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| 2. |
- Choi, J., et al.
(författare)
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Spatially inhomogeneous competition between superconductivity and the charge density wave in YBa2Cu3O6.67
- 2020
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 11:1
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Tidskriftsartikel (refereegranskat)abstract
- The charge density wave in the high-temperature superconductor YBa2Cu3O7−x (YBCO) has two different ordering tendencies differentiated by their c-axis correlations. These correspond to ferro- (F-CDW) and antiferro- (AF-CDW) couplings between CDWs in neighbouring CuO2 bilayers. This discovery has prompted several fundamental questions: how does superconductivity adjust to two competing orders and are either of these orders responsible for the electronic reconstruction? Here we use x-ray diffraction to study YBa2Cu3O6.67 as a function of magnetic field and temperature. We show that regions with F-CDW correlations suppress superconductivity more strongly than those with AF-CDW correlations. This implies that an inhomogeneous superconducting state exists, in which some regions show a fragile form of superconductivity. By comparison of F-CDW and AF-CDW correlation lengths, it is concluded that F-CDW ordering is sufficiently long-range to modify the electronic structure. Our study thus suggests that F-CDW correlations impact both the superconducting and normal state properties of YBCO.
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| 3. |
- Villanueva-Perez, P., et al.
(författare)
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Scanning Compton X-ray microscopy
- 2021
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Ingår i: Optics Letters. - 0146-9592. ; 46:8, s. 1920-1923
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Tidskriftsartikel (refereegranskat)abstract
- X-ray microscopy offers the opportunity to image biological and radiosensitive materials without special sample preparations, bridging optical and electron microscopy capabilities. However, the performance of such microscopes, when imaging radiosensitive samples, is not limited by their intrinsic resolution, but by the radiation damage induced on such samples. Here, we demonstrate a novel, to the best of our knowledge, radio-efficient microscope, scanning Compton X-ray microscopy (SCXM), which uses coherently and incoherently (Compton) scattered photons to minimize the deposited energy per unit of mass for a given imaging signal. We implemented SCXM, using lenses capable of efficiently focusing 60 keV X-ray photons into the sub-micrometer scale, and probe its radio-efficient capabilities. SCXM, when implemented in high-energy diffraction-limited storage rings, e.g., European Synchrotron Radiation Facility Extremely Brilliant Source and PETRA IV, will open the opportunity to explore the nanoscale of unstained, unsectioned, and undamaged radiosensitive materials.
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| 4. |
- Albertin, S., et al.
(författare)
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Surface optical reflectance combined with x-ray techniques during gas-surface interactions
- 2020
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Ingår i: Journal of Physics D. - : Institute of Physics (IOP). - 0022-3727 .- 1361-6463. ; 53:22
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Tidskriftsartikel (refereegranskat)abstract
- High energy surface x-ray diffraction (HESXRD), x-ray reflectivity (XRR), mass spectrometry (MS) and surface optical reflectance (SOR) have been combined to simultaneously obtain sub-second information on the surface structure and morphology from a Pd(100) model catalyst during in situ oxidation at elevated temperatures and pressures resulting in Pd bulk oxide formation. The results show a strong correlation between the HESXRD and SOR signal intensities during the experiment, enabling phase determination and a time-resolved thickness estimation of the oxide by HESXRD, complemented by XRR measurements. The experiments show a remarkable sensitivity of the SOR to changes in the surface phase and morphology, in particular to the initial stages of oxidation/reduction. The data imply that SOR can detect the formation of an ultrathin PdO surface oxide layer of only 2-3 angstrom thickness.
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| 5. |
- Gutowski, M. W., et al.
(författare)
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Interval Identification of FMR Parameters for Spin Reorientation Transition in (Ga,Mn)As
- 2012
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Ingår i: Acta Physica Polonica. Series A: General Physics, Physics of Condensed Matter, Optics and Quantum Electronics, Atomic and Molecular Physics, Applied Physics. - 0587-4246. ; 121:5-6, s. 1228-1230
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Tidskriftsartikel (refereegranskat)abstract
- In this work we report results of ferromagnetic resonance studies of a 6% 15 nm (Ga,Mn)As layer, deposited on (001)-oriented GaAs. The measurements were performed with in-plane oriented magnetic field, in the temperature range between 5 K and 120 K. We observe a temperature induced reorientation of the effective in-plane easy axis from [(1) over bar 10] to [110] direction close to the Curie temperature. The behavior of magnetization is described by anisotropy fields, H-eff (= 4 pi M - H-2 perpendicular to), H-2 parallel to, and H-4 parallel to. In order to precisely investigate this reorientation, numerical values of anisotropy fields have been determined using powerful - but still largely unknown - interval calculations. In simulation mode this approach makes possible to find all the resonance fields for arbitrarily oriented sample, which is generally intractable analytically. In "fitting" mode we effectively utilize full experimental information, not only those measurements performed in special, distinguished directions, to reliably estimate the values of important physical parameters as well as their uncertainties and correlations.
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| 6. |
- Hejral, U., et al.
(författare)
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Composition-Dependent Alloy Nanoparticle Shape Changes under Reaction Conditions : Kinetic and Thermodynamic Effects
- 2024
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Ingår i: The Journal of Physical Chemistry C. - 1932-7447 .- 1932-7455. ; 128:10, s. 4330-4342
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Tidskriftsartikel (refereegranskat)abstract
- Particle sintering and reshaping constitute the main cause for catalyst deactivation. An atomic-scale understanding of the correlation among the catalyst structure, its support, and the gas phase under realistic reaction conditions is required for its suppression. In this study, we combined high-energy grazing incidence X-ray diffraction, in situ mass spectrometry, ex situ scanning electron microscopy, and density functional theory calculations to unravel the driving force behind the composition-dependent particle shape changes and sintering processes of alpha-Al2O3(0001)-supported Pt-Pd alloy nanoparticles under realistic reaction conditions for CO oxidation. We find that pure Pt and Pt-rich particles, initially kinetically trapped in metastable flat particle shapes, undergo a strong reaction-induced height increase to adopt a more stable, theoretically predicted compact equilibrium shape. Contrarily, Pd-rich particles prove to be more resistant against shape changes, since they exhibit already a shape close to equilibrium. We thus conclude that the observed initial deviations in particle shape from the theoretical predictions are due to kinetic limitations during growth. Our data provide information on the segregation state of the alloy particles, indicating a Pt core and Pd shell structure under strongly reducing conditions and the alloying of Pt and Pd under the reaction conditions for CO oxidation close to stoichiometry.
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| 7. |
- Pfaff, S., et al.
(författare)
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Combining high-energy X-ray diffraction with Surface Optical Reflectance and Planar Laser Induced Fluorescence for operando catalyst surface characterization
- 2019
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Ingår i: Review of Scientific Instruments. - : AIP Publishing. - 0034-6748 .- 1089-7623. ; 90:3
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Tidskriftsartikel (refereegranskat)abstract
- We have combined three techniques, High Energy Surface X-Ray Diffraction (HESXRD), Surface Optical Reflectance, and Planar Laser Induced Fluorescence in an operando study of CO oxidation over a Pd(100) catalyst. We show that these techniques provide useful new insights such as the ability to verify that the finite region being probed by techniques such as HESXRD is representative of the sample surface as a whole. The combination is also suitable to determine when changes in gas composition or surface structure and/or morphology occur and to subsequently correlate them with high temporal resolution. In the study, we confirm previous results which show that the Pd(100) surface reaches high activity before an oxide can be detected. Furthermore, we show that the single crystal catalyst surface does not behave homogeneously, which we attribute to the surface being exposed to inhomogeneous gas conditions in mass transfer limited scenarios.
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| 8. |
- Simutis, Gediminas, et al.
(författare)
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In situ uniaxial pressure cell for x-ray and neutron scattering experiments
- 2023
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Ingår i: Review of Scientific Instruments. - : AIP Publishing. - 1089-7623 .- 0034-6748. ; 94:1
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Tidskriftsartikel (refereegranskat)abstract
- We present an in situ uniaxial pressure device optimized for small angle x-ray and neutron scattering experiments at low-temperatures and high magnetic fields. A stepper motor generates force, which is transmitted to the sample via a rod with an integrated transducer that continuously monitors the force. The device has been designed to generate forces up to 200 N in both compressive and tensile configurations, and a feedback control allows operating the system in a continuous-pressure mode as the temperature is changed. The uniaxial pressure device can be used for various instruments and multiple cryostats through simple and exchangeable adapters. It is compatible with multiple sample holders, which can be easily changed depending on the sample properties and the desired experiment and allow rapid sample changes.
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