Change search
Refine search result
1 - 22 of 22
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Rows per page
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sort
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
Select
The maximal number of hits you can export is 250. When you want to export more records please use the Create feeds function.
  • 1.
    Beaussant Törne, Karin
    KTH, School of Engineering Sciences (SCI), Applied Physics, Material Physics, MF.
    Investigation of corrosion properties of metals for degradable implant applications2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Degradable metallic implants are a new class of biomaterials with potentialto replace permanent materials in temporary applications to reduce therisk of long term adverse effects.This thesis focuses on in vitro testing of zinc and magnesium based metals.As new degradable metals are developed screening of new materials within vitro test methods is an attractive option to avoid unnecessary, time consumingand expensive animal studies. The influence of factors such as ioniccomposition of the test solution, buffer system, strain and alloy compositionwas investigated. By employing electrochemical in situ techniques such asimpedance spectroscopy it is possible to study the metal-solution interfaceand determine the properties of the corroding surface. Ex situ surface characterizationtechniques such as scanning electron microscopy and infraredspectroscopy were then used to complement the results of the electrochemicalmeasurements.The importance of appropriate selection of the test solution is highlightedin this work. Zinc was found to corrode in Ringer’s solution by a mechanismcloser to in vivo corrosion than in a phosphate buffered saline solution(PBS).Ringer’s solution is therefore the more appropriate test environment for longterm evaluation of zinc based metals.When evaluating the corrosion of Zn-Mg and Zn-Ag alloys in Ringer’ssolution selective dissolution was found to occur for both types of alloys. Localprecipitation and formation of a porous, less protective, layer of corrosionproducts was found for Zn-Mg alloys. The selective dissolution of Zn-Agalloy caused an enrichment of AgZn3 on the surface which may affect thebiocompatibility of the alloy.The use of HEPES to maintain the pH of the test solution increasedthe corrosion rate of magnesium due to formation of a less protective layerof corrosion products. Magnesium corrosion should therefore preferably bestudied in solutions where the pH is maintained by the biological buffer systemCO2/H2CO3.In addition to saline solutions human whole blood and plasma were evaluatedas more clinically relevant in vitro environments. They were found toproduce reproducible results and to be suitable for short term experiments.Formation of a corrosion product layer comprised of both organic and inorganicmaterial was detected on zinc in both plasma and whole blood.During anodic polarization the adsorption of organic species on the zincsurface was found to increase the surface coverage of Zn ions in whole blood.The increased surface coverage then allowed for precipitation of a protectivelayer of Zn5(PO4)3 and a subsequent decrease in corrosion rate at higherpotentials.When subjecting zinc samples to strain the organic/inorganic corrosionproduct formed in whole blood was observed by impedance spectroscopy toprevent micro cracking and premature failure.The cracking of magnesium alloy samples under applied strain was alsocharacterized by impedance. Changes in surface properties due to crack initiation

  • 2.
    Besharat, Zahra
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Material Physics, MF. KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Ghadami Yazdi, Milad
    KTH, School of Engineering Sciences (SCI), Applied Physics, Material Physics, MF.
    Wakeham, Deborah
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Johnson, Magnus
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Rutland, Mark W.
    SP Technical Research Institute of Sweden, Sweden.
    Göthelid, Mats
    KTH, School of Engineering Sciences (SCI), Applied Physics, Material Physics, MF.
    Grönbeck, Henrik
    Se-C Cleavage of Hexane Selenol at Steps on Au(111)2018In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 34, no 8, p. 2630-2636Article in journal (Refereed)
    Abstract [en]

    Selenols are considered as an alternative to thiols in self-assembled monolayers, but the Se-C bond is one limiting factor for their usefulness. In this study, we address the stability of the Se-C bond by a combined experimental and theoretical investigation of gas phase-deposited hexane selenol (CH3(CH2)(5)SeH) on Au(111) using photoelectron spectroscopy, scanning tunneling microscopy, and density functional theory (DFT). Experimentally, we find that initial adsorption leaves atomic Se on the surface without any carbon left on the surface, whereas further adsorption generates a saturated selenolate layer. The Se 3d component from atomic Se appears at 0.85 eV lower binding energy than the selenolate-related component. DFT calculations show that the most stable structure of selenols on Au(111) is in the form of RSe-Au-SeR complexes adsorbed on the unreconstructed Au(111) surface. This is similar to thiols on Au(111). Calculated Se 3d core-level shifts between elemental Se and selenolate in this structure nicely reproduce the experimentally recorded shifts. Dissociation of RSeH and subsequent formation of RH are found to proceed with high barriers on defect-free Au(111) terraces, with the highest barrier for scissoring R-Se. However, at steps, these barriers are considerably lower, allowing for Se-C bond breaking and hexane desorption, leaving elemental Se at the surface. Hexane is the selenol to selenolate formed by replacing the Se-C bond with a H-C bond by using the hydrogen liberated from transformation.

  • 3.
    Besharat, Zahra
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Material Physics, MF. KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Halldin Stenlid, Joakim
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Soldemo, Markus
    KTH, School of Engineering Sciences (SCI), Applied Physics, Material Physics, MF.
    Marks, Kess
    Önsten, Anneli
    KTH, School of Engineering Sciences (SCI), Applied Physics, Material Physics, MF.
    Johnson, Magnus
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Öström, Henrik
    Weissenrieder, Jonas
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Brinck, Tore
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Göthelid, Mats
    KTH, School of Engineering Sciences (SCI), Applied Physics, Material Physics, MF.
    Dehydrogenation of methanol on Cu2O(100) and (111)2017In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 146, no 24Article in journal (Refereed)
    Abstract [en]

    Adsorption and desorption of methanol on the (111) and (100) surfaces of  Cu2O have been studied using high-resolution photoelectron spectroscopy in the temperature range 120–620 K, in combination with density functional theorycalculations and sum frequency generation spectroscopy. The bare (100) surfaceexhibits a (3,0; 1,1) reconstruction but restructures during the adsorption process into a Cu-dimer geometry stabilized by methoxy and hydrogen binding in Cu-bridge sites. During the restructuring process, oxygen atoms from the bulk that can host hydrogen appear on the surface. Heating transforms methoxy to formaldehyde, but further dehydrogenation is limited by the stability of the surface and the limited access to surface oxygen. The (√3 × √3)R30°-reconstructed (111) surface is based on ordered surface oxygen and copper ions and vacancies, which offers a palette of adsorption and reaction sites. Already at 140 K, a mixed layer of methoxy, formaldehyde, and CHxOy is formed. Heating to room temperature leaves OCH and CHx. Thus both CH-bond breaking and CO-scission are active on this  surface at low temperature. The higher ability to dehydrogenate methanol on (111) compared to (100) is explained by the multitude of adsorption sites and, in particular, the availability of surfaceoxygen.

  • 4.
    Elgammal, Karim
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Material Physics, MF. KTH Royal Institute of Technology.
    Delin, Anna
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics. KTH, Superseded Departments (pre-2005), Materials Science and Engineering. KTH, Centres, SeRC - Swedish e-Science Research Centre. Uppsala University.
    Adsorption of carbon dioxide and water molecules on graphene on top of silica substrates: dispersion corrected density functional calculationsManuscript (preprint) (Other academic)
    Abstract [en]

    We report on systematic computational studies of carbon dioxide and water molecule adsorption on graphene, with the graphene layer deposited on top of a substrate. Specifically, we address the influence of cristobalite and quartz substrates, i.e. two different types of silicon dioxide. The computations are based on density functional theory (DFT), with a nonempirical nonlocal van der Waals density functional included to account for dispersion forces.We calculate the binding energies and equilibrium positions of the molecules, as well as charge transfer and how the charge density of the graphene layer changes due to the interactions with the substrate and the molecules. The molecule-graphene bonding distances are found to be in the range 3.3-3.4 Å, and the graphene-substrate bonding distances around 3.6 Å. These values are slightly larger than what we have found previously, using an empirical expression for the van der Waals density functional. At the same time, the values for the binding energies are increased, compared to what we have obtained in a previous study. We find, in all cases, a net electron transfer from the adsorbed molecule to the graphene+substrate system. For quartz, the total charge transfer is between 0.1 and 0.2 electrons per adsorbed molecule. For cristobalite, it is only about a tenth of that. Our findings are consistent with earlier calculations as well as experimental data.

  • 5.
    Elgammal, Karim
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Material Physics, MF. KTH Royal Institute of Technology.
    Delin, Anna
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics. KTH, Superseded Departments (pre-2005), Materials Science and Engineering. KTH, Centres, SeRC - Swedish e-Science Research Centre. Uppsala University.
    Graphene adhesion on surfaces: a van der Waals density functional studyManuscript (preprint) (Other academic)
    Abstract [en]

    We present a van der Waals density functional (vdW-DF) calculations study of graphene adhesion to different types of substrates with different surface conditions. The study expands to both metal and semiconductor substrates with different surface endings. All substrate surfaces were the 111 surfaces where they have hexagonal lattice parameters perfectly matching with the graphene's. Adsorption geometries, energies, bader charges, dipole moments and electronic structure in terms of density of states are investigated. The results are showing a general agrement with both experimental results as well as theoritical findings done with similar setup. The results reveal that the degree of adhesive of graphene to different surfaces can affect the electronic structure of graphene ending in having different applications when designing graphene in building nano-electronic devices.

  • 6.
    Faure, Quentin
    et al.
    Univ Grenoble Alpes, CEA, INAC MEM, Grenoble, France.;Univ Grenoble Alpes, Inst NEEL, Grenoble, France..
    Takayoshi, Shintaro
    Univ Geneva, Dept Quantum Matter Phys, Geneva, Switzerland..
    Petit, Sylvain
    Univ Paris Saclay, CNRS, CEA, CE Saclay,Lab Leon Brillouin, Gif Sur Yvette, France..
    Simonet, Virginie
    Univ Grenoble Alpes, Inst NEEL, Grenoble, France..
    Raymond, Stephane
    Univ Grenoble Alpes, CEA, INAC MEM, Grenoble, France..
    Regnault, Louis-Pierre
    Univ Grenoble Alpes, CEA, INAC MEM, Grenoble, France..
    Boehm, Martin
    Inst Laue Langevin, Grenoble, France..
    White, Jonathan S.
    Paul Scherrer Inst, Lab Neutron Scattering & Imaging, Villigen, Switzerland..
    Månsson, Martin
    KTH, School of Engineering Sciences (SCI), Applied Physics, Material Physics, MF. Paul Scherrer Inst, Lab Neutron Scattering & Imaging, Villigen, Switzerland.
    Rueegg, Christian
    Univ Geneva, Dept Quantum Matter Phys, Geneva, Switzerland.;Paul Scherrer Inst, Lab Neutron Scattering & Imaging, Villigen, Switzerland..
    Lejay, Pascal
    Univ Grenoble Alpes, Inst NEEL, Grenoble, France..
    Canals, Benjamin
    Univ Grenoble Alpes, Inst NEEL, Grenoble, France..
    Lorenz, Thomas
    Univ Cologne, Phys Inst 2, Cologne, Germany..
    Furuya, Shunsuke C.
    RIKEN, Condensed Matter Theory Lab, Wako, Saitama, Japan..
    Giamarchi, Thierry
    Univ Geneva, Dept Quantum Matter Phys, Geneva, Switzerland..
    Grenier, Beatrice
    Univ Grenoble Alpes, CEA, INAC MEM, Grenoble, France..
    Topological quantum phase transition in the Ising-like antiferromagnetic spin chain BaCo2V2O82018In: Nature Physics, ISSN 1745-2473, E-ISSN 1745-2481, Vol. 14, no 7, p. 716-722Article in journal (Refereed)
    Abstract [en]

    Since the seminal ideas of Berezinskii, Kosterlitz and Thouless, topological excitations have been at the heart of our understanding of a whole novel class of phase transitions. In most cases, those transitions are controlled by a single type of topological objects. There are, however, some situations, still poorly understood, where two dual topological excitations fight to control the phase diagram and the transition. Finding experimental realizations of such cases is thus of considerable interest. We show here that this situation occurs in BaCo2V2O8, a spin-1/2 Ising-like quasi-one-dimensional antiferromagnet, when subjected to a uniform magnetic field transverse to the Ising axis. Using neutron scattering experiments, we measure a drastic modification of the quantum excitations beyond a critical value of the magnetic field. This quantum phase transition is identified, through a comparison with theoretical calculations, to be a transition between two different types of solitonic topological object, which are captured by different components of the dynamical structure factor.

  • 7.
    Ghadami Yazdi, Milad
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Material Physics, MF.
    H. Moud, Pouya
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology. KTH.
    Marks, Kess
    Piskorz, Witold
    Öström, Henrik
    Hansson, Tony
    Kotarba, Andrzej
    Engvall, Klas
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
    Göthelid, Mats
    KTH, School of Engineering Sciences (SCI), Applied Physics, Material Physics, MF.
    Naphthalene on Ni(111): experimental and theoretical insights into adsorption, dehydrogenation and carbon passivationManuscript (preprint) (Other academic)
    Abstract [en]

    An attractive solution to mitigate tars and also to decompose lighter hydrocarbons in biomass gasification is secondary catalytic reforming, converting hydrocarbons to useful permanent gases. Albeit in use for long time in fossil feedstock catalytic steam reforming, the understanding of the catalytic processes is still limited. Naphthalene is typically present in the biomass gasification gas and to further understand the elementary steps of naphthalene transformation, we investigated the temperature dependent naphthalene adsorption, dehydrogenation and passivation on Ni(111). TPD (temperature programmed desorption) and STM (scanning tunneling microscopy) in ultra-high vacuum environment from 110 K up to 780 K, combined with DFT (density functional theory) were used in the study. Room temperature adsorption results in a flat naphthalene monolayer. DFT favors the di-bridge[7] geometry but the potential energy surface is rather smooth. DFT also reveals a pronounced dearomatization and charge transfer from the adsorbed molecule into the nickel surface. Dehydrogenation occurs in two steps, with two desorption peaks at approximately 450 K and 600 K. The first step is due to partial dehydrogenation generating active hydrocarbon species that at higher temperatures migrates over the surface forming graphene. The graphene formation is accompanied by desorption of hydrogen in the high temperature TPD peak. The formation of graphene effectively passivates the surface both for hydrogen adsorption and naphthalene dissociation. In conclusion, the obtained results on the model naphthalene and Ni(111) system, provides insight into elementary steps of naphthalene adsorption, dehydrogenation and carbon passivation, which may serve as a good starting point for rational design, development and optimization of the Ni catalyst surface, as well as process conditions, for the aromatic hydrocarbon reforming process.

  • 8.
    Göthelid, Mats
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Material Physics, MF.
    Hosseinpour, S.
    Ahmadi, S.
    Leygraf, Christofer
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Johnson, C. Magnus
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Hexane selenol dissociation on Cu: The protective role of oxide and water2017In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 423, p. 716-720Article in journal (Refereed)
    Abstract [en]

    Hexane selenol (CH3(CH2)5SeH) was adsorbed from gas phase in ultra-high vacuum on polycrystalline Cu and studied with synchrotron radiation based photoelectron spectroscopy (PES) and Near edge X-ray absorption fine structure spectroscopy (NEXAFS). Adsorption was done on a bare copper surface at room temperature (RT), on a thin oxide on Cu at room temperature, and on a thin layer of water on Cu at 140 K.

  • 9.
    Ji, Shaozheng
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Material Physics, MF.
    Piazza, Luca
    KTH, School of Engineering Sciences (SCI), Applied Physics, Material Physics, MF.
    Cao, Gaolong
    KTH, School of Engineering Sciences (SCI), Applied Physics, Material Physics, MF.
    Park, S. T.
    Reed, B. W.
    Masiel, D. J.
    Weissenrieder, Jonas
    KTH, School of Engineering Sciences (SCI), Applied Physics, Material Physics, MF.
    Influence of cathode geometry on electron dynamics in an ultrafast electron microscope2017In: Structural Dynamics, ISSN 2329-7778, Vol. 4, no 5, article id 054303Article in journal (Refereed)
    Abstract [en]

    Efforts to understand matter at ever-increasing spatial and temporal resolutions have led to the development of instruments such as the ultrafast transmission electron microscope (UEM) that can capture transient processes with combined nanometer and picosecond resolutions. However, analysis by UEM is often associated with extended acquisition times, mainly due to the limitations of the electron gun. Improvements are hampered by tradeoffs in realizing combinations of the conflicting objectives for source size, emittance, and energy and temporal dispersion. Fundamentally, the performance of the gun is a function of the cathode material, the gun and cathode geometry, and the local fields. Especially shank emission from a truncated tip cathode results in severe broadening effects and therefore such electrons must be filtered by applying a Wehnelt bias. Here we study the influence of the cathode geometry and the Wehnelt bias on the performance of a photoelectron gun in a thermionic configuration. We combine experimental analysis with finite element simulations tracing the paths of individual photoelectrons in the relevant 3D geometry. Specifically, we compare the performance of guard ring cathodes with no shank emission to conventional truncated tip geometries. We find that a guard ring cathode allows operation at minimum Wehnelt bias and improve the temporal resolution under realistic operation conditions in an UEM. At low bias, the Wehnelt exhibits stronger focus for guard ring than truncated tip cathodes. The increase in temporal spread with bias is mainly a result from a decrease in the accelerating field near the cathode surface. Furthermore, simulations reveal that the temporal dispersion is also influenced by the intrinsic angular distribution in the photoemission process and the initial energy spread. However, a smaller emission spot on the cathode is not a dominant driver for enhancing time resolution. Space charge induced temporal broadening shows a close to linear relation with the number of electrons up to at least 10 000 electrons per pulse. The Wehnelt bias will affect the energy distribution by changing the Rayleigh length, and thus the interaction time, at the crossover.

  • 10. Klyushina, E. S.
    et al.
    Lake, B.
    Islam, A. T. M. N.
    Park, J. T.
    Schneidewind, A.
    Guidi, T.
    Goremychkin, E. A.
    Klemke, B.
    Månsson, Martin
    KTH, School of Engineering Sciences (SCI), Applied Physics, Material Physics, MF.
    Investigation of the spin-1 honeycomb antiferromagnet BaNi2V2O8 with easy-plane anisotropy2017In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 96, no 21, article id 214428Article in journal (Refereed)
    Abstract [en]

    The magnetic properties of the two-dimensional, S = 1 honeycomb antiferromagnet BaNi2V2O8 have been comprehensively studied using dc susceptibility measurements and inelastic neutron scattering techniques. The magnetic excitation spectrum is found to be dispersionless within experimental resolution between the honeycomb layers, while it disperses strongly within the honeycomb plane where it consists of two gapped spin-wave modes. The magnetic excitations are compared to linear spin-wave theory allowing the Hamiltonian to be determined. The first-and second-neighbor magnetic exchange interactions are antiferromagnetic and lie within the ranges 10.90 meV <= J(n) <= 13.35 meV and 0.85 meV <= J(nn) <= 1.65 meV, respectively. The interplane coupling J(out) is four orders of magnitude weaker than the intraplane interactions, confirming the highly two-dimensional magnetic behavior of this compound. The sizes of the energy gaps are used to extract the magnetic anisotropies and reveal substantial easy-plane anisotropy and a very weak in-plane easy-axis anisotropy. Together these results reveal that BaNi2V2O8 is a candidate compound for the investigation of vortex excitations and Berezinsky-Kosterliz-Thouless phenomenon.

  • 11.
    Linnarsson, Margareta K.
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Material Physics, MF.
    Hallén, Anders
    KTH, School of Information and Communication Technology (ICT), Electronics, Integrated devices and circuits.
    Khartsev, Sergiy
    KTH, School of Information and Communication Technology (ICT), Electronics, Integrated devices and circuits.
    Suvanam, Sethu Saveda
    KTH, School of Information and Communication Technology (ICT).
    Usman, Muhammad
    KTH, School of Information and Communication Technology (ICT), Electronics, Integrated devices and circuits.
    Interface between Al2O3 and 4H-SiC investigated by time-of-flight medium energy ion scattering2017In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 50, no 49, article id 495111Article in journal (Refereed)
    Abstract [en]

    The formation of interfacial oxides during heat treatment of dielectric films on 4H-SiC has been studied. The 4H-SiC surface has been carefully prepared to create a clean and abrupt interface to Al2O3. An amorphous, 3 nm thick, Al2O3 film has been prepared on 4H-SiC by atomic layer deposition and rapid thermal annealing was then performed in N2O ambient at 700 degrees C and 1100 degrees C during 1 min. The samples were studied by time-of-flight medium energy ion scattering (ToF-MEIS), with sub-nanometer depth resolution and it is seen that, at both annealing temperatures, a thin SiOx (1 <= x <= 2) is formed at the interface. Our results further indicate that carbon remains in the silicon oxide in samples annealed at 700 degrees C. Additional electrical capacitance voltage measurements indicate that a large concentration of interface traps is formed at this temperature. After 1100 degrees C annealing, both MEIS and XRD measurements show that these features disappear, in accordance with electrical data.

  • 12. Matt, C. E.
    et al.
    Sutter, D.
    Cook, A. M.
    Sassa, Y.
    Månsson, Martin
    KTH, School of Engineering Sciences (SCI), Applied Physics, Material Physics, MF.
    Tjernberg, Oscar
    KTH, School of Engineering Sciences (SCI), Applied Physics, Material Physics, MF.
    Das, L.
    Horio, M.
    Destraz, D.
    Fatuzzo, C. G.
    Hauser, K.
    Shi, M.
    Kobayashi, M.
    Strocov, V. N.
    Schmitt, T.
    Dudin, P.
    Hoesch, M.
    Pyon, S.
    Takayama, T.
    Takagi, H.
    Lipscombe, O. J.
    Hayden, S. M.
    Kurosawa, T.
    Momono, N.
    Oda, M.
    Neupert, T.
    Chang, J.
    Direct observation of orbital hybridisation in a cuprate superconductor2018In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 9, article id 972Article in journal (Refereed)
    Abstract [en]

    The minimal ingredients to explain the essential physics of layered copper-oxide (cuprates) materials remains heavily debated. Effective low-energy single-band models of the copper-oxygen orbitals are widely used because there exists no strong experimental evidence supporting multi-band structures. Here, we report angle-resolved photoelectron spectroscopy experiments on La-based cuprates that provide direct observation of a two-band structure. This electronic structure, qualitatively consistent with density functional theory, is parametrised by a two-orbital (d(x2-y2) and d(z2)) tight-binding model. We quantify the orbital hybridisation which provides an explanation for the Fermi surface topology and the proximity of the van-Hove singularity to the Fermi level. Our analysis leads to a unification of electronic hopping parameters for single-layer cuprates and we conclude that hybridisation, restraining d-wave pairing, is an important optimisation element for superconductivity.

  • 13.
    Mirsakiyeva, Amina
    KTH, School of Engineering Sciences (SCI), Applied Physics, Material Physics, MF.
    Electronic and optical properties of conducting polymers from quantum mechanical computations2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

        Conductive polymers are also known as "organic metals" due to their semiconducting properties. They are found in a wide range of applications in the field of organic electronics. However, the growing number of experimental works is not widely supported with theoretical calculations. Hence, the field of conductive polymers is experiencing lack of understanding of mechanisms occurring in the polymers. In this PhD thesis, the aim is to increase understanding of conductive polymers by performing theoretical calculations.       

    The polymers poly(3,4-ethylenedioxythiophene) (PEDOT) together with its selenium (PEDOS) and tellurium (PEDOTe) derivatives, poly(p-phenylene) (PPP) and naphthobischalcogenadiazoles (NXz) were studied. Several computational methods were applied for analysis of mentioned structures, including density functional theory (DFT), tight-binding modelling (TB), and Car-Parrinello molecular dynamics (CPMD) calculations. The combination of CPMD and DFT calculations was applied to investigate the PEDOT, PEDOS and PEDOTe. The polymers were studied using four different functionals in order to investigate the full picture of structural changes, electronic and optical properties. Temperature effects were studied using molecular dynamics simulations. Wide statistics for structural and molecular orbitals analysis were collected.        

    The TB method was employed for PPP. The formation and motion of the excitations, polarons and bipolarons, along the polymer backbone was investigated in presence of electric and magnetic fields. The influence of non-magnetic and magnetic impurities was determined.       

    The extended π-conjugated structures of NXz were computed using B3LYP and ωB97XD functionals in combination with the 6-31+G(d) basis set. Here, the structural changes caused by polaron formation were analyzed. The combined analysis of densities of states and absorption spectra was used for understanding of the charge transition.

  • 14. Muehlbauer, S.
    et al.
    Brandl, G.
    Månsson, Martin
    KTH, School of Engineering Sciences (SCI), Applied Physics, Material Physics, MF.
    Garst, M.
    Formation of incommensurate long-range magnetic order in the Dzyaloshinskii-Moriya antiferromagnet Ba-2 CuGe2O7 studied by neutron diffraction2017In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 96, no 13, article id 134409Article in journal (Refereed)
  • 15.
    Nguyen, T. N. A.
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Material Physics, MF. Institute of Materials Science, Vietnam Academy of Science and Technology, 18 Hoang Quoc Viet, Hanoi, Viet Nam Department of Physics, University of Gothenburg, Gothenburg, 41296, Sweden.
    Fedotova, J.
    Kasiuk, J.
    Bayev, V.
    Kupreeva, O.
    Lazarouk, S.
    Manh, D. H.
    Vu, D. L.
    Chung, Sunjae
    KTH, School of Engineering Sciences (SCI), Applied Physics, Material Physics, MF. University of Gothenburg, Sweden.
    Åkerman, Johan
    KTH, School of Engineering Sciences (SCI), Applied Physics, Material Physics, MF. University of Gothenburg, Sweden.
    Altynov, V.
    Maximenko, A.
    Effect of flattened surface morphology of anodized aluminum oxide templates on the magnetic properties of nanoporous Co/Pt and Co/Pd thin multilayered films2018In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 427, p. 649-655Article in journal (Refereed)
    Abstract [en]

    For the first time, nanoporous Al2O3 templates with smoothed surface relief characterized by flattened interpore areas were used in the fabrication of Co/Pd and Co/Pt multilayers (MLs) with strong perpendicular magnetic anisotropy (PMA). Alternating gradient magnetometry (AGM) revealed perfectly conserved PMA in the Co/Pd and Co/Pt porous MLs (antidot arrays) with a ratio of remanent magnetization (Mr) to saturation magnetization (MS) of about 0.99, anisotropy fields (Ha) of up to 2.6 kOe, and a small deviation angle of 8° between the easy magnetization axis and the normal to the film surface. The sufficient magnetic hardening of the porous MLs with enhanced coercive field HC of up to ∼1.9 kOe for Co/Pd and ∼1.5 kOe for Co/Pt MLs, as compared to the continuous reference samples (∼1.5–2 times), is associated with the pinning of the magnetic moments on the nanopore edges. Application of the Stoner–Wohlfarth model for fitting the experimental M/MS(H) curves yielded clear evidence of the predominantly coherent rotation mechanism of magnetization reversal in the porous films.

  • 16. Polley, Craig M.
    et al.
    Buczko, Ryszard
    Forsman, Alexander
    Dziawa, Piotr
    Szczerbakow, Andrzej
    Rechcinski, Rafal
    Kowalski, Bogdan J.
    Story, Tomasz
    Trzyna, Malgorzata
    Bianchi, Marco
    Cabo, Antonija Grubisic
    Hofmann, Philip
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Tjernberg, Oscar
    KTH, School of Engineering Sciences (SCI), Applied Physics, Material Physics, MF.
    Balasubramanian, Thiagarajan
    Fragility of the Dirac Cone Splitting in Topological Crystalline Insulator Heterostructures2018In: ACS Nano, ISSN 1936-0851, E-ISSN 1936-086X, Vol. 12, no 1, p. 617-626Article in journal (Refereed)
    Abstract [en]

    The "double Dirac cone" 2D topological interface states found on the (001) faces of topological crystalline insulators such as Pb1-xSnxSe feature degeneracies located away from time reversal invariant momenta and are a manifestation of both mirror symmetry protection and valley interactions. Similar shifted degeneracies in 1D interface states have been highlighted as a potential basis for a topological transistor, but realizing such a device will require a detailed understanding of the intervalley physics involved. In addition, the operation of this or similar devices outside of ultrahigh vacuum will require encapsulation, and the consequences of this for the topological interface state must be understood. Here we address both topics for the case of 2D surface states using angle-resolved photoemission spectroscopy. We examine bulk Pb1-xSnxSe(001) crystals overgrown with PbSe, realizing trivial/topological heterostructures. We demonstrate that the valley interaction that splits the two Dirac cones at each (X) over bar is extremely sensitive to atomic-scale details of the surface, exhibiting non-monotonic changes as PbSe deposition proceeds. This includes an apparent total collapse of the splitting for sub-monolayer coverage, eliminating the Lifshitz transition. For a large overlayer thickness we observe quantized PbSe states, possibly reflecting a symmetry confinement mechanism at the buried topological interface.

  • 17. Razzoli, E.
    et al.
    Matt, C. E.
    Sassa, Y.
    Månsson, Martin
    KTH, School of Engineering Sciences (SCI), Applied Physics, Material Physics, MF. Ecole Polytech Fed Lausanne, Switzerland.
    Tjernberg, Oscar
    KTH, School of Engineering Sciences (SCI), Applied Physics, Material Physics, MF.
    Drachuck, G.
    Monomo, M.
    Oda, M.
    Kurosawa, T.
    Huang, Y.
    Plumb, N. C.
    Radovic, M.
    Keren, A.
    Patthey, L.
    Mesot, J.
    Shi, M.
    Rotation symmetry breaking in La2-xSrxCuO4 revealed by angle-resolved photoemission spectroscopy2017In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 95, no 22, article id 224504Article in journal (Refereed)
    Abstract [en]

    Using angle-resolved photoemission spectroscopy it is revealed that in the vicinity of optimal doping the electronic structure of La2-x SrxCuO4 cuprate undergoes an electronic reconstruction associated with a wave vector q(a) = (pi, 0). The reconstructed Fermi surface and folded band are distinct to the shadow bands observed in BSCCO cuprates and in underdoped La2-xSrxCuO4 with x <= 0.12, which shift the primary band along the zone diagonal direction. Furthermore, the folded bands appear only with q(a) = (pi, 0) vector, but not with q(b) = (0, pi). We demonstrate that the absence of q(b) reconstruction is not due to thematrix-element effects in the photoemission process, which indicates the fourfold symmetry is broken in the system.

  • 18.
    Soldemo, Markus
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Material Physics, MF.
    Halldin Stenlid, Joakim
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Besharat, Zahra
    KTH, School of Engineering Sciences (SCI), Applied Physics, Material Physics, MF.
    Johansson, N.
    Önsten, Anneli
    KTH, School of Engineering Sciences (SCI), Applied Physics, Material Physics, MF.
    Knudsen, J.
    Schnadt, J.
    Göthelid, Mats
    KTH, School of Engineering Sciences (SCI), Applied Physics, Material Physics, MF.
    Brinck, Tore
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Weissenrieder, Jonas
    KTH, School of Engineering Sciences (SCI), Applied Physics, Material Physics, MF.
    Interaction of Sulfur Dioxide and Near-Ambient Pressures of Water Vapor with Cuprous Oxide Surfaces2017In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 121, no 43, p. 24011-24024Article in journal (Refereed)
    Abstract [en]

    The interaction of water vapor and sulfur dioxide (SO2) with single crystal cuprous oxide (Cu2O) surfaces of (100) and (111) termination was studied by photoelectron spectroscopy (PES) and density functional theory (DFT). Exposure to near-ambient pressures of water vapor, at 5 × 10-3 %RH and 293 K, hydroxylates both Cu2O surfaces with OH coverage up to 0.38 copper monolayers (ML) for (100) and 0.25 ML for (111). O 1s surface core level shifts indicate that the hydroxylation lifts the (3,0;1,1) reconstruction of the clean (100) surface. On both clean Cu2O terminations, SO2 adsorbs to unsaturated surface oxygen atoms to form SO3 species with coverage, after a saturating SO2 dose, corresponding to 0.20 ML on the Cu2O(100) surface and 0.09 ML for the Cu2O(111) surface. Our combined DFT and PES results suggest that the SO2 to SO3 transformation is largely facilitated by unsaturated copper atoms at the Cu2O(111) surface. SO3-terminated surfaces exposed to low doses of water vapor (≤100 langmuirs) in ultrahigh vacuum show no adsorption or reaction. However, during exposure to near-ambient pressures of water vapor, the SO3 species dissociate, and sulfur replaces a Cu2O lattice oxygen in a reaction that forms Cu2S. The hydroxylation of the Cu2O surfaces is believed to play a central role in the reaction.

  • 19. Sugiyama, Jun
    et al.
    Nozaki, Hiroshi
    Umegaki, Izumi
    Miwa, Kazutoshi
    Higemoto, Wataru
    Ansaldo, Eduardo J.
    Brewer, Jess H.
    Sakurai, Hiroya
    Isobe, Masahiko
    Takagi, Hidenori
    Månsson, Martin
    KTH, School of Engineering Sciences (SCI), Applied Physics, Material Physics, MF.
    Magnetism of the A-site ordered perovskites CaCu3Cr4O12 and LaCu3Cr4O122018In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 97, no 2, article id 024416Article in journal (Refereed)
    Abstract [en]

    The microscopic magnetic nature of the A-site ordered chromium perovskites CaCu3Cr4O12 and LaCu3Cr4O12 and their solid-solution system, Ca1-x LaxCu3Cr4O12, with x = 0.2, 0.4, and 0.8, has been studied with muon spin rotation and relaxation (mu+SR) measurements down to 2 K using a powder sample. For CaCu3Cr4O12, mu+SR revealed the formation of static antiferromagnetic (AF) order below 122 K (=T-N), although magnetization measurements showed a very small change at T-N. Analyses of the internal magnetic field H-int at the muon sites, predicted with first-principles calculations, suggested G-type AF order as a ground state. For LaCu3Cr4O12 with T-N = 225 K, mu+SR also supported the presence of aG-type AF ordered state, which was recently proposed based on neutron diffraction measurements. However, the ordered Cr moments were found to change the direction at around 10 K. For Ca1-xLaxCu3Cr4O12, both T-N and H-int at 2 K increase monotonically with x.

  • 20. Umegaki, Izumi
    et al.
    Kawauchi, Shigehiro
    Sawada, Hiroshi
    Nozaki, Hiroshi
    Higuchi, Yuki
    Miwa, Kazutoshi
    Kondo, Yasuhito
    Månsson, Martin
    KTH, School of Engineering Sciences (SCI), Applied Physics, Material Physics, MF.
    Telling, Mark
    Coomer, Fiona C.
    Cottrell, Stephen P.
    Sasaki, Tsuyoshi
    Kobayashi, Tetsuro
    Sugiyama, Jun
    Li-ion diffusion in Li intercalated graphite C6Li and C12Li probed by mu+SR2017In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 19, no 29, p. 19058-19066Article in journal (Refereed)
    Abstract [en]

    In order to study a diffusive behavior of Li+ in Li intercalated graphites, we have measured muon spin relaxation (mu+SR) spectra for C6Li and C12Li synthesized with an electrochemical reaction between Li and graphite in a Li-ion battery. For both compounds, it was found that Li+ ions start to diffuse above 230 K and the diffusive behavior obeys a thermal activation process. The activation energy (E-a) for C6Li is obtained as 270(5) meV, while E-a = 170(20) meV for C12Li. Assuming a jump diffusion of Li+ in the Li layer of C6Li and C12Li, a self-diffusion coefficient D-Li at 310 K was estimated as 7.6(3) x 10(-11) (cm(2) s(-1)) in C6Li and 14.6(4) x 10(-11) (cm(2) s(-1)) in C12Li.

  • 21.
    Usman, Muhammad
    et al.
    KTH, School of Information and Communication Technology (ICT). Natl Ctr Phys, Expt Phys Labs, Quaid I Azam Univ Campus,Shahdara Valley Rd, Islamabad, Pakistan.
    Suvanam, Sethu Saveda
    KTH, School of Information and Communication Technology (ICT).
    Linnarsson, Margareta
    KTH, School of Engineering Sciences (SCI), Applied Physics, Material Physics, MF.
    Hallén, Anders
    KTH, School of Information and Communication Technology (ICT), Electronics, Integrated devices and circuits.
    Improving the quality of Al2O3/4H-SiC interface for device applications2018In: Materials Science in Semiconductor Processing, ISSN 1369-8001, E-ISSN 1873-4081, Vol. 81, p. 118-121Article in journal (Refereed)
    Abstract [en]

    The present paper focuses on the investigation of Al2O3/4H-SiC dielectric interface upon annealing, its consequent structural modifications, and the link to electrical properties. For this purpose, the test structures are prepared by depositing Al2O3, using atomic layer deposition (ALD), on low doped n-type 4H-SiC epitaxial layers. The structures are annealed from 300 degrees C to 1100 degrees C for different time duration (from 5 to 60 mins) and ambient such as, low vacuum (10(-1) Torr), N-2, and N2O. The structural studies on these samples are conducted using synchrotron-based high resolution x-ray photoelectron spectroscopy (HR-XPS), lab-based XPS, time of flight elastic recoil detection analysis (ToF-ERDA), and time of flight medium energy ion scattering (ToF-MEIS). The electrical response of capacitive structures is monitored through capacitance voltage (CV) measurements for as-deposited and annealed structures. It is found that the annealing at high temperatures, such as 1100 degrees C, and in N-2 or N2O environment, improves the dielectric properties due to the introduction of a thin layer of about 1 nm stable SiO2 between the Al2O3 and 4H-SiC.

  • 22. Xiao, D.
    et al.
    Tiberkevich, V.
    Liu, Y. H.
    Liu, Y. W.
    Mohseni, S. M.
    Chung, Sunjae
    KTH, School of Engineering Sciences (SCI), Applied Physics, Material Physics, MF. University of Gothenburg, Sweden.
    Ahlberg, M.
    Slavin, A. N.
    Åkerman, Johan
    KTH, School of Engineering Sciences (SCI), Applied Physics, Material Physics, MF. University of Gothenburg, Sweden.
    Zhou, Yan
    Parametric autoexcitation of magnetic droplet soliton perimeter modes2017In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 95, no 2, article id 024106Article in journal (Refereed)
    Abstract [en]

    Recent experiments performed in current-driven nanocontacts with strong perpendicular anisotropy have shown that spin-transfer torque can drive self-localized spin waves [W. H. Rippard, A. M. Deac, M. R. Pufall, J. M. Shaw, M. W. Keller, S. E. Russek, G. E. W. Bauer, and C. Serpico, Phys. Rev. B 81, 014426 (2010); S. M. Mohseni, S. R. Sani, J. Persson, T. N. A. Nguyen, S. Chung, Y. Pogoryelov, and J. Akerman, Phys. Status Solidi RRL, 5, 432 (2011)], that above a certain intensity threshold can condense into a nanosized and highly nonlinear dynamic state known as a magnetic droplet soliton [S. M. Mohseni, S. R. Sani, J. Persson, T. N. A. Nguyen, S. Chung, Y. Pogoryelov, P. K. Muduli, E. Iacocca, A. Eklund, R. K. Dumas, S. Bonetti, A. Deac, M. A. Hoefer, and J. Akerman, Science 339, 1295 (2013)]. Here we demonstrate analytically, numerically, and experimentally that at sufficiently large driving currents and for a spin polarization direction tilted away from the normal to a nanocontact plane, the circular droplet soliton can become unstable against the excitations in the form of periodic deformations of its perimeter. We also show that these perimeter excitation modes (PEMs) can be excited parametrically when the fundamental droplet soliton precession frequency is close to the double frequency of one of the PEMs. As a consequence, with increasing magnitude of a bias magnetic field the PEMs with progressively higher indices and frequencies can be excited. Full qualitative and partly quantitative agreement with experiment confirm the presented theoretical picture.

1 - 22 of 22
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf