| 1. |
- Estrada, Karol, et al.
(författare)
-
Genome-wide meta-analysis identifies 56 bone mineral density loci and reveals 14 loci associated with risk of fracture.
- 2012
-
Ingår i: Nature genetics. - : Springer Science and Business Media LLC. - 1546-1718 .- 1061-4036. ; 44:5, s. 491-501
-
Tidskriftsartikel (refereegranskat)abstract
- Bone mineral density (BMD) is the most widely used predictor of fracture risk. We performed the largest meta-analysis to date on lumbar spine and femoral neck BMD, including 17 genome-wide association studies and 32,961 individuals of European and east Asian ancestry. We tested the top BMD-associated markers for replication in 50,933 independent subjects and for association with risk of low-trauma fracture in 31,016 individuals with a history of fracture (cases) and 102,444 controls. We identified 56 loci (32 new) associated with BMD at genome-wide significance (P < 5 × 10(-8)). Several of these factors cluster within the RANK-RANKL-OPG, mesenchymal stem cell differentiation, endochondral ossification and Wnt signaling pathways. However, we also discovered loci that were localized to genes not known to have a role in bone biology. Fourteen BMD-associated loci were also associated with fracture risk (P < 5 × 10(-4), Bonferroni corrected), of which six reached P < 5 × 10(-8), including at 18p11.21 (FAM210A), 7q21.3 (SLC25A13), 11q13.2 (LRP5), 4q22.1 (MEPE), 2p16.2 (SPTBN1) and 10q21.1 (DKK1). These findings shed light on the genetic architecture and pathophysiological mechanisms underlying BMD variation and fracture susceptibility.
|
|
| 2. |
- Ignatova, K., et al.
(författare)
-
Reversible exchange bias in epitaxial V2O3/Ni hybrid magnetic heterostructures
- 2022
-
Ingår i: Journal of Physics. - : Institute of Physics (IOP). - 0953-8984 .- 1361-648X. ; 34:49
-
Tidskriftsartikel (refereegranskat)abstract
- In this work we present a temperature and angular dependent study of the structural and magnetic properties in highly crystalline V2O3/Ni/Zr magnetic heterostructure films. Our investigation focuses on the coupling between the ferromagnetic Ni layer and V2O3 layer which undergoes an antiferromagnetic/paramagnetic phase transition coupled to the structural phase transition of the material at around 150 K. Structural investigations using x-ray diffraction reveal highly crystalline films of a quality which has previously not been reported in the literature. The Ni layers display an absence of in-plane magnetic anisotropy owing to the highly textured (1 1 1) layering of the Ni films on the underlying V2O3(0 0 0 1) oriented layer. During the transition we observe a strain related enhancement of the coercivity and the onset of a weak exchange bias for cooling under an external magnetic field. Heating the films to above the transition temperature, the exchange bias in the Ni is removed and can be reversed upon subsequent cooling under an inverted external magnetic field. Using temperature dependent polarized neutron reflectometry we investigate the film structure at the interface, capturing the magnetic and nuclear profiles.
|
|
| 3. |
- Kapaklis, Vassilios, et al.
(författare)
-
Temperature dependence of the electrical resistivity and electronic structure of amorphous Fe100-xZrx films and multilayers
- 2012
-
Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 24:49, s. 495402-
-
Tidskriftsartikel (refereegranskat)abstract
- The electrical resistivity of amorphous Fe100-xZrx metal alloy films and multilayers has been investigated in a wide temperature and composition range. The overall behavior of the resistivity is consistent with bulk measurements, exhibiting prominent semiconductor-like changes at low temperatures. The transition from positive (metallic) to negative temperature coefficient of resistivity behavior is accompanied by minute changes in magnetoresistance and we can therefore rule out magnetic phase changes as being the cause for the observed changes in the resistivity. Using x-ray absorption and emission spectroscopies we are able to probe the unoccupied and occupied electronic densities of states. The corresponding spectra are found to significantly overlap, as expected for a metallic-like electronic structure and the absence of a band gap. Besides a broadening of the x-ray emission lines expected from an amorphous material, remarkably small differences are observed in the electronic structures when changing the amount of Zr. The resistivity data were modeled and agreement with the Mott variable range hopping model was found, indicating localized electronic states due the disordered structure of the Fe100-xZrx alloys.
|
|
| 4. |
- Keqi, A., et al.
(författare)
-
Electronic structure of the dilute magnetic semiconductor Ga1-xMnxP from hard x-ray photoelectron spectroscopy and angle-resolved photoemission
- 2018
-
Ingår i: Physical Review B. - 2469-9950 .- 2469-9969. ; 97:15
-
Tidskriftsartikel (refereegranskat)abstract
- We have investigated the electronic structure of the dilute magnetic semiconductor (DMS) Ga0.98Mn0.02P and compared it to that of an undoped GaP reference sample, using hard x-ray photoelectron spectroscopy (HXPS) and hard x-ray angle-resolved photoemission spectroscopy (HARPES) at energies of about 3 keV. We present experimental data, as well as theoretical calculations, to understand the role of the Mn dopant in the emergence of ferromagnetism in this material. Both core-level spectra and angle-resolved or angle-integrated valence spectra are discussed. In particular, the HARPES experimental data are compared to free-electron final-state model calculations and to more accurate one-step photoemission theory. The experimental results show differences between Ga0.98Mn0.02P and GaP in both angle-resolved and angle-integrated valence spectra. The Ga0.98Mn0.02P bands are broadened due to the presence of Mn impurities that disturb the long-range translational order of the host GaP crystal. Mn-induced changes of the electronic structure are observed over the entire valence band range, including the presence of a distinct impurity band close to the valence-band maximum of the DMS. These experimental results are in good agreement with the one-step photoemission calculations and a prior HARPES study of Ga0.97Mn0.03As and GaAs [Gray et al., Nat. Mater. 11, 957 (2012)], demonstrating the strong similarity between these two materials. The Mn 2p and 3s core-level spectra also reveal an essentially identical state in doping both GaAs and GaP.
|
|
| 5. |
- Singh-Bhalla, Guneeta, et al.
(författare)
-
Unexpected termination switching and polarity compensation in LaAlO3/SrTiO3 heterostructures
- 2018
-
Ingår i: Physical Review Materials. - : AMER PHYSICAL SOC. - 2475-9953. ; 2:11
-
Tidskriftsartikel (refereegranskat)abstract
- Polar crystals composed of charged ionic planes cannot exist in nature without acquiring surface changes to balance an ever-growing dipole. The necessary changes can manifest structurally or electronically as observed in semiconductors and ferroelectric materials through screening charges and/or domain wall formation. In the case of prototypical polar complex oxides such as the LaAlO3/SrTiO3 system the nature of screening charges for different interface terminations is not symmetric. Electron accumulation is observed near the LaAlO3/TiO2-SrTiO3 interface, while the LaAlO3/SrO-SrTiO3 stack is insulating. Here, we observe evidence for an asymmetry in the surface chemical termination for nominally stoichiometric LaAlO3 films in contact with the two different surface layers of SrTiO3 crystals, TiO2 and SrO. Using several element-specific probes, we find that the surface termination of LaAlO3 remains AlO2 irrespective of the starting termination of SrTiO3 substrate surface. We use a combination of cross-plane tunneling measurements and first-principles calculations to understand the effects of this unexpected termination on band alignments and polarity compensation of LaAlO3/SrTiO3 heterostructures. An asymmetry in LaAlO3 polarity compensation and resulting electronic properties will fundamentally limit atomic level control of oxide heterostructures.
|
|
| 6. |
- Thorarinsdottir, K. A., et al.
(författare)
-
Giant magnetic proximity effect in amorphous layered magnets
- 2019
-
Ingår i: Physical Review Materials. - 2475-9953. ; 3:5
-
Tidskriftsartikel (refereegranskat)abstract
- Here we study the magnetic proximity effect in amorphous layered magnets of alternating high- and low-T-c materials using magnetometry and polarized neutron reflectivity. By altering the thickness of either the high-or low-T-c layer we are able to extract the induced magnetic moment in the low-T-c layer directly and study how it scales with thickness. We observe that the ordering temperature of the low-T-c layer is enhanced and above which a second magnetically ordered state with a very large extension is observed. This induced magnetic state survives to a temperature at least three times that of the ordering temperature of the low-T-c layer and the induced magnetization is approximately constant throughout at least a 10-nm-thick layer. The induced magnetic region within the low-T-c layer does not depend on the thickness of the adjacent high-T-c layer.
|
|
| 7. |
- Adlmann, Franz, et al.
(författare)
-
Depth resolved grazing incidence neutron scattering experiments from semi-infinite interfaces : a statistical analysis of the scattering contributions
- 2018
-
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.
|
|
| 8. |
- Azofeifa, D. E., et al.
(författare)
-
Hydrogen induced changes in the optical properties of Pd capped V thin films
- 2013
-
Ingår i: Journal of Alloys and Compounds. - : Elsevier BV. - 0925-8388 .- 1873-4669. ; 580:Suppl. 1, s. S114-S118
-
Tidskriftsartikel (refereegranskat)abstract
- Optical properties of 50 nm thick single crystal vanadium films deposited on double side polished MgO substrates have been obtained from spectrophotometric measurements. The films were coated with a polycrystalline Pd layer (5 nm thick) to protect them from oxidation and to favor absorption of atomic hydrogen. Electrical resistance was recorded while hydrogen pressure was increased slowly up to 750 mbar keeping temperature constant. Simultaneously, under normal incidence of non-polarized radiation [350-950 nm], transmittance spectra of this Pd/V/MgO system were measured. These were numerically inverted to obtain the spectral behavior of the Pd, V. PdHy, and VHx dielectric functions at 22 and 140 degrees C, and at 750 mbar. Hydrogen concentration in V film was first determined from a resisto-optical method. Finally, we demonstrate the possibility to determine the concentration in the Pd and the V layers independently, solely using the changes in the optical transmission.
|
|
| 9. |
- Badell, Maria Valldeperas, et al.
(författare)
-
Lipid Sponge-Phase Nanoparticles as Carriers for Enzymes
- 2018
-
Ingår i: Biophysical Journal. - : Cell Press. - 0006-3495 .- 1542-0086. ; 114:3, suppl 1, s. 15A-15A
-
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Immobilization of enzymes into different support materials has been widely studied as means to control their activity and stability. Here we will consider lipid liquid crystalline phases as enzyme carriers, as they have been demonstrated to have a high potential in a range of applications such as drug delivery, protein encapsulation or crystallization thanks to the wide range of self-assembly structures they can form, which have cavities of nano-scale dimensions. Furthermore, such structures have also been observed in a range of living organisms. Although, reverse cubic or hexagonal lipid aqueous phase can be used to entrap smaller biomolecules, it is still challenging to encapsulate bioactive macromolecules, such as proteins. Here, we will present a novel lipid system able to form highly swollen sponge phases (L3), with aqueous pores up to 13 nm of diameter. We will show that this structure is preserved even in excess aqueous solution, where they form sponge-like nanoparticles (L3 NPs) in which two enzymes of different sizes, Aspartic protease and beta-galactosidase (34 KDa and 460 KDa, respectively), could be included. To reveal the nature of the interaction between the enzymes and the lipid matrix, we studied the adsorption of both proteins on the lipid layers formed by the L3 NPs. The results will be discussed in terms of the ability of these nanoparticles to encapsulate and release of the proteins in the lipid matrix.
|
|
| 10. |
- Baldi, A., et al.
(författare)
-
Mg/Ti multilayers : Structural and hydrogen absorption properties
- 2010
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 81:22, s. 224203-
-
Tidskriftsartikel (refereegranskat)abstract
- Mg-Ti alloys have uncommon optical and hydrogen absorbing properties, originating from a "spinodal-like" microstructure with a small degree of chemical short-range order in the atomic distribution. In the present study we artificially engineer short-range order by depositing Pd-capped Mg/Ti multilayers with different periodicities. Notwithstanding the large lattice mismatch between Mg and Ti, the as-deposited metallic multilayers show good structural coherence. On exposure to H-2 gas a two-step hydrogenation process occurs with the Ti layers forming the hydride before Mg. From in situ measurements of the bilayer thickness Lambda at different hydrogen pressures, we observe large out-of-plane expansions of Mg and Ti layers on hydrogenation, indicating strong plastic deformations in the films and a consequent shortening of the coherence length. On unloading at room temperature in air, hydrogen atoms remain trapped in the Ti layers due to kinetic constraints. Such loading/unloading sequence can be explained in terms of the different thermodynamic properties of hydrogen in Mg and Ti, as shown by diffusion calculations on a model multilayered systems. Absorption isotherms measured by hydrogenography can be interpreted as a result of the elastic clamping arising from strongly bonded Mg/Pd and broken Mg/Ti interfaces.
|
|
| 11. |
- Blomqvist, Andreas, et al.
(författare)
-
Significance of self-trapping on hydrogen diffusion
- 2010
-
Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 105:18, s. 185901-
-
Tidskriftsartikel (refereegranskat)abstract
- The diffusion rate of hydrogen in Nb was calculated using ab initio molecular dynamics simulations. At low temperatures the hydrogen is strongly trapped in a local strain field which is caused by the elastic response of the lattice. At elevated temperatures, the residence time (τ) of hydrogen in an interstitial site is not sufficient for fully developing the local strain field. This unbinding of the interstitial hydrogen and the strain field increases the hopping rate (1/τ) at elevated temperatures (>400 K). These results call for a revision of the conceptual framework of diffusion of hydrogen in transition metals at elevated temperatures.
|
|
| 12. |
- Bylin, Johan, et al.
(författare)
-
Hydrogen-induced volume changes, dipole tensor, and elastic hydrogen-hydrogen interaction in a metallic glass
- 2022
-
Ingår i: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 106:10
-
Tidskriftsartikel (refereegranskat)abstract
- Hydrogen and its isotopes, absorbed in metals, induce local stress on the atomic structure, which generates a global expansion in proportion to the concentration of hydrogen. The dipole force tensor and its interaction with the stress fields give rise to an effective attractive nonlocal potential between hydrogen atoms-the elastic hydrogen-hydrogen interaction-which is a key quantity governing the phase transitions of hydrogen in metals. While the dipole tensor and the elastic interaction have been researched in crystalline materials, they remain experimentally unexplored in metallic glasses and it is unclear how these quantities are affected by the lack of point group symmetries. Here, we investigate both experimentally and theoretically the volume changes, the components of the force dipole tensor, and ultimately the elastic hydrogen-hydrogen interaction in the metallic glass V80Zr20. In situ neutron reflectometry was used to determine the deuterium-induced volume changes as a function of deuterium concentration. The one-dimensional volume expansion is found to change by more than 14% without any structural degradation, up to concentrations of one deuterium atom per metal atom. From the expansion, we determine that the out-of-plane component of the elastic dipole tensor is remarkably similar to a composition weighted sum of the ones found in crystalline vanadium and zirconium. Via ab initio calculations of both free and biaxially constrained expanded metallic structures, we determine that the trace of the dipole tensor varies with hydrogen concentration and is essentially invariant of global elastic boundary conditions. As a consequence, the elastic hydrogen-hydrogen interaction energy is found to be concentration-dependent as well, illustrating that the disordered nature of a metallic glass does not impede the mediation of the elastic attraction, but rather allows it to vary with hydrogen content.
|
|
| 13. |
- Bylin, Johan, et al.
(författare)
-
One-shot pair distribution functions of thin films using lab-based x-ray sources
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- We demonstrate the feasibility of obtaining accurate pair distribution functions of thin amorphous films down to 80 nm, using modern laboratory-based x-ray sources. The pair distribution functions are obtained using a single diffraction scan (one-shot) without the requirement of additional scans of the substrate or of the air. By using a crystalline substrate combined with an oblique scattering geometry, most of the Bragg scattering of the substrate is avoided, rendering the substrate Compton scattering the primary contribution. By utilizing a discriminating energy filter, available in the latest generation of modern detectors, we demonstrate that the Compton intensity can further be reduced to negligible levels at higher wavevector values. We minimize scattering from the sample holder and the air by the systematic selection of pixels in the detector image based on the projected detection footprint of the sample and the use of a 3D printed sample holder. Finally, x-ray optical effects in the absorption factors and the ratios between the Compton intensity of the substrate and film are taken into account by using a theoretical tool that simulates the electric field inside the film and the substrate, which aids in planning both the sample design and measurement protocol.
|
|
| 14. |
- Bylin, Johan, et al.
(författare)
-
The influence of hydrogen on the electronic structure in transition metallic glasses
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- We investigate the influence of hydrogen on the electronic structure of a binary transition metallic glass of V80Zr20. We examine the hybridization between the hydrogen and metal atoms with the aid of hard x-ray photoelectron spectroscopy. Combined with ab initio density functional theory, we are able to show and predict the formation of s-d hybridized energy states. With optical transmission and resistivity measurements, we investigate the emergent electronic properties formed out of those altered energy states, and together with the theoretical calculations of the frequency-dependent conductivity tensor, we qualitatively support the observed strong wavelength-dependency of the hydrogen-induced changes on the optical absorption and a positive parabolic change in resistivity with hydrogen concentration.
|
|
| 15. |
- Bylin, Johan
(författare)
-
The interaction of hydrogen with metallic glass
- 2024
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Combining theoretical ab initio calculations with high-purity thin film sample synthesis and in situ measurements is a compelling way to bridge the gap in our understanding concerning hydrogen in metallic glasses, which is the primary work of this dissertation thesis. The main emphasis has been on how hydrogen affects the structure of metallic glasses, and how those changes influence not only the electronic properties of the amorphous metals but also their thermal stability. The real-space correlations in the form of the pair distribution functions in thin metallic films have primarily only been accessible through synchrotron radiation. An effective methodological procedure using laboratory-based x-ray sources is here brought forth, which, for the first time, can produce accessible and accurate pair distribution functions from thin films down to a thickness of 80 nm. The underpinning mechanisms behind the hydrogen-induced volume expansion of metallic glasses in the form of the dipole force tensor and an elastic hydrogen-hydrogen interaction were examined using in situ neutron reflectometry and first-principles calculations of expanding V80Zr20 amorphous structures. The dipole force tensor was concluded to be similar in magnitude to a mole-fraction-weighted sum of the ones found in hydrogen-contained vanadium and zirconium crystals, and the theoretical calculations demonstrated that it and the interaction energy varies with hydrogen concentration. The electronic structure of the metallic glass V80Zr20 was determined via hard x-ray photoemission spectrometry and confirmed by first-principles calculations to be modified by the presence of hydrogen, in which a collection of s-d hybridized states 7 eV below the Fermi level was formed. The changes closer to the Fermi level, together with the volume expansion, were via experiments and ab initio calculations established to cause a parabolic change in resistance and a strong wavelength dependence on the optical transmission. The thermal stability of amorphous VxZr1-x metals, investigated via ab initio calculations of the thermodynamic driving force towards crystallization, was found to affirm the observed hydrogen-induced enhancement in thermal stability.
|
|
| 16. |
- Conlon, C. S., et al.
(författare)
-
Hard x-ray standing-wave photoemission insights into the structure of an epitaxial Fe/MgO multilayer magnetic tunnel junction
- 2019
-
Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 126:7
-
Tidskriftsartikel (refereegranskat)abstract
- The Fe/MgO magnetic tunnel junction is a classic spintronic system, with current importance technologically and interest for future innovation. The key magnetic properties are linked directly to the structure of hard-to-access buried interfaces, and the Fe and MgO components near the surface are unstable when exposed to air, making a deeper probing, nondestructive, in-situ measurement ideal for this system. We have thus applied hard x-ray photoemission spectroscopy (HXPS) and standing-wave (SW) HXPS in the few kilo-electron-volt energy range to probe the structure of an epitaxially grown MgO/Fe superlattice. The superlattice consists of 9 repeats of MgO grown on Fe by magnetron sputtering on an MgO(001) substrate, with a protective Al2O3 capping layer. We determine through SW-HXPS that 8 of the 9 repeats are similar and ordered, with a period of 33 +/- 4 angstrom, with the minor presence of FeO at the interfaces and a significantly distorted top bilayer with ca. 3 times the oxidation of the lower layers at the top MgO/Fe interface. There is evidence of asymmetrical oxidation on the top and bottom of the Fe layers. We find agreement with dark-field scanning transmission electron microscope (STEM) and x-ray reflectivity measurements. Through the STEM measurements, we confirm an overall epitaxial stack with dislocations and warping at the interfaces of ca. 5 angstrom. We also note a distinct difference in the top bilayer, especially MgO, with possible Fe inclusions. We thus demonstrate that SW-HXPS can be used to probe deep buried interfaces of novel magnetic devices with few-angstrom precision.
|
|
| 17. |
- Dabkowska, Aleksandra P., et al.
(författare)
-
Non-lamellar lipid assembly at interfaces : controlling layer structure by responsive nanogel particles
- 2017
-
Ingår i: Interface Focus. - : ROYAL SOC. - 2042-8898 .- 2042-8901. ; 7:4
-
Tidskriftsartikel (refereegranskat)abstract
- Biological membranes do not only occur as planar bilayer structures, but depending on the lipid composition, can also curve into intriguing three-dimensional structures. In order to fully understand the biological implications as well as to reveal the full potential for applications, e.g. for drug delivery and other biomedical devices, of such structures, well-defined model systems are required. Here, we discuss the formation of lipid non-lamellar liquid crystalline (LC) surface layers spin-coated from the constituting lipids followed by hydration of the lipid layer. We demonstrate that hybrid lipid polymer films can be formed with different properties compared with the neat lipid LC layers. The nanostructure and morphologies of the lipid films formed reflect those in the bulk. Most notably, mixed lipid layers, which are composed of glycerol monooleate and diglycerol monooleate with poly(N-isopropylacrylamide) nanogels, can form films of reverse cubic phases that are capable of responding to temperature stimulus. Owing to the presence of the nanogel particles, changing the temperature not only regulates the hydration of the cubic phase lipid films, but also the lateral organization of the lipid domains within the lipid self-assembled film. This opens up the possibility for new nanostructured materials based on lipid-polymer responsive layers.
|
|
| 18. |
- Droulias, Sotirios A., et al.
(författare)
-
Beating effects in multilayer systems studied with neutron reflectometry
-
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.
|
|
| 19. |
- Droulias, Sotirios A., et al.
(författare)
-
Crystal perfection by strain engineering : The case of Fe/V (001)
- 2017
-
Ingår i: Thin Solid Films. - : Elsevier BV. - 0040-6090 .- 1879-2731. ; 636, s. 608-614
-
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.
|
|
| 20. |
- Droulias, S. A., et al.
(författare)
-
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
-
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.
|
|
| 21. |
- Droulias, Sotirios A., et al.
(författare)
-
Limitations of the kinematic approximation in neutron reflectivity measurements for the analysis of bilayers
- 2018
-
Ingår i: Journal of applied crystallography. - : INT UNION CRYSTALLOGRAPHY. - 0021-8898 .- 1600-5767. ; 51, s. 1556-1563
-
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.
|
|
| 22. |
- Droulias, Sotirios A., et al.
(författare)
-
Tailoring thermodynamic properties of metal hydrides with interfaces
-
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.
|
|
| 23. |
- Droulias, Sotirios A.
(författare)
-
The effect of nano-confinement on hydrogen uptake in metallic superlattices
- 2018
-
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.
|
|
| 24. |
- Droulias, Sotirios A., et al.
(författare)
-
Using interfaces to influence thermodynamic properties of metal hydrides
-
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.
|
|
| 25. |
- Huang, Wen, et al.
(författare)
-
Concentration dependence of hydrogen diffusion in clamped vanadium (001) films
- 2017
-
Ingår i: Journal of Physics. - 0953-8984 .- 1361-648X. ; 29:4
-
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.
|
|
| 26. |
- Huang, Wen, et al.
(författare)
-
Experimental observation of hysteresis in a coherent metal-hydride phase transition
- 2017
-
Ingår i: Journal of Physics. - : IOP PUBLISHING LTD. - 0953-8984 .- 1361-648X. ; 29:49
-
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.
|
|
| 27. |
|
|
| 28. |
|
|
| 29. |
- Huang, Wen, et al.
(författare)
-
Finite size effects : deuterium diffusion in nm thick vanadium layers
- 2017
-
Ingår i: New Journal of Physics. - : Institute of Physics Publishing (IOPP). - 1367-2630. ; 19
-
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.
|
|
| 30. |
|
|
| 31. |
- Ingason, Arni Sigurdur, et al.
(författare)
-
Long-range antiferromagnetic order in epitaxial Mn2GaC thin films from neutron reflectometry
- 2016
-
Ingår i: PHYSICAL REVIEW B. - : AMER PHYSICAL SOC. - 2469-9950. ; 94:2, s. 024416-
-
Tidskriftsartikel (refereegranskat)abstract
- The nature of the magnetic structure in magnetic so-called MAX phases is a topic of some controversy. Here we present unpolarized neutron-diffraction data between 3.4 and 290.0 K and momentum transfer between Q = 0.0 and 1.1 angstrom(-1), as well as complementary x-ray-diffraction data on epitaxial thin films of the MAX phase material Mn2GaC. This inherently layered material exhibits neutron-diffraction peaks consistent with long-ranged antiferromagnetic order with a periodicity of two structural unit cells. The magnetic structure is present throughout the measured temperature range. The results are in agreement with first-principles calculations of antiferromagnetic structures for this material where the Mn-C-Mn atomic trilayers are found to be ferromagnetically coupled internally but spin flipped or rotated across the Ga layers. The present findings have significant bearing on the discussion regarding the nature of the magnetic structure in magnetic MAX phases.
|
|
| 32. |
|
|
| 33. |
- Kaplan, Maciej, 1991-, et al.
(författare)
-
Hydrogen-induced enhancement of thermal stability in VZr(H) metallic glasses
- 2022
-
Ingår i: Materialia. - : Elsevier BV. - 2589-1529. ; 24
-
Tidskriftsartikel (refereegranskat)abstract
- Prediction of crystallization temperatures in metallic glasses is still an open question. Investigations of multi component alloys are common in the literature, however, binary and ternary alloys are more suitable for funda-mental studies due to their simplicity. Here, we show that a low thermodynamic driving force for crystallization can be associated with a high crystallization temperature. The driving force is determined by calculating - for the first time in metallic glasses - the temperature dependent Gibbs free energies of the alloys using ab initio density functional theory, in combination with the stochastic quenching method. The crystallization tempera-tures of VxZr100-x and VxZr67-xH33 have been determined using simultaneous in-situ x-ray scattering techniques and resistivity measurements. The onset of crystallization is found to exhibit a parabolic dependence throughout the composition range, whereas alloying with hydrogen increases the thermal stability up to 150 K close to the amorphous-crystalline boundaries. These findings suggest that hydrogen acts as an alloying element with the ability to dynamically tune the intrinsic properties of the material. Lastly, temperature-dependent descriptions of the Gibbs free energy and kinetic considerations of a metallic glass are necessary for a complete characterization of the crystallization process.
|
|
| 34. |
- Kaplan, Maciej, et al.
(författare)
-
Phase formation and thermal stability of amorphous ZrNbCrMo thin films
- 2021
-
Ingår i: Journal of Non-Crystalline Solids. - : Elsevier BV. - 0022-3093 .- 1873-4812 .- 2590-1591. ; 9-10, s. 100061-100061
-
Tidskriftsartikel (refereegranskat)abstract
- We demonstrate that the atomic size mismatch, δ, can be used to predict the boundary between amorphous and crystalline phase formation ranges in ZrNbCrMo thin films. The concentrations of all alloying elements are varied systematically, which induces a change in δ. The formation of an amorphous phase is observed by x-ray diffraction for δ ≥ 6.9%, whereas crystallization is detected for δ ≤ 6.9%. The crystallization temperature increases from 575 to 625 ∘C by increasing Nb + Mo content from 10 to 34 at.%, and decreases to 475 ∘C upon further additions of Nb + Mo. Calphad calculated liquidus temperatures, Tl, increases monotonously and δ decreases monotonously with Nb and Mo additions. Consequently, δ and Tl do not serve as predictors for thermal stability of ZrNbCrMo thin films.
|
|
| 35. |
- Kiemeney, Lambertus A, et al.
(författare)
-
A sequence variant at 4p16.3 confers susceptibility to urinary bladder cancer.
- 2010
-
Ingår i: Nature genetics. - : Springer Science and Business Media LLC. - 1546-1718 .- 1061-4036. ; 42:5, s. 415-9
-
Tidskriftsartikel (refereegranskat)abstract
- Previously, we reported germline DNA variants associated with risk of urinary bladder cancer (UBC) in Dutch and Icelandic subjects. Here we expanded the Icelandic sample set and tested the top 20 markers from the combined analysis in several European case-control sample sets, with a total of 4,739 cases and 45,549 controls. The T allele of rs798766 on 4p16.3 was found to associate with UBC (odds ratio = 1.24, P = 9.9 x 10(-12)). rs798766 is located in an intron of TACC3, 70 kb from FGFR3, which often harbors activating somatic mutations in low-grade, noninvasive UBC. Notably, rs798766[T] shows stronger association with low-grade and low-stage UBC than with more aggressive forms of the disease and is associated with higher risk of recurrence in low-grade stage Ta tumors. The frequency of rs798766[T] is higher in Ta tumors that carry an activating mutation in FGFR3 than in Ta tumors with wild-type FGFR3. Our results show a link between germline variants, somatic mutations of FGFR3 and risk of UBC.
|
|
| 36. |
- Komander, Kristina, et al.
(författare)
-
Accurate measurement of hydrogen concentration in transition metal hydrides utilizing electronic excitations by MeV ions
- 2024
-
Ingår i: International journal of hydrogen energy. - : Elsevier. - 0360-3199 .- 1879-3487. ; 57, s. 583-588
-
Tidskriftsartikel (refereegranskat)abstract
- This study focuses on enhancing the accuracy of hydrogen content verification in hydrogen-rich ultrathin materials relevant for sustainable energy applications. Ion beams are used for distinctive real-space detection leveraging elastic and inelastic interactions with hydrogen atoms. However, the lack of experimental reference data on electronic interactions poses a challenge to the accuracy of analytical techniques. We investigate the effect of absorbed hydrogen on the electronic energy deposition of 15N-ions in amorphous transition metal compounds, specifically V and Zr, covering concentrations >1H/M. Employing resonant nuclear reactions and Rutherford backscattering, the energy loss is found to increase considerably with hydrogen content, in line with Bragg's additivity. The electronic energy loss cross section for 15N-ions at 6.5 MeV measured (64.55±3.38) eV cm2/1015 atoms. Results are compared to semi-empirical and theoretical models. The findings improve hydrogen profiling accuracy using 15N-nuclear reaction analysis and enable unprecedented methods for hydrogen quantification by other, commonly available ion beams.
|
|
| 37. |
- Komander, Kristina, et al.
(författare)
-
Hydrogen site location in ultrathin vanadium layers by N-15 nuclear reaction analysis
- 2019
-
Ingår i: Nuclear Instruments and Methods in Physics Research Section B. - : ELSEVIER. - 0168-583X .- 1872-9584. ; 455, s. 57-60
-
Tidskriftsartikel (refereegranskat)abstract
- We present a method using resonant nuclear reaction analysis combined with optical transmission and heavy-ion Rutherford backscattering spectrometry to study the absorption of hydrogen in single crystalline thin vanadium films. Probing with the resonant H-1(N-15,alpha gamma)C-12 reaction allows for highly resolved hydrogen depth profiling, while measurements along the crystal axes render possible the direct identification of the interstitial site occupancy. First experiments were performed on thin vanadium hydrides in Fe(Cr)/V superlattices revealing differences in site occupancy.
|
|
| 38. |
- Komander, Kristina, et al.
(författare)
-
Interstitial Hydrogen in Fe/V Superstructures : Lattice Site Location and Thermal Vibration
- 2021
-
Ingår i: Physical Review Letters. - : American Physical Society. - 0031-9007 .- 1079-7114. ; 127:13
-
Tidskriftsartikel (refereegranskat)abstract
- We report real space location of hydrogen in single crystalline Fe/V superstructures. Anisotropic strain is quantified versus hydrogen concentration by using the yield of backscattered primary 2 MeV He-4 ions for incidence in different crystallographic directions. From a comparison of ion channeling in combination with H-1(N-15, alpha gamma)C-12 nuclear reaction analysis and Monte Carlo simulations we show that hydrogen is located in octahedral z sites and quantify its vibrational amplitude of 0.2 angstrom.
|
|
| 39. |
- Komander, Kristina
(författare)
-
Nanoscale Metal Hydrides from MeV-Ion Perspectives: A Unique View
- 2024
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis work set out to investigate interstitial hydrogen in material systems of reduced dimensionality or high loading capacities. Experimental methodologies utilizing MeV-ions were developed addressing metal hydride formation in various transition metal alloys and in the presence of interfaces and lattice strain. Enhanced concentration measurement accuracy by 15N-resonant nuclear reaction analysis (NRA) in hydrogen-rich transition metal films was achieved by examining the influence of hydrogen on electronic excitations by 15N-ions. A non-iterative method combining NRA with Rutherford backscattering spectrometry (RBS) revealed the energy deposition of 15N-ions in various hydrogenated V/Zr-alloys, promoting reliable energy loss predictions. The findings imply the potential for indirect hydrogen concentration measurements via RBS, increasing accessibility across multiple facilities as a broader range of ion species can be utilized.To identify locations of interstitial hydrogen within thin single-crystalline films, the applicability of different MeV-ions species was explored, performing channeling experiments on Fe/V-superlattices as model systems. 4He-ions reveal hydrogen-induced anisotropic lattice expansion by RBS, while dechanneling effects and hydrogen recoils provide insights into lattice site locations. However, challenges for unambiguous site-location extraction were identified concerning deflections from channeling trajectories and limitations of simulations confined to backscattering geometry. Employing 15N-ions for channeling NRA and RBS, combined with Monte-Carlo simulations, enables quantitative real-space investigation of subsurface hydrogen site locations and thermal vibrational motion in nanosized transition metals. The 15N-channeling method was applied to study the influence of different adjacent metals on vanadium hydrides, comparing hydrogenated Fe/V- to Cr/V-superlattices. In combination with in-situ measurements of electrical resistivity and optical transmission – which serve as indirect measures for hydrogen order and concentration, respectively – the investigation revealed significant proximity effects. Specifically, Fe/V absorbs smaller integral amounts of hydrogen, and the critical temperature is lower than for Cr/V. Thereby, hydrogen atoms occupy octahedral z-sites with identical thermal vibrational amplitudes of 0.20-0.25 Å in both samples over an extensive range of hydrogen concentrations. The findings are consistent with the effects of a size reduction induced by hydrogen-depleted layers at interfaces, larger toward Fe than to Cr.The developed methodologies offer unique insights into alloying and boundary effects on metal hydride formation, which can control phase transitions and enhance the loading capacity, providing avenues to optimize material properties for sustainable energy solutions.
|
|
| 40. |
- Komander, Kristina, et al.
(författare)
-
Proximity and dimensionality effects on interstitial hydrogen
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- In this study, we investigate the proximity effects on hydrogen distribution in ultrathin single crystalline vanadium films, by comparing the absorption in Fe/V- and Cr/V-superlattices. Pressure concentration isotherms show higher absolute solubility of hydrogen in a Cr/V-superlattice. Isotherms of excess resistivity are used to locate phase boundaries which yielded a higher critical temperature and concentration in Cr/V. Measurements of hydrogen site location and thermal vibrations using 15N-nuclear reaction analysis demonstrate identical site occupation of 0Z at room temperature with a vibrational amplitude of 0.20‑0.25 Å over a wide range of hydrogen concentrations in both superlattices. The analysis excludes changes in site occupancy as the primary cause for variations in thermodynamics across different temperatures due to proximity. Our findings are consistent with a more extended region of hydrogen depletion in the vicinity of Fe and resolve previously puzzling differences in the hydrogen loading of Fe/V- and Cr/V-superlattices, implying an inverse spillover effect.
|
|
| 41. |
- Komander, Kristina, et al.
(författare)
-
The influence of the distribution of interstitial hydrogen on optical transmission of vanadium hydride
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Hydrogen-induced changes of optical absorption in Fe/V (001) and Cr/V (001) superlattices are found to be dominated by the distribution of microscopic lattice expansions in vanadium. We relate optical transmission spectra between 400-1000nm to hydrogen distribution and site location in vanadium determined with 15N-NRA and compare to first-principles calculations of a uniaxial lattice expansion. An energy shift of a broad absorption peak induces non-trivial changes in the absorbance as a function of wavelength and hydrogen-induced strain. Differently sized hydrogen-depleted layers in otherwise structurally similar vanadium films containing equal hydrogen inventory [H/V], introduce a different optical response due to differing distribution of the induced microscopic volume change.
|
|
| 42. |
- Luchini, Alessandra, et al.
(författare)
-
Neutron Reflectometry reveals the interaction between functionalized SPIONs and the surface of lipid bilayers
- 2017
-
Ingår i: Colloids and Surfaces B. - : ELSEVIER SCIENCE BV. - 0927-7765 .- 1873-4367. ; 151, s. 76-87
-
Tidskriftsartikel (refereegranskat)abstract
- The safe application of nanotechnology devices in biomedicine requires fundamental understanding on how they interact with and affect the different components of biological systems. In this respect, the cellular membrane, the cell envelope, certainly represents an important target or barrier for nanosystems. Here we report on the interaction between functionalized SuperParamagnetic Iron Oxide Nanoparticles (SPIONs), promising contrast agents for Magnetic Resonance Imaging (MRI), and lipid bilayers that mimic the plasma membrane. Neutron Reflectometry, supported by Quartz Crystal Microbalance with Dissipation monitoring (QCM-D) experiments, was used to characterize this interaction by varying both SPION coating and lipid bilayer composition. In particular, the interaction of two different SPIONs, functionalized with a cationic surfactant and a zwitterionic phospholipid, and lipid bilayers, containing different amount of cholesterol, were compared. The obtained results were further validated by Dynamic Light Scattering (DLS) measurements and Cryogenic Transmission Electron Microscopy (Cryo-TEM) images. None of the investigated functionalized SPIONs were found to disrupt the lipid membrane. However, in all case we observed the attachment of the functionalized SPIONs onto the surface of the bilayers, which was affected by the bilayer rigidity, i.e. the cholesterol concentration.
|
|
| 43. |
- Magnus, Fridrik, et al.
(författare)
-
Sequential magnetic switching in Fe/MgO(001) superlattices
- 2018
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 97:17
-
Tidskriftsartikel (refereegranskat)abstract
- Polarized neutron reflectometry is used to determine the sequence of magnetic switching in interlayer exchangecoupled Fe/MgO(001) superlattices in an applied magnetic field. For 19.6 Å thick MgO layers we obtain a 90◦periodic magnetic alignment between adjacent Fe layers at remanence. In an increasing applied field the toplayer switches first followed by its second-nearest neighbor. For 16.4 Å MgO layers, a 180◦periodic alignment isobtained at remanence and with increasing applied field the layer switching starts from the two outermost layersand proceeds inwards. This sequential tuneable switching opens up the possibility of designing three-dimensionalmagnetic structures with a predefined discrete switching sequence
|
|
| 44. |
- Magnus, Fridrik, et al.
(författare)
-
Tuneable exchange-spring stiffness in amorphous magnetic trilayer structures
- 2021
-
Ingår i: Journal of Physics. - : Institute of Physics Publishing (IOPP). - 0953-8984 .- 1361-648X. ; 33:44
-
Tidskriftsartikel (refereegranskat)abstract
- We investigate the magnetic properties of amorphous Sm10Co90/Co-60(Al70Zr30)(40)/Co-85(Al70Zr30)(15) exchange-spring magnet trilayers. The magnetically soft Co-85(Al70Zr30)(15) layer is coupled to the magnetically hard Sm10Co90 layer through the weakly magnetic low-T (c) Co-60(Al70Zr30)(40) spacer layer. The strength of the coupling can be controlled with temperature and the coupling persists above the intrinsic T (c) of the spacer layer due to a long-range magnetic proximity effect. Polarized neutron reflectivity is used to examine the magnetic profile of the trilayers during magnetization reversal. A two-step switching occurs, with the switching angle of the soft layer strongly dependent on the strength of the coupling. In the strong coupling regime a magnetic state can be achieved where the soft layer magnetization is perpendicular to the hard layer whereas in the weak coupling regime the soft layer reverses fully.
|
|
| 45. |
- Naidjonoka, Polina, et al.
(författare)
-
On the interaction of softwood hemicellulose with cellulose surfaces in relation to molecular structure and physicochemical properties of hemicellulose
- 2020
-
Ingår i: Soft Matter. - : Royal Society of Chemistry (RSC). - 1744-683X .- 1744-6848. ; 16:30, s. 7063-7076
-
Tidskriftsartikel (refereegranskat)abstract
- The substantial part of the water-soluble hemicellulose fraction, obtained when processing cellulose to produce paper and other products, has so far been discarded. The aim of this work is to reveal the interfacial properties of softwood hemicellulose (galactoglucomannan, GGM) in relation to their molecular and solution structure. In this study the sugar composition of GGM was characterised by chemical analysis as well as 1D and 2D NMR spectroscopy. Previously it has been demonstrated that hemicellulose has high affinity towards cellulose and has the ability to alter the properties of cellulose based products. This study is focused on the interactions between hemicellulose and the cellulose surface. Therefore, adsorption to hydrophobized silica and cellulose surfaces of two softwood hemicellulose samples and structurally similar seed hemicelluloses (galactomannans, GMs) was studied with ellipsometry, QCM-D and neutron reflectometry. Aqueous solutions of all samples were characterized with light scattering to determine how the degree of side-group substitution and molecular weight affect the conformation and aggregation of these polymers in the bulk. In addition, hemicellulose samples were studied with SAXS to investigate backbone flexibility. Light scattering results indicated that GM polymers form globular particles while GGMs were found to form rod-like aggregates in the solution. The polysaccharides exhibit higher adsorption to cellulose than on hydrophobic surfaces. A clear correlation between the increase in molecular weight of polysaccharides and increasing adsorbed amount on cellulose was observed, while the adsorbed amount on the hydrophobic surface was fairly independent of the molecular weight. The obtained layer thickness was compared with bulk scattering data and the results indicated flat conformation of the polysaccharides on the surface.
|
|
| 46. |
- Nouhi, Shirin, et al.
(författare)
-
Interactions of perfluoroalkyl substances with a phospholipid bilayer studied by neutron reflectometry
- 2018
-
Ingår i: Journal of Colloid and Interface Science. - : Elsevier. - 0021-9797 .- 1095-7103. ; 511, s. 474-481
-
Tidskriftsartikel (refereegranskat)abstract
- The interactions between perfluoroalkyl substances (PFASs) and a phospholipid bilayer (1,2-dimyristoyl-sn-glycero-3-phosphocholine) were investigated at the molecular level using neutron reflectometry. Representative PFASs with different chain length and functional groups were selected in this study including: perfluorobutane sulfonate (PFBS), perfluorohexanoate (PFHxA), perfluorohexane sulfonate (PFHxS), perfluorononanoate (PFNA), perfluorooctane sulfonate (PFOS), and perfluorooctane sulfonamide (FOSA). All PFASs were found to interact with the bilayer by incorporation, indicating PFAS ability to accumulate once ingested or taken up by organisms. The interactions were observed to increase with chain length and vary with the functional group as SO2NH2" role="presentation">(FOSA) > SO2O−" role="presentation">(PFOS) > COO−(PFNA). The PFAS hydrophobicity, which is strongly correlated with perfluorocarbon chain length, was found to strongly influence the interactions. Longer chain PFASs showed higher tendency to penetrate into the bilayer compared to the short-chain compounds. The incorporated PFASs could for all substances but one (PFNA) be removed from the lipid membrane by gentle rinsing with water (2 mL min−1). Although short-chain PFASs have been suggested to be the potentially less bioaccumulative alternative, we found that in high enough concentrations they can also disturb the bilayer. The roughness and disorder of the bilayer was observed to increase as the concentration of PFASs increased (in particular for the high concentrations of short-chain substances i.e. PFHxA and PFBS), which can be an indication of aggregation of PFASs in the bilayer.
|
|
| 47. |
- Oei, Ling, et al.
(författare)
-
A genome-wide copy number association study of osteoporotic fractures points to the 6p25.1 locus
- 2014
-
Ingår i: Journal of Medical Genetics. - : BMJ Publishing Group. - 0022-2593 .- 1468-6244. ; 51:2, s. 122-131
-
Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND: Osteoporosis is a systemic skeletal disease characterised by reduced bone mineral density and increased susceptibility to fracture; these traits are highly heritable. Both common and rare copy number variants (CNVs) potentially affect the function of genes and may influence disease risk.AIM: To identify CNVs associated with osteoporotic bone fracture risk.METHOD: We performed a genome-wide CNV association study in 5178 individuals from a prospective cohort in the Netherlands, including 809 osteoporotic fracture cases, and performed in silico lookups and de novo genotyping to replicate in several independent studies.RESULTS: A rare (population prevalence 0.14%, 95% CI 0.03% to 0.24%) 210 kb deletion located on chromosome 6p25.1 was associated with the risk of fracture (OR 32.58, 95% CI 3.95 to 1488.89; p=8.69×10(-5)). We performed an in silico meta-analysis in four studies with CNV microarray data and the association with fracture risk was replicated (OR 3.11, 95% CI 1.01 to 8.22; p=0.02). The prevalence of this deletion showed geographic diversity, being absent in additional samples from Australia, Canada, Poland, Iceland, Denmark, and Sweden, but present in the Netherlands (0.34%), Spain (0.33%), USA (0.23%), England (0.15%), Scotland (0.10%), and Ireland (0.06%), with insufficient evidence for association with fracture risk.CONCLUSIONS: These results suggest that deletions in the 6p25.1 locus may predispose to higher risk of fracture in a subset of populations of European origin; larger and geographically restricted studies will be needed to confirm this regional association. This is a first step towards the evaluation of the role of rare CNVs in osteoporosis.
|
|
| 48. |
- Palonen, Heikki, et al.
(författare)
-
The magnetization profile induced by the double magnetic proximity effect in an Fe/Fe0.30V0.70 superlattice
- 2019
-
Ingår i: Applied Physics Letters. - : AMER INST PHYSICS. - 0003-6951 .- 1077-3118. ; 115:1
-
Tidskriftsartikel (refereegranskat)abstract
- The double magnetic proximity effect (MPE) in an Fe/Fe0.30V0.70 superlattice is studied by a direct measurement of the magnetization profile using polarized neutron reflectivity. The experimental magnetization profile is shown to qualitatively agree with a profile calculated using density functional theory. The profile is divided into a short range interfacial part and a long range tail. The interfacial part is explained by charge transfer and induced magnetization, while the tail is attributed to the inhomogeneous nature of the FeV alloy. The long range tail in the magnetization persists up to 170% above the intrinsic ordering temperature of the FeV alloy. The observed effects can be used to design systems with a direct exchange coupling between layers over long distances through a network of connected atoms. When combined with the recent advances in tuning and switching, the MPE with electric fields and currents, the results can be applied in spintronic devices. Published under license by AIP Publishing.
|
|
| 49. |
- Pálsson, Gunnar K., et al.
(författare)
-
Deuterium-induced volume expansion in Fe0.5V0.5/V superlattices
- 2010
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 82:24, s. 245424-
-
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.
|
|
| 50. |
- Pálsson, Gunnar K., et al.
(författare)
-
Examination of the reliability of X-ray techniques for determining hydrogen-induced volume changes
- 2008
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 78:10, s. 104118-
-
Tidskriftsartikel (refereegranskat)abstract
- The Bragg peaks in x-ray diffraction experiments are generally taken to be a reliable measure of the average lattice distance in crystals. We show that this assumption can be misleading when determining hydrogen-induced volume changes. Experiments based on simultaneous determination of the position of the Bragg peak and the sample volume of an Fe/V(001) superlattice while expanding the lattice by in situ hydrogen loading serve as an illustration of this counter-intuitive effect.
|
|
