of Ce(III) formate undergoes a polymerization during the crystallization process. KW - Crystal structure KW - Ce complexes KW - EXAFS KW - XANES PY - 2013 DO - https://doi.org/10.1021/ic400999j SN - 0020-1669 SN - 1520-510X VL - 52 IS - 20 SP - 11734 EP - 11743 PB - American Chemical Society CY - Washington, DC AN - OPUS4-29850 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Grehn, M. A1 - Reinhardt, F. A1 - Bonse, Jörn A1 - Eberstein, M. A1 - Seuthe, T. T1 - Response to "comment on 'femtosecond laser-induced modification of potassium-magnesium silicate glasses: an analysis of structural changes by near edge x-ray absorption spectroscopy'" KW - Bond lengths KW - Glass KW - High-speed optical techniques KW - Magnesium compounds KW - Monochromators KW - Potassium compounds KW - Silicon compounds KW - XANES PY - 2013 DO - https://doi.org/10.1063/1.4804148 SN - 0003-6951 SN - 1077-3118 VL - 102 SP - 196102-1 EP - 196102-2 PB - American Institute of Physics CY - Melville, NY AN - OPUS4-28520 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Darlatt, Erik A1 - Nefedov, A. A1 - Traulsen, C.H.-H. A1 - Poppenberg, J. A1 - Richter, S. A1 - Dietrich, Paul A1 - Lippitz, Andreas A1 - Illgen, René A1 - Kühn, Julius A1 - Schalley, C.A. A1 - Wöll, Ch. A1 - Unger, Wolfgang T1 - Interperetation of experimental N K NEXAFS of azide, 1,2,3-triazole and terpyridyl groups by DFT spectrum simulations N2 - Experimental N K-edge NEXAFS data of surface immobilized azide, 1,2,3-triazole and terpyridyl groups are interpreted with the help of DFT spectrum simulations. Assignments of π* resonances in experimental N K-edge NEXAFS spectra to nitrogen atoms within these functional groups have been made. The azide was immobilized on gold as the head group of a thiol SAM, 1,2,3-triazole was formed on this SAM by click reaction and terpyridyl groups were introduced as substituents of the acetylene used for the click reaction. For azide-terminated molecules, DFT spectrum simulations are found to be useful to find measurement conditions delivering experimental N K-edge NEXAFS data with negligible X-ray damage. The 1,2,3-triazole group is found to be rather stable under X-ray irradiation. KW - N K-edge NEXAFS KW - XANES KW - Surface click chemistry KW - Density functional theory KW - Azide KW - 1,2,3-Triazole PY - 2012 DO - https://doi.org/10.1016/j.elspec.2012.09.008 SN - 0368-2048 SN - 1873-2526 VL - 185 IS - 12 SP - 621 EP - 624 PB - Elsevier CY - Amsterdam AN - OPUS4-27774 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Mandel, K. A1 - Szczerba, Wojciech A1 - Thünemann, Andreas A1 - Riesemeier, Heinrich A1 - Girod, Matthias A1 - Sextl, G. T1 - Nitric acid-stabilized superparamagnetic iron oxide nanoparticles studied with X-rays N2 - Agglomerated superparamagnetic iron oxide nanoparticles can easily and in large scale be precipitated from iron salt solutions. Although the process is well known, it is ambiguously either assumed that magnetite or maghemite is obtained. The first part of our study clarifies this question using X-ray absorption spectroscopy. For further processing of the nanoparticles, i.e., for giving them a surface functionality or incorporating them into composites, it is important to break the agglomerates and individualize the particles at first. This can effectively be done with nitric acid treatment. The influence of this process on the particles chemistry and structure was analyzed in great detail using X-ray diffraction, X-ray absorption, and smallangle X-ray scattering. In contrast to our expectation, no oxidation from magnetite (Fe3O4) to maghemite (γ- Fe2O3) was found; the formal valence of the particles in any case is magnetite (Fe3O4). Instead, an increase in the particles' surface disorder was discovered from X-ray absorption analyses and high-resolution transmission electron microscopy. The acid treatment roughens and distorts the surface of the nanoparticles which is connected with an increased spin disorder. KW - XANES KW - EXAFS KW - SAXS KW - Coprecipitation KW - Iron oxide spectra KW - Ferrofluid PY - 2012 DO - https://doi.org/10.1007/s11051-012-1066-3 SN - 1388-0764 SN - 1572-896X VL - 14 IS - 8 SP - 1 EP - 9 PB - Kluwer CY - Dordrecht AN - OPUS4-26357 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -