| 1. |
- Redondo, A. B., et al.
(författare)
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Nanoparticle-Induced Charge Redistribution of the Air-Water Interface
- 2015
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 119:5, s. 2661-2668
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Tidskriftsartikel (refereegranskat)abstract
- The airwater interface is believed to carry a negative electrostatic potential that is nontrivial to invert through pH, electrolyte, or electrolyte strength. Here, through a combined experimental and theoretical study, we show that the close approach of a negatively charged nanoparticle induces a charge redistribution of the airwater interface. Using different electrolytes to control the interfacial potential of the nanoparticles, X-ray photoelectron spectroscopy (XPS) results establish that nanoparticles with a more negative zeta potential adsorb closer to the airwater interface than do the same particles with a less negative zeta potential. The short-ranged attractive force between two (nominally) negative surfaces is caused by charge redistribution under the strong electric field of the nanoparticle that locally inverts the charge density of the airwater interface from negative to positive. The nature of the nanoparticles counterions modulates the attractive interaction, which thus could be used to control reactivity, stability, and nanoparticle self-assembly at airwater interfaces.
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| 2. |
- Lytvynenko, Y., et al.
(författare)
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Control of the asymmetric band structure in Mn2Au by a ferromagnetic driver layer
- 2023
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Ingår i: Physical Review B. - 2469-9950 .- 2469-9969. ; 108:10
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Tidskriftsartikel (refereegranskat)abstract
- Hard x-ray angle-resolved photoemission spectroscopy reveals the momentum-resolved band structure in an epitaxial Mn2Au(001) film capped by a 2-nm-thick ferromagnetic permalloy layer. By magnetizing the permalloy capping layer, the exceptionally strong exchange bias aligns the Néel vector in the Mn2Au(001) film accordingly. Uncompensated interface Mn magnetic moments in Mn2Au were identified as the origin of the exchange bias using x-ray magnetic circular dichroism in combination with photoelectron emission microscopy. Using time-of-flight momentum microscopy, we measure the asymmetry of the band structure, E(k)≠E(-k), in Mn2Au resulting from the homogeneous orientation of the Néel vector. Comparison with theory shows that the Néel vector, determined by the magnetic moment of the top Mn layer, is antiparallel to the permalloy magnetization. The experimental results demonstrate that hard x-ray photoemission spectroscopy can measure the band structure of epitaxial layers beneath a metallic capping layer and corroborate the asymmetric band structure in Mn2Au that was previously inferred only indirectly.
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| 3. |
- Valencia, S., et al.
(författare)
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Quadratic X-Ray Magneto-Optical Effect upon Reflection in a Near-Normal-Incidence Configuration at the M Edges of 3d-Transition Metals
- 2010
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 104:18, s. 187401-
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Tidskriftsartikel (refereegranskat)abstract
- We have observed a quadratic x-ray magneto-optical effect in near-normal-incidence reflection at the M edges of iron. The effect appears as the magnetically induced rotation of similar to 0.1 degrees of the polarization plane of linearly polarized x-ray radiation upon reflection. A comparison of the measured rotation spectrum with results from x-ray magnetic linear dichroism data demonstrates that this is the first observation of the Schafer-Hubert effect in the x-ray regime. Ab initio density-functional theory calculations reveal that hybridization effects of the 3p core states necessarily need to be considered when interpreting experimental data. The discovered magneto-x-ray effect holds promise for future ultrafast and element-selective studies of ferromagnetic as well as antiferromagnetic materials.
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| 4. |
- 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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| 5. |
- 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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| 6. |
- 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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| 7. |
- 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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| 8. |
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| 9. |
- Waeckerlin, Christian, et al.
(författare)
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Magnetic exchange coupling of a synthetic Co(II)-complex to a ferromagnetic Ni substrate
- 2013
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Ingår i: Chemical Communications. - : Royal Society of Chemistry (RSC). - 1359-7345 .- 1364-548X. ; 49:91, s. 10736-10738
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Tidskriftsartikel (refereegranskat)abstract
- On-surface assembly of a spin-bearing and non-aromatic porphyrin-related synthetic Co(II)-complex on a ferromagnetic Ni thin film substrate and subsequent magnetic exchange interaction across the interface were studied by scanning tunnelling microscopy (STM), X-ray absorption spectroscopy (XAS), X-ray magnetic circular dichroism (XMCD) and density functional theory +U (DFT + U) calculations.
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| 10. |
- Waeckerlin, Christian, et al.
(författare)
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On-surface coordination chemistry of planar molecular spin systems : novel magnetochemical effects induced by axial ligands
- 2012
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Ingår i: CHEMICAL SCIENCE. - : Royal Society of Chemistry (RSC). - 2041-6520 .- 2041-6539. ; 3:11, s. 3154-3160
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Tidskriftsartikel (refereegranskat)abstract
- Paramagnetic transition-metal complexes assembled on surfaces are of great interest for potential applications in organic spintronics. The magnetochemical interactions of the spin of the metal centers with both ferromagnetic surfaces and optional axial ligands are yet to be understood. We use a combination of X-ray magnetic circular dichroism (XMCD) and quantum-chemical simulations based on density functional theory (DFT + U) to investigate these metal-organic interfaces with chemically tunable magnetization. The interplay between an optional axial ligand (NO, spin S = 1/2 or NH3, S = 0) and Ni and Co ferromagnetic surfaces affecting the spin of Co(II) tetraphenylporphyrin (d(7), S = 1/2), Fe(II) tetraphenylporphyrin (d(6), S = 1), Mn(II) tetraphenylporphyrin (d(5), S = 5/2) and Mn(II) phthalocyanine (d(5), S = 3/2) is studied. We find that the structural trans effect on the surface rules the molecular spin state, as well as the sign and strength of the exchange interaction with the substrate. We refer to this observation as the surface spin-trans effect.
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| 11. |
- Waeckerlin, Christian, et al.
(författare)
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Two-Dimensional Supramolecular Electron Spin Arrays
- 2013
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Ingår i: Advanced Materials. - : Wiley. - 0935-9648 .- 1521-4095. ; 25:17, s. 2404-2408
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Tidskriftsartikel (refereegranskat)abstract
- A bottom-up approach is introduced to fabricate two-dimensional self-assembled layers of molecular spin-systems containing Mn and Fe ions arranged in a chessboard lattice. We demonstrate that the Mn and Fe spin states can be reversibly operated by their selective response to coordination/decoordination of volatile ligands like ammonia (NH3).
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