| 1. |
- Abbondanza, Giuseppe, et al.
(författare)
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Templated electrodeposition as a scalable and surfactant-free approach to the synthesis of Au nanoparticles with tunable aspect ratios
- 2022
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Ingår i: Nanoscale Advances. - : Royal Society of Chemistry. - 2516-0230. ; 4:11, s. 2452-2467
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Tidskriftsartikel (refereegranskat)abstract
- A high-throughput method for the fabrication of ordered arrays of Au nanoparticles is presented. It is based on pulsed electrodeposition into porous anodic alumina templates. In contrast to many synthesis routes, it is cyanide-free, prior separation of the alumina template from the aluminium substrate is not required, and the use of contaminating surfactants/capping agents often found in colloidal synthesis is avoided. The aspect ratio of the nanoparticles can also be tuned by selecting an appropriate electrodeposition time. We show how to fabricate arrays of nanoparticles, both with branched bases and with hemispherical bases. Furthermore, we compare the different morphologies produced with electron microscopies and grazing-incidence synchrotron X-ray diffraction. We find the nanoparticles are polycrystalline in nature and are compressively strained perpendicular to the direction of growth, and expansively strained along the direction of growth. We discuss how this can produce dislocations and twinning defects that could be beneficial for catalysis.
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| 2. |
- Evertsson, Jonas, et al.
(författare)
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Self-organization of porous anodic alumina films studied in situ by grazing-incidence transmission small-angle X-ray scattering
- 2018
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Ingår i: RSC Advances. - 2046-2069. ; 8:34, s. 18980-18991
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Tidskriftsartikel (refereegranskat)abstract
- Self-ordered porous anodic alumina (PAA) films are studied extensively due to a large number of possible applications in nanotechnology and low cost of production. Whereas empirical relationships between growth conditions and produced oxides have been established, fundamental aspects regarding pore formation and self-organization are still under debate. We present in situ structural studies of PAA films using grazing-incidence transmission small-angle X-ray scattering. We have considered the two most used recipes where the pores self-organize: 0.3 M H2SO4 at 25 V and 0.3 M C2H2O4 at 40 V. During anodization we have followed the evolution of the structural parameters: average interpore distance, length of ordered pores domains, and thickness of the porous oxide layer. Compared to the extensively used ex situ investigations, our approach gives an unprecedented temporal accuracy in determination of the parameters. By using of Al(100), Al(110) and Al(111) surfaces, the influence of surface orientation on the structural evolution was studied, and no significant differences in the interpore distance and domain length could be observed. However, the rate of oxide growth in 0.3 M C2H2O4 at 40 V was significantly influenced by the surface orientation, where the slowest growth occurs for Al(111). In 0.3 M H2SO4 at 25 V, the growth rates were higher, but the influence of surface orientation was not obvious. The structural evolution was also studied on pre-patterned aluminum surfaces. These studies show that although the initial structures of the oxides are governed by pre-patterning geometry, the final structures are dictated by the anodization conditions.
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| 3. |
- Larsson, Alfred, et al.
(författare)
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Electrochemical Fabrication and Characterization of Palladium Nanowires in Nanoporous Alumina Templates
- 2020
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Ingår i: Journal of the Electrochemical Society. - : The Electrochemical Society. - 0013-4651 .- 1945-7111. ; 167:12
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Tidskriftsartikel (refereegranskat)abstract
- A method for the electrochemical synthesis of palladium nanowires, using porous alumina templates with diameters of 25 nm and 40 nm, is presented. Through an electrochemical barrier layer thinning step, pulsed electrodeposition can take place directly into the anodized aluminum; without need for extra removal, pore opening, and metal contact coating steps. A digital oscilloscope is used to record and integrate the current, allowing the efficiency of the electrodeposition to be calculated. We discuss how using a large 'off period' allows for the replenishment of the depleted diffusion layer. The nanowires are characterized by using a focused ion beam (FIB) to create cross-sections which can be accessed with a scanning electron microscope (SEM). With grazing-incidence X-ray diffraction (GI-XRD) we find that the nanowires have a slight compressive strain in the direction that they are confined by the pores (0.58 % and 0.51 % for the 25 nm and 40 nm pores respectively). Knowing the strain state of the nanowires inside the template is of importance for the use of templated nanowires in devices. Further characterization is made using high-resolution transmission electron microscopy (HR-TEM) and energy dispersive X-ray spectroscopy (EDS), after removal from the alumina templates.
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| 4. |
- Larsson, Alfred, et al.
(författare)
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In situ scanning x-ray diffraction reveals strain variations in electrochemically grown nanowires
- 2021
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Ingår i: Journal of Physics D: Applied Physics. - : IOP Publishing. - 0022-3727 .- 1361-6463. ; 54:23
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Tidskriftsartikel (refereegranskat)abstract
- Templated electrochemical growth in nanoporous alumina can be used to fabricate nanowires with applications in magnetic storage devices, hydrogen sensors, and electrocatalysis. It is known that nanowires, grown in such templates, are strained. The strain in nanoscale materials can influence their performance in applications such as catalysts and electronic devices. However, it is not well established how the nanoporous template affects the lattice strain in the nanowires and how this develops during the growth process due to the lack of non-destructive in situ studies with spatial resolution. We have measured the strain and grain size of palladium nanowires in nanoporous templates during the growth process. For this, we performed in situ scanning x-ray diffraction with a submicron focused x-ray beam. We found a tensile strain in the nanowires and that it is more pronounced along the growth direction than in the confined direction of the templates. The tensile strain measured in situ is higher than previous ex situ reports, possibly due to hydrogen absorption during the growth. With the spatial information made possible with the focused synchrotron x-ray beam, we could observe local variations in the strain as a function of height. A region of local strain variation is found near the bottom of the nanowires where growth is initiated in branches at the pore bottoms. Knowledge of how nanoporous templates influences the strain of the nanowires may allow for atomic scale tailoring of the catalytic activity of such nanowires or minimizing strain to optimize electronic device performance.
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| 5. |
- Linpe, Weronica
(författare)
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In situ observations of tin deposition into nanoporous anodic aluminium oxide
- 2019
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- AbstractIn this thesis, the electrochemical deposition process of Sn into ordered nanoporous anodic aluminium oxide (NP-AAO) have been studied. The deposition process was studied in situ using the X-ray techniques: X-ray diffraction (XRD), Grazing incidence Transmission Small-Angle X-ray Scattering (GTSAXS), X-ray Fluorescence (XRF) and X-ray Absorption Near Edge Structure (XANES) and ex situ using Focused Ion Beam-Scanning Electron Microscopy and Transmission Electron Microscopy measurements.The NP-AAO will under certain anodisation conditions order into a hexagonalarrangement. These ordered NP-AAO can be used as a template to grow orderednanowires as well as for colouring of aluminium products. Sn, which is investigated in this thesis, is used in industry to colour aluminium products in brown and black colours. To follow the electrochemical deposition of Sn into the NP-AAO with X-ray measurements is of interests as it gives fundamental knowledge of where and how the metal is deposited within the pores.In situ X-ray measurements are used to follow the electrochemical deposition of Sn using an alternating deposition voltage into pre-prepared NP-AAO templates, which had been grown using a two-step self-ordering anodisation process with an extra step for thinning down the barrier layer. The X-ray measurements showed how the Sn filled the pores from the bottom up, where the GTSAXS measurements indicate a non-uniform pore filling. The oxidation state of the deposited Sn was determined with XANES to be metallic and with the XRD measurements, the crystal structure was determined to be β-Sn. Ex situ measurements used Focused Ion Beam to cut into the sample to expose the Sn inside the pores. Scanning Electron Microscopy and Transmission Electron Microscopy measurements were used to visualize the Sn within the pores and showed the Sn as nanopillars inside the pores.These results show that different X-ray techniques can be used to gain a deeperknowledge about the electrochemical deposition processes into NP-AAO. Themeasurements focused on Sn, however, these techniques are also applicable toinvestigate deposition of other metals within the oxide. This knowledge about how the Sn deposits within a confined structure, can be used for creating better templates and to understand how to grow ordered nanowires in a controlled manner inside of these kinds of templates.
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| 6. |
- Linpé, Weronica, et al.
(författare)
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Revisiting Optical Reflectance from Au(111) Electrode Surfaces with Combined High-Energy Surface X-ray Diffraction
- 2021
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Ingår i: Journal of the Electrochemical Society. - : Electrochemical Society. - 0013-4651 .- 1945-7111. ; 168:9
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Tidskriftsartikel (refereegranskat)abstract
- We have combined high-energy surface X-ray diffraction (HESXRD) with 2D surface optical reflectance (2D-SOR) to perform in situ electrochemical measurements of a Au(111) electrode in 0.1 M HClO4 electrolyte. We show that electrochemically induced changes to Au(111) surface during cyclic voltammetry can be simultaneously observed with 2D-SOR and HESXRD. We discuss how small one atom high 1x1 islands, accommodating excess atoms after the lifting of the surface reconstruction, can lead to discrepancies between the two techniques. The use of HESXRD allows us to simultaneously detect parts of the truncation rods from the (1 x 1) surface termination and the p x root 3 electrochemically induced surface reconstruction, during cyclic voltammetry. The presence of reconstruction phenomena is shown to not depend on having an ideally prepared surface and can in fact be observed after going to very oxidizing potentials. 2D-SOR can also detect the oxidation of the Au surface, however no oxide peaks are detected in the HESXRD signal, which is evidence that any Au oxide is X-ray amorphous.
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| 7. |
- Linpé, Weronica, et al.
(författare)
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The State of Electrodeposited Sn Nanopillars within Porous Anodic Alumina from In-situ X-ray Observations
- 2019
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Ingår i: ACS Applied Nano Materials. - : American Chemical Society (ACS). - 2574-0970. ; 2:5, s. 3031-3038
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Tidskriftsartikel (refereegranskat)abstract
- Porous anodic alumina (PAA) can be used as a template for controlled electrodeposition and growth of nano-structures, it is also essential for long-lasting decorative coloring of aluminum. We have investigated the deposition of Sn nanopillars into PAA in-situ, with Grazing transmission small angle X-ray scattering, X-ray fluorescence and X-ray absorption near edge structure spectroscopy. An accumulation of Sn could be detected in the pores during the electrodeposition. From the X-ray absorption near edge structure spectroscopy measurements we could conclude that the deposited Sn was primarily in the metallic state. Ex-situ scanning electron microscopy cross-section measurements show Sn nanopillars inside the PAA.
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| 8. |
- Linpe, Weronica
(författare)
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Using Light to Probe Surface Electrochemical Processes
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis shows how various light-based in situ techniques can be used to follow different surface electrochemical processes such as electrochemical deposition into Nanoporous Anodic Aluminium Oxide (NP-AAO) templates and the surface structure of electrodes. Techniques based on both x-rays and visible light were used to follow surface structures and compositions, in situ. The samples were alsoinvestigated with ex situ techniques, such as scanning electron microscopy (SEM), transmission electron microscopy (TEM) and various other techniques. Templated electrodeposition processes, which can be used for growing various nanostructures with applications in for example gas sensors, catalysts, electrocatalysts and colouring of metal products were studied. Cyclic voltammetry (CV) for investigating electrooxidation and corrosion of model systems as well as real industrial materials was combined with Surface X-ray Diffraction and 2-Dimensional Surface Optical Reflectance.Electrochemical deposition of Sn, Pd and Au into NP-AAO was investigated with both in situ and ex situ methods to gain information about the deposition process, the influence of the NP-AAO template on the growth of the nanostructures and the chemical and crystallographic nature of the grown nanostructures. For the Sn, it was possible to determine that the grown nanostructures were metallic with a beta-Sn crystal structure and a compression of the nanostructures due to the confinement of the pores were measured. Both the Pd and the Au nanostructures were constructedof crystalline grains with grain sizes in the range of the pore diameter. A compressive and tensile strain could be measured across and along thenanostructures, respectively. The combination of 2-Dimensional Surface Optical Reflectance (2D-SOR), an optical microscope, with a modified electrochemical cell, was investigated through cyclic voltammetry measurements on Au, Pd and Super Duplex Stainless Steel and anodization of aluminium. The measured reflectance could be correlated with characteristic features in the CV curve corresponding to oxidation and reduction of the surface. By combining 2D-SOR with High Energy Surface X-ray Diffraction (HESXRD) during CV measurements the reflectance could be correlated with theatomic changes of the Au(111) surface. It was also shown that 2D-SOR could detect monolayer changes of the surface, due to its sensitivity to the increased electron density of the Herringbone reconstruction, a rearrangement of the atoms in the topmost layer of the Au(111) single crystal surface. By applying this method to polycrystalline samples, it was possible to follow how differently oriented grains react differently during the same experimental conditions, showing the possibility for 2D-SOR to image inhomogeneous surfaces.The Au(111) single crystal was further studied using CV and potential stepping going into the oxygen evolution reaction (OER). The combined HESXRD and 2D- SOR measurements detected a roughening of the surface as it was oxidized and during the OER. These measurements also suggest that the oxide on the Au(111) single crystal is amorphous, due to the lack of oxidation peaks in the measured diffraction pattern. With X-ray photoelectron spectroscopy measurements, it could be shown that sulphate species absorb on the surface before any oxide is detected,the oxide is then formed and detected as the sulphate desorbs. The possibility to follow and understand these different surface reactions gives knowledge which in the future could be used for example for the continued development of fuel cells, the development of devices, sensors, catalysts and to develop more corrosion-resistant materials.
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| 9. |
- Långberg, Marie, 1988-, et al.
(författare)
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Redefining passivity breakdown of super duplex stainless steel by electrochemical operando synchrotron near surface X-ray analyses
- 2019
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Ingår i: npj Materials Degradation. - Stockholm, : Springer Science and Business Media LLC. - 2397-2106. ; 3:1
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Tidskriftsartikel (refereegranskat)abstract
- Passivity determines corrosion resistance and stability of highly-alloyed stainless steels, and passivity breakdown is commonly believed to occur at a fixed potential due to formation and dissolution of Cr(VI) species. In this work, the study of a 25Cr–7Ni super duplex stainless steel in 1 M NaCl solution revealed that the passivity breakdown is a continuous degradation progress of the passive film over a potential range, associated with enhanced Fe dissolution before rapid Cr dissolution and removal of the oxide. The breakdown involves structural and compositional changes of the passive film and the underlying alloy surface layer, as well as selective metal dissolution depending on the anodic potential. The onset of passivity breakdown occurred at 1000 mV/Ag/AgCl, and Fe dissolved more on the ferrite than the austenite phase. With increasing potential, the passive film became thicker but less dense, while the underlying alloy surface layer became denser indicating Ni and Mo enrichment. Rapid Cr dissolution occurred at ≥1300 mV/Ag/AgCl.
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| 10. |
- Pfaff, Sebastian, et al.
(författare)
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Operando Reflectance Microscopy on Polycrystalline Surfaces in Thermal Catalysis, Electrocatalysis, and Corrosion
- 2021
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Ingår i: ACS applied materials & interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 13:16, s. 19530-19540
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Tidskriftsartikel (refereegranskat)abstract
- We have developed a microscope with a spatial resolution of 5 μm, which can be used to image the two-dimensional surface optical reflectance (2D-SOR) of polycrystalline samples in operando conditions. Within the field of surface science, operando tools that give information about the surface structure or chemistry of a sample under realistic experimental conditions have proven to be very valuable to understand the intrinsic reaction mechanisms in thermal catalysis, electrocatalysis, and corrosion science. To study heterogeneous surfaces in situ, the experimental technique must both have spatial resolution and be able to probe through gas or electrolyte. Traditional electron-based surface science techniques are difficult to use under high gas pressure conditions or in an electrolyte due to the short mean free path of electrons. Since it uses visible light, SOR can easily be used under high gas pressure conditions and in the presence of an electrolyte. In this work, we use SOR in combination with a light microscope to gain information about the surface under realistic experimental conditions. We demonstrate this by studying the different grains of three polycrystalline samples: Pd during CO oxidation, Au in electrocatalysis, and duplex stainless steel in corrosion. Optical light-based techniques such as SOR could prove to be a good alternative or addition to more complicated techniques in improving our understanding of complex polycrystalline surfaces with operando measurements.
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