| 1. |
- Theis-Broehl, Katharina, et al.
(författare)
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Self assembly of magnetic nanoparticles at silicon surfaces
- 2015
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Ingår i: Soft Matter. - : Royal Society of Chemistry (RSC). - 1744-683X .- 1744-6848. ; 11:23, s. 4695-4704
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Tidskriftsartikel (refereegranskat)abstract
- Neutron reflectometry was used to study the assembly of magnetite nanoparticles in a water-based ferrofluid close to a silicon surface. Under three conditions, static, under shear and with a magnetic field, the depth profile is extracted. The particles have an average diameter of 11 nm and a volume density of 5% in a D2O-H2O mixture. They are surrounded by a 4 nm thick bilayer of carboxylic acid for steric repulsion. The reflectivity data were fitted to a model using a least square routine based on the Parratt formalism. From the scattering length density depth profiles the following behavior is concluded: the fits indicate that excess carboxylic acid covers the silicon surface and almost eliminates the water in the densely packed wetting layer that forms close to the silicon surface. Under constant shear the wetting layer persists but a depletion layer forms between the wetting layer and the moving ferrofluid. Once the flow is stopped, the wetting layer becomes more pronounced with dense packing and is accompanied by a looser packed second layer. In the case of an applied magnetic field the prolate particles experience a torque and align with their long axes along the silicon surface which leads to a higher particle density.
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| 2. |
- Theis-Broehl, Katharina, et al.
(författare)
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Self-Assembly of Magnetic Nanoparticles in Ferrofluids on Different Templates Investigated by Neutron Reflectometry
- 2020
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Ingår i: Nanomaterials. - : MDPI AG. - 2079-4991. ; 10:6
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Forskningsöversikt (refereegranskat)abstract
- In this article we review the process by which magnetite nanoparticles self-assemble onto solid surfaces. The focus is on neutron reflectometry studies providing information on the density and magnetization depth profiles of buried interfaces. Specific attention is given to the near-interface "wetting" layer and to examples of magnetite nanoparticles on a hydrophilic silicon crystal, one coated with (3-Aminopropyl)triethoxysilane, and finally, one with a magnetic film with out-of-plane magnetization.
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| 3. |
- Theis-Bröhl, Katharina, et al.
(författare)
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Self-Assembled Layering of Magnetic Nanoparticles in a Ferrofluid on Silicon Surfaces
- 2018
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Ingår i: ACS Applied Materials and Interfaces. - : AMER CHEMICAL SOC. - 1944-8244 .- 1944-8252. ; 10:5, s. 5050-5060
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Tidskriftsartikel (refereegranskat)abstract
- This article describes the three-dimensional self assembly of monodisperse colloidal magnetite nanoparticles (NPs) from a dilute water-based ferrofluid onto a silicon surface and the dependence of the resultant magnetic structure on the applied field. The NPs assemble into close-packed layers on the surface followed by more loosely packed ones. The magnetic field-dependent magnetization of the individual NP layers depends on both the rotational freedom of the layer and the magnetization of the adjacent layers. For layers in which the NPs are more free to rotate, the easy axis of the NP can readily orient along the field direction. In more dense packing, free rotation of the NPs is hampered, and the NP ensembles likely build up quasi-domain states to minimize energy, which leads to lower magnetization in those layers. Detailed analysis of polarized neutron reflectometry data together with model calculations of the arrangement of the NPs within the layers and input from small-angle scattering measurements provide full characterization of the core/shell NP dimensions, degree of chaining, arrangement of the NPs within the different layers, and magnetization depth profile.
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| 4. |
- Mazzei, Laura, 1988, et al.
(författare)
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Structure and Conductivity of Epitaxial Thin Films of In-Doped BaZrO3-Based Proton Conductors
- 2016
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 120:50, s. 28415-28422
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Tidskriftsartikel (refereegranskat)abstract
- Epitaxial thin films of the proton-conducting perovskite BaZr0.53In0.47O3-delta H0.47-2 delta, grown by pulsed laser deposition, were investigated in their hydrated and dehydrated conditions through a multitechniqu approach with the aim to study the structure and proton concentration depth profile and their relationship to proton conductivity. The techniques used were X-ray diffraction, X-ray and neutron reflectivity, nuclear reaction analysis, and Rutherford backscattering, together with impedance spectroscopy. The obtained proton conductivity and activation energy are comparable to literature values for the bulk conductivity of similar materials, thus showing that grain-boundary conductivity is negligible due to the high crystallinity of the film. The results reveal an uneven proton concentration depth profile, with the presence of a 3-4 nm thick, proton-rich layer with altered composition, likely characterized by cationic deficiency. While this surface layer either retains or reobtains protons after desorption and cooling to room temperature, the bulk of the film absorbs and desorbs protons in the expected mariner. It is suggested that the protons in the near-surface, proton rich region are located in proton sites characterized by relatively strong O-H bonds due to weak hydrogen-bond interactions to neighboring oxygen atoms and that the mobility of protons in these sites is generally lower than in proton sites associated with stronger hydrogen bonds. It follows that strongly hydrogen-bonding configurations are important for high proton mobility.
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| 5. |
- Pálsson, Gunnar K., et al.
(författare)
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Deuterium-induced volume expansion in Fe0.5V0.5/V superlattices
- 2010
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 82:24, s. 245424-
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Tidskriftsartikel (refereegranskat)abstract
- Neutron reflectometry was used to investigate the deuterium uptake in a thin metal superlattice that displays an anisotropic elastic response [Fe0.5V0.5/V (6/21 monolayers)]. We see evidence of the presence of a coexistence region which has never before been seen in vanadium-based superlattices. The loading process is completely reversible from which we conclude that the phases must be coherent, in stark contrast to bulk VDx, where the two-phase region displays hysteresis. The deuterium-induced volume expansion exhibits changes in slope that correlate with the plateau region and the expansion is comparable and even larger than in the bulk. The spectacular cooperation between the elastic fields seems to be found only in one-dimensionally confined structures with biaxial compressive strain states.
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| 6. |
- Wolff, Max, et al.
(författare)
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Hydrogen distribution in Nb/Ta superlattices
- 2012
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Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 24:25, s. 255306-
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Tidskriftsartikel (refereegranskat)abstract
- The distribution of hydrogen in Nb/Ta superlattices has been investigated by combined neutron reflectivity and x-ray scattering. We provide evidence to support that strain modulations determined with x-ray diffraction can be interpreted as modulations in hydrogen content. We show that the hydrogen concentration is modulated and favors Nb, in agreement with previous studies. We measure the concentration directly using neutron reflectivity and demonstrate no detectable change in the distribution of hydrogen with temperature, in stark contrast to previous studies.
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| 7. |
- Wolff, Max, et al.
(författare)
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Nuclear Spin Incoherent Neutron Scattering from Quantum Well Resonators
- 2019
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Ingår i: Physical Review Letters. - : American Physical Society. - 0031-9007 .- 1079-7114. ; 123:1
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Tidskriftsartikel (refereegranskat)abstract
- We report the detection and quantification of nuclear spin incoherent scattering from hydrogen occupying interstitial sites in a thin film of vanadium. The neutron wave field is enhanced in a quantum resonator with magnetically switchable boundaries. Our results provide a pathway for the study of dynamics at surfaces and in ultrathin films using inelastic and/or quasielastic neutron scattering methods.
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