| 1. |
- Abbondanza, Giuseppe, et al.
(författare)
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Anisotropic strain variations during the confined growth of Au nanowires
- 2023
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 122:12
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Tidskriftsartikel (refereegranskat)abstract
- The electrochemical growth of Au nanowires in a template of nanoporous anodic aluminum oxide was investigated in situ by means of grazing-incidence transmission small- and wide-angle x-ray scattering (GTSAXS and GTWAXS), x-ray fluorescence (XRF), and two-dimensional surface optical reflectance. The XRF and the overall intensity of the GTWAXS patterns as a function of time were used to monitor the progress of the electrodeposition. Furthermore, we extracted powder diffraction patterns in the direction of growth and in the direction of confinement to follow the evolution of the direction-dependent strain. Quite rapidly after the beginning of the electrodeposition, the strain became tensile in the vertical direction and compressive in the horizontal direction, which showed that the lattice deformation of the nanostructures can be artificially varied by an appropriate choice of the deposition time. By alternating sequences of electrodeposition with sequences of rest, we observed fluctuations of the lattice parameter in the direction of growth, attributed to stress caused by electromigration. Furthermore, the porous domain size calculated from the GTSAXS patterns was used to monitor how homogeneously the pores were filled.
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| 2. |
- Abbondanza, Giuseppe, 1991, et al.
(författare)
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Au-Pd Barcode Nanowires with Tailored Lattice Parameters and Segment Lengths for Catalytic Applications
- 2024
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Ingår i: ACS Applied Nano Materials. - 2574-0970. ; 7:4, s. 3861-3874
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Tidskriftsartikel (refereegranskat)abstract
- In this study, we present a systematic investigation of the controlled fabrication of Au-Pd barcode nanowires within nanoporous anodic aluminum oxide (NP-AAO) templates. By using a combination of in situ X-ray diffraction (XRD), focused ion beam scanning electron microscopy (FIB-SEM), and transmission electron microscopy (TEM), we elucidate the influence of template preparation methods on the resulting nanowire properties. The template treatment, involving either pore widening or barrier layer thinning, significantly impacts nanowire growth. Through the analysis of the XRD data, we observe sequential deposition of Au and Pd segments with lattice parameter variations and strain effects. Particularly, the lattice parameters of Au and Pd segments display intricate temporal dependencies, influenced by interfacial effects and strain caused by growth under confinement. FIB-SEM imaging reveals uniform and reproducible nanowire lengths in the template treated with pore widening. Furthermore, TEM analysis confirms the presence of distinct Au and Pd segments, while scanning TEM-energy-dispersive X-ray spectroscopy revealed minor evidence of interdiffusion between the first and the second electrodeposited segments. Our findings emphasize the potential of the electrodeposition process within nanoporous templates for producing barcode nanowires with precise segmental properties. The combination of in situ XRD and electron microscopy offers valuable insights into the growth dynamics and structural characteristics of the fabricated Au-Pd barcode nanowires. This controlled fabrication strategy opens doors to tailoring nanowire properties for diverse applications, particularly in catalysis.
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| 3. |
- Abbondanza, Giuseppe, 1991, et al.
(författare)
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Hydride formation and dynamic phase changes during template-assisted Pd electrodeposition
- 2023
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Ingår i: Nanotechnology. - 1361-6528 .- 0957-4484. ; 34:50
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Tidskriftsartikel (refereegranskat)abstract
- We investigated the structural evolution of electrochemically fabricated Pd nanowires in situ by means of grazing-incidence transmission small- and wide-angle x-ray scattering (GTSAXS and GTWAXS), x-ray fluorescence (XRF) and two-dimensional surface optical reflectance (2D-SOR). This shows how electrodeposition and the hydrogen evolution reaction (HER) compete and interact during Pd electrodepositon. During the bottom-up growth of the nanowires, we show that beta-phase Pd hydride is formed. Suspending the electrodeposition then leads to a phase transition from beta-phase Pd hydride to alpha-phase Pd. Additionally, we find that grain coalescence later hinders the incorporation of hydrogen in the Pd unit cell. GTSAXS and 2D-SOR provide complementary information on the volume fraction of the pores occupied by Pd, while XRF was used to monitor the amount of Pd electrodeposited.
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| 4. |
- Larsson, Alfred, et al.
(författare)
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Dynamics of early-stage oxide formation on a Ni-Cr-Mo alloy
- 2024
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Ingår i: NPJ MATERIALS DEGRADATION. - : Springer Nature. - 2397-2106. ; 8:1
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Tidskriftsartikel (refereegranskat)abstract
- Corrosion results in large costs and environmental impact but can be controlled by thin oxide films that passivate the metal surfaces and hinder further oxidation or dissolution in an aqueous environment. The structure, chemistry, and thickness of these oxide films play a significant role in determining their anti-corrosion properties and the early-stage oxidation dynamics affect the properties of the developed oxide. Here, we use in situ X-ray Photoelectron Spectroscopy (XPS) to study the early-stage oxidation of a Ni-Cr-Mo alloy at room temperature and up to 400 degrees C. Cr and Mo begin to oxidize immediately after exposure to O2, and Cr3+, Mo4+, and Mo6+ oxides are formed. In contrast, Ni does not contribute significantly to the oxide film. A self-limiting oxide thickness, which did not depend on temperature below 400 degrees C, is observed. This is attributed to the consumption of available Cr and Mo near the surface, which results in an enrichment of metallic Ni under the oxide. The self-limited oxide thickness is 6-8 angstrom, which corresponds to 3-4 atomic layers of cations in the oxide. At 400 degrees C, sublimation of Mo6+ oxide is observed, resulting in the formation of an almost pure layer of Cr2O3 on the alloy surface. Lastly, a mechanism is presented that explains the formation of the bi-layer oxide structure observed for Ni-Cr-Mo alloys, which involves the enhanced migration of hexavalent Mo ions in the electric field, which drives mass transport during oxidation according to both the Cabrera Mott model and the Point Defect Model.
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| 5. |
- Larsson, Alfred, et al.
(författare)
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In situ quantitative analysis of electrochemical oxide film development on metal surfaces using ambient pressure X-ray photoelectron spectroscopy : Industrial alloys
- 2023
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Ingår i: Applied Surface Science. - : Elsevier BV. - 0169-4332 .- 1873-5584. ; 611
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Tidskriftsartikel (refereegranskat)abstract
- Ambient Pressure X-ray Photoelectron Spectroscopy combined with an electrochemical setup is used to study, in situ, the electrochemical oxide growth on an in-dustrial Ni-Cr-Mo alloy. The native oxide film was characterized in vacuum and in water vapor at 17 mbar, and was found to be 11.4 & ANGS; thick and rich in Cr3+. In 0.1 M NaCl electrolyte, anodic growth of the oxide film at potentials up to 700 mV vs Ag/AgCl nearly doubled the thickness of the oxide film. Moreover, a transformation of the oxide composition occurred, as the oxide became enriched in Mo6+ with a chemical fingerprint more like that of pure MoO3. Both thermodynamics and kinetics of the oxidation of the alloying elements dictate the oxide film growth and composition. Furthermore, we develop the quantitative analysis of oxide composition and thickness to take into account the attenuation through the liquid water and the water vapor atmosphere. Finally, we discuss the differences between ex situ, UHV, in situ, and operando measurements. Our approach is robust, fast, simple, and suitable for systematically probing metal surfaces after aqueous exposure and electro-chemical polarization, which promises wide applications for studies of solid-liquid interfaces in corrosion, batteries, fuel cells, and electrocatalysis.
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| 6. |
- Larsson, Alfred, et al.
(författare)
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The Oxygen Evolution Reaction Drives Passivity Breakdown for Ni–Cr–Mo Alloys
- 2023
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Ingår i: Advanced Materials. - : Wiley. - 0935-9648 .- 1521-4095. ; 35:39
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Tidskriftsartikel (refereegranskat)abstract
- Corrosion is the main factor limiting the lifetime of metallic materials, and a fundamental understanding of the governing mechanism and surface processes is difficult to achieve since the thin oxide films at the metal–liquid interface governing passivity are notoriously challenging to study. In this work, a combination of synchrotron-based techniques and electrochemical methods is used to investigate the passive film breakdown of a Ni–Cr–Mo alloy, which is used in many industrial applications. This alloy is found to be active toward oxygen evolution reaction (OER), and the OER onset coincides with the loss of passivity and severe metal dissolution. The OER mechanism involves the oxidation of Mo4+ sites in the oxide film to Mo6+ that can be dissolved, which results in passivity breakdown. This is fundamentally different from typical transpassive breakdown of Cr-containing alloys where Cr6+ is postulated to be dissolved at high anodic potentials, which is not observed here. At high current densities, OER also leads to acidification of the solution near the surface, further triggering metal dissolution. The OER plays an important role in the mechanism of passivity breakdown of Ni–Cr–Mo alloys due to their catalytic activity, and this effect needs to be considered when studying the corrosion of catalytically active alloys.
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| 7. |
- Yue, Xiaoqi, et al.
(författare)
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Synchrotron-based near ambient-pressure X-ray photoelectron spectroscopy and electrochemical studies of passivation behavior of N- and V-containing martensitic stainless steel
- 2023
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Ingår i: Corrosion Science. - : Elsevier BV. - 0010-938X .- 1879-0496. ; 214, s. 111018-
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Tidskriftsartikel (refereegranskat)abstract
- Passivation behavior of a N-and V-containing martensite stainless steel was studied by synchrotron-based near ambient-pressure X-ray photoelectron spectroscopy, electrochemical analyses, and thermodynamic calculation. The passive film consists of Cr3+, Fe(2, 3)+, and V(2, 3, 4)+ oxides as inner layer, and Cr3+ and Fe3+ hydroxides as outer layer. Austenitization at 1080 oC (rather than 1010 oC) and anodic polarization facilitate transformation of CrN to Cr2O3 leading to further enrichment of Cr3+ oxide in the passive film. Whereas higher Cl- concentration promotes film dissolution leading to higher level of point defects and higher fraction of remaining V oxides in the passive film.
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