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| 2. |
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| 3. |
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| 4. |
- Delheusy, M., et al.
(författare)
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X-ray investigation of subsurface interstitial oxygen at Nb/oxide interfaces
- 2008
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 92:10
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Tidskriftsartikel (refereegranskat)abstract
- We have investigated the dissolution of a natural oxide layer on a Nb(110) surface upon heating, combining x-ray reflectivity, grazing incidence diffuse scattering, and core-level spectroscopy. The natural oxide reduces after heating to 145 degrees C partially from Nb2O5 to NbO2, and an enrichment in subsurface interstitial oxygen by similar to 70% in a depth of 100 A is observed. After heating to 300 degrees C, the oxide reduces to NbO and the surplus subsurface oxygen gets dissolved into the bulk. Our approach can be applied for further investigation of the effect of subsurface interstitial oxygen on the performance of niobium rf cavities. (C) 2008 American Institute of Physics. (C) 2008 American Institute of Physics.
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| 5. |
- Långberg, Marie, et al.
(författare)
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Characterization of Native Oxide and Passive Film on Austenite/Ferrite Phases of Duplex Stainless Steel Using Synchrotron HAXPEEM
- 2019
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Ingår i: Journal of the Electrochemical Society. - : Electrochemical Society. - 0013-4651 .- 1945-7111. ; 166:11, s. C3336-C3340
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Tidskriftsartikel (refereegranskat)abstract
- A new measurement protocol was used for microscopic chemical analysis of surface oxide films with lateral resolution of 1 mu m. The native air-formed oxide and an anodic passive film on austenite and ferrite phases of a 25Cr-7Ni super duplex stainless steel were investigated using synchrotron hard X-ray photoemission electron microscopy (HAXPEEM). Pre-deposited Pt-markers, in combination with electron backscattering diffraction mapping (EBSD), allowed analysis of the native oxide on individual grains of the two phases and the passive film formed on the same area after electrochemical polarization of the sample. The results showed a certain difference in the composition of the surface films between the two phases. For the grains with (001) crystallographic face // sample surface, the native oxide film on the ferrite contained more Cr oxide than the austenite. Anodic polarization up to 1000 mV/(Ag/AgCl) in 1M NaCl solution at room temperature resulted in a growth of the Cr- and Fe-oxides, diminish of Cr-hydroxide, and an increased proportion of Fe3+ species. by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 License (CC BY, http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse of the work in any medium, provided the original work is properly cited.
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| 6. |
- Långberg, Marie, 1988-, et al.
(författare)
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Lateral variation of the native passive film on super duplex stainless steel resolved by synchrotron hard X-ray photoelectron emission microscopy
- 2020
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Ingår i: Corrosion Science. - Stockholm, : Elsevier BV. - 0010-938X .- 1879-0496. ; 174
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Tidskriftsartikel (refereegranskat)abstract
- A native passive film on 25Cr-7Ni super duplex stainless steel was analyzed using synchrotron hard X-ray photoemission electron microscopy, focusing on variations between individual grains of ferrite and austenite phases. The film consists of an oxide inner layer and an oxyhydroxide outer layer, in total 2.3 nm thick. The Cr content is higher in the outer than the inner layer, ca. 80 % on average. The Cr content is higher on ferrite than austenite, whereas the thickness is rather uniform. The grain orientation has a small but detectable influence, ferrite (111) grains have a lower Cr content than other ferrite grains.
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| 7. |
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| 8. |
- Schmid, M, et al.
(författare)
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Structure of Ag(111)-p(4x4)-O: No silver oxide
- 2006
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Ingår i: Physical Review Letters. - 1079-7114. ; 96:14
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Tidskriftsartikel (refereegranskat)abstract
- The structure of the oxygen-induced p(4x4) reconstruction of Ag(111) is determined by a combination of scanning tunneling microscopy, surface x-ray diffraction, core level spectroscopy, and density functional theory. We demonstrate that all previous models of this surface structure are incorrect and propose a new model which is able to explain all our experimental findings but has no resemblance to bulk silver oxide. We also shed some light on the limitations of current density functional theories and the potential role of van der Waals interactions in the stabilization of oxygen-induced surface reconstructions of noble metals.
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| 9. |
- Stierle, A., et al.
(författare)
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Real time observation of ultrathin epitaxial oxide growth during alloy oxidation
- 2007
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Ingår i: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 9, s. 331-331
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Tidskriftsartikel (refereegranskat)abstract
- We have studied the thermal oxidation of the intermetallic alloy CoGa in situ, in real time on the atomic scale, during the growth of an ultrathin, epitaxial Ga oxide layer. On the basis of an extended set of surface x-ray diffraction data, density functional theory calculations and core level spectroscopy data, we find that the oxide film consists of an oxygen ion double layer, which contains the basic building block of bulk beta- Ga2O3. The oxide formation takes place via the nucleation of two- dimensional, anisotropic oxide islands which laterally grow and coalesce. A dramatic increase of the oxide island size is observed for low O-2 pressures in the 10(-8) mbar regime, which we interpret as the onset of a step flow like growth mode. This allows us to conclude that thermal oxidation can be considered as a hetero- epitaxial growth process, that follows similar atomistic growth principles to molecular beam epitaxy. As a consequence, the structural perfection of the oxide layer can be tailored by the appropriate choice of oxygen pressure and temperature.
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| 10. |
- Gleißner, Robert, et al.
(författare)
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Role of Oxidation–Reduction Dynamics in the Application of Cu/ZnO-Based Catalysts
- 2023
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Ingår i: ACS Applied Nano Materials. - 2574-0970. ; 6:9, s. 8004-8016
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Tidskriftsartikel (refereegranskat)abstract
- We investigated Cu nanoparticles (NPs) on vicinal and basal ZnO supports to obtain an atomistic picture of the catalyst’s structure under in situ oxidizing and reducing conditions. The Cu/ZnO model catalysts were investigated at elevated gas pressures by high energy grazing incidence X-ray diffraction and ambient pressure X-ray photoelectron spectroscopy (AP-XPS). We find that the Cu nanoparticles are fully oxidized to Cu2O under atmospheric conditions at room temperature. As the nanoparticles swell during oxidation, they maintain their epitaxy on basal ZnO (000 ± 1) surfaces, whereas on the vicinal ZnO (101̅4) surface, the nanoparticles undergo a coherent tilt. We find that the oxidation process is fully reversible under H2 flow at 500 K, resulting in predominantly well-aligned nanoparticles on the basal surfaces, whereas the orientation of Cu NPs on vicinal ZnO was only partially restored. The analysis of the substrate crystal truncation rods evidences the stability of basal ZnO surfaces under all gas conditions. No Cu–Zn bulk alloy formation is observed. Under CO2 flow, no diffraction signal from the nanoparticles is detected, pointing to their completely disordered state. The AP-XPS results are in line with the formation of CuO. Scanning electron microscopy images show that massive mass transport has set in, leading to the formation of larger agglomerates.
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| 11. |
- Gustafson, Johan, et al.
(författare)
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Structure of a thin oxide film on Rh(100)
- 2005
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Ingår i: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 71:11
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Tidskriftsartikel (refereegranskat)abstract
- The initial oxidation of Rh(100) has been studied using high resolution core level spectroscopy, low energy electron diffraction, surface x-ray diffraction, scanning tunneling microscopy, and density functional theory. We report a structural study of an oxygen induced structure displaying a c(8x2) periodicity at an oxygen pressure above 10(-5) mbar and using a sample temperature of 700 K. Our experimental and theoretical data demonstrate that this structure is due to the formation of a thin surface oxide with a hexagonal trilayer O-Rh-O structure.
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| 12. |
- 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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| 13. |
- Hejral, U., et al.
(författare)
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High-energy x-ray diffraction from surfaces and nanoparticles
- 2017
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Ingår i: Physical Review B. - 2469-9950. ; 96:19
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Tidskriftsartikel (refereegranskat)abstract
- High-energy surface-sensitive x-ray diffraction (HESXRD) is a powerful high-energy photon technique (E > 70 keV) that has in recent years proven to allow a fast data acquisition for the 3D structure determination of surfaces and nanoparticles under in situ and operando conditions. The use of a large-area detector facilitates the direct collection of nearly distortion-free diffraction patterns over a wide q range, including crystal truncation rods perpendicular to the surface and large-area reciprocal space maps from epitaxial nanoparticles, which is not possible in the conventional low-photon energy approach (E=10-20keV). Here, we present a comprehensive mathematical approach, explaining the working principle of HESXRD for both single-crystal surfaces and epitaxial nanostructures on single-crystal supports. The angular calculations used in conventional crystal truncation rod measurements at low-photon energies are adopted for the high-photon-energy regime, illustrating why and to which extent large reciprocal-space areas can be probed in stationary geometry with fixed sample rotation. We discuss how imperfections such as mosaicity and finite domain size aid in sampling a substantial part of reciprocal space without the need of rotating the sample. An exact account is given of the area probed in reciprocal space using such a stationary mode, which is essential for in situ or operando time-resolved experiments on surfaces and nanostructures.
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| 14. |
- Hejral, U., et al.
(författare)
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Identification of a Catalytically Highly Active Surface Phase for CO Oxidation over PtRh Nanoparticles under Operando Reaction Conditions
- 2018
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Ingår i: Physical Review Letters. - 0031-9007. ; 120:12
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Tidskriftsartikel (refereegranskat)abstract
- Pt-Rh alloy nanoparticles on oxide supports are widely employed in heterogeneous catalysis with applications ranging from automotive exhaust control to energy conversion. To improve catalyst performance, an atomic-scale correlation of the nanoparticle surface structure with its catalytic activity under industrially relevant operando conditions is essential. Here, we present x-ray diffraction data sensitive to the nanoparticle surface structure combined with in situ mass spectrometry during near ambient pressure CO oxidation. We identify the formation of ultrathin surface oxides by detecting x-ray diffraction signals from particular nanoparticle facets and correlate their evolution with the sample's enhanced catalytic activity. Our approach opens the door for an in-depth characterization of well-defined, oxide-supported nanoparticle based catalysts under operando conditions with unprecedented atomic-scale resolution.
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| 15. |
- Lundgren, Edvin, et al.
(författare)
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Kinetic hindrance during the initial oxidation of Pd(100) at ambient pressures
- 2004
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Ingår i: Physical Review Letters. - 1079-7114. ; 92:4
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Tidskriftsartikel (refereegranskat)abstract
- The oxidation of the Pd(100) surface at oxygen pressures in the 10(-6) to 10(3) mbar range and temperatures up to 1000 K has been studied in situ by surface x-ray diffraction (SXRD). The results provide direct structural information on the phases present in the surface region and on the kinetics of the oxide formation. Depending on the (T,p) environmental conditions, we observe either a thin (root5 x root5)R27degrees surface oxide or the growth of a rough, poorly ordered bulk oxide film of PdO predominantly with (001) orientation. By either comparison to the surface phase diagram from first-principles atomistic thermodynamics or by explicit time-resolved measurements we identify a strong kinetic hindrance to the bulk oxide formation even at temperatures as high as 675 K.
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| 16. |
- Martin, Natalia, et al.
(författare)
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High-resolution core-level spectroscopy study of the ultrathin aluminum oxide film on NiAl(110)
- 2011
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Ingår i: Physical Review B - Condensed Matter and Materials Physics. - 2469-9950 .- 2469-9969 .- 1098-0121. ; 83:12
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Tidskriftsartikel (refereegranskat)abstract
- We have studied the ultrathin aluminum oxide film on NiAl(110) by a combination of high-resolution core-level spectroscopy and density functional theory calculations. Energy-dependent core-level data from the O 1s and Al 2p levels allows for a distinction between oxygen and aluminum atoms residing at the surface or inside the aluminum oxide film. A comparison to calculated core-level binding energies from the recent model by Kresse et al. [Science 308, 1440 (2005)] reveals good agreement with experiment, and the complex spectroscopic signature of the thin Al oxide on NiAl(110) can be explained. Our assignment of a shifted component in the O 1s spectra to oxygen atoms at the surface with a particular Al and oxygen coordination may have implications for the interpretation of photoelectron-diffraction experiments from similar ultrathin aluminum oxide films.
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| 17. |
- Shipilin, Mikhail, et al.
(författare)
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The influence of incommensurability on the long-range periodicity of the Pd(100)-(root 5 x root 5)R27 degrees-PdO(101)
- 2017
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Ingår i: Surface Science. - : Elsevier BV. - 0039-6028. ; 660, s. 1-8
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Tidskriftsartikel (refereegranskat)abstract
- The structural model of the (root 5 x root 5)R27 degrees PdO(101) surface oxide grown on Pd(100) has been proposed and refined by a number of authors over more than a decade. In the current contribution we discuss the long-range periodicity of this structure arising along one of the crystallographic directions due to its incommensurability with the substrate. Analyzing the results of surface sensitive diffraction studies, we determined a slight distortion of the previously reported perfect (root 5 x root 5)R27 degrees surface oxide unit cell. Considering it, we were able to achieve both qualitatively and quantitatively better fit to the experimental diffraction data than it was possible for the perfect structure. Further, taking into account the experimentally obtained scanning tunneling microscopy data and closely examining high-resolution patterns recorded by means of high-energy surface X-ray diffraction, we developed a qualitative structural model based on a larger non-orthogonal surface unit cell to shed more light on the long-range order of the PdO(101) surface oxide. The model comprises a shift of the atoms of the PdO perpendicularly to the direction of the incommensurability to correct for it. This structural model reproduces the fine details of the high-resolution diffraction patterns and qualitatively explains the periodic stripes of structural distortion observed in the images recorded by a scanning tunneling microscope.
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| 18. |
- Stierle, A, et al.
(författare)
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Surface core level shift observed on NiAl(110)
- 2003
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Ingår i: Surface Science. - 0039-6028. ; 529:3, s. 263-268
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Tidskriftsartikel (refereegranskat)abstract
- Using high resolution core level spectroscopy, a surface core level shift towards lower binding energy of -0.13 eV is determined for the 2p level of the outwardly relaxed Al surface atoms on NiAl(110). Density functional theory based calculations with inclusion of final state effects yield a value of -0.14 eV for this shift in excellent agreement with experiment. We show that the initial state approximation yields a value of +0.09 eV, i.e. the inclusion of final state relaxation effects is vital not only to obtain the correct value but even the correct sign for this shift. (C) 2003 Elsevier Science B.V. All rights reserved.
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| 19. |
- Stierle, A, et al.
(författare)
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Surface x-ray study of the structure and morphology of the oxidized Pd(001) surface
- 2005
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 122:4
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Tidskriftsartikel (refereegranskat)abstract
- The oxidation of Pd(100) and the formation of PdO was studied in situ using surface x-ray diffraction. A bulklike, epitaxial PdO film is formed at oxygen partial pressures beyond 1 mbar and sample temperatures exceeding 650 K. The main orientation is PdO(001)/Pd(001), based upon bulk reflections from the PdO film. By comparing with measurements from the Pd crystal truncation rods, we estimate an rms surface roughness of 6 Angstrom, in good agreement with previous high pressure scanning tunneling microscopy measurements. Finally, we observed the transformation from the (root5 x root5) surface oxide to PdO bulk oxide at 675 K and 50 mbar O-2 pressure.
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| 20. |
- Westerström, Rasmus, et al.
(författare)
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Lack of surface oxide layers and facile bulk oxide formation on Pd(110)
- 2009
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Ingår i: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 80:12
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Tidskriftsartikel (refereegranskat)abstract
- The oxidation of the Pd(110) surface has been studied from ultrahigh vacuum up to atmospherical pressures by combining scanning tunneling microscopy, low-energy electron diffraction and high-resolution core-level spectroscopy with in situ surface x-ray diffraction, and density-functional theory calculations. Under in situ conditions, we observe a c(2x4) structure which transforms via the formation of antiphase domain boundaries to a "complex" structure with increasing partial oxygen pressure. Contrary to other closed packed and vicinal Pd surfaces investigated so far, no surface oxide is formed, which allows for the formation of the PdO bulk oxide closer to the thermodynamic limit at temperatures relevant for catalysis.
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| 21. |
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