| 1. |
- Artiglia, Luca, et al.
(författare)
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A surface-stabilized ozonide triggers bromide oxidation at the aqueous solution-vapour interface
- 2017
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 8
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Tidskriftsartikel (refereegranskat)abstract
- Oxidation of bromide in aqueous environments initiates the formation of molecular halogen compounds, which is important for the global tropospheric ozone budget. In the aqueous bulk, oxidation of bromide by ozone involves a [Br center dot OOO-] complex as intermediate. Here we report liquid jet X-ray photoelectron spectroscopy measurements that provide direct experimental evidence for the ozonide and establish its propensity for the solution-vapour interface. Theoretical calculations support these findings, showing that water stabilizes the ozonide and lowers the energy of the transition state at neutral pH. Kinetic experiments confirm the dominance of the heterogeneous oxidation route established by this precursor at low, atmospherically relevant ozone concentrations. Taken together, our results provide a strong case of different reaction kinetics and mechanisms of reactions occurring at the aqueous phase-vapour interface compared with the bulk aqueous phase.
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| 2. |
- Brown, Matthew, et al.
(författare)
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Determination of Surface Potential and Electrical Double-Layer Structure at the Aqueous Electrolyte-Nanoparticle Interface
- 2016
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Ingår i: Physical Review X. - 2160-3308. ; 6:1
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Tidskriftsartikel (refereegranskat)abstract
- The structure of the electrical double layer has been debated for well over a century, since it mediates colloidal interactions, regulates surface structure, controls reactivity, sets capacitance, and represents the central element of electrochemical supercapacitors. The surface potential of such surfaces generally exceeds the electrokinetic potential, often substantially. Traditionally, a Stern layer of nonspecifically adsorbed ions has been invoked to rationalize the difference between these two potentials; however, the inability to directly measure the surface potential of dispersed systems has rendered quantitative measurements of the Stern layer potential, and other quantities associated with the outer Helmholtz plane, impossible. Here, we use x-ray photoelectron spectroscopy from a liquid microjet to measure the absolute surface potentials of silica nanoparticles dispersed in aqueous electrolytes. We quantitatively determine the impact of specific cations (Li + , Na + , K + , and Cs + ) in chloride electrolytes on the surface potential, the location of the shear plane, and the capacitance of the Stern layer. We find that the magnitude of the surface potential increases linearly with the hydrated-cation radius. Interpreting our data using the simplest assumptions and most straightforward understanding of Gouy-Chapman-Stern theory reveals a Stern layer whose thickness corresponds to a single layer of water molecules hydrating the silica surface, plus the radius of the hydrated cation. These results subject electrical double-layer theories to direct and falsifiable tests to reveal a physically intuitive and quantitatively verified picture of the Stern layer that is consistent across multiple electrolytes and solution conditions.
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| 3. |
- Brown, Matthew, et al.
(författare)
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Effect of Surface Charge Density on the Affinity of Oxide Nanoparticles for the Vapor–Water Interface
- 2013
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 29:16, s. 5023-5029
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Tidskriftsartikel (refereegranskat)abstract
- Using in-situ X-ray photoelectron spectroscopy at the vapor–water interface, the affinity of nanometer-sized silica colloids to adsorb at the interface is shown to depend on colloid surface charge density. In aqueous suspensions at pH 10 corrected Debye–Hückel theory for surface complexation calculations predict that smaller silica colloids have increased negative surface charge density that originates from enhanced screening of deprotonated silanol groups (≡Si–O–) by counterions in the condensed ion layer. The increased negative surface charge density results in an electrostatic repulsion from the vapor–water interface that is seen to a lesser extent for larger particles that have a reduced charge density in the XPS measurements. We compare the results and interpretation of the in-situ XPS and corrected Debye–Hückel theory for surface complexation calculations with traditional surface tension measurements. Our results show that controlling the surface charge density of colloid particles can regulate their adsorption to the interface between two dielectrics.
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| 4. |
- Buzzi, Michele, et al.
(författare)
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Single-shot Monitoring of Ultrafast Processes via X-ray Streaking at a Free Electron Laser
- 2017
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Ingår i: Scientific Reports. - : Nature Publishing Group. - 2045-2322. ; 7
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Tidskriftsartikel (refereegranskat)abstract
- The advent of x-ray free electron lasers has extended the unique capabilities of resonant x-ray spectroscopy techniques to ultrafast time scales. Here, we report on a novel experimental method that allows retrieving with a single x-ray pulse the time evolution of an ultrafast process, not only at a few discrete time delays, but continuously over an extended time window. We used a single x-ray pulse to resolve the laser-induced ultrafast demagnetisation dynamics in a thin cobalt film over a time window of about 1.6 ps with an excellent signal to noise ratio. From one representative single shot measurement we extract a spin relaxation time of (130 +/- 30) fs with an average value, based on 193 single shot events of (113 +/- 20) fs. These results are limited by the achieved experimental time resolution of 120 fs, and both values are in excellent agreement with previous results and theoretical modelling. More generally, this new experimental approach to ultrafast x-ray spectroscopy paves the way to the study of non-repetitive processes that cannot be investigated using traditional repetitive pump-probe schemes.
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| 5. |
- Ciuciulkaite, Agne, MSc, 1991-, et al.
(författare)
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Magnetic and all-optical switching properties of amorphous TbxCo100-x alloys
- 2020
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Ingår i: Physical Review Materials. - : American Physical Society (APS). - 2475-9953. ; 4:10
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Tidskriftsartikel (refereegranskat)abstract
- Amorphous TbxCo100-x magnetic alloys exhibit a list of intriguing properties, such as perpendicular magnetic anisotropy, high magneto-optical activity, and magnetization switching using ultrashort optical pulses. Varying the Tb:Co ratio in these alloys allows for tuning properties such as the saturation magnetic moment, coercive field, and the performance of light-induced magnetization switching. In this paper, we investigate the magnetic, optical, and magneto-optical properties of various TbxCo100-x thin-film alloy compositions. We report on the effect the choice of different seeding layers has on the structural and magnetic properties of TbxCo100-x layers. We also demonstrate that for a range of alloys, deposited on fused silica substrates, with Tb content of 24-30 at. %, helicity-dependent all-optical switching of magnetization can be achieved, albeit in a multishot framework. We explain this property to arise from the helicity-dependent laser-induced magnetization on the Co sublattice due to the inverse Faraday effect. Our paper provides an insight into material aspects for future potential hybrid magnetoplasmonic TbCo-based architectures.
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| 6. |
- Girovsky, Jan, et al.
(författare)
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Antiferromagnetic coupling of Cr-porphyrin to a bare Co substrate
- 2014
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 90:22, s. 220404-
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Tidskriftsartikel (refereegranskat)abstract
- We report the discovery of an antiferromagnetic coupling of the magnetic moment of chromium(II) tetraphenylporphyrin (CrTPP) molecules to the magnetization of the clean ferromagnetic Co(001) substrate. We assign this unusual molecule-substrate exchange coupling to the less than half-filled chromium 3d orbitals interacting with Co valence band electrons via porphyrin-ligand molecular orbitals. X-ray magnetic circular dichroism, x-ray photoelectron spectroscopy, and scanning tunneling microscopy are combined with DFT + U calculations and provide evidence for a surprising type of antiferromagnetic 90 degrees indirect magnetic exchange coupling.
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| 7. |
- Girovsky, Jan, et al.
(författare)
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Investigating magneto-chemical interactions at molecule-substrate interfaces by X-ray photo-emission electron microscopy
- 2014
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Ingår i: Chemical Communications. - : Royal Society of Chemistry (RSC). - 1359-7345 .- 1364-548X. ; 50:40, s. 5190-5192
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Tidskriftsartikel (refereegranskat)abstract
- The magneto-chemical interaction of spin-bearing molecules with substrates is interesting from a coordination chemistry point of view and relevant for spintronics. Unprecedented insight is provided by X-ray photo-emission electron microscopy combined with X-ray magnetic circular dichroism spectroscopy. Here the coupling of a Mn-porphyrin ad-layer to the ferromagnetic Co substrate through suitably modified interfaces is analyzed with this technique.
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| 8. |
- Grigorev, Vladimir, et al.
(författare)
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Optically Triggered Néel Vector Manipulation of a Metallic Antiferromagnet Mn2Au under Strain
- 2022
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Ingår i: ACS Nano. - : American Chemical Society (ACS). - 1936-0851 .- 1936-086X. ; 16:12, s. 20589-20597
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Tidskriftsartikel (refereegranskat)abstract
- The absence of stray fields, their insensitivity to external magnetic fields, and ultrafast dynamics make antiferromagnets promising candidates for active elements in spintronic devices. Here, we demonstrate manipulation of the Néel vector in the metallic collinear antiferromagnet Mn2Au by combining strain and femtosecond laser excitation. Applying tensile strain along either of the two in-plane easy axes and locally exciting the sample by a train of femtosecond pulses, we align the Néel vector along the direction controlled by the applied strain. The dependence on the laser fluence and strain suggests the alignment is a result of optically triggered depinning of 90° domain walls and their motion in the direction of the free energy gradient, governed by the magneto-elastic coupling. The resulting, switchable state is stable at room temperature and insensitive to magnetic fields. Such an approach may provide ways to realize robust high-density memory device with switching time scales in the picosecond range.
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| 9. |
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| 10. |
- Shchyrba, Aneliia, et al.
(författare)
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Controlling the dimensionality of on-surface coordination polymers via endo- or exoligation
- 2014
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 136:26, s. 9355-9363
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Tidskriftsartikel (refereegranskat)abstract
- The formation of on-surface coordination polymers is controlled by the interplay of chemical reactivity and structure of the building blocks, as well as by the orientating role of the substrate registry. Beyond the predetermined patterns of structural assembly, the chemical reactivity of the reactants involved may provide alternative pathways in their aggregation. Organic molecules, which are transformed in a surface reaction, may be subsequently trapped via coordination of homo- or heterometal adatoms, which may also play a role in the molecular transformation. The amino-functionalized perylene derivative, 4,9-diaminoperylene quinone-3,10-diimine (DPDI), undergoes specific levels of dehydrogenation (-1 H-2 or -3 H-2) depending on the nature of the present adatoms (Fe, Co, Ni or Cu). In this way, the molecule is converted to an endo- or an exoligand, possessing a concave or convex arrangement of ligating atoms, which is decisive for the formation of either ID or 2D coordination polymers.
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