| 1. |
- Wolff, Nicole, et al.
(författare)
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Temperature dependent cubic and hexagonal close packing in micellar structures
- 2014
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Ingår i: Soft Matter. - : Royal Society of Chemistry (RSC). - 1744-683X .- 1744-6848. ; 10:42, s. 8420-8426
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Tidskriftsartikel (refereegranskat)abstract
- The interfacial structure and phase diagram of a micellar solution formed by the three block copolymer ( EO20-PO70-EO20) also known as P123 solved in deuterated water close to a solid boundary is investigated with respect to temperature. We find a hysteretic behavior of the d-spacing of the micellar crystal and a spontaneous change in the lateral correlation length going hand in hand with a structural reorganization between cubic and hexagonal. The phase transitions may be initiated by a change in the shape of the micelles from spherical to elongated together with a minimization of the polymer water interface.
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| 2. |
- Adalsteinsson, Sigurbjörn Már, et al.
(författare)
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Correlating chemical composition and optical properties of photochromic rare-earth oxyhydrides using ion beam analysis
- 2020
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Ingår i: Nuclear Instruments and Methods in Physics Research Section B. - : ELSEVIER. - 0168-583X .- 1872-9584. ; 485, s. 36-40
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Tidskriftsartikel (refereegranskat)abstract
- We relate the photochromic response of rare-earth oxyhydride thin films (YHO, NdHO, GdHO and DyHO) synthesized by reactive magnetron sputtering to chemical composition. Depth profiles of the sample composition are extracted by a multi-method ion beam analysis approach. The total areal density of the thin films is deduced from Rutherford Backscattering Spectrometry while coincidence Time-of-Flight/Energy Elastic Recoil Detection Analysis provides depth-profiles of the film constituents. High-resolution depth profiles of the concentration of light species, i.e. hydrogen and oxygen, are additionally extracted from Nuclear Reaction Analysis and Elastic Backscattering Spectrometry, respectively. The photochromic response of the films is measured by optical transmission spectroscopy before and after illumination. We report photochromic properties for YHO, NdHO, GdHO and DyHO for chemical compositions described by the formula REH2-delta O delta in the range of 0.45 < 6 < 1.5.
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| 3. |
- Adlmann, Franz A., et al.
(författare)
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Towards neutron scattering experiments with sub-millisecond time resolution
- 2015
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Ingår i: Journal of applied crystallography. - 0021-8898 .- 1600-5767. ; 48, s. 220-226
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Tidskriftsartikel (refereegranskat)abstract
- Neutron scattering techniques offer several unique opportunities in materials research. However, most neutron scattering experiments suffer from the limited flux available at current facilities. This limitation becomes even more severe if time-resolved or kinetic experiments are performed. A new method has been developed which overcomes these limitations when a reversible process is studied, without any compromise on resolution or beam intensity. It is demonstrated that, by recording in absolute time the neutron detector events linked to an excitation, information can be resolved on sub-millisecond timescales. Specifically, the concept of the method is demonstrated by neutron reflectivity measurements in time-of-flight mode at the Liquids Reflectometer located at the Spallation Neutron Source, Oak Ridge National Laboratory, Tennessee, USA, combined with in situ rheometry. The opportunities and limitations of this new technique are evaluated by investigations of a micellar polymer solution offering excellent scattering contrast combined with high sensitivity to shear.
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| 4. |
- Adlmann, Franz A., et al.
(författare)
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Överlåtaren : a fast way to transfer and orthogonalize two-dimensional off-specular reflectivity data
- 2016
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Ingår i: Journal of applied crystallography. - 0021-8898 .- 1600-5767. ; 49, s. 2091-2099
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Tidskriftsartikel (refereegranskat)abstract
- Reflectivity measurements offer unique opportunities for the study of surfaces and interfaces, and specular reflectometry has become a standard tool in materials science to resolve structures normal to the surface of a thin film. Off-specular scattering, which probes lateral structures, is more difficult to analyse, because the Fourier space being probed is highly anisotropic and the scattering pattern is truncated by the interface. As a result, scattering patterns collected with (especially time-of-flight) neutron reflectometers are difficult to transform into reciprocal space for comparison with model calculations. A program package is presented for a generic two-dimensional transformation of reflectometry data into q space and back. The data are represented on an orthogonal grid, allowing cuts along directions relevant for theoretical modelling. This treatment includes background subtraction as well as a full characterization of the resolution function. The method is optimized for computational performance using repeatable operations and standardized instrument settings.
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| 5. |
- Adlmann, Franz, et al.
(författare)
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Depth resolved grazing incidence neutron scattering experiments from semi-infinite interfaces : a statistical analysis of the scattering contributions
- 2018
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Ingår i: Journal of Physics. - : Institute of Physics Publishing (IOPP). - 0953-8984 .- 1361-648X. ; 30
-
Tidskriftsartikel (refereegranskat)abstract
- Grazing incidence neutron scattering experiments offer surface sensitivity by reflecting from an interface at momentum transfers close to total external reflection. Under these conditions the penetration depth is strongly non-linear and may change by many orders of magnitude. This fact imposes severe challenges for depth resolved experiments, since the brilliance of neutron beams is relatively low in comparison to e.g. synchrotron radiation. In this article we use probability density functions to calculate the contribution of scattering at different distances from an interface to the intensities registered on the detector. Our method has the particular advantage that the depth sensitivity is directly extracted from the scattering pattern itself. Hence for perfectly known samples exact resolution functions can be calculated and visa versa. We show that any tails in the resolution function, e.g. Gaussian shaped, hinders depth resolved experiments. More importantly we provide means for a descriptive statistical analysis of detector images with respect to the scattering contributions and show that even for perfect resolution near surface scattering is hardly accessible.
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| 6. |
- Adlmann, Franz, et al.
(författare)
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Normalization of stroboscopic neutron scattering experiments
- 2018
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Ingår i: Nuclear Instruments and Methods in Physics Research Section B. - : Elsevier BV. - 0168-583X .- 1872-9584. ; 434, s. 61-65
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Tidskriftsartikel (refereegranskat)abstract
- Neutron scattering studies of kinetic processes are often flux limited. For processes which can be repeated many times, this can be mitigated by stroboscopic reintegration. The recorded scattering events are assigned to different time slices of the process and corresponding slices from all repetitions are summed up. The normalization of such data with respect to the incident beam spectrum can be challenging since the incident neutron flux may not necessarily be evenly distributed over all time slices. In this paper, we discuss how this can result in misleading information and we expand on a technique to amend these issues.
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| 7. |
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| 8. |
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| 9. |
- Baba, Elbruz Murat, et al.
(författare)
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Preferential Orientation of Photochromic Gadolinium Oxyhydride Films
- 2020
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Ingår i: Molecules. - : MDPI. - 1431-5157 .- 1420-3049. ; 25:14
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Tidskriftsartikel (refereegranskat)abstract
- We report preferential orientation control in photochromic gadolinium oxyhydride (GdHO) thin films deposited by a two-step process. Gadolinium hydride (GdH2-x) films were grown by reactive magnetron sputtering, followed by oxidation in air. The preferential orientation, grain size, anion concentrations and photochromic response of the films were strongly dependent on the deposition pressure. The GdHO films showed a preferential orientation along the [100] direction and exhibited photochromism when synthesized at deposition pressures of up to 5.8 Pa. The photochromic contrast was larger than 20% when the films were deposited below 2.8 Pa with a 0.22 H-2/Ar flow ratio. We argue that the relation of preferential orientation and the post deposition oxidation since oxygen concentration is known to be a key parameter for photochromism in rare-earth oxyhydride thin films. The experimental observations described above were explained by the decrease of the grain size as a result of the increase of the deposition pressure of the sputtering gas, followed by a higher oxygen incorporation.
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| 10. |
- Bernal, Ximena E., et al.
(författare)
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Empowering Latina scientists
- 2019
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Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 363:6429, s. 825-826
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
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| 11. |
- Bruessing, F., et al.
(författare)
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Magnetization and magnetization reversal in epitaxial Fe/Cr/Co asymmetric spin-valve systems
- 2012
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 85:17, s. 174409-
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Tidskriftsartikel (refereegranskat)abstract
- We have investigated asymmetric Fe/Cr/Co/Cr superlattices with two magnetic layers of Fe and Co, which are different with respect to their magnetic properties: magnetization, coercivity, and magnetic anisotropy. The magnetic layers are weakly coupled via a mediating Cr spacer layer providing an antiferromagnetic alignment of adjacent layers. The magnetic structure of these spin-valve-like Fe/Cr/Co/Cr superlattices was analyzed from the remanent state up to saturation via polarized neutron scattering and polarized neutron reflectivity (PNR). Furthermore, the domain structure in remanence was imaged via polarized x-ray photoemission electron microscopy (XPEEM). This analysis reveals that the Co magnetization strongly affects the Fe domain structure, while the layer magnetization is collinear from the remanent antiparallel state up to the ferromagnetic saturation state. However, for certain Co layer thicknesses, the as-grown remanent state exhibits a noncollinear antiferromagnetic spin structure, which cannot be recovered after applying a magnetic field. However, the noncollinear structure is reproducible with freshly grown superlattices.
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| 12. |
- Cariou, Pierre, et al.
(författare)
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Evidence on target factors used for port state control inspections
- 2009
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Ingår i: Marine Policy. - : Elsevier BV. - 1872-9460 .- 0308-597X. ; 33:5, s. 847-859
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Tidskriftsartikel (refereegranskat)abstract
- Target factors aim at setting criteria to select foreign vessels that should be inspected by port state control authorities. Although a relative consensus exists on the main factors to consider in selecting vessels, the weight to be given to these factors is still unclear. Using data on 26 515 PSC inspections that took place within the Indian Ocean MoU region from 2002 to 2006, we investigate the determinants of the number of deficiencies and of the probability of detention. Our results show that the main contributors to detention are the age of the vessel at inspection (40%), the recognised organization (31%) and the place where the inspection occurs (17%). Also, differences in detention rates amongst various inspecting authorities are essentially explained by differences in the characteristics of vessels calling in a specific country rather than by differences in the way inspections are done. (C) 2009 Elsevier Ltd. All rights reserved.
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| 13. |
- Cariou, Pierre, et al.
(författare)
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On the effectiveness of port state control inspections
- 2008
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Ingår i: Transportation Research. Part E: Logistics and Transportation Review. - : Elsevier BV. - 1366-5545. ; 44:3, s. 491-503
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Tidskriftsartikel (refereegranskat)abstract
- This paper uses 4080 observations from the Swedish Maritime Administration (1996-2001) to test how vessel's characteristics influence the length of time between two port state control inspections (PSC) along with the number of deficiencies detected during PSC. It also investigates whether a ship that has undergone PSC inspection at a certain time exhibits a reduction in the total number of deficiencies detected during the next control. Estimates from Poisson models stress that the age of the vessel, ship type, and flag of registry appear to be significant predictors. Subsequently, the analysis oil 874 repeated inspections shows that following a PSC inspection, the reported deficiencies during next inspection is reduced by 63%.
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| 14. |
- Carstensen, Hauke, et al.
(författare)
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Phase formation in colloidal systems with tunable interaction
- 2015
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Ingår i: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics. - 1539-3755 .- 1550-2376. ; 92:1
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Tidskriftsartikel (refereegranskat)abstract
- Self-assembly is one of the most fascinating phenomena in nature and is one key component in the formation of hierarchical structures. The formation of structures depends critically on the interaction between the different constituents, and therefore the link between these interactions and the resulting structure is fundamental for the understanding of materials. We have realized a two-dimensional system of colloidal particles with tunable magnetic dipole forces. The phase formation is studied by transmission optical microscopy and a phase diagram is constructed. We report a phase transition from hexagonal to random and square arrangements when the magnetic interaction between the individual particles is tuned from antiferromagnetic to ferrimagnetic.
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| 15. |
- Carstensen, Hauke, et al.
(författare)
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Self-assembly and percolation in two dimensional binary magnetic colloids
- 2022
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Ingår i: Soft Matter. - : Royal Society of Chemistry (RSC). - 1744-683X .- 1744-6848. ; 18:33, s. 6222-6228
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Tidskriftsartikel (refereegranskat)abstract
- We study the self-assembly of branching-chain networks and crystals in a binary colloidal system with tunable interactions. The particle positions are extracted from microscopy images and order parameters are extracted by image processing and statistical analysis. With these, we construct phase diagrams with respect to particle density, ratio and interaction. In order to draw a more complete picture, we complement the experiments with computer simulations. We establish a region in the phase diagram, where bead ratios and interactions are symmetric, promoting percolated structures.
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| 16. |
- Carstensen, Hauke
(författare)
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Self-assembly of magnetic particles
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Self-assembly is the spontaneous formation of larger structures from small building blocks. This process is driven and determined by the interactions between the constituents. Examples of self assembly are found almost everywhere and, in particular, biological systems in general rely on a hierarchical formation of structures over a range of length scales. Technologically, self-assembly can be used to form mesoscopic structures and artificial crystals. In the case of particles with micrometer size suspended in a liquid phase, it is possible to use optical microscopy for the the investigation of self-assembly.In this thesis, the self-assembly of microbeads with tunable magnetic interactions is studied, based on the statistic analysis of microscope images and computer simulations. Magnetic and non-magnetic microbeads are suspended in a ferrofluid, which is a dispersion of magnetic nanoparticles in water. As a result, the magnetic properties of the microbeads in the ferrofluid are altered and can be described by effective magnetic susceptibilities and magnetic dipole moments, which can be tuned continuously. The liquid is confined between glass slides and effectively the microbeads are studied in a 2D geometry under a magnetic field, applied either in- or out-of-plane. The resulting structures are detected by image analysis algorithms, analyzed and correlated to the dipolar interaction between the beads, as well as to macroscopic quantities, like the particle density and ratio. For the in-plane field a phase transition from square to hexagonal lattice is observed. This phase transition is explained by the change in dipole interaction between the microbeads as the moments change from anti-parallel to parallel alignment. For the out-of-plane field the situation becomes diverse and more phases appear. It turns out that the phase formation in this case is strongly dependent on the bead ratio, density and interactions.We identify regions in the phase diagram, where isolated beads, percolated structures, and crystals dominate. To cover a wide parameter range the experiments are complemented by computer simulations. The tools developed in this thesis enable us to construct phase diagrams extracted from direct imaging and dependence on the extracted relevant parameters.
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| 17. |
- Carstensen, Hauke, et al.
(författare)
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Statistical analysis of phase formation in 2D colloidal systems
- 2018
-
Ingår i: The European Physical Journal E Soft matter. - : SPRINGER. - 1292-8941 .- 1292-895X. ; 41:1
-
Tidskriftsartikel (refereegranskat)abstract
- Colloidal systems offer unique opportunities for the study of phase formation and structure since their characteristic length scales are accessible to visible light. As a model system the two-dimensional assembly of colloidal magnetic and non-magnetic particles dispersed in a ferrofluid (FF) matrix is studied by transmission optical microscopy. We present a method to statistically evaluate images with thousands of particles and map phases by extraction of local variables. Different lattice structures and long-range connected branching chains are observed, when tuning the effective magnetic interaction and varying particle ratios.
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| 18. |
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| 19. |
- Chulapakorn, Thawatchart, 1988-, et al.
(författare)
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Si-nanoparticle synthesis using ion implantation and MeV ion irradiation
- 2015
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Ingår i: Physica Status Solidi (C) Current Topics in Solid State Physics. - : Wiley-VCH Verlagsgesellschaft. - 1862-6351.
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Tidskriftsartikel (refereegranskat)abstract
- A dielectric matrix with embedded Si-nanoparticles may show strong luminescence depending on nanoparticles size, surface properties, Si-excess concentration and matrix type. Ion implantation of Si ions with energies of a few tens to hundreds of keV in a SiO2 matrix followed by thermal annealing was identified as a powerful method to form such nanoparticles. The aim of the present work is to optimize the synthesis of Si-nanoparticles produced by ion implantation in SiO2 by employing MeV ion irradiation as an additional annealing process. The luminescence properties are measured by spectrally resolved photoluminescence including PL lifetime measurement, while X-ray reflectometry, atomic force microscopy and ion beam analysis are used to characterize the nanoparticle formation process. The results show that the samples implanted at 20%-Si excess atomic concentration display the highest luminescence and that irradiation of 36 MeV 127I ions affects the luminosity in terms of wavelength and intensity. It is also demonstrated that the nanoparticle luminescence lifetime decreases as a function of irradiation fluence.
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| 20. |
- Delavari, Hamid H., et al.
(författare)
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Magnetic domain regime-controlled synthesis of nickel nano-particles by applying statistical experimental design in modified polyol process
- 2015
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Ingår i: Materials Chemistry and Physics. - : Elsevier BV. - 0254-0584 .- 1879-3312. ; 168, s. 117-121
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Tidskriftsartikel (refereegranskat)abstract
- In this work, central composite design (CCD) as a statistical experimental design method is performed to prepare nickel nano-particle of different magnetic domain regimes by the modified polyol process. It is shown that not only the concentration of the different chemicals but also the injection rate is determining for the morphology and magnetic properties. The average diameter of the synthesized nickel NPs is smaller than the critical single domain size and thus the single domain or pseudo-single domain nickel nano-particles can be prepared based on Day's plot.
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| 21. |
- Delavari, Hamid H., et al.
(författare)
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Modeling of self-controlling hyperthermia based on nickel alloy ferrofluids : Proposition of new nanoparticles
- 2013
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Ingår i: Journal of Magnetism and Magnetic Materials. - : Elsevier BV. - 0304-8853 .- 1873-4766. ; 335, s. 59-63
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Tidskriftsartikel (refereegranskat)abstract
- In order to provide sufficient heat without overheating healthy tissue in magnetic fluid hyperthermia (MFH), a careful design of the magnetic properties of nanoparticles is essential. We perform a systematic calculation of magnetic properties of Ni-alloy nanoparticles. Stoner-Wohlfarth model based theories (SWMBTs) are considered and the linear response theory (LRT) is used to extract the hysteresis loop of nickel alloy nanoparticles in alternating magnetic fields. It is demonstrated that in the safe range of magnetic field intensity and frequency the LRT cannot be used for the calculation of the area in the hysteresis for magnetic fields relevant for hyperthermia. The best composition and particle size for self-controlling hyperthermia with nickel alloys is determined based on SWMBTs. It is concluded that Ni-V and Ni-Zn are good candidates for self-controlling hyperthermia.
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| 22. |
- Dennison, Andrew J. C., et al.
(författare)
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Graphite intercalation compound (GIC) crystal monochromators for cold neutron instruments : Characterization of KC24 by time-of-flight neutron diffraction
- 2021
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Ingår i: Review of Scientific Instruments. - : American Institute of Physics (AIP). - 0034-6748 .- 1089-7623. ; 92:2
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Tidskriftsartikel (refereegranskat)abstract
- Graphite intercalation compounds (GICs) are a group of layered materials that are suitable as monochromators for cold neutrons. KC24 is a particularly interesting compound in this regard as it features a large c-axis lattice spacing of 8.74 angstrom, high reflectivity, and the possibility to produce large crystals with mosaicity that matches the beam divergence of cold neutron guides. GICs can be synthesized with different levels of intercalation, known as the stage of the compounds. Each stage displays a specific d-spacing. Impure GIC-monochromators containing multiple stages produce mixing of neutron wavelengths, which complicates data analysis on neutron reflectometers. We discuss the implications of GIC crystal purity and stage contamination for neutron reflectometry and show how GIC crystals can be characterized by time-of-flight neutron diffraction providing an efficient and quantifiable measure of the reflected wavelength spectrum. This allows taking into account multiple wavelength contaminations and ascertains the robustness of reflectometry measurements.
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| 23. |
- Devishvili, A., et al.
(författare)
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SuperADAM : Upgraded polarized neutron reflectometer at the Institut Laue-Langevin
- 2013
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Ingår i: Review of Scientific Instruments. - : AIP Publishing. - 0034-6748 .- 1089-7623. ; 84:2, s. 025112-
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Tidskriftsartikel (refereegranskat)abstract
- A new neutron reflectometer SuperADAM has recently been built and commissioned at the Institut Laue-Langevin, Grenoble, France. It replaces the previous neutron reflectometer ADAM. The new instrument uses a solid state polarizer/wavelength filter providing a highly polarized (up to 98.6%) monochromatic neutron flux of 8 x 10(4) n cm(-2) s(-1) with monochromatization Delta lambda/lambda = 0.7% and angular divergence Delta alpha = 0.2 mrad. The instrument includes both single and position sensitive detectors. The position sensitive detector allows simultaneous measurement of specular reflection and off-specular scattering. Polarization analysis for both specular reflection and off-specular scattering is achieved using either mirror analyzers or a He-3 spin filter cell. High efficiency detectors, low background, and high flux provides a dynamic range of up to seven decades in reflectivity. Detailed specifications and the instrument capabilities are illustrated with examples of recently collected data in the fields of thin film magnetism and thin polymer films.
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| 24. |
- Droulias, Sotirios A., et al.
(författare)
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Beating effects in multilayer systems studied with neutron reflectometry
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- We demonstrate the limitations of a partial, phenomenological tting approach comparedto full simulations, including reection and refraction at all interfaces on theexample of hydrogen loading in ultra thin vanadium layers. Fe/V superlattices areloaded with deuterium and the lattice expansion and deuterium concentration isextracted from neutron reectivity data. We nd a noticeable dierence betweenthe direct extraction of concentrations and bilayer thicknesses from the superlatticepeaks and ts of the full density prole using the Parratt formalism. Our results underlinethe importance of carefully considering the limitations of phenomenologicalapproaches, in order to obtain robust results.
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| 25. |
- Droulias, Sotirios A., et al.
(författare)
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Crystal perfection by strain engineering : The case of Fe/V (001)
- 2017
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Ingår i: Thin Solid Films. - : Elsevier BV. - 0040-6090 .- 1879-2731. ; 636, s. 608-614
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Tidskriftsartikel (refereegranskat)abstract
- We study the effect of bilayer thickness at fixed volume fraction on the structural quality of Fe/V (001)superlattices. We find that such artificial metallic superlattices can be manufactured with excellent crystalquality and layering up to at least 50 Å in repeat distance (K = LFe +LV). For an intended fixed ratio of theconstituents: LFe/LV= 1/7, out-of-plane coherence lengths comparable to the thicknesses of the sampleswere obtained. We evaluate the strain in- and out-of-plane of both layers as a function of the bilayer thicknessand comment on the growth using the framework of linear elasticity theory. We interpret the stabilityof the superlattice against crystal degradation due to the alternating compressive and tensile strain, yieldingclose to ideal lattice matching to the substrate.
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| 26. |
- Droulias, S. A., et al.
(författare)
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Influence of deuterium-induced volume changes on optical transmission in Fe/V (001) and Cr/V (001) superlattices
- 2022
-
Ingår i: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 105:19
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Tidskriftsartikel (refereegranskat)abstract
- The deuterium-induced changes of the optical transmission in Fe/V (001) and Cr/V (001) superlattices are found experimentally to be dominated by the volume changes of the vanadium layers and thus indirectly linked to concentration. The deuterium-induced expansion is 67% larger in Cr/V 2/14 monolayers (ML) as compared to Fe/V 2/14 ML. This large difference can be explained by a difference in the site of deuterium from tetrahedral in Fe/V to octahedral in Cr/V. First-principles calculations based on this assumption give quantitative agreement with both the measured optical transmission and the deuterium-induced expansion coefficient. Placing hydrogen in the middle of the vanadium layers results in total energies at 0 K that favor tetrahedral occupancy at low concentrations, although the energy difference is of the order of the thermal energy available in the experiments. Hence small changes in strain, defect concentration, and/or vibrational spectrum of the superlattices may tip the balance to octahedral occupancy at low concentrations. Given this link to concentration and the linear scaling, optical transmission can, therefore, be used in a straightforward way to obtain pressure-composition isotherms also in thin metal films that do not undergo metal-insulator transitions upon hydrogenation.
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| 27. |
- Droulias, Sotirios A., et al.
(författare)
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Limitations of the kinematic approximation in neutron reflectivity measurements for the analysis of bilayers
- 2018
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Ingår i: Journal of applied crystallography. - : INT UNION CRYSTALLOGRAPHY. - 0021-8898 .- 1600-5767. ; 51, s. 1556-1563
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Tidskriftsartikel (refereegranskat)abstract
- The limitations of a phenomenological fitting approach compared to simulations of the optical model including reflection and refraction at all interfaces are demonstrated using the example of hydrogen loading in ultra-thin vanadium layers. Fe/V superlattices are loaded with deuterium and the lattice expansion and deuterium concentration are extracted from neutron reflectivity data. A noticeable difference is found between the extraction of concentrations and bilayer thicknesses directly from the superlattice peaks and fits of the density profile using the Parratt formalism. The results underline the importance of carefully considering the limitations of phenomenological approaches, in order to obtain robust results. The limitations of the kinematic approximation for the analysis are discussed in detail.
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| 28. |
- Droulias, Sotirios A., et al.
(författare)
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Tailoring thermodynamic properties of metal hydrides with interfaces
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- We report profound changes in the enthalpy of solution and critical temperature of nano-sizedmetal hydrides in proximity to dierent non-absorbing metals. We use Cr/V and Fe/V (001) superlatticesas model systems to map out these eects since the superlattices can be made singlecrystalline,have identical strain states and are fully reversible. The thermodynamic propertiesare determined using isothermal pressure and optical transmission measurements. We determinethe mechanism underlying the changes in the thermodynamic properties as well as the ecacyof optical transmission by utilizing simultaneous neutron reectometry and optical transmissionmeasurements, combined with rst principle calculations. The underlying mechanism, which issupported by quantitative agreement between theory and experiment is found to be rooted in aradically dierent volume expansion in the two systems. The commonly used optical transmissionmethod is found to be linear with concentration in both types of superlattices and is attributed tochanges in electron density, rather than a direct inuence from a redistribution of electronic states.The conclusions are generalized to other metal hydride systems and can open up for exploration ofproximity induced eects in metal hydrides.
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| 29. |
- Droulias, Sotirios A.
(författare)
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The effect of nano-confinement on hydrogen uptake in metallic superlattices
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The absorption of hydrogen is exothermic in vanadium whereas it is endothermic in iron and chromium. Investigations of the hydrogen uptake within Fe/V(001) and Cr/V(001) superlattices allow therefore a detailed exploration of finite size effects and the influence of boundaries on hydrogen absorption. Fe/V(001) and Cr/V(001) superlattices can be grown as single crystal structures with a small mosaic spread, as determined by X-ray reflectometry and diffraction. Furthermore when the thickness ratio of the constituents is kept constant the crystal quality can be retained in the range from a few up to 40 monolayer repeat distances (Λ). Neutron reflectometry was used to simultaneously determine the volume expansion and concentration of hydrogen in the vanadium layers. Large differences are found in the expansion of Fe/V(001) and Cr/V(001) superlattices, in good agreement with density functional theory (DFT) calculations. The findings are consistent with tetrahedral and octahedral site occupancy in Cr/V(001) and Fe/V(001) superlattices, respectively. Full fitting of the reflectivity pattern is required to obtainan accurate measure of expansion if the number of repeats is small. Under these conditions, the shift of the first order superlattice peak can be an inaccurate measure of the volume changes. By using a specially designed neutron scattering chamber, allowing simultaneous neutron and optical transmission measurements, it is found that the optical transmission scales linearly with hydrogen concentration. By comparing the experimental results to ab-initio DFT calculations, it is shown that optical transmission scales with electron density changes in the samples, explaining the linearity with concentration. This change is dominated by the hydrogen induced expansion of the lattices and depends therefore strongly on the site occupancy of the hydrogen. Finally, X-ray diffraction was used to address the local strain fields and the α to β phase transition, typically observed in bulk vanadium. Below 448 K the results are consistent with an α to β phase co-existence, separated along the surface normal of the samples.
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| 30. |
- Droulias, Sotirios A., et al.
(författare)
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Using interfaces to influence thermodynamic properties of metal hydrides
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- We report profound proximity effects on the enthalpy of solution and critical temperature ofnano-sized vanadium hydrides. We use single crystalline Cr/V and Fe/V (001) superlattices forthese studies, in which the V layers are under close to identical strain. The thermodynamic propertiesare determined using isothermal pressure and optical transmission measurements, utilisingthe fully reversibel hydrogen uptake and release.The underlying mechanism is argued to be rootedin a radically different volume expansion in the two systems, arising from different site occupancyof hydrogen in Fe/V(001) and Cr/V(001). The optical transmission is found to be linear withconcentration in both types of superlattices, while exhibiting different slopes. The differences areattributed to changes in electron density arising from the volume expansion, rather than a directinfluence from a redistribution of electronic states.
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| 31. |
- Elías-Wolff, Federico, 1983-
(författare)
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A computational approach to curvature sensing in lipid bilayers
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Local curvature is a key driving force for spatial organization of cellular membranes, via a phenomenon known as membrane curvature sensing, where the binding energy of membrane associated macromolecules depends on the local membrane shape. However, the microscopic mechanisms of curvature sensing are not well understood. Molecular dynamics simulations offer a powerful complement to biochemical experiments, yet their contribution to the study of curvature sensing has been limited, due in part to the lack of efficient methods, not least because of methodological difficulties in dealing with curved membranes. We develop a method based on simulated buckling, which has been previously employed to study mechanical properties of membranes. Here, we describe, validate and evaluate this method. We then apply to study curvature sensing properties of three model systems, using coarse-grained simulations. On the first system, we study lipid sorting in a three-component lipid mixture with emphasis on cardiolipin. We find that if curvature is high, curvature sensing is strong enough to drive cardiolipin molecules to negative curvature regions, outcompeting other lipids, without the need of external interactions or cooperative effects. We then simulated three systems consisting of a short amphipathic peptide attached to the surface of a buckled membrane. All three peptides localize to positive curvature, in agreement with the so-called cylindrical hydrophobic insertion mechanism. Their orientational preferences, however, defy the prediction of alignment perpendicular to the direction of maximum curvature. They also fail to show expected symmetries, indicating there is more to the picture than purely shape-based effects. The curvature sensing probe of the next system is a transmembrane trimeric protein, which shows preference to intermediate curvature, in agreement with theoretical predictions. But the lack of an expected 2-fold rotation symmetry indicates that the trimer senses the local curvature gradient, and not just the point-wise local curvature. Finally, dispensing with the buckling methodology, we simulated a series of symmetric transmembrane multimers embedded in cylindrical bilayers. Based on the results of these simulations and theoretical arguments, we discuss the relationship between structural symmetry and curvature sensitivity. We conclude that anisotropic (i.e. orientation-dependent) curvature sensing is strongly limited by odd and high order rotational symmetries. However, measurements of in-plane orientation on peptides and asymmetric proteins, as well as dimers and tetramers, should yield valuable information. Our method, along with our initial conclusions, provides an useful tool for the understanding of the relationship between membrane shape and membrane protein function, and should prove useful to biophysicists in the design and interpretation of experimental curvature sensing assays.
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| 32. |
- Fischer, Hubertus, et al.
(författare)
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Palaeoclimate constraints on the impact of 2 °C anthropogenic warming and beyond
- 2018
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Ingår i: Nature Geoscience. - : Springer Science and Business Media LLC. - 1752-0894 .- 1752-0908. ; 11:7, s. 474-485
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Tidskriftsartikel (refereegranskat)abstract
- Over the past 3.5 million years, there have been several intervals when climate conditions were warmer than during the pre-industrial Holocene. Although past intervals of warming were forced differently than future anthropogenic change, such periods can provide insights into potential future climate impacts and ecosystem feedbacks, especially over centennial-to-millennial timescales that are often not covered by climate model simulations. Our observation-based synthesis of the understanding of past intervals with temperatures within the range of projected future warming suggests that there is a low risk of runaway greenhouse gas feedbacks for global warming of no more than 2 °C. However, substantial regional environmental impacts can occur. A global average warming of 1–2 °C with strong polar amplification has, in the past, been accompanied by significant shifts in climate zones and the spatial distribution of land and ocean ecosystems. Sustained warming at this level has also led to substantial reductions of the Greenland and Antarctic ice sheets, with sea-level increases of at least several metres on millennial timescales. Comparison of palaeo observations with climate model results suggests that, due to the lack of certain feedback processes, model-based climate projections may underestimate long-term warming in response to future radiative forcing by as much as a factor of two, and thus may also underestimate centennial-to-millennial-scale sea-level rise.
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| 33. |
- Forooqi Motlaq, Vahid, et al.
(författare)
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Dissolution mechanism of supported phospholipid bilayer in the presence of amphiphilic drug investigated by neutron reflectometry and quartz crystal microbalance with dissipation monitoring
- 2022
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Ingår i: Biochimica et Biophysica Acta - Biomembranes. - : Elsevier. - 0005-2736 .- 1879-2642. ; 1864:10
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Tidskriftsartikel (refereegranskat)abstract
- The influence and interaction of the ionizable amphiphilic drug amitriptyline hydrochloride (AMT) on a 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) phospholipid bilayer supported on a silica surface have been investigated using a combination of neutron reflectometry and quartz crystal microbalance with dissipation monitoring. Adding AMT solutions with concentrations 3, 12, and 50 mM leaves the lipid bilayer mainly intact and we observe most of the AMT molecules attached to the head-group region of the outer bilayer leaflet. Virtually no AMT penetrates into the hydrophilic head-group region of the inner leaflet close to the silica surface. By adding 200 mM AMT solution, the lipid bilayer dissolved entirely, indicating a threshold concentration for the solubilization of the bilayer by AMT. The observed threshold concentration is consistent with the observation that various bilayer structures abruptly transform into mixed AMT-DOPC micelles beyond a certain AMT-DOPC composition. Based on our experimental observations, we suggest that the penetration of drug into the phospholipid bilayer, and subsequent solubilization of the membrane, follows a two-step mechanism with the outer leaflet being removed prior to the inner leaflet.
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| 34. |
- Gutfreund, Philipp, et al.
(författare)
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Depletion at solid/liquid interfaces : Flowing hexadecane on functionalized surfaces
- 2011
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 134:6, s. 064711-
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Tidskriftsartikel (refereegranskat)abstract
- We present a neutron reflectivity study on interfaces in contact with flowing hexadecane, which is known to exhibit surface slip on functionalized solid surfaces. The single crystalline silicon substrates were either chemically cleaned Si(100) or Si(100) coated by octadecyl-trichlorosilane (OTS), which resulted in different interfacial energies. The liquid was sheared in situ and changes in reflectivity profiles were compared to the static case. For the OTS surface, the temperature dependence was also recorded. For both types of interfaces, density depletion of the liquid at the interface was observed. In the case of the bare Si substrate, shear load altered the structure of the depletion layer, whereas for the OTS covered surface no effect of shear was observed. Possible links between the depletion layer and surface slip are discussed. The results show that, in contrast to water, for hexadecane the enhancement of the depletion layer with temperature and interfacial energy reduces the amount of slip. Thus a density depletion cannot be the origin of surface slip in this system.
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| 35. |
- Gutfreund, Philipp, et al.
(författare)
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The Search for Nanobubbles by Using Specular and Off-Specular Neutron Reflectometry
- 2016
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 32:35, s. 9091-9096
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Tidskriftsartikel (refereegranskat)abstract
- We apply specular and off-specular neutron reflection at the hydrophobic silicon/water interface to check for evidence of nanoscopic air bubbles whose presence is claimed after an ad hoc procedure of solvent exchange. Nanobubbles and/or a depletion layer at the hydrophobic/water interface have long been discussed and generated a plethora of controversial scientific results. By combining neutron reflectometry (NR), off-specular reflectometry (OSS), and grazing incidence small angle neutron scattering (GISANS), we studied the interface between hydrophobized silicon and heavy water before and after saturation with nitrogen gas. Our specular reflectometry results can be interpreted by assuming a submolecular sized depletion layer and the off-specular measurements show no change with nitrogen super saturated water. This picture is consistent with the assumption that, following the solvent exchange, no additional nanobubbles are introduced at significant concentrations (if present at all). Furthermore, we discuss the results in terms of the maximum surface coverage of nanobubbles that could be present on the hydrophobic surface compatibly with the sensitivity limit of these techniques.
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| 36. |
- Gvaramia, Manuchar, et al.
(författare)
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Neutron spin echo spectroscopy with a moving sample
- 2023
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Ingår i: Scientific Reports. - : Springer Nature. - 2045-2322. ; 13:1
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Tidskriftsartikel (refereegranskat)abstract
- Neutron spin echo spectroscopy is a high resolution inelastic neutron scattering method probing nanosecond dynamics. It is well suited to study the atomistic motion in polymer systems and contributes to our understanding of viscoelasticity. However, for samples under shear, or moving samples in general, Doppler scattering has to be considered. We compare the measured phase shift and depolarisation due to Doppler scattering from a rotating graphite disk to numerical and analytical calculations and find excellent agreement. This allows to take into account Doppler scattering during the data processing and makes longer Fourier times as well as higher shear rates and Q ranges possible with neutron spin echo spectroscopy, enabling for example the study of polymers under high shear.
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| 37. |
- Hans, Marcus, et al.
(författare)
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Photochromic Mechanism and Dual-Phase Formation in Oxygen-Containing Rare-Earth Hydride Thin Films
- 2020
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Ingår i: Advanced Optical Materials. - : WILEY-V C H VERLAG GMBH. - 2162-7568 .- 2195-1071. ; 8:19
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Tidskriftsartikel (refereegranskat)abstract
- The phase formation of a photochromic Gd-0.31(H0.55O0.45)(0.69)thin film, grown by reactive magnetron sputtering, is critically evaluated. Oxygen is preferably incorporated into the underdense columnar grain boundaries, when the as-deposited gadolinium hydride film is exposed to ambient conditions. Two phases, Gd(2)O(3)and GdH2, are formed with significant compressive residual stress of 5.9 +/- 1.5 GPa. These findings, extracted from transmission electron microscopy, X-ray diffraction and atom probe tomography, provide a straightforward explanation for the photochromic effect. The mechanism can be understood as photon-induced hydrogen transfer between the two phases, identical in nature to the photochromic effect in bulk yttrium hydride at high pressure.
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| 38. |
- Hjörvarsson, Björgvin, et al.
(författare)
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The influence of weak links on magnetic ordering in layered structures
- 2008
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Ingår i: Europhysics letters. - : IOP Publishing. - 0295-5075 .- 1286-4854. ; 61:1, s. 17008-
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Tidskriftsartikel (refereegranskat)abstract
- We discuss the magnetic ordering in layered magnets with two different inherent ordering temperatures. A [V(12 ML)Fe(2 ML)/V(12 ML)(/Fe(3 ML)](70) superlattice with anti-ferromagnetic interlayer exchange coupling is used for this purpose. The more rapid decrease of the magnetic moment in the 2 monolayer thick Fe layers influences the ordering in a non-trivial way. A distribution of the effective ordering temperature is inferred, originating from a more rapid decrease of the magnetic moment in the near-surface region, as compared to the interior of the sample. The results clearly demonstrate the need to consider all energy and length scales when addressing ordering in materials with finite extension.
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| 39. |
- Huang, Wen, et al.
(författare)
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Combined Light and Electron Scattering for Exploring Proximity Effects on Hydrogen Absorption in Vanadium
- 2021
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Ingår i: Energies. - : MDPI. - 1996-1073. ; 14:24
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Tidskriftsartikel (refereegranskat)abstract
- We investigate proximity effects on hydrogen absorption in ultra-thin vanadium layers through combing light transmission and electron scattering. We compare the thermodynamic properties of the vanadium layers, which are based on the superlattice structure of Cr/V (001) and Fe/V (001). We find an influence of the proximity effects on the finite-size scaling of the critical temperatures, which can be explained by a variation of dead layers in the vanadium. In addition to this, the proximity effects on hydrogen absorption are also verified from the changes of excess resistivity.
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| 40. |
- Huang, Wen, et al.
(författare)
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Concentration dependence of hydrogen diffusion in clamped vanadium (001) films
- 2017
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Ingår i: Journal of Physics. - 0953-8984 .- 1361-648X. ; 29:4
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Tidskriftsartikel (refereegranskat)abstract
- The chemical diffusion coefficient of hydrogen in a 50 nm thin film of vanadium (0 0 1) is measured as a function of concentration and temperature, well above the known phase boundaries. Arrhenius analysis of the tracer diffusion constants reveal large changes in the activation energy with concentration: from 0.10 at 0.05 in II V-1 to 0.5 eV at 0.2 in II V-1. The results are consistent with a change from tetrahedral to octahedral site occupancy, in that concentration range. The change in site occupancy is argued to be caused by the uniaxial expansion of the film originating from the combined hydrogen induced expansion and the clamping of the film to the substrate.
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| 41. |
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| 42. |
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| 43. |
- Huang, Wen, et al.
(författare)
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Diffusion of hydrogen in ultra-thin V(001) layers
- 2017
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Ingår i: Journal of Alloys and Compounds. - : Elsevier BV. - 0925-8388 .- 1873-4669. ; 723, s. 484-487
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Tidskriftsartikel (refereegranskat)abstract
- We report on investigations of the influence of one dimensional confinement on the diffusion of hydrogen, in the low concentration limit (alpha-phase). The confinement is obtained by utilising single crystal Fe/V(001) superlattices, in which hydrogen preferably resides in the V layers. The diffusion along the [110] direction in the V(001) layers can thereby be determined. Activation energy and attempt jump rates are extracted from an Arrhenius analysis. No effects are observed from the confinement on the hydrogen diffusion in the thickness range 7-28 monolayers (approximate to 1.1-4.2 nm) of V(001).
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| 44. |
- Huang, Wen, et al.
(författare)
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Experimental observation of hysteresis in a coherent metal-hydride phase transition
- 2017
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Ingår i: Journal of Physics. - : IOP PUBLISHING LTD. - 0953-8984 .- 1361-648X. ; 29:49
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the hysteresis obtained in the hydrogen absorption and desorption cycle for a single crystal Pd/V-28 [Fe-4/V-28](11) superlattice. Below the critical temperature, a small but clear hysteresis is observed in the pressure-composition isotherms, while it is absent above. The experimental results thereby prove the relevance of macroscopic energy barriers for obtaining hysteresis in coherent structural transformations. The textured Pd layer exhibits substantially larger hysteresis effects, which can be related to an irreversible energy loss caused by defect generation in Pd.
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| 45. |
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| 46. |
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| 47. |
- Huang, Wen, et al.
(författare)
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Finite size effects : deuterium diffusion in nm thick vanadium layers
- 2017
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Ingår i: New Journal of Physics. - : Institute of Physics Publishing (IOPP). - 1367-2630. ; 19
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the effect of finite size on the chemical diffusion of deuterium in extremely thin V(001) layers. A five fold increase in the diffusion coefficient is observed at concentrations around 0.2 [D/V], when the thickness of the V is decreased from 28 to 14 atomic layers (approximate to 2.1-4.2 nm). The size dependent deuterium-deuterium interaction energy is argued to be the root of the observed changes as the diffusion rates are similar at low concentrations. The results demonstrate the feasibility of using finite-size effects to enhance the chemical diffusion of light interstitials in solids. We discuss the general applicability of these effects to other systems.
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| 48. |
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| 49. |
- Huang, Wen
(författare)
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Hydrogen in nano-sized metals : Diffusion and hysteresis effects
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Metal hydrides can be used as hydrogen storage materials for fuel cells and batteries, and as sensors for detecting hydrogen gas. The use of metal hydrides for hydrogen storage can be hindered by poor kinetics and low capacity. Moreover, poor sensitivity, long recovery and response time, limit the applications of metal hydrides as hydrogen sensors. Diffusion is an important factor affecting the hydrogen kinetics and response time. Hysteresis effects accompany the phase transition of hydrogen in metals and can influence the properties of metal hydrides as well. These need to be considered in their applications as storage materials or sensors.This thesis concerns the possibility of tuning hydrogen diffusion and studies the mechanism of hysteresis effects of hydrogen absorption in metals. In these experiments, nano-sized vanadium is used as the model system for these studies. Hydrogen concentration is determined by the light transmission. By measuring the concentration profiles and isotherms of hydrogen, it is possible to determine the diffusion coefficients and hysteresis effects.A profound decrease of hydrogen diffusion in Fe/V(001) superlattice has been found, as compared to that in bulk vanadium. This result is interpreted as lower zero-point energy in octahedral site than that in tetrahedral site. Profound isotope effect on diffusion has also been found. Influence of clamping of the substrate on the diffusion of hydrogen with concentration in vanadium thin film is discovered. The diffusion coefficient below c = 0.1 [H/V] is close to that in bulk vanadium and decreases substantially when c > 0.1 [H/V] compared with that in bulk vanadium. This finding is interpreted as the site change from tetrahedral to octahedral occupancy when the hydrogen concentration increases. Large finite size effect on deuterium chemical diffusion is observed, which is concluded to be caused by D-D interaction change that will influence the deuterium chemical diffusion at different thickness of vanadium layers. However, finite size has no effect on hydrogen transport at extremely low hydrogen concentrations in Fe/V (001) superlattices, this illustrates that the interface can not influence the mean free path of hydrogen in any way. This is completely different from electron transport condition in nano-sized metals. Hysteresis effect is observed below critical temperature in Fe/V(001) superlattices; this occurrence confirms the hypothesis that hysteresis effect is caused by coherency strain in coherent transformation.
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| 50. |
- Kantre, Karim-Alexandros, et al.
(författare)
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SIGMA : A Set-up for In-situ Growth, Material modification and Analysis by ion beams
- 2020
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Ingår i: Nuclear Instruments and Methods in Physics Research Section B. - : ELSEVIER. - 0168-583X .- 1872-9584. ; 463, s. 96-100
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Tidskriftsartikel (refereegranskat)abstract
- We present a set-up for in-situ non-destructive high-resolution composition depth profiling by ion beams developed at the 5 MV 15 SDH-2 Tandem accelerator at the Angstrom laboratory at Uppsala University. The scattering chamber allows thin film deposition, modification and characterization which can be used to study the very initial stages of near-surface processes such as thin film growth, oxidation, annealing or ion implantation. We describe the available instrumentation with its specifications in detail and present experimental applications, i.e. the characterization of reactive in-situ thin film growth and controlled oxidation, as well as a study of ion implantation and the impact of thermal annealing and surface oxidation on the implantation profiles.
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