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  • 1.
    Aakash, förnamn
    et al.
    Department of Electronics and Communication Engg., Birla Institute of Technology.
    Nordblad, Per
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Mohan, Rajendra
    Department of Physics, National Institute of Technology Patna.
    Mukherjee, Samrat
    Department of Physics, National Institute of Technology Patna.
    Structural, magnetic and hyperfine characterizations of nanocrystalline Zn-Cd doped nickel ferrites2017In: Journal of Magnetism and Magnetic Materials, ISSN 0304-8853, E-ISSN 1873-4766, Vol. 441, p. 710-717Article in journal (Refereed)
    Abstract [en]

    In our present work, we have synthesized a series of Cd-Zn doped nickel ferrite ((Cd-0.5 Zn-x(x)) Ni0(.5)Fe(2)O(4); x = 0, 0.1, 0.2, 0.3, 0.4 and 0.5) through standard chemical co-precipitation method to study the influence of diamagnetic ions (Cd, Zn) on the magnetic properties of ferrites. XRD and Raman spectroscopy were employed for the structural characterizations. The refinement of the X-ray diffractogram data augmented by the Williamson-Hall plots showed the presence of Cd2+ vacancies and a strained crystal structure. The vibrational spectroscopy indicated the presence of lower space-group symmetry and a distorted crystal structure. Magnetic measurements showed the samples possessed low magnetic anisotropy along with a canted spin structure. The Mossbauer measurements confirmed the cation distribution and gave evidence of super transferred hyperfine interactions arising due to canted spin structure of the system.

  • 2.
    Abdel-Baset, T. A.
    et al.
    Taibah Univ, Fac Sci, Dept Phys, Yanbu 46423, Saudi Arabia.;Fayoum Univ, Fac Sci, Dept Phys, Al Fayyum 63514, Egypt..
    Abdel-Hafiez, Mahmoud
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Effect of metal dopant on structural and magnetic properties of ZnO nanoparticles2021In: Journal of materials science. Materials in electronics, ISSN 0957-4522, E-ISSN 1573-482X, Vol. 32, no 12, p. 16153-16165Article in journal (Refereed)
    Abstract [en]

    Zn1-xRxO (R = Li, Mg, Cr, Mn, Fe and Cd) were obtained by using co-precipitation synthesis technique with constant weight percent of 3% from R ions. The phase composition, crystal structure, morphology, density functional theory (DFT), and magnetic properties were examined to comprehend the influence of Zn2+ partial substitution with R ions. X-ray diffraction shows that the ZnO lattice parameters were slightly affected by R doping and the doped sample crystallinity is enhanced. Our results show that introducing Cr, Mn and Fe along with Mg into ZnO induces a clear magnetic moment without any apparent distortion in the structural morphology. The spatial configuration of dopant atoms is determined from first-principles calculations, giving a better understanding of the position of the dopant atom responsible for the magnetism. The magnetic moments obtained from our calculations are 3.67, 5.0, and 4.33 mu B per dopant atom for Cr, Mn, and Fe, respectively, which agree with the experimental values. While Cr and Fe tend to form clusters, Mn has more propensity to remain evenly distributed within the system, avoiding cluster-derived magnetism.

  • 3.
    Abdeldaim, Aly H.
    et al.
    Chalmers Univ Technol, Dept Chem & Chem Engn, Energy & Mat, SE-41296 Gothenburg, Sweden;Univ Liverpool, Dept Chem, 51 Oxford St, Oxford L7 3NY, Merseyside, England;Univ Liverpool, Mat Innovat Factory, 51 Oxford St, Oxford L7 3NY, Merseyside, England;Sci & Technol Facil Council, ISIS Neutron & Muon Source, Didcot OX11 0QX, Oxon, England.
    Badrtdinov, Danis, I
    Ural Fed Univ, Theoret Phys & Appl Math Dept, Ekaterinburg 620002, Russia.
    Gibbs, Alexandra S.
    Sci & Technol Facil Council, ISIS Neutron & Muon Source, Didcot OX11 0QX, Oxon, England.
    Manuel, Pascal
    Sci & Technol Facil Council, ISIS Neutron & Muon Source, Didcot OX11 0QX, Oxon, England.
    Walker, Helen C.
    Sci & Technol Facil Council, ISIS Neutron & Muon Source, Didcot OX11 0QX, Oxon, England.
    Le, Manh Duc
    Wu, Chien Hung
    Sci & Technol Facil Council, ISIS Neutron & Muon Source, Didcot OX11 0QX, Oxon, England.
    Wardecki, Dariusz
    Chalmers Univ Technol, Dept Chem & Chem Engn, Energy & Mat, SE-41296 Gothenburg, Sweden.
    Eriksson, Sten-Gunnar
    Chalmers Univ Technol, Dept Chem & Chem Engn, Energy & Mat, SE-41296 Gothenburg, Sweden.
    Kvashnin, Yaroslav
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Tsirlin, Alexander A.
    Ural Fed Univ, Theoret Phys & Appl Math Dept, Ekaterinburg 620002, Russia;Univ Augsburg, Inst Phys, Ctr Elect Correlat & Magnetism, Expt Phys 6, D-86135 Augsburg, Germany.
    Nilsen, Göran J.
    Sci & Technol Facil Council, ISIS Neutron & Muon Source, Didcot OX11 0QX, Oxon, England.
    Large easy-axis anisotropy in the one-dimensional magnet BaMo(PO4)(2)2019In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 100, no 21, article id 214427Article in journal (Refereed)
    Abstract [en]

    We present an extensive experimental and theoretical study on the low-temperature magnetic properties of the monoclinic anhydrous alum compound BaMo(PO4)(2). The magnetic susceptibility reveals strong antiferromagnetic interactions theta(CW) = -167 K and long-range magnetic order at T-N = 22 K, in agreement with a recent report. Powder neutron diffraction furthermore shows that the order is collinear, with the moments near the ac plane. Neutron spectroscopy reveals a large excitation gap Delta = 15 meV in the low-temperature ordered phase, suggesting a much larger easy-axis spin anisotropy than anticipated. However, the large anisotropy justifies the relatively high ordered moment, Neel temperature, and collinear order observed experimentally and is furthermore reproduced in a first-principles calculations by using a new computational scheme. We therefore propose BaMo(PO4)(2) to host S = 1 antiferromagnetic chains with large easy-axis anisotropy, which has been theoretically predicted to realize novel excitation continua.

  • 4.
    Abdel-Hafiez, Mahmoud
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics. Ctr High Pressure Sci & Technol Adv Res, Shanghai 201203, Peoples R China;Harvard Univ, Lyman Lab Phys, Cambridge, MA 02138 USA;Natl Univ Sci & Technol MISiS, Moscow 119049, Russia.
    Thiyagarajan, R.
    Ctr High Pressure Sci & Technol Adv Res, Shanghai 201203, Peoples R China.
    Majumdar, Arnab
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Luo, Wei
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Vasiliev, A. N.
    Natl Univ Sci & Technol MISiS, Moscow 119049, Russia;Natl Res South Ural State Univ, Chelyabinsk 454080, Russia;Moscow MV Lomonosov State Univ, Moscow 119991, Russia.
    Maarouf, A. A.
    Imam Abdulrahman Bin Faisal Univ, Inst Res & Med Consultat, Dept Phys, Dammam 31441, Saudi Arabia.
    Zybtsev, S. G.
    RAS, Inst Radioengn & Elect, Moscow 125009, Russia.
    Pokrovskii, V. Ya
    RAS, Inst Radioengn & Elect, Moscow 125009, Russia.
    V-Zaitsev-Zotov, S.
    RAS, Inst Radioengn & Elect, Moscow 125009, Russia.
    Pavlovskiy, V. V.
    RAS, Inst Radioengn & Elect, Moscow 125009, Russia.
    Pai, Woei Wu
    Natl Taiwan Univ, Ctr Condensed Matter Sci, Taipei 106, Taiwan;Natl Taiwan Univ, Dept Phys, Taipei 10610, Taiwan.
    Yang, W.
    Ctr High Pressure Sci & Technol Adv Res, Shanghai 201203, Peoples R China.
    Kulik, L. , V
    Pressure-induced reentrant transition in NbS3 phases: Combined Raman scattering and x-ray diffraction study2019In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 99, no 23, article id 235126Article in journal (Refereed)
    Abstract [en]

    We report the evolution of charge density wave states under pressure for two NbS3 phases: triclinic (phase I) and monoclinic (phase II) at room temperature. Raman and x-ray diffraction (XRD) techniques are applied. The x-ray studies on the monoclinic phase under pressure show a compression of the lattice at different rates below and above similar to 7 GPa but without a change in space group symmetry. The Raman spectra of the two phases evolve similarly with pressure; all peaks almost disappear in the similar to 6-8 GPa range, indicating a transition from an insulating to a metallic state, and peaks at new positions appear above 8 GPa. The results suggest suppression of the ambient charge-density waves and their subsequent recovery with new orderings above 8 GPa.

  • 5.
    Abdul-Hafidh, Esam H.
    et al.
    Taibah Univ Yanbu, Phys Dept, Fac Sci, King Khalid Rd, Al Amoedi 51000, Yanbu El Bahr, Saudi Arabia..
    Abdel-Hafiez, Mahmoud
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Condensed Matter Physics of Energy Materials.
    Incompressibility of face-centered cubic structure in Metallic Nanosolids2021In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 96, no 12, article id 125717Article in journal (Refereed)
    Abstract [en]

    A simple and general theoretical model has been constructed to study the bulk modulus 'B' of FCC nanoparticles and nanostructures. In order to justify the experimental results of the anomalous behavior of B in nanosolids, this method considers the competing effect of both size and shape of a nanoparticle on B. In this work, the relationship between B and the surface energy has been derived based on the dangling bond energy model. The results show that B depends on size, shape and structure of FCC nanocrystalline solids (nanosolids). Our results show that as the shape changes from spherical to deformed, nanosolids become incompressible and B increases as the size decreases. The obtained theoretical results were compared with the experimental predictions for silver, gold and nickel. A very good agreement between theoretical results and experiments was found for silver and nickel. While in gold, we noticed a deviation from the experiment, which is attributed to extreme deformation of the nanogold.

  • 6.
    Aboulfadl, Hisham
    et al.
    Chalmers Univ Technol, Dept Phys, S-41296 Gothenburg, Sweden.
    Keller, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Larsen, Jes K
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Thuvander, Mattias
    Chalmers Univ Technol, Dept Phys, S-41296 Gothenburg, Sweden.
    Riekehr, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Edoff, Marika
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Platzer Björkman, Charlotte
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Microstructural Characterization of Sulfurization Effects in Cu(In,Ga)Se-2 Thin Film Solar Cells2019In: Microscopy and Microanalysis, ISSN 1431-9276, E-ISSN 1435-8115, Vol. 25, no 2, p. 532-538Article in journal (Refereed)
    Abstract [en]

    Surface sulfurization of Cu(In,Ga)Se-2 (CIGSe) absorbers is a commonly applied technique to improve the conversion efficiency of the corresponding solar cells, via increasing the bandgap towards the heterojunction. However, the resulting device performance is understood to be highly dependent on the thermodynamic stability of the chalcogenide structure at the upper region of the absorber. The present investigation provides a high-resolution chemical analysis, using energy dispersive X-ray spectrometry and laser-pulsed atom probe tomography, to determine the sulfur incorporation and chemical re-distribution in the absorber material. The post-sulfurization treatment was performed by exposing the CIGSe surface to elemental sulfur vapor for 20 min at 500 degrees C. Two distinct sulfur-rich phases were found at the surface of the absorber exhibiting a layered structure showing In-rich and Ga-rich zones, respectively. Furthermore, sulfur atoms were found to segregate at the absorber grain boundaries showing concentrations up to similar to 7 at% with traces of diffusion outwards into the grain interior.

  • 7.
    Abou-Ras, Daniel
    et al.
    Helmholtz Zentrum Berlin Mat & Energie GmbH, Hahn Meitner Pl 1, D-14109 Berlin, Germany..
    Wagner, Sigurd
    Princeton Univ, Dept Elect Engn, Princeton, NJ 08544 USA..
    Stanbery, Bill J.
    Siva Power, 5102 Calle Sol, Santa Clara, CA 95054 USA..
    Schock, Hans-Werner
    Helmholtz Zentrum Berlin Mat & Energie GmbH, Hahn Meitner Pl 1, D-14109 Berlin, Germany..
    Scheer, Roland
    Martin Luther Univ Halle Wittenberg, Inst Phys, Photovolta Grp, D-06120 Halle, Saale, Germany..
    Stolt, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics. Solibro Res AB, Sweden.
    Siebentritt, Susanne
    Univ Luxembourg, Phys & Mat Sci Res Unit, Lab Photovolta, Belvaux, Luxembourg..
    Lincot, Daniel
    CNRS EDF Chim Paristech PSL, Inst Photovolta Ile France IPVF, IRDEP, 6 Quai Watier, F-78401 Chatou, France..
    Eberspacher, Chris
    Solopower Syst Inc, Corp & Mfg Headquarters, 6308 North Marine Dr, Portland, OR 97203 USA..
    Kushiya, Katsumi
    Solar Frontier KK, 123-1 Shimo Kawairi, Atsugi, Kanagawa, Japan..
    Tiwari, Ayodhya N.
    Empa Swiss Fed Labs Mat Sci & Technol, Lab Thin Films & Photovolta, Ueberlandstr 129, CH-8600 Dubendorf, Switzerland..
    Innovation highway: Breakthrough milestones and key developments in chalcopyrite photovoltaics from a retrospective viewpoint2017In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 633, p. 2-12Article in journal (Refereed)
    Abstract [en]

    The present contribution is a summary of an event that was organized as a special evening session in Symposium V "Chalcogenide Thin-Film Solar Cells" at the E-MRS 2016 Spring Meeting, Lille, France. The presentations in this session were given by the coauthors of this paper. These authors present retrospectives of key developments in the field of Cu(In,Ga)(S,Se)(2) solar cells as they themselves had witnessed in their laboratories or companies. Also, anecdotes are brought up, which captured interesting circumstances in that evolutionary phase of the field. Because the focus was on historical perspectives rather than a comprehensive review of the field, recent developments intentionally were not addressed.

  • 8.
    Adalsteinsson, Sigurbjörn Már
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Moro, Marcos V.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics.
    Moldarev, Dmitrii
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics. Moscow Engn Phys Inst, Dept Mat Sci, Moscow 115409S, Russia..
    Droulias, Sotiris
    Uppsala University, Disciplinary Domain of Science and Technology, För teknisk-naturvetenskapliga fakulteten gemensamma enheter, Tandem Laboratory.
    Wolff, Max
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics. Moscow Engn Phys Inst, Dept Mat Sci, Moscow 115409S, Russia..
    Primetzhofer, Daniel
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics. Sweden.;Uppsala Univ, Tandem Lab, Box 529, S-75120 Uppsala, Sweden..
    Correlating chemical composition and optical properties of photochromic rare-earth oxyhydrides using ion beam analysis2020In: Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, ISSN 0168-583X, E-ISSN 1872-9584, Vol. 485, p. 36-40Article in journal (Refereed)
    Abstract [en]

    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.

  • 9. Adeyev, V.M.
    et al.
    Vasylyev, M.O.
    Pogorelov, Ye.
    Features of auger-investigations of ultrathin periodic metallic film structures2006In: Metallofizika i novejsie tehnologii, ISSN 1024-1809, Vol. 28, no 2, p. 193-200Article in journal (Refereed)
    Abstract [en]

    In the presented work the applicability of Auger Electron Spectroscopy for studying layered metal film structures Fe/(Au, Cu)/Tb on Si substrate with thickness of layers up to 30 Å was shown. It was ascertained that Fe layer is interacting with Si substrate and as a result Fe-silicide is formed. The thickness of buffer layers aimed to protect Fe layer appeared to be insufficient for complete suppression of silicide formation

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  • 10.
    Adiba, Adiba
    et al.
    Aligarh Muslim Univ, Dept Phys, Aligarh 202002, India..
    Pandey, Vidit
    Aligarh Muslim Univ, Dept Phys, Aligarh 202002, India..
    Ahmad, Tufail
    Aligarh Muslim Univ, Dept Phys, Aligarh 202002, India..
    Nehla, Priyanka
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering.
    Munjal, Sandeep
    Natl Forens Sci Univ, Ponda 403401, Goa, India.;Univ Delhi, Dept Phys & Astrophys, New Delhi 110007, India..
    Multilevel resistive switching with negative differential resistance in Al/ NiO/ZnFe2O4/ITO ReRAM device2023In: Physica. B, Condensed matter, ISSN 0921-4526, E-ISSN 1873-2135, Vol. 654, article id 414742Article in journal (Refereed)
    Abstract [en]

    The Resistive Random Access Memory devices have emerged as an energy-efficient alternative to Von Neumann computers by enabling in-memory computing. Here we demonstrate bipolar resistive switching in thin films of Nickel oxide (NiO) and Zinc Ferrite (ZFO) using a simple Al/NiO/ZFO/ITO configuration, making them a possible candidate for the next generation memory devices. The fabricated device demonstrated excellent resistive switching behavior with high endurance for up to 1000 cycles, good retention for more than 10(4) s, and a good resistance ratio of HRS to LRS similar to 10(2). Ohmic conduction was observed in the LRS, while in the HRS, along with ohmic conduction, space charge limited current (SCLC) and Schottky mechanisms were observed. Besides the LRS and HRS, a number of stable intermediate resistance states can also be obtained during the RESET process using different stop voltages, which makes the current device a multilevel resistive switching device.

  • 11.
    Adlmann, Franz Alois
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Opportunities and challenges of surface scattering at next generation neutron sources2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Complex fluids and soft matter are ubiquitously found in the world and all contacts in life are made over surfaces. To describe the mechanical behavior of such substances, rheological methods are used. Flow instabilities are a big challenge in rheology since they will be reflected in the macroscopic variables probed, like e. g. the viscosity. Many such discontinuities may actually originate at the surface. Investigating the properties of liquids in contact with the surface under mechanical load is the main course of the thesis. Neutron reflectometry and GISANS are perfect tools in this context to access the solid liquid interfaces, since they can penetrate many engineering materials and show a comparably large scattering potential at deuterated samples. In this thesis shear was applied on a model solution and neutron scattering techniques were used to investigate the structure under load. The focus was set on the development of the measurement methods themselves to enable new scientific insights in the future. First, by stroboscopic measurements the flux limitations are overcome for oscillatory rheology. By reintegration in the post processing it is shown that kinetic measurements with neutrons are possible with a time resolution below one millisecond. Second, the transformation of grazing incidence data from the laboratory system into q-space is strongly non-linear resulting in a need for re-binning. In this thesis a universal tool has been developed for this purpose. Finally, there is an ongoing discussion on depth sensitive neutron scattering experiments from solid-liquid boundaries. By using emission densities we show that such experiments face severe limitations due to the low absorption cross section of the neutron.

    List of papers
    1. Depth-resolved grazing-incidence time-of-flight neutron scattering from a solid-liquid interface
    Open this publication in new window or tab >>Depth-resolved grazing-incidence time-of-flight neutron scattering from a solid-liquid interface
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    2014 (English)In: Journal of applied crystallography, ISSN 0021-8898, E-ISSN 1600-5767, Vol. 47, p. 130-135Article in journal (Refereed) Published
    Abstract [en]

    Small-angle scattering in grazing-incidence beam geometry has been applied on a time-of-flight neutron instrument to investigate a solid-liquid boundary. Owing to the broad wavelength distribution provided for a specific incident beam angle, the penetration depth of the neutron beam is varied over a wide range in a single measurement. The near surface structures of block copolymer micelles close to silicon substrates with distinct surface energies are resolved. It is observed that the very near surface structure strongly depends on the surface coating, whereas further away from the surface, bulk-like ordering is found.

    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:uu:diva-219976 (URN)10.1107/S1600576713028665 (DOI)000330485100018 ()
    Available from: 2014-03-12 Created: 2014-03-09 Last updated: 2018-04-11Bibliographically approved
    2. Polymer Brush Collapse under Shear Flow
    Open this publication in new window or tab >>Polymer Brush Collapse under Shear Flow
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    2017 (English)In: Macromolecules, ISSN 0024-9297, E-ISSN 1520-5835, Vol. 50, no 3, p. 1215-1224Article in journal (Refereed) Published
    Abstract [en]

    Shear responsive surfaces offer potential advances in a number of applications. Surface functionalization using polymer brushes is one route to such properties, particularly in the case of entangled polymers. We report on neutron reflectometry measurements of polymer brushes in entangled polymer solutions performed under controlled shear as well as coarse-grained computer simulations corresponding to these interfaces. Here we show a reversible and reproducible collapse of the brushes, increasing with the shear rate. Using two brushes of greatly different chain lengths and grafting densities, we demonstrate that the dynamics responsible for the structural change of the brush are governed by the free chains in solution rather than the brush itself, within the range of parameters examined. The phenomenon of the brush collapse could find applications in the tailoring of nanosensors and as a way to dynamically control surface friction and adhesion.

    Place, publisher, year, edition, pages
    American Chemical Society (ACS), 2017
    National Category
    Materials Engineering
    Identifiers
    urn:nbn:se:uu:diva-320464 (URN)10.1021/acs.macromol.6b02525 (DOI)000394410200053 ()
    Available from: 2017-04-26 Created: 2017-04-26 Last updated: 2018-04-11Bibliographically approved
    3. Probing the dynamics of high-viscosity entangled polymers under shear using Neutron Spin Echo spectroscopy
    Open this publication in new window or tab >>Probing the dynamics of high-viscosity entangled polymers under shear using Neutron Spin Echo spectroscopy
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    2016 (English)In: VI European Conference On Neutron Scattering (ECNS2015), 2016, article id UNSP 012014Conference paper, Published paper (Refereed)
    Abstract [en]

    Neutron Spin Echo spectroscopy provides unique insight into molecular and submolecular dynamics as well as intra-and inter-molecular interactions in soft matter. These dynamics may change drastically under shear flow. In particular in polymer physics a stress plateau is observed, which might be explained by an entanglement-disentanglement transition. However, such a transition is difficult to identify directly by experiments. Neutron Spin Echo has been proven to provide information about entanglement length and degree by probing the local dynamics of the polymer chains. Combining shear experiments and neutron spin echo is challenging since, first the beam polarisation has to be preserved during scattering and second, Doppler scattered neutrons may cause inelastic scattering. In this paper we present a new shear device adapted for these needs. We demonstrate that a high beam polarisation can be preserved and present first data on an entangled polymer solution under shear. To complement the experiments on the dynamics we present novel SANS data revealing shear-induced conformational changes in highly entangled polymers.

    Series
    Journal of Physics Conference Series, ISSN 1742-6588 ; 746
    National Category
    Accelerator Physics and Instrumentation
    Identifiers
    urn:nbn:se:uu:diva-346197 (URN)10.1088/1742-6596/746/1/012014 (DOI)000409470900014 ()
    Conference
    6th European Conference on Neutron Scattering (ECNS), AUG 30-SEP 04, 2015, Univ Zaragoza, CSIC, Mat Sci Inst Aragon, Zaragoza, SPAIN
    Available from: 2018-03-15 Created: 2018-03-15 Last updated: 2019-02-19Bibliographically approved
    4. Depth resolved grazing incidence neutron scattering experiments from semi-infinite interfaces: a statistical analysis of the scattering contributions
    Open this publication in new window or tab >>Depth resolved grazing incidence neutron scattering experiments from semi-infinite interfaces: a statistical analysis of the scattering contributions
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    2018 (English)In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 30, article id 165901Article in journal, Letter (Refereed) Published
    Abstract [en]

    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.

    Place, publisher, year, edition, pages
    Institute of Physics Publishing (IOPP), 2018
    Keywords
    GISANS, neutrons, interfaces, depth profiling, resolution
    National Category
    Condensed Matter Physics
    Research subject
    Physics with spec. in Atomic, Molecular and Condensed Matter Physics
    Identifiers
    urn:nbn:se:uu:diva-348219 (URN)10.1088/1361-648X/aab573 (DOI)000428466400001 ()29521272 (PubMedID)
    Funder
    Swedish Research Council, 2016-04645The Swedish Foundation for International Cooperation in Research and Higher Education (STINT), IG-2011-2067
    Available from: 2018-04-11 Created: 2018-04-11 Last updated: 2018-06-20Bibliographically approved
    5. Normalization of stroboscopic neutron scattering experiments
    Open this publication in new window or tab >>Normalization of stroboscopic neutron scattering experiments
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    2018 (English)In: Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, ISSN 0168-583X, E-ISSN 1872-9584, Vol. 434, p. 61-65Article in journal (Refereed) Published
    Abstract [en]

    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.

    National Category
    Condensed Matter Physics
    Research subject
    Physics with spec. in Atomic, Molecular and Condensed Matter Physics
    Identifiers
    urn:nbn:se:uu:diva-348265 (URN)10.1016/j.nimb.2018.08.030 (DOI)000447577000011 ()
    Funder
    Swedish Research Council, C0511501
    Available from: 2018-04-11 Created: 2018-04-11 Last updated: 2018-12-19Bibliographically approved
    6. Överlåtaren: a fast way to transfer and orthogonalize two-dimensional off-specular reflectivity data
    Open this publication in new window or tab >>Överlåtaren: a fast way to transfer and orthogonalize two-dimensional off-specular reflectivity data
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    2016 (English)In: Journal of applied crystallography, ISSN 0021-8898, E-ISSN 1600-5767, Vol. 49, p. 2091-2099Article in journal (Refereed) Published
    Abstract [en]

    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.

    Keywords
    off-specular scattering, neutron reflectometry, interfaces, surfaces
    National Category
    Atom and Molecular Physics and Optics Other Physics Topics Computational Mathematics
    Identifiers
    urn:nbn:se:uu:diva-315086 (URN)10.1107/S1600576716014382 (DOI)000391195900025 ()
    Funder
    Swedish Research Council, C0511501The Swedish Foundation for International Cooperation in Research and Higher Education (STINT), IG-2011-2067
    Available from: 2017-02-09 Created: 2017-02-09 Last updated: 2018-04-11Bibliographically approved
    7. Towards neutron scattering experiments with sub-millisecond time resolution
    Open this publication in new window or tab >>Towards neutron scattering experiments with sub-millisecond time resolution
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    2015 (English)In: Journal of applied crystallography, ISSN 0021-8898, E-ISSN 1600-5767, Vol. 48, p. 220-226Article in journal (Refereed) Published
    Abstract [en]

    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.

    Keywords
    neutron scattering, in situ rheology, block copolymers, time-resolved studies, surface kinetics, large amplitude oscillatory shear (LAOS), time-of-flight reflectometry
    National Category
    Other Physics Topics
    Identifiers
    urn:nbn:se:uu:diva-246826 (URN)10.1107/S1600576714027848 (DOI)000349210700028 ()
    Available from: 2015-03-10 Created: 2015-03-10 Last updated: 2018-04-11Bibliographically approved
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  • 12.
    Adlmann, Franz
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Busch, S.
    Vacaliuc, B.
    Nelson, A.
    Ankner, J.F.
    Browning, J.F.
    Parizzi, A.
    Bilheux, J. -K.
    Halbert, C.E.
    Korolkovas, Airidas
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Wolff, Max
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Normalization of stroboscopic neutron scattering experiments2018In: Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, ISSN 0168-583X, E-ISSN 1872-9584, Vol. 434, p. 61-65Article in journal (Refereed)
    Abstract [en]

    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.

  • 13.
    Adlmann, Franz
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Herbel, Jörg
    ETH Zürich, Zürich, Switzerland.
    Korolkovas, Airidas
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Bliersbach, Andreas
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Toperverg, Boris
    Petersburg Nuclear Physics Institute, Gatchina, Russia.
    Van Herck, Walter
    Forschungszentrum Jülich GmbH, Garching, Germany.
    Pálsson, Gunnar K.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Kitchen, Brian
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Wolff, Max
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Depth resolved grazing incidence neutron scattering experiments from semi-infinite interfaces: a statistical analysis of the scattering contributions2018In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 30, article id 165901Article in journal (Refereed)
    Abstract [en]

    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.

  • 14.
    Adranno, Brando
    et al.
    Stockholm Univ, Dept Mat & Environm Chem, Svante Arrhenius vag 16C, S-10691 Stockholm, Sweden..
    Renier, Olivier
    Stockholm Univ, Dept Mat & Environm Chem, Svante Arrhenius vag 16C, S-10691 Stockholm, Sweden..
    Bousrez, Guillaume
    Stockholm Univ, Dept Mat & Environm Chem, Svante Arrhenius vag 16C, S-10691 Stockholm, Sweden.;Linköping Univ, Dept Sci & Technol, Lab Organ Elect, S-60174 Norrköping, Sweden..
    Paterlini, Veronica
    Stockholm Univ, Dept Mat & Environm Chem, Svante Arrhenius vag 16C, S-10691 Stockholm, Sweden..
    Baryshnikov, Glib V.
    Smetana, Volodymyr
    Stockholm Univ, Dept Mat & Environm Chem, Svante Arrhenius vag 16C, S-10691 Stockholm, Sweden..
    Tang, Shi
    Umeå Univ, Organ Photon & Elect Grp, S-90187 Umeå, Sweden..
    Ågren, Hans
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Chemical and Bio-Molecular Physics.
    Metlen, Andreas
    Queens Univ Belfast, QUILL Res Ctr, Sch Chem & Chem Engn, Belfast BT95AG, North Ireland..
    Edman, Ludvig
    Umeå Univ, Organ Photon & Elect Grp, S-90187 Umeå, Sweden..
    Anja-Verena, Mudring
    Stockholm Univ, Dept Mat & Environm Chem, Svante Arrhenius vag 16C, S-10691 Stockholm, Sweden.;Aarhus Univ, Dept Biol & Chem Engn & iNANO, Intelligent Adv Mat iAM, DK-8000 Aarhus, Denmark..
    Rogers, Robin D.
    Stockholm Univ, Dept Mat & Environm Chem, Svante Arrhenius vag 16C, S-10691 Stockholm, Sweden.;Queens Univ Belfast, QUILL Res Ctr, Sch Chem & Chem Engn, Belfast BT95AG, North Ireland.;Univ Alabama, Dept Chem & Biochem, Tuscaloosa, AL 35487 USA..
    The 8-Hydroxyquinolinium Cation as a Lead Structure for Efficient Color-Tunable Ionic Small Molecule Emitting Materials2023In: ADVANCED PHOTONICS RESEARCH, ISSN 2699-9293, Vol. 4, no 3, article id 2200279Article in journal (Refereed)
    Abstract [en]

    Albeit tris(8-hydroxyquinolinato) aluminum (Alq(3)) and its derivatives are prominent emitter materials for organic lighting devices, and the optical transitions occur among ligand-centered states, the use of metal-free 8-hydroxyquinoline is impractical as it suffers from strong nonradiative quenching, mainly through fast proton transfer. Herein, it is shown that the problem of rapid proton exchange and vibration quenching of light emission can be overcome not only by complexation, but also by organization of the 8-hydroxyquinolinium cations into a solid rigid network with appropriate counter-anions (here bis(trifluoromethanesulfonyl)imide). The resulting structure is stiffened by secondary bonding interactions such as pi-stacking and hydrogen bonds, which efficiently block rapid proton transfer quenching and reduce vibrational deactivation. Additionally, the optical properties are tuned through methyl substitution from deep blue (455 nm) to blue-green (488 nm). Time-dependent density functional theory (TDFT) calculations reveal the emission to occur from which an unexpectedly long-lived S-1 level, unusual for organic fluorophores. All compounds show comparable, even superior photoluminescence compared to Alq(3) and related materials, both as solids and thin films with quantum yields (QYs) up to 40-50%. In addition, all compounds show appreciable thermal stability with decomposition temperatures above 310 degrees C.

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  • 15.
    Ageev, Dmitry S.
    et al.
    Russian Acad Sci, Steklov Math Inst, Gubkin St 8, Moscow 119991, Russia.
    Bagrov, Andrey A.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Ural Fed Univ, Theoret Phys & Appl Math Dept, Mira Str 19, Ekaterinburg 620002, Russia.
    Iliasov, Askar A.
    Radboud Univ Nijmegen, Inst Mol & Mat, Heyendaalseweg 135, NL-6525 AJ Nijmegen, Netherlands; Russian Acad Sci, Space Res Inst, Moscow 117997, Russia.
    Deterministic chaos and fractal entropy scaling in Floquet conformal field theories2021In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 103, no 10, article id L100302Article in journal (Refereed)
    Abstract [en]

    In this Letter, we study two-dimensional Floquet conformal field theory, where the external periodic driving is described by iterated logistic or tent maps. These maps are known to be typical examples of dynamical systems exhibiting the order-chaos transition, and we show that, as a result of such driving, the entanglement entropy scaling develops fractal features when the corresponding dynamical system approaches the chaotic regime. For the driving set by the logistic map, the fractal contribution to the scaling dominates, making entanglement entropy a highly oscillating function of the subsystem size.

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  • 16.
    Agosta, Lorenzo
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Arismendi-Arrieta, Daniel
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Dzugutov, Mikhail
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Hermansson, Kersti
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Origin of the Hydrophobic Behaviour of Hydrophilic CeO22023In: Angewandte Chemie International Edition, ISSN 1433-7851, E-ISSN 1521-3773, Vol. 62, no 35, article id e202303910Article in journal (Refereed)
    Abstract [en]

    The nature of the hydrophobicity found in rare-earth oxides is intriguing. The CeO2 (100) surface, despite its strongly hydrophilic nature, exhibits hydrophobic behaviour when immersed in water. In order to understand this puzzling and counter-intuitive effect we performed a detailed analysis of the water structure and dynamics. We report here an ab-initio molecular dynamics simulation (AIMD) study which demonstrates that the first water layer, in immediate contact with the hydroxylated CeO2 surface, is responsible for the effect behaving as a hydrophobic interface with respect to the rest of the liquid water. The hydrophobicity is manifested in several ways: a considerable diffusion enhancement of the confined liquid water as compared with bulk water at the same thermodynamic condition, a weak adhesion energy and few H-bonds above the hydrophobic water layer, which may also sustain a water droplet. These findings introduce a new concept in water/rare-earth oxide interfaces: hydrophobicity mediated by specific water patterns on a hydrophilic surface.

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  • 17.
    Ahlberg, Martina
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Critical Phenomena and Exchange Coupling in Magnetic Heterostructures2012Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The continuous phase transition in thin magnetic films and superlattices has been studied using the magneto-optical Kerr effect (MOKE) and polarized neutron scattering (PNR).  It has been shown that the critical behavior of amorphous thin films belonging to the 2D XY universality class can be described within the same theory as crystalline sample. This means that quenched disorder only serves as a marginal perturbation in systems with this symmetry.

    The connection between interlayer exchange coupling and the observed critical behavior in Fe/V superlattices was explored. The results prove that the origin of unusually high values of the exponent β can be traced to a position dependence of the magnetization at elevated temperatures. The magnetization of the outermost layers within the superlattice shows a more pronounced decrease at lower temperatures, compared to the inner layers, which in turn have a more abrupt decrease in the vicinity of the critical temperature. This translates to a high exponent, especially when the layers are probed by a technique where more weight is given to the layers close to the surface, e.g.MOKE.  The interlayer exchange coupling as a function of spacer thickness and temperature was also studied in its own right. The data was compared to the literature, and a dependence on the thickness of the magnetic layers was concluded.

    The phase transition in amorphous FeZr/CoZr multilayers, where the magnetization emanates from ferromagnetic proximity effects, was investigated. Even though the determined exponents of the zero-field magnetization, the susceptibility and the critical isotherm did not correspond to any universality class, scaling plots displayed an excellent data collapse.

    Samples consisting of Fe δ-layers (0.3-1.4 monolayers) embedded in Pd were studied using element-specific resonant x-ray magnetic scattering. The magnetization of the two constituents showed distinctly different temperature dependences.

    List of papers
    1. Influence of boundaries on magnetic ordering in Fe/V superlattices
    Open this publication in new window or tab >>Influence of boundaries on magnetic ordering in Fe/V superlattices
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    2010 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 81, no 21, p. 214429-Article in journal (Refereed) Published
    Abstract [en]

    We study the role of surface boundaries on the magnetic properties of [Fe/V](n) superlattice structures, with n=2-10. Using the magneto-optical Kerr effect and polarized neutron reflectivity measurements, we examine the evolution of both the total and the layer-resolved magnetizations as a function of temperature. By varying n, we observe a large shift in the transition temperatures T-c and a substantial change in the total magnetization critical exponent beta. In particular, the thicker samples exhibit nonuniversal exponent values. By resolving the magnetization as a function of position within the superlattice, we show that this behavior arises from contributions of the surfaces. Furthermore, we attribute the large shift in T-c to long-ranged interactions present in the superlattice.

    National Category
    Physical Sciences
    Identifiers
    urn:nbn:se:uu:diva-136258 (URN)10.1103/PhysRevB.81.214429 (DOI)000278936900004 ()
    Available from: 2010-12-11 Created: 2010-12-11 Last updated: 2022-01-28Bibliographically approved
    2. Two-dimensional XY-like amorphous Co68Fe24Zr8/Al70Zr30 multilayers
    Open this publication in new window or tab >>Two-dimensional XY-like amorphous Co68Fe24Zr8/Al70Zr30 multilayers
    2011 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 83, no 22, p. 224404-Article in journal (Refereed) Published
    Abstract [en]

    We present an experimental realization of a magnetic two-dimensional XY system using amorphous materials. The classification of the dimensionality is based on the critical behavior of amorphous Co68Fe24Zr8(d)/Al70O30 (20 angstrom) multilayers, where d = 11 - 16 angstrom. Analysis of the remanent magnetization, the magnetic isotherms, the initial susceptibility, and the magnetic correlation length shows that the magnetic phase transition can be described by the 2D XY model. The samples are not paramagnetic above the critical temperature but are characterized by local magnetic order manifested in the field and temperature dependence of the magnetization. Furthermore, an average spin-spin interaction length of 8.1 angstrom was estimated using the thickness dependence of the Curie temperature.

    National Category
    Condensed Matter Physics
    Identifiers
    urn:nbn:se:uu:diva-155916 (URN)10.1103/PhysRevB.83.224404 (DOI)000291727600006 ()
    Available from: 2011-07-05 Created: 2011-07-04 Last updated: 2017-12-11Bibliographically approved
    3. Experimental realization of amorphous two-dimensional XY magnets
    Open this publication in new window or tab >>Experimental realization of amorphous two-dimensional XY magnets
    2011 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 84, no 2, p. 024430-Article in journal (Refereed) Published
    Abstract [en]

    The temperature dependence of the magnetization of thin amorphous Fe(89)Zr(11)/Al(78)Zr(22) layerswas investigated. Dimensionality analysis of the ferromagnetic transition of 15 A thick layers yielded critical exponents characteristic of the 2D XY (planar rotor) model. Above the ordering temperature significant polarizability with an applied field is observed, due to the existence of large-scale magnetic correlations, of which the extent and origin have been determined.

    National Category
    Physical Sciences
    Identifiers
    urn:nbn:se:uu:diva-156953 (URN)10.1103/PhysRevB.84.024430 (DOI)000292873700002 ()
    Available from: 2011-08-20 Created: 2011-08-11 Last updated: 2017-12-08Bibliographically approved
    4. Temperature dependence of magnetic properties in weakly exchange coupled Fe/V superlattices
    Open this publication in new window or tab >>Temperature dependence of magnetic properties in weakly exchange coupled Fe/V superlattices
    2013 (English)In: Journal of Magnetism and Magnetic Materials, ISSN 0304-8853, E-ISSN 1873-4766, Vol. 341, p. 142-147Article in journal (Refereed) Published
    Abstract [en]

    We use Fe(3)/V(x)Fe(3)/V(x) superlattices, x = 16-27 monolayers (ML) to explore the interlayer exchange coupling (IEC) as a function of both spacer layer thickness and temperature. Fe/V is a common model system for studies addressing the IEC, but the behavior in the weakly exchange coupled regime, complemented with the temperature dependence of the magnetic properties, have remained unexplored. We observe clear regions with ferro- and antiferromagnetic coupling, which is manifested in oscillations in the saturation field, the remanence and the critical temperature. The oscillation in the interlayer coupling (J') has a period of 5.8(1) ML. This is approximate to 0.8 ML smaller than observed for Fe(7)/V(x) superlattices which illustrates the influence of the magnetic layer thickness on the interlayer coupling. The temperature dependence of the remanent magnetization was proven to be significantly affected by the strength of the ferromagnetic coupling, leading to high values of the effective critical exponent beta(eff).

    Keywords
    Magnetic superlattice, Magnetic phase transition, Exchange interaction
    National Category
    Condensed Matter Physics
    Identifiers
    urn:nbn:se:uu:diva-168308 (URN)10.1016/j.jmmm.2013.04.058 (DOI)000320583800026 ()
    Available from: 2012-02-16 Created: 2012-02-08 Last updated: 2022-01-28Bibliographically approved
    5. Effect of ferromagnetic proximity on critical behavior
    Open this publication in new window or tab >>Effect of ferromagnetic proximity on critical behavior
    2012 (English)In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 85, no 22, p. 224425-1-224425-6Article in journal (Refereed) Published
    Abstract [en]

    We have investigated the magnetic phase transition in amorphous Fe93Zr7(x angstrom)/Co95Zr5(1 angstrom) multilayers, where x = 25, 50, and 75. The extremely thin CoZr layer induces magnetic order at temperatures well above the inherent ordering temperature of Fe93Zr7. The changes in the critical exponent beta, associated with the temperature dependence of the magnetization, imply a crossover from two-to three-dimensional behavior as the FeZr thickness is reduced, consistent with a substantial magnetic induction in the FeZr layers. In addition we determined the exponents delta and gamma, of the critical isotherm and the susceptibility, respectively, and their values confirm the nonuniversal character of the phase transition. Scaling of the results yields an excellent data collapse and is found to hold in the crossover regime where the universality hypothesis is not applicable. 

    National Category
    Condensed Matter Physics
    Research subject
    Physics with spec. in Atomic, Molecular and Condensed Matter Physics
    Identifiers
    urn:nbn:se:uu:diva-168796 (URN)10.1103/PhysRevB.85.224425 (DOI)000305532200002 ()
    Funder
    Swedish Research CouncilKnut and Alice Wallenberg Foundation
    Available from: 2012-02-16 Created: 2012-02-15 Last updated: 2017-12-07Bibliographically approved
    6. Element specific magnetization in Fe/Pd quantum well structures
    Open this publication in new window or tab >>Element specific magnetization in Fe/Pd quantum well structures
    Show others...
    (English)Manuscript (preprint) (Other academic)
    National Category
    Condensed Matter Physics
    Identifiers
    urn:nbn:se:uu:diva-168443 (URN)
    Available from: 2012-02-16 Created: 2012-02-10 Last updated: 2012-08-01
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  • 18.
    Ahlberg, Martina
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Andersson, Gabriella
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Hjörvarsson, Björgvin
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Two-dimensional XY-like amorphous Co68Fe24Zr8/Al70Zr30 multilayers2011In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 83, no 22, p. 224404-Article in journal (Refereed)
    Abstract [en]

    We present an experimental realization of a magnetic two-dimensional XY system using amorphous materials. The classification of the dimensionality is based on the critical behavior of amorphous Co68Fe24Zr8(d)/Al70O30 (20 angstrom) multilayers, where d = 11 - 16 angstrom. Analysis of the remanent magnetization, the magnetic isotherms, the initial susceptibility, and the magnetic correlation length shows that the magnetic phase transition can be described by the 2D XY model. The samples are not paramagnetic above the critical temperature but are characterized by local magnetic order manifested in the field and temperature dependence of the magnetization. Furthermore, an average spin-spin interaction length of 8.1 angstrom was estimated using the thickness dependence of the Curie temperature.

    Download full text (pdf)
    fulltext
  • 19.
    Ahlberg, Martina
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Korelis, Panagiotis
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Andersson, Gabriella
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Hjörvarsson, Björgvin
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Effect of ferromagnetic proximity on critical behavior2012In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 85, no 22, p. 224425-1-224425-6Article in journal (Refereed)
    Abstract [en]

    We have investigated the magnetic phase transition in amorphous Fe93Zr7(x angstrom)/Co95Zr5(1 angstrom) multilayers, where x = 25, 50, and 75. The extremely thin CoZr layer induces magnetic order at temperatures well above the inherent ordering temperature of Fe93Zr7. The changes in the critical exponent beta, associated with the temperature dependence of the magnetization, imply a crossover from two-to three-dimensional behavior as the FeZr thickness is reduced, consistent with a substantial magnetic induction in the FeZr layers. In addition we determined the exponents delta and gamma, of the critical isotherm and the susceptibility, respectively, and their values confirm the nonuniversal character of the phase transition. Scaling of the results yields an excellent data collapse and is found to hold in the crossover regime where the universality hypothesis is not applicable. 

    Download full text (pdf)
    fulltext
  • 20.
    Ahlberg, Martina
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Papaioannou,, Evangelos Th
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Hjörvarsson, Björgvin
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Temperature dependence of magnetic properties in weakly exchange coupled Fe/V superlattices2013In: Journal of Magnetism and Magnetic Materials, ISSN 0304-8853, E-ISSN 1873-4766, Vol. 341, p. 142-147Article in journal (Refereed)
    Abstract [en]

    We use Fe(3)/V(x)Fe(3)/V(x) superlattices, x = 16-27 monolayers (ML) to explore the interlayer exchange coupling (IEC) as a function of both spacer layer thickness and temperature. Fe/V is a common model system for studies addressing the IEC, but the behavior in the weakly exchange coupled regime, complemented with the temperature dependence of the magnetic properties, have remained unexplored. We observe clear regions with ferro- and antiferromagnetic coupling, which is manifested in oscillations in the saturation field, the remanence and the critical temperature. The oscillation in the interlayer coupling (J') has a period of 5.8(1) ML. This is approximate to 0.8 ML smaller than observed for Fe(7)/V(x) superlattices which illustrates the influence of the magnetic layer thickness on the interlayer coupling. The temperature dependence of the remanent magnetization was proven to be significantly affected by the strength of the ferromagnetic coupling, leading to high values of the effective critical exponent beta(eff).

  • 21.
    Ahmad, Mariam
    et al.
    Univ Southern Denmark, Mads Clausen Inst, SDU Ctr Adv Photovolta & Thin Film Energy Devices, DK-6400 Sonderborg, Denmark.;Univ Southern Denmark, SDU Climate Cluster, DK-5230 Odense, Denmark..
    Cruguel, Herve
    Sorbonne Univ, Inst Nanosci Paris, CNRS, UMR 7588, F-75005 Paris, France..
    Ahmadpour, Mehrad
    Univ Southern Denmark, Mads Clausen Inst, SDU Ctr Adv Photovolta & Thin Film Energy Devices, DK-6400 Sonderborg, Denmark..
    Vannucchi, Noemi
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy. Sorbonne Univ, Inst Nanosci Paris, CNRS, UMR 7588, F-75005 Paris, France..
    Samie, Nahed Mohammad
    Sorbonne Univ, Inst Nanosci Paris, CNRS, UMR 7588, F-75005 Paris, France..
    Leuillet, Celine
    Sorbonne Univ, Inst Nanosci Paris, CNRS, UMR 7588, F-75005 Paris, France..
    Generalov, Alexander
    Lund Univ, MAX Lab 4, S-22100 Lund, Sweden..
    Li, Zheshen
    Aarhus Univ, Ctr Storage Ring Facil, Dept Phys & Astron, ISA, DK-8000 Aarhus C, Denmark..
    Madsen, Morten
    Univ Southern Denmark, Mads Clausen Inst, SDU Ctr Adv Photovolta & Thin Film Energy Devices, DK-6400 Sonderborg, Denmark.;Univ Southern Denmark, SDU Climate Cluster, DK-5230 Odense, Denmark..
    Witkowski, Nadine
    Sorbonne Univ, Inst Nanosci Paris, CNRS, UMR 7588, F-75005 Paris, France..
    Uncovering the Electronic State Interplay at Metal Oxide Electron Transport Layer/Nonfullerene Acceptor Interfaces in Stable Organic Photovoltaic Devices2023In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 15, no 47, p. 55065-55072Article in journal (Refereed)
    Abstract [en]

    The implementation of sputter-deposited TiOx as an electron transport layer in nonfullerene acceptor-based organic photovoltaics has been shown to significantly increase the long-term stability of devices compared to conventional solution-processed ZnO due to a decreased photocatalytic activity of the sputtered TiOx. In this work, we utilize synchrotron-based photoemission and absorption spectroscopies to investigate the interface between the electron transport layer, TiOx prepared by magnetron sputtering, and the nonfullerene acceptor, ITIC, prepared in situ by spray deposition to study the electronic state interplay and defect states at this interface. This is used to unveil the mechanisms behind the decreased photocatalytic activity of the sputter-deposited TiOx and thus also the increased stability of the organic solar cell devices. The results have been compared to similar measurements on anatase TiOx since anatase TiOx is known to have a strong photocatalytic activity. We show that the deposition of ITIC on top of the sputter-deposited TiOx results in an oxidation of Ti3+ species in the TiOx and leads to the emergence of a new O 1s peak that can be attributed to the oxygen in ITIC. In addition, increasing the thickness of ITIC on TiOx leads to a shift in the O 1s and C 1s core levels toward higher binding energies, which is consistent with electron transfer at the interface. Resonant photoemission at the Ti L-edge shows that oxygen vacancies in sputtered TiOx lie mostly in the surface region, which contrasts the anatase TiOx where an equal distribution between surface and subsurface oxygen vacancies is observed. Furthermore, it is shown that the subsurface oxygen vacancies in sputtered TiOx are strongly reduced after ITIC deposition, which can reduce the photocatalytic activity of the oxide, while the oxygen vacancies in model anatase TiOx are not affected upon ITIC deposition. This difference can explain the inferior photocatalytic activity of the sputter-deposited TiOx and thus also the increased stability of devices with sputter-deposited TiOx used as an electron transport layer.

  • 22.
    Ahmadi, Sareh
    et al.
    Materialfusik,KTH-Electrum.
    Shariati, Masumeh-Nina
    Yu, Shun
    Göthelid, Mats
    Charge transfer and chemical interaction of ZnPc and FePc with Au(111)Manuscript (preprint) (Other academic)
  • 23.
    Aijaz, Asim
    et al.
    Linkoping Univ, Dept Phys Chem & Biol, IFM Mat Phys, SE-58183 Linkoping, Sweden.;Uppsala Univ, Dept Engn Sci, Angstrom Lab, POB 534, SE-75121 Uppsala, Sweden..
    Louring, Sascha
    Aarhus Univ, Interdisciplinary Nanosci Ctr iNANO, Ny Munkegade 120, DK-8000 Aarhus C, Denmark.;Danish Technol Inst, Tribol Ctr, Teknol Pk,Kongsvang Alle 29, DK-8000 Aarhus C, Denmark..
    Lundin, Daniel
    Univ Paris Saclay, Univ Paris Sud, LPGP, CNRS,UMR 8578, F-91405 Orsay, France..
    Kubart, Tomas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Jensen, Jens
    Linkoping Univ, Dept Phys Chem & Biol, IFM Mat Phys, SE-58183 Linkoping, Sweden..
    Sarakinos, Kostas
    Linkoping Univ, Dept Phys Chem & Biol, IFM Mat Phys, SE-58183 Linkoping, Sweden..
    Helmersson, Ulf
    Linkoping Univ, Dept Phys Chem & Biol, IFM Mat Phys, SE-58183 Linkoping, Sweden..
    Synthesis of hydrogenated diamondlike carbon thin films using neon-acetylene based high power impulse magnetron sputtering discharges2016In: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films, ISSN 0734-2101, E-ISSN 1520-8559, Vol. 34, no 6, article id 061504Article in journal (Refereed)
    Abstract [en]

    Hydrogenated diamondlike carbon (DLC:H) thin films exhibit many interesting properties that can be tailored by controlling the composition and energy of the vapor fluxes used for their synthesis. This control can be facilitated by high electron density and/or high electron temperature plasmas that allow one to effectively tune the gas and surface chemistry during film growth, as well as the degree of ionization of the film forming species. The authors have recently demonstrated by adding Ne in an Ar-C high power impulse magnetron sputtering (HiPIMS) discharge that electron temperatures can be effectively increased to substantially ionize C species [Aijaz et al., Diamond Relat. Mater. 23, 1 (2012)]. The authors also developed an Ar-C2H2 HiPIMS process in which the high electron densities provided by the HiPIMS operation mode enhance gas phase dissociation reactions enabling control of the plasma and growth chemistry [Aijaz et al., Diamond Relat. Mater. 44, 117 (2014)]. Seeking to further enhance electron temperature and thereby promote electron impact induced interactions, control plasma chemical reaction pathways, and tune the resulting film properties, in this work, the authors synthesize DLC: H thin films by admixing Ne in a HiPIMS based Ar/C2H2 discharge. The authors investigate the plasma properties and discharge characteristics by measuring electron energy distributions as well as by studying discharge current characteristics showing an electron temperature enhancement in C2H2 based discharges and the role of ionic contribution to the film growth. These discharge conditions allow for the growth of thick (>1 mu m) DLC: H thin films exhibiting low compressive stresses (similar to 0.5 GPa), high hardness (similar to 25 GPa), low H content (similar to 11%), and density in the order of 2.2 g/cm(3). The authors also show that film densification and change of mechanical properties are related to H removal by ion bombardment rather than subplantation.

  • 24.
    Akansel, Serkan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Magnetization Dynamics in Ferromagnetic Thin Films: Evaluation of Different Contributions to Damping in Co2FeAl and FeCo Film Structures2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Static and dynamic magnetic properties of Co2FeAl and Fe65Co35 alloys have been investigated. Co2FeAl films were deposited at different temperatures and the deposition parameters were optimized with respect to structural and magnetic properties. As a result, a film with B2 crystalline phase was obtained without any post-annealing process. A lowest magnetic damping parameter of  was obtained for the film deposited at 573K. This obtained low value is comparable to the lowest values reported in research literature.  After optimizing the deposition parameters of this alloy, different seed layers and capping layers were added adjacent to the Co2FeAl layer and the effect of these layers on the magnetic relaxation was investigated. In addition to adding nonmagnetic layers to Co2FeAl, the dependence of the magnetic damping parameter with respect to the thickness of Co2FeAl was investigated by depositing films with different thicknesses. A temperature dependent study of the magnetic damping parameter was also performed and the measured damping parameters were compared with theoretically calculated intrinsic Gilbert damping parameters. Different extrinsic contributions to the magnetic damping, such as two magnon scattering, spin pumping, eddy-current damping and radiative damping, were identified and subtracted from the experimentally obtained damping parameter. Hence, it was possible to obtain the intrinsic damping parameter, that is called the Gilbert damping parameter.

    In the second part of the thesis, Fe65Co35 alloys were investigated in terms of static and dynamic magnetic properties. Fe65Co35 films were deposited without and with different seed layers in order to first understand the effect of the seed layer on static magnetic properties of the films, such as the coercivity of the films. Then the films with seed layers yielding the lowest coercivity were investigated in terms of dynamic magnetic properties. Fe65Co35 films with different rhenium dopant concentrations and with ruthenium as the seed and capping layer were also investigated. The purpose of this study was to increase the damping parameter of the films and an increase of about ~230% was obtained by adding the dopant to the structure. This study was performed at different temperatures and after subtraction of the extrinsic contributions to the damping, the experimental values were compared with theoretically calculated values of the Gilbert damping parameter. During the thesis work, magnetic looper and superconducting quantum interference device magnetometers set-ups were used for static magnetic measurements and cavity, broadband in-plane and broadband out-of-plane ferromagnetic resonance set-ups were used for dynamic measurements.

    List of papers
    1. Thickness dependent enhancement of damping in Co2FeAl/β-Ta thin films
    Open this publication in new window or tab >>Thickness dependent enhancement of damping in Co2FeAl/β-Ta thin films
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    2018 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 97, no 13, article id 134421Article in journal (Refereed) Published
    Abstract [en]

    In the present work Co2FeAl (CFA) thin films were deposited by ion beam sputtering on Si (100) substrates at the optimized deposition temperature of 300°C. A series of CFA films with different thickness (tCFA ); 8, 10, 12, 14, 16, 18 and 20 nm were prepared and all samples were capped with a 5 nm thick b-Ta layer. The thickness dependent static and dynamic properties of the films were studied by SQUID magnetometry, in-plane as well as out-of-plane broadband VNA-FMR measurements and angle dependent cavity FMR measurements. The saturation magnetization and the coercive field were found to be weakly thickness dependent and lie in the range 900 – 950 kA/m and 0.53 – 0.87 kA/m, respectively. The effective damping parameter ( αeff) extracted from in-plane and out-of-plane FMR results reveal a 1/tCFA dependence, the values for the in-plane αeff being larger due to two-magnon scattering (TMS). The origin of the αeff thickness dependence is spin pumping into the non-magnetic b-Ta layer and in case of the in-plane  αeff also a thickness dependent TMS contribution. From the out-of-plane FMR results, it was possible to disentangle the different contributions to αeff   and to the extract values for the intrinsic Gilbert damping (αG ) and the effective spin-mixing conductance (g_eff^↑↓ ) of the CFA/ b-Ta interface, yielding αG=1.1X10-3 and g_eff^↑↓=2.90x1019 m-2.

    Place, publisher, year, edition, pages
    American Physical Society, 2018
    Keywords
    Magnetization dynamics, magnetic thin films, Gilbert damping, ferromagnetic resonance
    National Category
    Condensed Matter Physics Materials Engineering
    Research subject
    Physics with spec. in Atomic, Molecular and Condensed Matter Physics
    Identifiers
    urn:nbn:se:uu:diva-345848 (URN)10.1103/PhysRevB.97.134421 (DOI)000430544300002 ()
    Funder
    Knut and Alice Wallenberg Foundation, 2012.0031
    Available from: 2018-03-12 Created: 2018-03-12 Last updated: 2018-06-26Bibliographically approved
    2. Enhanched Gilbert Damping in Re doped FeCo Films: A combined experimental and theoretical study
    Open this publication in new window or tab >>Enhanched Gilbert Damping in Re doped FeCo Films: A combined experimental and theoretical study
    Show others...
    (English)Manuscript (preprint) (Other academic)
    Abstract [en]

    The effects of rhenium doping in the range 0 – 10 at% on the static and dynamic magnetic properties of Fe65Co35 thin films have been studied experimentally as well as with first principles electronic structure calculations focussing on the change of the saturation magnetization (Ms ) and the Gilbert damping parameter (α ). Both experimental and theoretical results show that Ms decreases with increasing Re doping level, while at the same time α increases.  The experimental low temperature saturation magnetic induction exhibits a 29% decrease, from 2.31T to 1.64T, in the investigated doping concentration range, which is more than predicted by the theoretical calculations. The room temperature value of the damping parameter obtained from ferromagnetic resonance measurements, correcting for extrinsic contributions to the damping, is for the undoped sample 2.7X103, which is close to the Gilbert damping parameter extracted from the theoretical calculations. The room temperature experimental value for the damping parameter increases to  9X103 when doping with 10 at% Re; the corresponding increase of the Gilbert damping parameter obtained from theoretical calculations is 7.3X103. Both experimental and theoretical values for the damping parameter weakly decrease with decreasing temperature.

    Keywords
    Magnetization dynamics, magnetic thin films, Gilbert damping, ferromagnetic resonance
    National Category
    Condensed Matter Physics
    Research subject
    Physics with spec. in Atomic, Molecular and Condensed Matter Physics
    Identifiers
    urn:nbn:se:uu:diva-345854 (URN)
    Funder
    Knut and Alice Wallenberg Foundation, 2012.0031
    Available from: 2018-03-12 Created: 2018-03-12 Last updated: 2018-03-12
    3. Effect of seed layers on dynamic and static magnetic properties of Fe65Co35 thin films
    Open this publication in new window or tab >>Effect of seed layers on dynamic and static magnetic properties of Fe65Co35 thin films
    Show others...
    2018 (English)In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 51, no 30, article id 305001Article in journal (Refereed) Published
    Abstract [en]

    Fe65Co35 thin films have been deposited on SiO2 substrates using sputtering technique with different choices of seed layer; Ru, Ni82.5Fe17.5, Rh, Y and Zr. Best soft magnetic properties were observed with seed layers of Ru, Ni82.5Fe17.5 and Rh. Adding these seed layers, the coercivity of the Fe65Co35 films decreased to values of around 1.5 mT, which can be compared to the value of 12.5 mT obtained for films deposited without seed layer. Further investigations were performed on samples with these three seed layers in terms of dynamic magnetic properties, both on as prepared and annealed samples, using constant frequency cavity and broadband ferromagnetic resonance measurements. Damping parameters of around 8.0X10-3 and 4.5X10-3 were obtained from in-plane and out-of-plane measurements, respectively, for as prepared samples, values that were reduced to 6.5X10-3 and 4.0X10-3 for annealed samples.

    Keywords
    Magnetization dynamics, magnetic thin films, Gilbert damping, ferromagnetic resonance
    National Category
    Condensed Matter Physics Engineering and Technology
    Research subject
    Physics with spec. in Atomic, Molecular and Condensed Matter Physics
    Identifiers
    urn:nbn:se:uu:diva-345853 (URN)10.1088/1361-6463/aaccc0 (DOI)000437408700001 ()
    Funder
    Knut and Alice Wallenberg Foundation, 2012.0031
    Available from: 2018-03-12 Created: 2018-03-12 Last updated: 2021-10-29Bibliographically approved
    4. Growth of Co2FeAl Heusler alloy thin films on Si(100) having very small Gilbert damping by Ion beam sputtering
    Open this publication in new window or tab >>Growth of Co2FeAl Heusler alloy thin films on Si(100) having very small Gilbert damping by Ion beam sputtering
    Show others...
    2016 (English)In: Scientific Reports, E-ISSN 2045-2322, Vol. 6, article id 28692Article in journal (Refereed) Published
    Abstract [en]

    The influence of growth temperature T-s (300-773 K) on the structural phase ordering, static and dynamic magnetization behaviour has been investigated in ion beam sputtered full Heusler alloy Co2FeAl (CFA) thin films on industrially important Si(100) substrate. The B2 type magnetic ordering is established in these films based on the clear observation of the (200) diffraction peak. These ion beam sputtered CFA films possess very small surface roughness of the order of subatomic dimensions (<3 angstrom) as determined from the fitting of XRR spectra and also by AFM imaging. This is supported by the occurrence of distinct Kiessig fringes spanning over the whole scanning range (similar to 4 degrees) in the x-ray reflectivity (XRR) spectra. The Gilbert damping constant alpha and effective magnetization 4 pi M-eff are found to vary from 0.0053 +/- 0.0002 to 0.0015 +/- 0.0001 and 13.45 +/- 00.03 kG to 14.03 +/- 0.04 kG, respectively. These Co2FeAl films possess saturation magnetization ranging from 4.82 +/- 0.09 to 5.22 +/- 0.10 mu(B)/f.u. consistent with the bulk L2(1)-type ordering. A record low alpha-value of 0.0015 is obtained for Co2FeAl films deposited on Si substrate at T-s similar to 573 K.

    National Category
    Other Physics Topics Engineering and Technology
    Identifiers
    urn:nbn:se:uu:diva-299867 (URN)10.1038/srep28692 (DOI)000378783900001 ()27357004 (PubMedID)
    Available from: 2016-07-28 Created: 2016-07-28 Last updated: 2022-09-15Bibliographically approved
    5. Static and dynamic properties of Co2FeAl thin films: Effect of MgO and Ta as capping layers
    Open this publication in new window or tab >>Static and dynamic properties of Co2FeAl thin films: Effect of MgO and Ta as capping layers
    Show others...
    2017 (English)In: 61ST DAE-SOLID STATE PHYSICS SYMPOSIUM, 2017, Vol. 1832, article id 080007-1Conference paper, Published paper (Refereed)
    Abstract [en]

    The influence of MgO and Ta capping layers on the static and dynamic magnetic properties of Co2FeAl (CFA) Heusler alloy thin films has been investigated. It is observed that the CFA film deposited with MgO capping layer is preeminent compared to the uncapped or Ta capped CFA film. In particular, the magnetic inhomogeneity contribution to the ferromagnetic resonance line broadening and damping constant are found to be minimal for the MgO capped CFA thin film i.e., 0.12±0.01 Oe and 0.0074±0.00014, respectively. The saturationmagnetization was found to be 960±25emu/cc.

    Series
    AIP Conference Proceedings, ISSN 0094-243X
    Keywords
    Heusler alloy, MgO, Gilbert damping
    National Category
    Physical Sciences Engineering and Technology
    Identifiers
    urn:nbn:se:uu:diva-332482 (URN)10.1063/1.4980467 (DOI)000412824400289 ()978-0-7354-1500-3 (ISBN)
    Conference
    61st DAE-Solid State Physics Symposium, DEC 26-30, 2016, KIIT Univ, Bhubaneswar, INDIA
    Projects
    Knut and Alice Wallenberg (KAW) Foundation, Grant No. KAW 2012.0031.
    Available from: 2017-10-27 Created: 2017-10-27 Last updated: 2018-03-29Bibliographically approved
    6. Temperature-dependent Gilbert damping of Co2FeAl thin films with different degree of atomic order
    Open this publication in new window or tab >>Temperature-dependent Gilbert damping of Co2FeAl thin films with different degree of atomic order
    Show others...
    2017 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 96, no 224425Article in journal (Refereed) Published
    Abstract [en]

    Half-metallicity and low magnetic damping are perpetually sought for spintronics materials, and full Heusler compounds in this respect provide outstanding properties. However, it is challenging to obtain the well-ordered half-metallic phase in as-deposited full Heusler compound thin films, and theory has struggled to establish a fundamental understanding of the temperature-dependent Gilbert damping in these systems. Here we present a study of the temperature-dependent Gilbert damping of differently ordered as-deposited Co2FeAl full Heusler compound thin films. The sum of inter- and intraband electron scattering in conjunction with the finite electron lifetime in Bloch states governs the Gilbert damping for the well-ordered phase, in contrast to the damping of partially ordered and disordered phases which is governed by interband electronic scattering alone. These results, especially the ultralow room-temperature intrinsic damping observed for the well-ordered phase, provide fundamental insights into the physical origin of the Gilbert damping in full Heusler compound thin films.

    Place, publisher, year, edition, pages
    American Physical Society, 2017
    Keywords
    Gilbert damping, full Heusler compound, Temperature Dependent Gilbert damping, Thin Films, Density of states
    National Category
    Condensed Matter Physics Engineering and Technology
    Research subject
    Engineering Science with specialization in Solid State Physics
    Identifiers
    urn:nbn:se:uu:diva-337305 (URN)10.1103/PhysRevB.96.224425 (DOI)000418572700007 ()
    Funder
    Knut and Alice Wallenberg Foundation, KAW 2012.0031Göran Gustafsson Foundation for promotion of scientific research at Uppala University and Royal Institute of Technology, GGS1403ASwedish National Infrastructure for Computing (SNIC)
    Available from: 2017-12-22 Created: 2017-12-22 Last updated: 2018-03-12
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  • 25.
    Akansel, Serkan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Kumar, Ankit
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Behera, Nilamani
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Husain, Sajid
    Thin Film Laboratory, Department of Physics, Indian Institute of Technology Delhi, New Delhi 110016, India.
    Brucas, Rimantas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Chaudhary, Sujeet
    Thin Film Laboratory, Department of Physics, Indian Institute of Technology Delhi, New Delhi 110016, India.
    Svedlindh, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Thickness dependent enhancement of damping in Co2FeAl/β-Ta thin films2018In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 97, no 13, article id 134421Article in journal (Refereed)
    Abstract [en]

    In the present work Co2FeAl (CFA) thin films were deposited by ion beam sputtering on Si (100) substrates at the optimized deposition temperature of 300°C. A series of CFA films with different thickness (tCFA ); 8, 10, 12, 14, 16, 18 and 20 nm were prepared and all samples were capped with a 5 nm thick b-Ta layer. The thickness dependent static and dynamic properties of the films were studied by SQUID magnetometry, in-plane as well as out-of-plane broadband VNA-FMR measurements and angle dependent cavity FMR measurements. The saturation magnetization and the coercive field were found to be weakly thickness dependent and lie in the range 900 – 950 kA/m and 0.53 – 0.87 kA/m, respectively. The effective damping parameter ( αeff) extracted from in-plane and out-of-plane FMR results reveal a 1/tCFA dependence, the values for the in-plane αeff being larger due to two-magnon scattering (TMS). The origin of the αeff thickness dependence is spin pumping into the non-magnetic b-Ta layer and in case of the in-plane  αeff also a thickness dependent TMS contribution. From the out-of-plane FMR results, it was possible to disentangle the different contributions to αeff   and to the extract values for the intrinsic Gilbert damping (αG ) and the effective spin-mixing conductance (g_eff^↑↓ ) of the CFA/ b-Ta interface, yielding αG=1.1X10-3 and g_eff^↑↓=2.90x1019 m-2.

  • 26.
    Akansel, Serkan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Kumar, Ankit
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Venugopal, Vijayaharan A.
    Seagate Technol, Londonderry BT48 0BF, North Ireland.
    Esteban-Puyuelo, Raquel
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Banerjee, Rudra
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Autieri, Carmine
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Brucas, Rimantas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Behera, Nilamani
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Sortica, Mauricio A.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics.
    Primetzhofer, Daniel
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics.
    Basu, Swaraj
    Seagate Technol, Londonderry BT48 0BF, North Ireland.
    Gubbins, Mark A.
    Seagate Technol, Londonderry BT48 0BF, North Ireland.
    Sanyal, Biplab
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Svedlindh, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Enhanced Gilbert damping in Re-doped FeCo films: Combined experimental and theoretical study2019In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 99, no 17, article id 174408Article in journal (Refereed)
    Abstract [en]

    The effects of rhenium doping in the range 0-10 at.% on the static and dynamic magnetic properties of Fe65Co35 thin films have been studied experimentally as well as with first-principles electronic structure calculations focusing on the change of the saturation magnetization (M-s) and the Gilbert damping parameter (alpha). Both experimental and theoretical results show that M-s decreases with increasing Re-doping level, while at the same time alpha increases. The experimental low temperature saturation magnetic induction exhibits a 29% decrease, from 2.31 to 1.64 T, in the investigated doping concentration range, which is more than predicted by the theoretical calculations. The room temperature value of the damping parameter obtained from ferromagnetic resonance measurements, correcting for extrinsic contributions to the damping, is for the undoped sample 2.1 x 10(-3), which is close to the theoretically calculated Gilbert damping parameter. With 10 at.% Re doping, the damping parameter increases to 7.8 x 10(-3), which is in good agreement with the theoretical value of 7.3 x 10(-3). The increase in damping parameter with Re doping is explained by the increase in the density of states at the Fermi level, mostly contributed by the spin-up channel of Re. Moreover, both experimental and theoretical values for the damping parameter weakly decrease with decreasing temperature.

  • 27.
    Akansel, Serkan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Kumar, Ankit
    Venugopal, Vijayaharan
    Banerjee, Rudra
    Autieri, Carmine
    Brucas, Rimantas
    Behera, Nilamani
    Sortica, Mauricio
    Primetzhofer, Daniel
    Basu, Swaraj
    Gubbins, Mark
    Sanyal, Biplab
    Svedlindh, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Enhanched Gilbert Damping in Re doped FeCo Films: A combined experimental and theoretical studyManuscript (preprint) (Other academic)
    Abstract [en]

    The effects of rhenium doping in the range 0 – 10 at% on the static and dynamic magnetic properties of Fe65Co35 thin films have been studied experimentally as well as with first principles electronic structure calculations focussing on the change of the saturation magnetization (Ms ) and the Gilbert damping parameter (α ). Both experimental and theoretical results show that Ms decreases with increasing Re doping level, while at the same time α increases.  The experimental low temperature saturation magnetic induction exhibits a 29% decrease, from 2.31T to 1.64T, in the investigated doping concentration range, which is more than predicted by the theoretical calculations. The room temperature value of the damping parameter obtained from ferromagnetic resonance measurements, correcting for extrinsic contributions to the damping, is for the undoped sample 2.7X103, which is close to the Gilbert damping parameter extracted from the theoretical calculations. The room temperature experimental value for the damping parameter increases to  9X103 when doping with 10 at% Re; the corresponding increase of the Gilbert damping parameter obtained from theoretical calculations is 7.3X103. Both experimental and theoretical values for the damping parameter weakly decrease with decreasing temperature.

  • 28.
    Akansel, Serkan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Venugopal, Vijayaharan
    Kumar, Ankit
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Gupta, Rahul
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Brucas, Rimantas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    George, Sebastian
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Neagu, Alexandra
    Tai, Cheuk-Wai
    Gubbins, Mark
    Andersson, Gabriella
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Svedlindh, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Effect of seed layers on dynamic and static magnetic properties of Fe65Co35 thin films2018In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 51, no 30, article id 305001Article in journal (Refereed)
    Abstract [en]

    Fe65Co35 thin films have been deposited on SiO2 substrates using sputtering technique with different choices of seed layer; Ru, Ni82.5Fe17.5, Rh, Y and Zr. Best soft magnetic properties were observed with seed layers of Ru, Ni82.5Fe17.5 and Rh. Adding these seed layers, the coercivity of the Fe65Co35 films decreased to values of around 1.5 mT, which can be compared to the value of 12.5 mT obtained for films deposited without seed layer. Further investigations were performed on samples with these three seed layers in terms of dynamic magnetic properties, both on as prepared and annealed samples, using constant frequency cavity and broadband ferromagnetic resonance measurements. Damping parameters of around 8.0X10-3 and 4.5X10-3 were obtained from in-plane and out-of-plane measurements, respectively, for as prepared samples, values that were reduced to 6.5X10-3 and 4.0X10-3 for annealed samples.

  • 29.
    Akhtar, Sultan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences.
    Rubino, Stefano
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences.
    Leifer, Klaus
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    A simple TEM method for fast thickness characterization of suspendedgraphene flakesManuscript (preprint) (Other academic)
  • 30.
    Akhter, Shahida
    et al.
    Univ Chittagong, Dept Phys, Chittagong 4331, Bangladesh..
    Hakim, M. A.
    BUET, Dept Glass & Ceram Engn, Dhaka, Bangladesh..
    Hoque, S. M.
    Atom Energy Ctr, Mat Sci Div, Dhaka 1000, Bangladesh..
    Mathieu, Roland
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Nordblad, Per
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Glassy behavior of diluted Cu-Zn ferrites2018In: Journal of Magnetism and Magnetic Materials, ISSN 0304-8853, E-ISSN 1873-4766, Vol. 452, p. 261-265Article in journal (Refereed)
    Abstract [en]

    The magnetic behavior of Zn substituted Cu-Zn spinel ferrites having chemical formula Cu1-xZnxFe2O4 (x = 0.7, 0.8, 0.9 and 1.0) has been studied by SQUID magnetometry, by means of magnetic hysteresis, field-cooled (FC) and zero-field-cooled (ZFC) magnetization, memory effect and low field ac susceptibility measurements. These measurements suggest that the ferrimagnetic phase of the x <= 0.8 samples is gradually turned into a spin glass (x >= 0.9). The compound with x = 0.9 exhibits the typical dynamical behavior of spin glasses, with indication of aging, rejuvenation and memory effects. The evolution of the magnetic properties of Cu-Zn spinel ferrites with substitution of Zn for Cu is discussed.

  • 31. Akhter, Shahida
    et al.
    Paul, D. P.
    Hoque, S. M.
    Hakim, M. A.
    Hudl, Matthias
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Mathieu, Roland
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Nordblad, Per
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Magnetic and magnetocaloric properties of Cu1-xZnxFe2O4 (x=0.6, 0.7, 0.8) ferrites2014In: Journal of Magnetism and Magnetic Materials, ISSN 0304-8853, E-ISSN 1873-4766, Vol. 367, p. 75-80Article in journal (Refereed)
    Abstract [en]

    The effect of Zn substitution on the magnetic and magnetocaloric properties of Cu1-xZnxFe2O4 (x=0.6, 0.7, 0.8) ferrites over a wide temperature range has been investigated. The polycrystalline samples were synthesized using the solid-state reaction at sintering temperature 1050 degrees C (1323 K) for 2 h and has been characterized by SQUID magnetometry. Magnetization versus temperature showed that all samples exhibit a paramagnetic to ferromagnetic transition with decreasing temperature. The Curie temperature T-c is found to decrease from 373 K for x=0.6 to 140 K for x=0.8 as well as the saturation magnetization Ms which shifts from 100 to 44 emu/gm. The magnetocaloric effect was obtained by measuring a family of M-I1 curves at set temperature intervals and calculating the entropy change, LIS for this system using the Maxwell relation. The AS of all samples increased with increasing applied field and showed a maximum around their respective 'Fe. The entropy change (Delta S) decreased with increasing Zn content, whereas the relative cooling power (RCP) slightly increased. The large RCP and Delta S found in Zn substitution Cu-Zn ferrites will be interesting for magnetic refrigeration near room temperature.

  • 32.
    Albaalbaky, Ahmed
    et al.
    Normandie Univ, UNIROUEN, INSA Rouen, CNRS,GPM, F-76800 St Etienne Du Rouvray, France.
    Kvashnin, Yaroslav
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Patte, Renaud
    Normandie Univ, UNIROUEN, INSA Rouen, CNRS,GPM, F-76800 St Etienne Du Rouvray, France.
    Fresard, Raymond
    Normandie Univ, CRISMAT, CNRS, UNICAEN,ENSICAEN, F-14050 Caen, France.
    Ledue, Denis
    Normandie Univ, UNIROUEN, INSA Rouen, CNRS,GPM, F-76800 St Etienne Du Rouvray, France.
    Effects of Ga doping on magnetic and ferroelectric properties of multiferroic delafossite CuCrO2: Ab initio and Monte Carlo approaches2018In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 98, no 17, article id 174403Article in journal (Refereed)
    Abstract [en]

    The effects of nonmagnetic impurity doping on magnetic and ferroelectric properties of multiferroic delafossite CuCrO2 are investigated by means of density functional theory calculations and Monte Carlo simulations. Density functional theory calculations show that replacing up to 30% of Cr3+ ions by Ga3+ ones does not significantly affect the remaining Cr-Cr superexchange interactions. Monte Carlo simulations show that CuCr1-xGaxO2 preserves its magnetoelectric properties up to x similar or equal to 0.15 with a spiral ordering, while it becomes disordered at higher fractions. Antiferromagnetic transition shifts towards lower temperatures with increasing x and eventually disappears at x >= 0.2. Our simulations show that Ga3+ doping increases the Curie-Weiss temperature of CuCr1-xGaxO2, which agrees well with experimental observations. Moreover, our results show that the incommensurate ground-state configuration is destabilized by Ga3+ doping under zero applied field associated with an increase of frustration. Finally, coupling between noncollinear magnetic ordering and electric field is reported for x <= 0.15 through simulating P-E hysteresis loops, which leads to ferroelectricity in the extended inverse Dzyaloshinskii-Moriya model.

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  • 33.
    Albaalbaky, Ahmed
    et al.
    Normandie Univ, UNIROUEN, INSA Rouen, CNRS,GPM, F-76800 St Etienne Du Rouvray, France.
    Kvashnin, Yaroslav
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Patte, Renaud
    Normandie Univ, UNIROUEN, INSA Rouen, CNRS,GPM, F-76800 St Etienne Du Rouvray, France.
    Ledue, Denis
    Normandie Univ, UNIROUEN, INSA Rouen, CNRS,GPM, F-76800 St Etienne Du Rouvray, France.
    Analytical and numerical investigations of noncollinear magnetic ordering in the frustrated delafossite CuCrO22019In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 99, no 10, article id 104415Article in journal (Refereed)
    Abstract [en]

    The magnetic propagation vector in delafossite CuCrO2 with classical Heisenberg spins is calculated analytically as a function of exchange interactions up to fourth-nearest neighbors. Exchange interactions are estimated by a series of density functional theory calculations for several values of lattice distortion. Our calculations show that the magnetic propagation vector is directly affected by the considered distortions providing different stable commensurate or incommensurate magnetic configurations. A realistic set of exchange interactions corresponding to a 0.1% lattice distortion yields the experimental ground state with an incommensurate propagation vector q similar to (0.329, 0.329, 0). We find that a very weak antiferromagnetic interlayer interaction favors an incommensurate ordering even in the absence of lattice distortion. Moreover, the exchange energy of a magnetic configuration of a finite crystal of CuCrO2 with periodic boundary conditions is derived analytically. Based on that, highly accurate Monte Carlo simulations performed on CuCrO2 confirm both the proposed analytical calculations and the density functional theory estimations, where we obtain excellent convergence toward the experimental ground state with a magnetic propagation vector q = (0.3288, 0.3288, 0).

  • 34.
    Alberto, H. V.
    et al.
    Univ Coimbra, Dept Phys, CFisUC, R Larga, P-3004516 Coimbra, Portugal..
    Vilão, R. C.
    Univ Coimbra, Dept Phys, CFisUC, R Larga, P-3004516 Coimbra, Portugal..
    Ribeiro, E. F. M.
    Univ Coimbra, Dept Phys, CFisUC, R Larga, P-3004516 Coimbra, Portugal..
    Gil, J. M.
    Univ Coimbra, Dept Phys, CFisUC, R Larga, P-3004516 Coimbra, Portugal..
    Curado, M. A.
    Univ Coimbra, Dept Phys, CFisUC, R Larga, P-3004516 Coimbra, Portugal.;Int Iberian Nanotechnol Lab, P-4715330 Braga, Portugal..
    Teixeira, J. P.
    Int Iberian Nanotechnol Lab, P-4715330 Braga, Portugal.;Univ Aveiro, Dept Fis, i3N, Campus Univ Santiago, P-3810193 Aveiro, Portugal.;CIETI, Dept Fis, Inst Sup Eng Porto, Inst Pol Porto, P-4200072 Porto, Portugal..
    Fernandes, P. A.
    Int Iberian Nanotechnol Lab, P-4715330 Braga, Portugal.;Univ Aveiro, Dept Fis, i3N, Campus Univ Santiago, P-3810193 Aveiro, Portugal.;CIETI, Dept Fis, Inst Sup Eng Porto, Inst Pol Porto, P-4200072 Porto, Portugal..
    Cunha, J. M. V.
    Int Iberian Nanotechnol Lab, P-4715330 Braga, Portugal.;Univ Aveiro, Dept Fis, i3N, Campus Univ Santiago, P-3810193 Aveiro, Portugal.;Univ Aveiro, Dept Fis, Campus Univ Santiago, P-3810193 Aveiro, Portugal..
    Salomé, P. M. P.
    Int Iberian Nanotechnol Lab, P-4715330 Braga, Portugal.;Univ Aveiro, Dept Fis, Campus Univ Santiago, P-3810193 Aveiro, Portugal..
    Edoff, Marika
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Solid-State Electronics.
    Martins, M. I.
    Swiss Fed Inst Technol, Adv Power Semicond Lab, CH-8092 Zurich, Switzerland.;Paul Scherrer Inst, Lab Muon Spin Spect, CH-5232 Villigen, Switzerland..
    Prokscha, T.
    Paul Scherrer Inst, Lab Muon Spin Spect, CH-5232 Villigen, Switzerland..
    Salman, Z.
    Paul Scherrer Inst, Lab Muon Spin Spect, CH-5232 Villigen, Switzerland..
    Weidinger, A.
    Helmholtz Zentrum Berlin Mat & Energie, Dept ASPIN, D-14109 Berlin, Germany..
    Low energy muon study of the p-n interface in chalcopyrite solar cells2023In: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 2462, article id 012047Article in journal (Refereed)
    Abstract [en]

    The slow muon technique was used to study the p-n junction of chalcopyrite solar cells. A defect layer near the interface was identified and the passivation of the defects by buffer layers was studied. Several cover layers on top of the chalcopyrite Cu(In,Ga)Se2 (CIGS) semiconductor absorber were investigated in this work, namely CdS, ZnSnO, Al2O3 and SiO2. Quantitative results were obtained: The defect layer extends about 50 nm into the CIGS absorber, the relevant disturbance is strain in the lattice, and CdS provides the best passivation, oxides have a minor effect. In the present contribution, specific aspects of the low-energy muon technique in connection with this research are discussed.

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  • 35.
    Alberto, Helena, V
    et al.
    Univ Coimbra, Dept Phys, CFisUC, P-3004516 Coimbra, Portugal..
    Vilao, Rui C.
    Univ Coimbra, Dept Phys, CFisUC, P-3004516 Coimbra, Portugal..
    Ribeiro, Eduardo F. M.
    Univ Coimbra, Dept Phys, CFisUC, P-3004516 Coimbra, Portugal..
    Gil, Joao M.
    Univ Coimbra, Dept Phys, CFisUC, P-3004516 Coimbra, Portugal..
    Curado, Marco A.
    Univ Coimbra, Dept Phys, CFisUC, P-3004516 Coimbra, Portugal.;Int Iberian Nanotechnol Lab, P-4715330 Braga, Portugal..
    Teixeira, Jennifer P.
    Int Iberian Nanotechnol Lab, P-4715330 Braga, Portugal.;Univ Aveiro, Dept Fis, Campus Univ Santiago, P-3810193 Aveiro, Portugal.;Inst Pol Porto, Inst Sup Eng Porto, Dept Fis, CIETI, P-4200072 Porto, Portugal..
    Fernandes, Paulo A.
    Int Iberian Nanotechnol Lab, P-4715330 Braga, Portugal.;Univ Aveiro, Dept Fis, Campus Univ Santiago, P-3810193 Aveiro, Portugal.;Inst Pol Porto, Inst Sup Eng Porto, Dept Fis, CIETI, P-4200072 Porto, Portugal..
    Cunha, Jose M., V
    Int Iberian Nanotechnol Lab, P-4715330 Braga, Portugal.;Univ Aveiro, Dept Fis, Campus Univ Santiago, P-3810193 Aveiro, Portugal..
    Salome, Pedro M. P.
    Int Iberian Nanotechnol Lab, P-4715330 Braga, Portugal.;Univ Aveiro, Dept Fis, Campus Univ Santiago, P-3810193 Aveiro, Portugal..
    Edoff, Marika
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Solid-State Electronics.
    Martins, Maria, I
    Swiss Fed Inst Technol, Adv Power Semicond Lab, CH-8092 Zurich, Switzerland.;Paul Scherrer Inst, Lab Muon Spin Spect, CH-5232 Villigen, Switzerland..
    Prokscha, Thomas
    Paul Scherrer Inst, Lab Muon Spin Spect, CH-5232 Villigen, Switzerland..
    Salman, Zaher
    Paul Scherrer Inst, Lab Muon Spin Spect, CH-5232 Villigen, Switzerland..
    Weidinger, Alois
    Helmholtz Zentrum Berlin Mat & Energie, Dept ASPIN, D-14109 Berlin, Germany..
    Characterization of the Interfacial Defect Layer in Chalcopyrite Solar Cells by Depth-Resolved Muon Spin Spectroscopy2022In: Advanced Materials Interfaces, ISSN 2196-7350, Vol. 9, no 19, article id 2200374Article in journal (Refereed)
    Abstract [en]

    As devices become smaller and more complex, the interfaces between adjacent materials become increasingly important and are often critical to device performance. An important research goal is to improve the interface between the absorber and the window layer by inserting buffer layers to adjust the transition. Depth-resolved studies are key for a fundamental understanding of the interface. In the present experiment, the interface between the chalcopyrite Cu(In,Ga)Se-2 absorber and various buffer layers are investigated using low-energy muon spin rotation (mu SR) spectroscopy. Depth resolution in the nm range is achieved by implanting the muons with different energies so that they stop at different depths in the sample. Near the interface, a region about 50 nm wide is detected where the lattice is more distorted than further inside the absorber. The distortion is attributed to the long-range strain field caused by defects. These measurements allow a quantification of the corresponding passivation effect of the buffer layer. Bath-deposited cadmium sulfide provides the best defect passivation in the near interface region, in contrast to the dry-deposited oxides, which have a much smaller effect. The experiment demonstrates the great potential of low energy mu SR spectroscopy for microscopic interfacial studies of multilayer systems.

  • 36.
    Alcantara, Ricardo
    et al.
    Univ Cordoba, Dept Quim Inorgan Ingn Quim, Inst Quim Energia & Medioambiente IQEMA, Campus Rabanales,Edificio Marie Curie, E-14071 Cordoba, Spain..
    Lavela, Pedro
    Univ Cordoba, Dept Quim Inorgan Ingn Quim, Inst Quim Energia & Medioambiente IQEMA, Campus Rabanales,Edificio Marie Curie, E-14071 Cordoba, Spain..
    Edström, Kristina
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Fichtner, Maximilian
    Karlsruhe Inst Technol, Inst Nanotechnol, Hermann von Helmholtz Pl 1, D-76344 Eggenstein Leopoldshafen, Germany.;Helmholtz Inst Ulm HIU Electrochem Energy Storage, Helmholtzstr 11, D-89081 Ulm, Germany..
    Le, Top Khac
    Univ Sci, Fac Mat Sci & Technol, Ho Chi Minh City 700000, Vietnam.;Vietnam Natl Univ, Ho Chi Minh City 700000, Vietnam..
    Floraki, Christina
    Hellen Mediterranean Univ, Sch Engn, Dept Elect & Comp Engn, Iraklion 71410, Greece..
    Aivaliotis, Dimitris
    Hellen Mediterranean Univ, Sch Engn, Dept Elect & Comp Engn, Iraklion 71410, Greece..
    Vernardou, Dimitra
    Hellen Mediterranean Univ, Sch Engn, Dept Elect & Comp Engn, Iraklion 71410, Greece.;Hellen Mediterranean Univ Ctr, Inst Emerging Technol, Iraklion 71410, Greece..
    Metal-Ion Intercalation Mechanisms in Vanadium Pentoxide and Its New Perspectives2023In: Nanomaterials, E-ISSN 2079-4991, Vol. 13, no 24, article id 3149Article, review/survey (Refereed)
    Abstract [en]

    The investigation into intercalation mechanisms in vanadium pentoxide has garnered significant attention within the realm of research, primarily propelled by its remarkable theoretical capacity for energy storage. This comprehensive review delves into the latest advancements that have enriched our understanding of these intricate mechanisms. Notwithstanding its exceptional storage capacity, the compound grapples with challenges arising from inherent structural instability. Researchers are actively exploring avenues for improving electrodes, with a focus on innovative structures and the meticulous fine-tuning of particle properties. Within the scope of this review, we engage in a detailed discussion on the mechanistic intricacies involved in ion intercalation within the framework of vanadium pentoxide. Additionally, we explore recent breakthroughs in understanding its intercalation properties, aiming to refine the material's structure and morphology. These refinements are anticipated to pave the way for significantly enhanced performance in various energy storage applications.

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  • 37.
    Alekhin, A.
    et al.
    CNRS, Inst Mol & Mat Le Mans, UMR 6283, F-72085 Le Mans, France.
    Razdolski, I.
    CNRS, Inst Mol & Mat Le Mans, UMR 6283, F-72085 Le Mans, France;Max Planck Gesell, Fritz Haber Inst, D-14195 Berlin, Germany.
    Berritta, Marco
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Buerstel, D.
    Univ Duisburg Essen, Fac Chem, Univ Str 5, D-45141 Essen, Germany.
    Temnov, V.
    CNRS, Inst Mol & Mat Le Mans, UMR 6283, F-72085 Le Mans, France.
    Diesing, D.
    Univ Duisburg Essen, Fac Chem, Univ Str 5, D-45141 Essen, Germany.
    Bovensiepen, U.
    Univ Duisburg Essen, Fac Phys, Lotharstr 1, D-47057 Duisburg, Germany;Univ Duisburg Essen, Ctr Nanointegrat CENIDE, Lotharstr 1, D-47057 Duisburg, Germany.
    Woltersdorf, G.
    Martin Luther Univ Halle Wittenberg, Inst Phys, Von Danckelmann Pl 3, D-06120 Halle, Germany.
    Oppeneer, Peter M.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Melnikov, A.
    Max Planck Gesell, Fritz Haber Inst, D-14195 Berlin, Germany;Martin Luther Univ Halle Wittenberg, Inst Phys, Von Danckelmann Pl 3, D-06120 Halle, Germany.
    Magneto-optical properties of Au upon the injection of hot spin-polarized electrons across Fe/Au(001) interfaces2019In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 31, no 12, article id 124002Article in journal (Refereed)
    Abstract [en]

    We demonstrate a novel method for the excitation of sizable magneto-optical effects in Au by means of the laser-induced injection of hot spin-polarized electrons in Au/Fe/MgO(001) heterostructures. It is based on the energy- and spin-dependent electron transmittance of Fe/Au interface which acts as a spin filter for non-thermalized electrons optically excited in Fe. We show that after crossing the interface, majority electrons propagate through the Au layer with the velocity on the order of 1 nm fs(-1) (close to the Fermi velocity) and the decay length on the order of 100nm. Featuring ultrafast functionality and requiring no strong external magnetic fields, spin injection results in a distinct magneto-optical response of Au. We develop a formalism based on the phase of the transient complex MOKE response and demonstrate its robustness in a plethora of experimental and theoretical MOKE studies on Au, including our ab initio calculations. Our work introduces a flexible tool to manipulate magneto-optical properties of metals on the femtosecond timescale that holds high potential for active magneto-photonics, plasmonics, and spintronics.

  • 38.
    Alekseev, A. Y.
    et al.
    Belarusian State Univ Informat & Radioelect, P Browka 6, Minsk 220013, BELARUS.
    Migas, D. B.
    Belarusian State Univ Informat & Radioelect, P Browka 6, Minsk 220013, BELARUS;Natl Res Nucl Univ MEPhI, Moscow Engn Phys Inst, Kashirskoe Shosse 31, Moscow 115409, Russia;Belarusian State Univ, Inst Nucl Problems, Bobruiskaya 11, Minsk 220006, BELARUS.
    Filonov, A. B.
    Belarusian State Univ Informat & Radioelect, P Browka 6, Minsk 220013, BELARUS.
    Borisenko, V. E.
    Belarusian State Univ Informat & Radioelect, P Browka 6, Minsk 220013, BELARUS;Natl Res Nucl Univ MEPhI, Moscow Engn Phys Inst, Kashirskoe Shosse 31, Moscow 115409, Russia.
    Skorodumova, Natalia V.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Royal Inst Technol KTH, Dept Mat & Engn, Multiscale Mat Modelling, SE-10044 Stockholm, Sweden.
    Structural stability and electronic properties of 2D alkaline-earth metal silicides, germanides, and stannides2020In: Japanese Journal of Applied Physics, ISSN 0021-4922, E-ISSN 1347-4065, Vol. 59, article id SF0801Article, review/survey (Refereed)
    Abstract [en]

    We present the results of an extended theoretical study of the structure, phonon, electronic and optical properties of 2D alkaline-earth metal silicides, germanides and stannides (2D Me2X, where Me=Mg, Ca, Sr, Ba and X=Si, Ge, Sn). The performed analysis has shown the occurrence of the pseudo passivation effect and ionic chemical bonding in these 2D Me2X. In addition, the preformed investigation of their phonon spectra has shown the absence of imaginary frequencies indicating the stability of these 2D structures. The band structure calculations performed using the hybrid functional have revealed that all 2D Me2X are semiconductors with the gap varying from 0.12 to 1.01 eV. Among them Mg- and Ca-based 2D materials are direct band-gap semiconductors with the first direct transition having appreciable oscillator strength. We also propose to consider ternary 2D silicides, germanides and stannides with different Me atoms as a feasible way to modify properties of parent 2D Me2X.

  • 39.
    Alekseev, A. Yu
    et al.
    Belarusian State Univ Informat & Radioelect, P Browka 6, Minsk 220013, BELARUS.
    Chernykh, A. G.
    Belarusian State Univ Informat & Radioelect, P Browka 6, Minsk 220013, BELARUS.
    Filonov, A. B.
    Belarusian State Univ Informat & Radioelect, P Browka 6, Minsk 220013, BELARUS.
    Migas, D. B.
    Belarusian State Univ Informat & Radioelect, P Browka 6, Minsk 220013, BELARUS;Natl Res Nucl Univ MEPhI, Moscow Engn Phys Inst, Kashirskoe Shosse 31, Moscow 115409, Russia.
    Skorodumova, Natalia V.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Multiscale Materials Modelling, Department of Materials and Engineering, Royal Institute of Technology (KTH), SE-10044 Stockholm, Sweden.
    Stability of 2D Alkaline-Earth Metal Silicides, Germanides and Stannides2019In: International Journal of Nanoscience, ISSN 0219-581X, Vol. 18, no 3-4, article id 1940013Article in journal (Refereed)
    Abstract [en]

    By means of ab initio calculations, we have estimated stability of 2D Me2X (Me = Mg, Ca, Sr, Ba and X = Si, Ge, Sn) in the T and Td phases, which are similar to the ones of 2D transition metal chalcogenides, in addition to their phonon spectra. The T phase is found to be more stable for 2D Ca2X, Sr2X and Ba2X, whereas the Td phase is predicted to be the ground state for 2D Mg2X. We have also discussed that imaginary frequencies in the calculated phonon spectra of 2D Me2X, which appeared in the vicinity of the Gamma point, were not necessarily associated with the dynamic instability.

  • 40.
    Alekseev, A. Yu
    et al.
    Belarusian State Univ Informat & Radioelect, P Browka 6, Minsk 220013, BELARUS..
    Migas, D. B.
    Belarusian State Univ Informat & Radioelect, P Browka 6, Minsk 220013, BELARUS.;Natl Res Nucl Univ MEPhI, Moscow Engn Phys Inst, Kashirskoe Shosse 31, Moscow 115409, Russia.;Belarusian State Univ, Inst Nucl Problems, Bobruiskaya 11, Minsk 220006, BELARUS..
    Filonov, A. B.
    Belarusian State Univ Informat & Radioelect, P Browka 6, Minsk 220013, BELARUS..
    Chernykh, A. G.
    Belarusian State Univ Informat & Radioelect, P Browka 6, Minsk 220013, BELARUS..
    Borisenko, V. E.
    Belarusian State Univ Informat & Radioelect, P Browka 6, Minsk 220013, BELARUS.;Natl Res Nucl Univ MEPhI, Moscow Engn Phys Inst, Kashirskoe Shosse 31, Moscow 115409, Russia..
    Skorodumova, Natalia V.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Multiscale Materials Modelling, Department of Materials and Engineering, Royal Institute of Technology (KTH), SE-10044, Stockholm, Sweden.
    Curvature-induced effects in semiconducting alkaline-earth metal silicide nanotubes2021In: Physica. E, Low-Dimensional systems and nanostructures, ISSN 1386-9477, E-ISSN 1873-1759, Vol. 128, article id 114582Article in journal (Refereed)
    Abstract [en]

    By means of ab-initio techniques we have investigated changes in the structure and electronic properties of alkaline-earth metal silicide (Ca2Si, Mg2Si and MgCaSi) nanotubes caused by the curvature-induced effects. It is revealed that the curvature-induced effects can: 1) stabilize Mg2Si nanotubes in a phase, which is metastable for the parent 2D Mg2Si; 2) lead to an energy gain as a result of 2D to nanotube structural transformation in the case of ternary MgCaSi nanotubes; 3) modify the band dispersion and band gaps for nanotubes with the diameters less than 30 angstrom. In addition, Mg2Si and MgCaSi nanotubes are found to be direct band-gap (0.5-1.2 eV) materials with appreciable oscillator strength of the first direct transitions.

  • 41.
    Alhanash, Mirna
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Nuclear Physics.
    ELECTRONIC STRUCTURE AND THERMODYNAMIC PROPERTIES OF LI-IONINSERTION IN SULFONAMIDES COMPOUNDS AS ORGANIC HIGH-ENERGY DENSITY CATHODES2021Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The world’s ever-growing energy demand has evoked great interest in exploring renewable energy sources along with sustainable energy storage systems. While inorganic physics of rocking chair mechanism used in Li-ion battery have proven to provide high energy density and high performance, there are problems yet to be overcome in terms of sustainability and recyclability. This is why research in organic batteries has been on the rise, yet the diversity of organic battery frameworks remains limited and requires overcoming multiple obstacles that restrain the performance of an all-organic battery system. A recent advance in the design of organic electrode material by Wang et al. has shown the possibility of a new stable and tunable class of conjugated sulfonamides (CSA) with an experimental voltage range between 2.85V and 3.45V [5]. A theoretical approach to study these organic materials is taken in this thesis research where the effects of such compounds on the redox potential, physics of ion insertion, and other thermodynamical properties are examined. Density Functional Theory (DFT) is employed in this investigation along with an evolutionary algorithm to generate information about the crystal structure of mentioned systems, their density of states (DOS), and charge distribution in pristine form and after lithiation. Quinone systems with oxygen groups were investigated in a previous research project that complements this thesis which looks into a quinone system with sulfonamide compounds where a comparison between the two could offer more understanding of the electrochemistry of such systems for their application in batteries as high performing organic cathode materials on a par with other inorganic materials.

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    Mirna A. ELECTRONIC STRUCTURE AND THERMODYNAMIC PROPERTIES OF LI-ION INSERTION IN SULFONAMIDES COMPOUNDS AS ORGANIC HIGH-ENERGY DENSITY CATHODES
  • 42.
    Ali, Hasan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Towards atomically resolved magnetic measurements in the transmission electron microscope: A study of structure and magnetic moments in thin films2020Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The magnetic properties of thin metallic films are significantly different from the bulk properties due to the presence of interfaces. The properties shown by such thin films are influenced by the atomic level structure of the films and the interfaces. Transmission electron microscope (TEM) has the potential to analyse the structure and the magnetic properties of such systems with atomic resolution. In this work, the TEM is employed to characterize the structure of the Fe/V and Fe/Ni multilayers and the technique of electron magnetic circular dichroism (EMCD) is developed to obtain the quantitative magnetic measurements with high spatial resolution.

    From TEM analysis of short period Fe/V  multilayers, a coherent superlattice structure is found. In short period Fe/Ni multilayer samples with different repeat frequency, only the TEM technique could verify the existence of the multilayer structure in the thinnest layers. The methods of scanning TEM imaging and electron energy loss spectroscopy (EELS) results were used and refined to determine interdiffusion at the interfaces. The confirmation of the multilayer structure helped to explain the saturation magnetization of these samples.

    Electron magnetic circular dichroism (EMCD) has the potential to quantitatively measure the magnetic moments of the materials with atomic resolution, but the technique presents several challenges. First, the EMCD measurements need to acquire two EELS spectra at two different scattering angles. These spectra are mostly acquired one after the other which makes it difficult to guaranty the identical experimental conditions and the spatial registration between the two acquisitions. We have developed a technique to simultaneously acquire the two angle-resolved EELS spectra in a single acquisition. This not only ensures the accuracy of the measurements but also improves the signal to noise ratio as compared to the previously used methods. The second important question is the effect of crystal orientations on the measured EMCD signals, considering the fact that the crystal orientation of a real crystal does not remain the same in the measured area. We developed the methodology to simultaneously acquire the EMCD signals and the local crystal orientations with high precision and experimentally showed that the crystal tilt significantly changes the magnetic signal. The third challenge is to obtain EMCD measurements with atomic resolution  which is hampered by the need of high beam convergence angles. We further developed the simultaneous acquisition technique to obtain the quantitative EMCD measurements with beam convergence angles corresponding to atomic size electron probes. 

    List of papers
    1. Shrinking of silicon nanocrystals embedded in an amorphous silicon oxide matrix during rapid thermal annealing in a forming gas atmosphere
    Open this publication in new window or tab >>Shrinking of silicon nanocrystals embedded in an amorphous silicon oxide matrix during rapid thermal annealing in a forming gas atmosphere
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    2016 (English)In: Nanotechnology, ISSN 0957-4484, E-ISSN 1361-6528, Vol. 27, no 36, article id 365601Article in journal (Refereed) Published
    Abstract [en]

    We report the effect of hydrogen on the crystallization process of silicon nanocrystals embedded in a silicon oxide matrix. We show that hydrogen gas during annealing leads to a lower sub-band gap absorption, indicating passivation of defects created during annealing. Samples annealed in pure nitrogen show expected trends according to crystallization theory. Samples annealed in forming gas, however, deviate from this trend. Their crystallinity decreases for increased annealing time. Furthermore, we observe a decrease in the mean nanocrystal size and the size distribution broadens, indicating that hydrogen causes a size reduction of the silicon nanocrystals.

    Keywords
    silicon nanocrystals, rapid thermal annealing, oxidation, forming gas, hydrogen, defects, passivation
    National Category
    Materials Engineering
    Identifiers
    urn:nbn:se:uu:diva-306271 (URN)10.1088/0957-4484/27/36/365601 (DOI)000384064400019 ()27478921 (PubMedID)
    Available from: 2016-10-26 Created: 2016-10-26 Last updated: 2019-12-06Bibliographically approved
    2. Crystal perfection by strain engineering: The case of Fe/V (001)
    Open this publication in new window or tab >>Crystal perfection by strain engineering: The case of Fe/V (001)
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    2017 (English)In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 636, p. 608-614Article in journal (Refereed) Published
    Abstract [en]

    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.

    Keywords
    Superlattice; Iron/Vanadium; Sputtering; Epitaxy; Reciprocal space mapping; X-ray diffraction; X-ray reflectivity; Linear elasticity
    National Category
    Other Materials Engineering
    Identifiers
    urn:nbn:se:uu:diva-332050 (URN)10.1016/j.tsf.2017.07.005 (DOI)000408037800086 ()
    Available from: 2017-10-23 Created: 2017-10-23 Last updated: 2019-12-06Bibliographically approved
    3. Composition, structure and magnetic properties of ultra-thin Fe/Ni multilayers sputter deposited on epitaxial Cu/Si(001)
    Open this publication in new window or tab >>Composition, structure and magnetic properties of ultra-thin Fe/Ni multilayers sputter deposited on epitaxial Cu/Si(001)
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    2018 (English)In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 646, p. 117-125Article in journal (Refereed) Published
    Abstract [en]

    Sputter deposited symmetric multilayers of (n Fe)/(n Ni), with individual thicknesses from n = 4 to n = 48 monolayers (ML), were deposited on epitaxial Cu/Si(001), and their microstructural evolution and magnetic properties versus n have been studied. Elemental layering can be seen with transmission electron microscopy down to n = 4 ML layer thickness, although an intermixed region characterized by a finite interface width is found to be present. This width is composed of the interface roughness as well as the interdiffusion between layers, but the relative contributions from these two sources could not be concluded by the techniques used. The measured elemental layering and X-ray reflectivity (XRR) give an upper limit to the interface width which must be smaller than the thinnest layers, 4 ML. Electron energy loss spectroscopy (EELS), depth profiling X-ray photoelectron spectroscopy (XPS) and also XRR reveal that Fe has a higher tendency to mix with Ni than vice versa. XPS does not have the resolution to measure this thin elemental layering: composition variations for n = 8 ML which are clearly seen by EELS are barely resolved by XPS. The structure was determined by X-ray diffraction, and an epitaxial fcc (001) structure is found to be maintained throughout the multilayers up to n less than or similar to 8 ML. For larger n values, relaxation starts by Fe-fcc(001) layers changing into Fe-bcc(110), which is then followed by Ni-fcc(001) changing from (001) to (111) orientation along the growth direction. A decreased total measured magnetic moment for the fully epitaxial multilayers can be explained by the fcc Fe layers being partly anti-ferromagnetic, whereas the relaxed multilayers exhibit the expected magnetic properties of (bcc Fe) +(fcc Ni).

    National Category
    Condensed Matter Physics Engineering and Technology
    Identifiers
    urn:nbn:se:uu:diva-305519 (URN)10.1016/j.tsf.2017.11.023 (DOI)000418575900017 ()
    Funder
    Swedish Research Council
    Available from: 2016-10-22 Created: 2016-10-18 Last updated: 2019-12-06Bibliographically approved
    4. Quantitative EMCD by use of a double aperture for simultaneous acquisition of EELS
    Open this publication in new window or tab >>Quantitative EMCD by use of a double aperture for simultaneous acquisition of EELS
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    2019 (English)In: Ultramicroscopy, ISSN 0304-3991, E-ISSN 1879-2723, Vol. 196, p. 192-196Article in journal (Refereed) Published
    Abstract [en]

    The weak signal strength in electron magnetic circular dichroism (EMCD) measurements remains one of the main challenges in the quantification of EMCD related EELS spectra. As a consequence, small variations in peak intensity caused by changes of background intervals, choice of method for extraction of signal intensity and equally differences in sample quality can cause strong changes in the EMCD signal. When aiming for high resolution quantitative EMCD, an additional difficulty consists in the fact that the two angular resolved EELS spectra needed to obtain the EMCD signal are taken at two different instances and it cannot be guaranteed that the acquisition conditions for these two spectra are identical.  Here, we present an experimental setup where we use a double hole aperture in the transmission electron microscope to obtain the EMCD signal in a single acquisition. This geometry allows for the parallel acquisition of the two electron energy loss spectra (EELS) under exactly the same conditions. We also compare the double aperture acquisition mode with the qE acquisition mode which has been previously used for parallel acquisition of EMCD. We show that the double aperture mode not only offers better signal to noise ratio as compared to qE mode but also allows for much higher acquisition times to significantly improve the signal quality which is crucial for quantitative analysis of the magnetic moments.

    National Category
    Other Materials Engineering
    Research subject
    Materials Science
    Identifiers
    urn:nbn:se:uu:diva-364715 (URN)10.1016/j.ultramic.2018.10.012 (DOI)000451180800026 ()30439606 (PubMedID)
    Funder
    Swedish Research Council, C0367901Swedish Research Council, 2016-05259Knut and Alice Wallenberg Foundation
    Available from: 2018-10-31 Created: 2018-10-31 Last updated: 2020-10-20Bibliographically approved
    5. Simultaneous mapping of EMCD signals and crystal orientations in a transmission electron microscope
    Open this publication in new window or tab >>Simultaneous mapping of EMCD signals and crystal orientations in a transmission electron microscope
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    2021 (English)In: Scientific Reports, E-ISSN 2045-2322, Vol. 11, article id 2180Article in journal (Refereed) Published
    Abstract [en]

    When magnetic properties are analysed in a transmission electron microscope using the technique of electron magnetic circular dichroism (EMCD), one of the critical parameters is the sample orientation. Since small orientation changes can have a strong impact on the measurement of the EMCD signal and such measurements need two separate measurements of conjugate EELS spectra, it is experimentally non-trivial to measure the EMCD signal as a function of sample orientation. Here, we have developed a methodology to simultaneously map the quantitative EMCD signals and the local orientation of the crystal. We analyse, both experimentally and by simulations, how the measured magnetic signals evolve with a change in the crystal tilt. Based on this analysis, we establish an accurate relationship between the crystal orientations and the EMCD signals. Our results demonstrate that a small variation in crystal tilt can significantly alter the strength of the EMCD signal. From an optimisation of the crystal orientation, we obtain quantitative EMCD measurements.

    Place, publisher, year, edition, pages
    Springer NatureNATURE RESEARCH, 2021
    National Category
    Nano Technology
    Identifiers
    urn:nbn:se:uu:diva-398559 (URN)10.1038/s41598-021-81071-4 (DOI)000667505700002 ()33500427 (PubMedID)
    Funder
    Swedish Research Council, 2016 05259
    Available from: 2019-12-06 Created: 2019-12-06 Last updated: 2024-01-15Bibliographically approved
    6. Atomic resolution electron probe magnetic circular dichroism measurements enabled by patterned apertures
    Open this publication in new window or tab >>Atomic resolution electron probe magnetic circular dichroism measurements enabled by patterned apertures
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    (English)Manuscript (preprint) (Other academic)
    National Category
    Nano Technology
    Identifiers
    urn:nbn:se:uu:diva-398560 (URN)
    Available from: 2019-12-06 Created: 2019-12-06 Last updated: 2019-12-06
    7. An electron energy loss spectrometer based streak camera for time resolved TEM measurements
    Open this publication in new window or tab >>An electron energy loss spectrometer based streak camera for time resolved TEM measurements
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    2017 (English)In: Ultramicroscopy, ISSN 0304-3991, E-ISSN 1879-2723, Vol. 176, p. 5-10Article in journal (Refereed) Published
    Abstract [en]

    We propose an experimental setup based on a streak camera approach inside an energy filter to measure time resolved properties of materials in the transmission electron microscope (TEM). In order to put in place the streak camera, a beam sweeper was built inside an energy filter. After exciting the TEM sample, the beam is swept across the CCD camera of the filter. We describe different parts of the setup at the example of a magnetic measurement. This setup is capable to acquire time resolved diffraction patterns, electron energy loss spectra (EELS) and images with total streaking times in the range between 100 ns and 10 μs.

    Keywords
    Time resolved; TEM; Energy filter; Streak camera; Sweep
    National Category
    Physical Sciences Engineering and Technology
    Identifiers
    urn:nbn:se:uu:diva-329982 (URN)10.1016/j.ultramic.2016.11.026 (DOI)000403992200003 ()
    Available from: 2017-09-25 Created: 2017-09-25 Last updated: 2019-12-06Bibliographically approved
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  • 43.
    Ali, Hasan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Applied Material Science. Uppsala Univ, Dept Engn Sci, Appl Mat Sci, Electron Microscopy & Nanoengn, Box 534, S-75121 Uppsala, Sweden..
    Negi, Devendra Singh
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Uppsala Univ, Dept Phys & Astron, Box 516, S-75120 Uppsala, Sweden.;Max Planck Inst Solid State Res, Stuttgart Ctr Electron Microscopy, Heisenbergstr 1, D-70569 Stuttgart, Germany..
    Warnatz, Tobias
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics. Uppsala Univ, Dept Phys & Astron, Box 516, S-75120 Uppsala, Sweden..
    Hjörvarsson, Björgvin
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Uppsala Univ, Dept Phys & Astron, Box 516, S-75120 Uppsala, Sweden..
    Rusz, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Physics. Uppsala Univ, Dept Phys & Astron, Box 516, S-75120 Uppsala, Sweden..
    Leifer, Klaus
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Applied Material Science. Uppsala Univ, Dept Engn Sci, Appl Mat Sci, Electron Microscopy & Nanoengn, Box 534, S-75121 Uppsala, Sweden..
    Atomic resolution energy-loss magnetic chiral dichroism measurements enabled by patterned apertures2020In: Physical Review Research, E-ISSN 2643-1564, Vol. 2, no 2, article id 023330Article in journal (Refereed)
    Abstract [en]

    Electron energy-loss magnetic chiral dichroism (EMCD) has the potential to measure magnetic properties of the materials at atomic resolution but the complex distribution of magnetic signals in the zone axis and the overlapping diffraction discs at higher beam convergence angles make the EMCD signal acquisition challenging. Recently, the use of ventilator apertures to acquire the EMCD signals with atomic resolution was proposed. Here we give the experimental demonstration of several types of ventilator apertures and obtain a clear EMCD signal at beam semiconvergence angles of 5 mrad. To simplify the experimental procedures, we propose a modified ventilator aperture which not only simplifies the complex scattering conditions but reduces the influence of lens aberrations on the EMCD signal as compared to the originally proposed ventilator apertures. In addition, this modified aperture can be used to analyze magnetic crystals with various symmetries and we demonstrate this feature by acquiring EMCD signals on different zone axis orientations of an Fe crystal. With the same aperture we obtain EMCD signals with convergence angles corresponding to atomic resolution electron probes. After the theoretical demonstration of the EMCD signal on a zone axis orientation at high beam convergence angles, this work thus overcomes the experimental and methodological hurdles and enables atomic resolution EMCD on the zone axis by using apertures.

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  • 44.
    Ali, Hasan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Applied Material Science. Stockholm Univ, Dept Mat & Environm Chem, S-10691 Stockholm, Sweden.;Forschungszentrum Julich, Ernst Ruska Ctr Microscopy & Spect Electrons, D-52425 Julich, Germany..
    Rusz, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Buergler, Daniel E.
    Forschungszentrum Julich, Peter Grunberg Inst, D-52425 Julich, Germany..
    Adam, Roman
    Forschungszentrum Julich, Peter Grunberg Inst, D-52425 Julich, Germany..
    Schneider, Claus M.
    Forschungszentrum Julich, Peter Grunberg Inst, D-52425 Julich, Germany..
    Tai, Cheuk-Wai
    Stockholm Univ, Dept Mat & Environm Chem, S-10691 Stockholm, Sweden..
    Thersleff, Thomas
    Stockholm Univ, Dept Mat & Environm Chem, S-10691 Stockholm, Sweden..
    Noise-dependent bias in quantitative STEM-EMCD experiments revealed by bootstrapping2024In: Ultramicroscopy, ISSN 0304-3991, E-ISSN 1879-2723, Vol. 257, article id 113891Article in journal (Refereed)
    Abstract [en]

    Electron magnetic circular dichroism (EMCD) is a powerful technique for estimating element-specific magnetic moments of materials on nanoscale with the potential to reach atomic resolution in transmission electron microscopes. However, the fundamentally weak EMCD signal strength complicates quantification of magnetic moments, as this requires very high precision, especially in the denominator of the sum rules. Here, we employ a statistical resampling technique known as bootstrapping to an experimental EMCD dataset to produce an empirical estimate of the noise-dependent error distribution resulting from application of EMCD sum rules to bcc iron in a 3-beam orientation. We observe clear experimental evidence that noisy EMCD signals preferentially bias the estimation of magnetic moments, further supporting this with error distributions produced by Monte-Carlo simulations. Finally, we propose guidelines for the recognition and minimization of this bias in the estimation of magnetic moments.

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  • 45.
    Ali, Hasan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Applied Material Science. Stockholm Univ, Dept Mat & Environm Chem, S-10691 Stockholm, Sweden.;Forschungszentrum Julich, Ernst Ruska Ctr Microscopy & Spect Electrons & Pe, D-52425 Julich, Germany..
    Sathyanath, Sharath Kumar Manjeshwar
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Applied Material Science.
    Tai, Cheuk-Wai
    Stockholm Univ, Dept Mat & Environm Chem, S-10691 Stockholm, Sweden..
    Rusz, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Uusimaki, Toni
    Stockholm Univ, Dept Mat & Environm Chem, S-10691 Stockholm, Sweden..
    Hjörvarsson, Björgvin
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Thersleff, Thomas
    Stockholm Univ, Dept Mat & Environm Chem, S-10691 Stockholm, Sweden..
    Leifer, Klaus
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Applied Material Science.
    Single scan STEM-EMCD in 3-beam orientation using a quadruple aperture2023In: Ultramicroscopy, ISSN 0304-3991, E-ISSN 1879-2723, Vol. 251, article id 113760Article in journal (Refereed)
    Abstract [en]

    The need to acquire multiple angle-resolved electron energy loss spectra (EELS) is one of the several critical challenges associated with electron magnetic circular dichroism (EMCD) experiments. If the experiments are performed by scanning a nanometer to atomic-sized electron probe on a specific region of a sample, the precision of the local magnetic information extracted from such data highly depends on the accuracy of the spatial registration between multiple scans. For an EMCD experiment in a 3-beam orientation, this means that the same specimen area must be scanned four times while keeping all the experimental conditions same. This is a non-trivial task as there is a high chance of morphological and chemical modification as well as non-systematic local orientation variations of the crystal between the different scans due to beam damage, contamination and spatial drift. In this work, we employ a custom-made quadruple aperture to acquire the four EELS spectra needed for the EMCD analysis in a single electron beam scan, thus removing the above-mentioned complexities. We demonstrate a quantitative EMCD result for a beam convergence angle corresponding to sub-nm probe size and compare the EMCD results for different detector geometries.

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  • 46.
    Alippi, Paola
    et al.
    CNR ISM, Ist Struttura Mat Consiglio Nazl Ric, Via Salaria,Km 29-300, I-00015 Rome, Italy..
    Lanzilotto, Valeria
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics. CNR IOM, Lab Nazl TASC, C Area Sci Pk SS14 Km 163-5, I-34129 Trieste, Italy.;Univ Trieste, Dept Phys, Via Valerio 2, I-34127 Trieste, Italy..
    Paoletti, Anna Maria
    CNR ISM, Ist Struttura Mat Consiglio Nazl Ric, Via Salaria,Km 29-300, I-00015 Rome, Italy..
    Mattioli, Giuseppe
    CNR ISM, Ist Struttura Mat Consiglio Nazl Ric, Via Salaria,Km 29-300, I-00015 Rome, Italy..
    Zanotti, Gloria
    CNR ISM, Ist Struttura Mat Consiglio Nazl Ric, Via Salaria,Km 29-300, I-00015 Rome, Italy..
    Pennesi, Giovanna
    CNR ISM, Ist Struttura Mat Consiglio Nazl Ric, Via Salaria,Km 29-300, I-00015 Rome, Italy..
    Filippone, Francesco
    CNR ISM, Ist Struttura Mat Consiglio Nazl Ric, Via Salaria,Km 29-300, I-00015 Rome, Italy..
    Cossaro, Albano
    CNR IOM, Lab Nazl TASC, C Area Sci Pk SS14 Km 163-5, I-34129 Trieste, Italy..
    Verdini, Alberto
    CNR IOM, Lab Nazl TASC, C Area Sci Pk SS14 Km 163-5, I-34129 Trieste, Italy..
    Morgante, Alberto
    CNR IOM, Lab Nazl TASC, C Area Sci Pk SS14 Km 163-5, I-34129 Trieste, Italy.;Univ Trieste, Dept Phys, Via Valerio 2, I-34127 Trieste, Italy..
    Bonapasta, Aldo Amore
    CNR ISM, Ist Struttura Mat Consiglio Nazl Ric, Via Salaria,Km 29-300, I-00015 Rome, Italy..
    A Ru-Ru pair housed in ruthenium phthalocyanine: the role of a "cage" architecture in the molecule coupling with the Ag(111) surface2017In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 19, no 2, p. 1449-1457Article in journal (Refereed)
    Abstract [en]

    A number of studies have investigated the properties of monomeric and double-decker phthalocyanines (Pcs) adsorbed on metal surfaces, in view of applications in spintronics devices. In a combined experimental and theoretical study, we consider here a different member of the Pcs family, the (RuPc)(2) dimer, whose structure is characterized by two paired up magnetic centers embedded in a double-decker architecture. For (RuPc)(2) on Ag(111), we show that this architecture works as a preserving cage by shielding the Ru-Ru pair from a direct interaction with the surface atoms. In fact, while noticeable surface-to-molecule charge transfer occurs with the ensuing quenching of the molecular magnetic moment, such phenomena occur here in the absence of a direct Ru-Ag coupling or structural rearrangement, at variance with other Pcs and thanks to the above shielding effect. These unique properties of the (RuPc)(2) architecture are expected to permit an easy control of the surface-to-molecule charge-transfer process as well as of the molecular magnetic properties, thus making the (RuPc)(2) dimer a significant paradigm for innovative "cage" structures as well as a promising candidate for applications in spintronics nano or single-molecule devices.

  • 47.
    Aliramaji, Shamsa
    et al.
    Rhein Westfal TH Aachen, Mat Chem, Kopernikusstr 10, D-52074 Aachen, Germany..
    Keuter, Philipp
    Rhein Westfal TH Aachen, Mat Chem, Kopernikusstr 10, D-52074 Aachen, Germany..
    Neuss, Deborah
    Rhein Westfal TH Aachen, Mat Chem, Kopernikusstr 10, D-52074 Aachen, Germany..
    Hans, Marcus
    Rhein Westfal TH Aachen, Mat Chem, Kopernikusstr 10, D-52074 Aachen, Germany..
    Primetzhofer, Daniel
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics.
    Depla, Diederik
    Univ Ghent, Dept Solid State Sci, Krijgslaan 281 S1, B-9000 Ghent, Belgium..
    Schneider, Jochen M.
    Rhein Westfal TH Aachen, Mat Chem, Kopernikusstr 10, D-52074 Aachen, Germany..
    Effect of Growth Temperature and Atmosphere Exposure Time on Impurity Incorporation in Sputtered Mg, Al, and Ca Thin Films2023In: Materials, ISSN 1996-1944, E-ISSN 1996-1944, Vol. 16, no 1, article id 414Article in journal (Refereed)
    Abstract [en]

    Impurities can be incorporated during thin film deposition, but also can originate from atmosphere exposure. As impurities can strongly affect the composition-structure-property relations in magnetron sputter deposited thin films, it is important to distinguish between both incorporation channels. Therefore, the impurity incorporation by atmosphere exposure into sputtered Mg, Al, and Ca thin films is systematically studied by a variation of the deposition temperatures and atmosphere exposure times. Deposition temperature variation results in morphological modifications explained by considering surface and bulk diffusion as well as grain boundary motion and evaporation. The film morphologies exhibiting the lowest oxygen concentrations, as measured by energy dispersive X-ray spectroscopy, are obtained at a homologous temperature of 0.4 for both Mg and Al thin films. For Ca, preventing atmosphere exposure is essential to hinder impurity incorporation: By comparing the impurity concentration in Al-capped and uncapped thin films, it is demonstrated that Ca thin films are locally protected by Al-capping, while Mg (and Al) form native passivation layers. Furthermore, it can be learned that the capping (or self-passivation) efficiency in terms of hindering further oxidation of the films in atmosphere is strongly dependent on the underlying morphology, which in turn is defined by the growth temperature.

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  • 48. Alkhadi, H.S.
    et al.
    Tran, Tuan
    Department of Electronic Materials Engineering, Research School of Physics and Engineering, The Australian National University, Canberra, Australia.
    Kremer, F.
    Williams, J.S.
    The influence of capping layers on pore formation in Ge during ion implantation2016In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 120, no 21, article id 215706Article in journal (Refereed)
    Abstract [en]

    Ion induced porosity in Ge has been investigated with and without a cap layer for two ion species, Ge and Sn, with respect to ion fluence and temperature. Results without a cap are consistent with a previous work in terms of an observed ion fluence and temperature dependence of porosity, but with a clear ion species effect where heavier Sn ions induce porosity at lower temperature (and fluence) than Ge. The effect of a cap layer is to suppress porosity for both Sn and Ge at lower temperatures but in different temperatures and fluence regimes. At room temperature, a cap does not suppress porosity and results in a more organised pore structure under conditions where sputtering of the underlying Ge does not occur. Finally, we observed an interesting effect in which a barrier layer of a-Ge that is denuded of pores formed directly below the cap layer. The thickness of this layer (∼ 8 nm) is largely independent of ion species, fluence, temperature, and cap material, and we suggest that this is due to viscous flow of a-Ge under ion irradiation and wetting of the cap layer to minimize the interfacial free energy.

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  • 49.
    Allal, Adel
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Univ Amar Telidji, Lab Phys Mat, BP 37G, Laghouat 03000, Algeria..
    Bouchenafa, Mohamed
    Univ Amar Telidji, Fac Sci, Dept Sci Matiere, BP 37G, Laghouat 03000, Algeria.;Univ Blida 1, Theoret Phys & Radiat Matter Interact Lab LPTHIRM, Phys Dept, Blida, Algeria..
    Halit, Mohamed
    Univ Amar Telidji, Lab Phys Mat, BP 37G, Laghouat 03000, Algeria..
    Saib, Salima
    Univ Msila, Lab Mat Phys & Applicat, Msila 28000, Algeria..
    Liu, Zeliang
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Yanshan Univ, Coll Civil Engn & Mech, Qinhuangdao, Hebei, Peoples R China..
    Luo, Wei
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Structural stability, mechanical, electronic and optical behaviour of RbXS2 (X = Y and La) under high pressure: A first-principle study2020In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 848, article id 156401Article in journal (Refereed)
    Abstract [en]

    The high-pressure behaviour of the ternary sulphides, RbXS2 (X = Y and La), has been investigated by using first-principle calculations based on density functional theory. Upon applying hydrostatic pressure, the unit-cell parameters (a, c) decrease with different rates, indicating an anisotropic axial compression. The most of RbYS2 and RbLaS2 crystals compressibility comes from Rb+1-S-2 bonds. Elastic constants and their dependence on pressure and related mechanical properties have been reported and analysed. From Pugh's criterion, RbYS2 and RbLaS2 turn from brittle to ductile material for applied pressures beyond 3.1 GPa and 2.9 GPa, respectively. Stability criteria show that RbYS2 and RbLaS2 are not mechanically stable in ci-NaFeO2 crystal structure above 20.63 GPa and 16.24 GPa, respectively. Both RbYS2 and RbLaS2 have indirect band gap, which decreases with increasing pressure. However, no indirectdirect band gap transition is observed for both materials. Finally, the calculated optical spectrum of both compounds exhibits an anisotropy and a broadening at high pressures.

  • 50.
    Allal, Adel
    et al.
    Univ Amar Telidji, Lab Phys Mat, BP 37G, Laghouat 03000, Algeria.
    Halit, Mohamed
    Univ Amar Telidji, Lab Phys Mat, BP 37G, Laghouat 03000, Algeria.
    Saib, Salima
    Univ Msila, Lab Mat Phys & Its Applicat, Msila 28000, Algeria.
    Azzouz, Lahcene
    Univ Amar Telidji, Lab Phys Mat, BP 37G, Laghouat 03000, Algeria.
    Maabed, Said
    Univ Amar Telidji, Fac Sci, Dept Sci Matiere, BP 37G, Laghouat 03000, Algeria.
    Bouchenafa, Mohamed
    Univ Amar Telidji, Fac Sci, Dept Sci Matiere, BP 37G, Laghouat 03000, Algeria;Univ Blida 1, Phys Dept, Fundamental & Appl Phys Lab, Blida, Algeria.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    A comparative theoretical investigation of optoelectronic and mechanical properties of KYS2 and KLaS22020In: Materials Science in Semiconductor Processing, ISSN 1369-8001, E-ISSN 1873-4081, Vol. 113, article id 105048Article in journal (Refereed)
    Abstract [en]

    The ternary sulfides KYS2 and KLaS2 are two promising candidates for numerous applications, as much as white LED, X-ray phosphor and transparent conductor materials. However, theoretical studies on these materials are lacking, and many of their physical properties are still unknown. The aim of this work is to investigate the physical properties of the ternary sulfides KYS2 and KLaS2 namely, structural, elastic, optoelectronic, thermodynamic analysis, and set the substitution effect of Y and La elements in the two compounds. The fundamental properties calculations are based on ab-initio pseudopotential framework, with both local density approximation (LDA) and generalized gradient approximations (GGA) along with an expanded set of plane waves. The Becke, 3-parameter, Lee–Yang–Parr (B3LYP) hybrid functional is also employed to describe the electronic structures and optical properties. The optimized crystal parameters are correlated very well with the existing experimental data. The predicted values of the elastic constants demonstrate that the two compounds are mechanically stable and can be classified as brittle materials. The band structure analysis reveals that both KYS2 and KLaS2 have indirect band gap. The optical properties, like the refractive index, extinction, absorption and reflectivity coefficients, are determined for various polarizations of incident light, while both compounds present optical anisotropy. The obtained optical properties indicate the high transparency of KYS2 and KLaS2 in the infrared and visible regions, which makes them promising candidates for many of transparent applications. The thermodynamic properties are investigated with the help of quasiharmonic Debye model approximation. KYS2 has a larger bulk modulus value, which make it more beneficial in engineering applications. Calculations of thermodynamical properties indicate that KYS2 compound has better thermal conductivity, stronger chemical bonds and bigger hardness.

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