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Sökning: WFRF:(Magnuson Martin)

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1.
  • Kurmaev, E. Z., et al. (författare)
  • Spectroscopic observation of polaron-lattice band structure in the conducting polymer polyaniline
  • 2001
  • Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 13:17, s. 3907-3912
  • Tidskriftsartikel (refereegranskat)abstract
    • We present the results of soft x-ray emission measurements for undoped and protonated polyemeraldine. We show that the polaron-lattice band structure fully accounts for the observed x-ray transitions. A finite spectral intensity of C Kα and N Kα XES is observed at the Fermi level for protonated polyemeraldine, supporting the applicability of the polaronic-metal model for highly conducting polymers.
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2.
  • Butorin, SM, et al. (författare)
  • Low-energy d-d excitations in MnO studied by resonant x-ray fluorescence spectroscopy
  • 1996
  • Ingår i: PHYSICAL REVIEW B-CONDENSED MATTER. - 0163-1829. ; 54:7, s. 4405-4408
  • Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
    • We measured the Mn L(alpha,beta) x-ray fluorescence spectra of MnO excited by selected photon energies near the L(2,3) absorption edges. The resulting resonant inelastic x-ray scattering spectra probe low-lying electronic excited states, due to dd and cha
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3.
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4.
  • Butorin, S. M., et al. (författare)
  • Low-Energy d-d Excitations in MnO Studied by Resonant X-ray Fluorescence Spectroscopy
  • 1997
  • Ingår i: Advanced Light Source. - Berkely : Ernest Orlando Lawrence Berkeley National Laboratory University of California Berkeley, California. ; , s. 135-136
  • Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
    • Resonant soft X-ray emission spectroscopy has been demonstrated to possess interesting abilities for studies of electronic structure in various systems, such as symmetry probing, alignment and polarization dependence, sensitivity to channel interference, etc. (see other abstracts in this Annual Report). In the present abstract we focus on the feasibility of resonant soft X-ray emission to probe low energy excitations by means ofresonant electronic X-ray Raman scattenng....
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5.
  • Butorin, S. M., et al. (författare)
  • Low-energy d-d excitations in MnO studied by resonant x-ray fluorescence spectroscopy
  • 1996
  • Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 54, s. 4405-4408
  • Tidskriftsartikel (refereegranskat)abstract
    • We measured the Mn Lα,β x-ray fluorescence spectra of MnO excited by selected photon energies near the L2,3 absorption edges. The resulting resonant inelastic x-ray scattering spectra probe low-lying electronic excited states, due to dd and charge-transfer excitations. Using a two-step model and a purely atomic approximation, we reproduce both energies and varying intensities of dd excitations relative to the electronic recombination peak. Our results show that strongly varying line shapes in resonant x-ray emission need not be due to channel interference effects.
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6.
  • Butorin, S. M., et al. (författare)
  • Resonant inelastic soft X-ray scattering at the 4d edge of Ce-based heavy fermion materials
  • 1999
  • Ingår i: Journal of Electron Spectroscopy and Related Phenomena. - 0368-2048 .- 1873-2526. ; 101-103, s. 783-786
  • Tidskriftsartikel (refereegranskat)abstract
    • Resonant X-ray scattering measurements were performed on CeB6, CeAl, γ-Ce, and α-Ce at various incident-photon energies near the Ce 4d threshold. A pronounced inelastic scattering structure which has 4f character is observed at about 4 eV below the elastic peak. The structure shows a distinct resonant behavior as well as a dependence on the degree of 4f hybridization and can therefore be attributed to charge-transfer excitations to the 4f0 state. The intensity of the elastic peak increases when going from the systems with low Kondo temperature TK to those with high TK which is consistent with a Kondo scale behavior. By analyzing the scattering data, a controversial issue on the validity of a single-impurity Anderson model in heavy-fermion materials is addressed.
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7.
  • Butorin, S. M., et al. (författare)
  • Resonant inelastic soft-x-ray scattering from valence-band excitations in 3d0 compounds
  • 1997
  • Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 55, s. 4242-4249
  • Tidskriftsartikel (refereegranskat)abstract
    • Ti and Mn Lα,Β x-ray fluorescence spectra of FeTiO3 and KMnO4 were measured with monochromatic photon excitation on selected energies across the L2,3 absorption edges. The resulting inelastic x-ray-scattering structures and their changes with varying excitation energies are interpreted within the framework of a localized, many-body approach based on the Anderson impurity model, where the radiative process is characterized by transitions to low-energy interionic-charge-transfer excited states. Sweeping the excitation energy through the metal 2p threshold enhances the fluorescence transitions to the antibonding states pushed out of the band of continuous states due to strong metal 3d–ligand 2p hybridization and matching the low-photon-energy satellites in the spectra. Based on the energy position of these charge-transfer satellites with respect to the recombination peak the effective metal 3d–ligand 2p hybridization strength in the ground state of the system can be estimated directly from the experiment.
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8.
  • Butorin, SM, et al. (författare)
  • Resonant inelastic soft-X-ray scattering at the 4d edge of Ce-based heavy-fermion materials
  • 1999
  • Ingår i: JOURNAL OF ELECTRON SPECTROSCOPY AND RELATED PHENOMENA. - 0368-2048. ; 103, s. 783-786
  • Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
    • Resonant X-ray scattering measurements were performed on CeB6, CeAl, gamma-Ce, and alpha-Ce at various incident-photon energies near the Ce 4d threshold. A pronounced inelastic scattering structure which has 4f character is observed at about 4 eV below th
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9.
  • Butorin, SM, et al. (författare)
  • Resonant inelastic soft-x-ray scattering from valence-band excitations in 3d(0) compounds
  • 1997
  • Ingår i: PHYSICAL REVIEW B-CONDENSED MATTER. - 0163-1829. ; 55:7, s. 4242-4249
  • Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
    • Ti and Mn L(alpha,beta) x-ray fluorescence spectra of FeTiO3 and KMnO4 were measured with monochromatic photon excitation on selected energies across the L(2,3) absorption edges. The resulting inelastic x-ray-scattering structures and their changes with v
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10.
  • Chowdhury, Susmita, et al. (författare)
  • Thermoelectric properties and electronic structure of Cr(Mo,V)Nx thin films studied by synchrotron and lab-based x-ray spectroscopy
  • 2023
  • Ingår i: Physical Review B. - : AMER PHYSICAL SOC. - 2469-9950 .- 2469-9969. ; 108:20
  • Tidskriftsartikel (refereegranskat)abstract
    • Chromium-based nitrides are used in hard, resilient coatings and show promise for thermoelectric applications due to their combination of structural, thermal, and electronic properties. Here, we investigate the electronic structures and chemical bonding correlated to the thermoelectric properties of epitaxially grown chromium-based multicomponent nitride Cr(Mo,V)Nx thin films. The small amount of N vacancies causes Cr 3d and N 2p states to appear at the Fermi level and reduces the band gap in Cr0.51N0.49. Incorporating holes by alloying of V in N-deficient CrN results in an enhanced thermoelectric power factor with marginal change in the charge transfer of Cr to N compared with Cr0.51N0.49. Further alloying of Mo, isoelectronic to Cr, increases the density of states at the Fermi level due to hybridization of the (Cr, V) 3d and Mo 4d-N 2p states in Cr(Mo,V)Nx. This hybridization and N off-stoichiometry result in more metal-like electrical resistivity and reduction in Seebeck coefficient. The N deficiency in Cr(Mo,V)Nx also depicts a critical role in reduction of the charge transfer from metal to N site compared with Cr0.51N0.49 and Cr0.50V0.03N0.47. In this paper, we envisage ways for enhancing thermoelectric properties through electronic band engineering by alloying and competing effects of N vacancies.
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11.
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12.
  • Duda, L.-C., et al. (författare)
  • Resonant inelastic X-ray scattering at the NiO O K-resonance: non-local charge-transfer and double singlet excitations
  • 2007
  • Ingår i: MAX-lab. - Lund : MAX-lab. ; , s. 270-271
  • Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
    • NiO is one of the prototypical compounds that has highlighted the importance of correlation effects in transition metal oxides. Core level spectroscopies bear evidence for the highly correlated nature of low energy excitations. For instance, the asymmetry of the Ni2p-line shape has been attributed to non-local charge transfer excitations and multi-site cluster calculations show that solidstate effects generally are appreciable for correlated materials, such as cuprates and high Tc-compounds.....
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13.
  • Duda, Laurent, et al. (författare)
  • Resonant Inelastic X-Ray Scattering at the Oxygen K Resonance of NiO: Nonlocal Charge Transfer and Double-Singlet Excitations
  • 2006
  • Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 96:067402
  • Tidskriftsartikel (refereegranskat)abstract
    • We report high-resolution polarization-dependent resonant inelastic x-ray scattering (RIXS) at the O K resonance of NiO showing a rich excitation spectrum. We perform multisite Ni6O19 cluster model calculations, revealing that solid state effects are substantial. We identify a nonlocal charge transfer excitation at 4–5 eV and double-singlet creation at 1.75 eV, both exhibiting significant scattering geometry dependence. Apart from an intense band of local charge transfer excitations (above 5 eV) also dd excitations at 1 eV are observed. Finally, we point out that O K RIXS of correlated metal oxides allows a quantitative and consistent determination of the charge transfer energy and the Hund coupling energy JH.
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14.
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15.
  • Fink, Reinhold, et al. (författare)
  • Specific production of very long-lived core-excited sulfur atoms by 2p(-1)sigma* excitation of the OCS molecule followed by ultrafast dissociation
  • 2006
  • Ingår i: Journal of Physics B. - 0953-4075 .- 1361-6455. ; 39:12, s. L269-L275
  • Tidskriftsartikel (refereegranskat)abstract
    • A core-excited sulfur state with a lifetime almost one order of magnitude longer than in molecular 2p core-hole states is selectively produced by ultrafast dissociation of S 2p -> sigma* excited OCS. Clear evidence for this is provided by strong atomic peaks (20% of the total intensity) in x-ray fluorescence but very weak ones (2%) in the corresponding resonant Auger spectrum. Corroborating the assignment of the spectra, ab initio calculations explain the enhanced lifetime: the Auger decay of the produced D-3(3) (2p(5)3p(5)) sulfur state is strongly decreased as it contradicts a newly derived propensity rule of the L2,3MM Auger decay.
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16.
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17.
  • Furlan, Andrej, et al. (författare)
  • Crystallization characteristics and chemical bonding properties of nickel carbide thin film nanocomposites
  • 2014
  • Ingår i: Journal of Physics. - : Institute of Physics Publishing (IOPP). - 0953-8984 .- 1361-648X. ; 26:41
  • Tidskriftsartikel (refereegranskat)abstract
    • The crystal structure and chemical bonding of magnetron-sputtering deposited nickel carbide Ni1−xCx (0.05 ⩽ x⩽0.62) thin films have been investigated by high-resolution x-ray diffraction, transmission electron microscopy, x-ray photoelectron spectroscopy, Raman spectroscopy, and soft x-ray absorption spectroscopy. By using x-ray as well as electron diffraction, we found carbon-containing hcp-Ni (hcp-NiCy phase), instead of the expected rhombohedral-Ni3C. At low carbon content (4.9 at%), the thin film consists of hcp-NiCy nanocrystallites mixed with a smaller amount of fcc-NiCx. The average grain size is about 10–20 nm. With the increase of carbon content to 16.3 at%, the film contains single-phase hcp-NiCy nanocrystallites with expanded lattice parameters. With a further increase of carbon content to 38 at%, and 62 at%, the films transform to x-ray amorphous materials with hcp-NiCy and fcc-NiCx nanodomain structures in an amorphous carbon-rich matrix. Raman spectra of carbon indicate dominant sp2 hybridization, consistent with photoelectron spectra that show a decreasing amount of C–Ni phase with increasing carbon content. The Ni 3d–C 2p hybridization in the hexagonal structure gives rise to the salient double-peak structure in Ni 2p soft x-ray absorption spectra at 16.3 at% that changes with carbon content. We also show that the resistivity is not only governed by the amount of carbon, but increases by more than a factor of two when the samples transform from crystalline to amorphous.
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18.
  • Furlan, Andrej, et al. (författare)
  • Structure and bonding in amorphous iron carbide thin films
  • 2015
  • Ingår i: Journal of Physics. - : Institute of Physics Publishing (IOPP). - 0953-8984 .- 1361-648X. ; 27:4, s. 045002-
  • Tidskriftsartikel (refereegranskat)abstract
    • We investigate the amorphous structure, chemical bonding, and electrical properties ofmagnetron sputtered Fe1−xCx (0.21 < x < 0.72) thin films. X-ray, electron diffraction andtransmission electron microscopy show that the Fe1−xCx films are amorphousnanocomposites, consisting of a two-phase domain structure with Fe-rich carbidic FeCy , and acarbon-rich matrix. Pair distribution function analysis indicates a close-range order similar tothose of crystalline Fe3C carbides in all films with additional graphene-like structures at highcarbon content (71.8 at% C). From x-ray photoelectron spectroscopy measurements, we findthat the amorphous carbidic phase has a composition of 15–25 at% carbon that slightlyincreases with total carbon content. X-ray absorption spectra exhibit an increasing number ofunoccupied 3d states and a decreasing number of C 2p states as a function of carbon content.These changes signify a systematic redistribution in orbital occupation due to charge-transfereffects at the domain-size-dependent carbide/matrix interfaces. The four-point proberesistivity of the Fe1−xCx films increases exponentially with carbon content from ∼200μcm(x = 0.21) to ∼1200μcm (x = 0.72), and is found to depend on the total carbon contentrather than the composition of the carbide. Our findings open new possibilities for modifyingthe resistivity of amorphous thin film coatings based on transition metal carbides through thecontrol of amorphous domain structures.
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19.
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20.
  • Guo, J.-H., et al. (författare)
  • How the phenyle rings (benzene) act as building blocks in pi conjugated polymers
  • 1998
  • Ingår i: Advanced Light Source. - Berkeley : Ernest Orlando Lawrence Berkeley National Laboratory, University of California Berkeley, California, USA. ; , s. 129-132
  • Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
    • Organic conjugated polymers have the electronic structure of semiconductors and can be doped to become good conductors (1). Conjugated polymers are now used as active materials in a wide variety of prototype applications such as light emitting diodes [2] and organic transistors [3,4]. Most of the interesting chemistry and physics of conjugated polymers is associated with the details of the electronic structure at the valence and conduction band edges and, in this connection, various electron spectroscopies can be used as tools for diagnosis of the relevant electronic and geometric properties....
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21.
  • Guo, J.-H., et al. (författare)
  • Resonant and nonresonant x-ray scattering spectra of some poly(phenylenevinylene)s
  • 1998
  • Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 108:14, s. 5990-5996
  • Tidskriftsartikel (refereegranskat)abstract
    • The electronic structure of some poly(phenylenevinylene)s have been investigated by resonant and nonresonant x-ray inelastic scattering spectroscopies. The nonresonant as well as all resonant spectra for each polymer demonstrate benzene-like features, indicating a local character of the x-ray emission in which the phenyl ring acts as a building block. Theoretical simulations of x-ray energies and intensities taking the repeat unit as a model molecule of the polymer agree with the experimental spectra fairly well. The edges of the occupied bands have been identified in the nonresonant spectra of each polymer. By subtracting the emission energy of the highest occupied molecular orbital in the nonresonant spectrum from the core excitation energy in the resonant spectrum an alternative way to determine the optical band gap is obtained. As for free benzene the outer π band in the polymer spectra show a depletion of the emission going from the nonresonant to the resonant x-ray emission spectra. It is demonstrated that this transition, which is strictly symmetry forbidden for free benzene, becomes effectively forbidden in the polymer case as a result of strong interference effects, and it is argued that this is the general case for resonant x-ray emission of conjugated polymers as far as the frozen orbital approximation holds.
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22.
  • Guo, JH, et al. (författare)
  • Resonant and nonresonant x-ray scattering spectra of some poly(phenylenevinylene)s
  • 1998
  • Ingår i: JOURNAL OF CHEMICAL PHYSICS. - 0021-9606. ; 108:14, s. 5990-5996
  • Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
    • The electronic structure of some poly(phenylenevinylene)s have been investigated by resonant and nonresonant x-ray inelastic scattering spectroscopies. The nonresonant as well as all resonant spectra for each polymer demonstrate benzene-like features, ind
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23.
  • Hague, C F, et al. (författare)
  • Ferrimagnetic order in thin-film Fe3O4 studied by resonant inelastic X-ray scattering
  • 2000
  • Rapport (övrigt vetenskapligt/konstnärligt)abstract
    • We have set out to use the ID21 microfocusing beamline to perform resonant inelastic x-ray scattering (RIXS) experiments on magnetic materials. For the first tests and experiments we start off with Fe oxide thin films of potential interest in new technical applications. Of main interest are thin films of Fe3O4 epitaxially grown on alumina. Note that RIXS is particularly well adapted to experiments involving samples on insulating substrates (no charging effects) prepared ex-situ (bulk sensitivity) which can be magnetized (all-photons experiment)....
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24.
  • Hahlin, Maria, et al. (författare)
  • Mapping the frontier electronic structures of triphenylamine based organic dyes at TiO2 interfaces
  • 2011
  • Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 13:8, s. 3534-3546
  • Tidskriftsartikel (refereegranskat)abstract
    • The frontier electronic structures of a series of organic dye molecules containing a triphenylamine moiety, a thiophene moiety and a cyanoacrylic acid moiety have been investigated by photoelectron spectroscopy (PES), X-ray absorption spectroscopy (XAS), X-ray emission spectroscopy (XES) and resonant photoelectron spectroscopy (RPES). The experimental results were compared to electronic structure calculations on the molecules, which are used to confirm and enrich the assignment of the spectra. The approach allows us to experimentally measure and interpret the basic valence energy level structure in the dye, including the highest occupied energy level and how it depends on the interaction between the different units. Based on N 1s X-ray absorption and emission spectra we also obtain insight into the structure of the excited states, the molecular orbital composition and dynamics. Together the results provide an experimentally determined energy level map useful in the design of these types of materials. Included are also results indicating femtosecond charge redistribution at the dye/TiO2 interface.
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25.
  • Halim, Joseph, 1985- (författare)
  • Synthesis and Characterization of 2D Nanocrystals and Thin Films of Transition Metal Carbides (MXenes)
  • 2014
  • Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Two dimensional (2D) materials have received growing interest because of their unique properties compared to their bulk counterparts. Graphene is the archetype 2D solid, but other materials beyond graphene, such as MoS2 and BN have become potential candidates for several applications. Recently, a new family of 2D materials of early transition metal carbides and carbonitrides (Ti2CTx, Ti3C2Tx, Ti3CNTx, Ta4C3Tx, and more), labelled MXenes, has been discovered, where T stands for the surface-terminating groups.Before the present work, MXenes had only been synthesized in the form of exfoliated and delaminated powders, which is not suitable for electronic applications. In this thesis, I demonstrate the synthesis of MXenes as epitaxial thin films, a more suitable form for electronic and photonic applications. Results show that 2D epitaxial Ti3C2Tx films - produced by HF and NH4HF2 etching of magnetron sputter-grown Ti3AlC2 - exhibit metallic conductive behaviour down to 100 K and are 90% transparent to light in the visible-infrared range. The results from this work may open the door for MXenes as potential candidates for transparent conductive electrodes as well as in electronic, photonic and sensing applications.MXenes have been shown to intercalate cations and molecules between their layers that in turn can alter the surface termination groups. There is therefore a need to study the surface chemistries of synthetized MXenes to be able to study the effect of intercalation as well as altering the surface termination groups on the electronic structure and chemical states of the elements present in MXene layers. X-ray Photoelectron Spectroscopy (XPS) in-depth characterization was used to investigate surface chemistries of Ti3C2Tx and Ti2CTx. This thesis includes the discussion of the effect of Ar+ sputtering and the number of layers on the surface chemistry of MXenes. This study serves as a baseline for chemical modification and tailoring of the surface chemistry groups to potential uses and applications.New MXene phases, Nb2CTx and V2CTx, are shown in this thesis to be produced from HF chemical etching of Nb2AlC and V2AlC powders. Characterization of the produced MXenes was carried out using Scanning Electron Microscopy (SEM), X-Ray Diffraction (XRD), Transmission Electron Microscope (TEM) and XPS. Nb2CTx and V2CTx showed promising performance as electrodes for Li-ion batteries.In this thesis, electrochemical etching was used in an attempt to produce 2D metal carbides (MXene) from their ternary metal carbides, Ti3SiC2, Ti3AlC2 and Ti2AlC MAX phases. MAX phases in the form of highly dense bulk produced by Hot Isostatic Press. Several etching solutions were used such as HF, NaCl and HCl. Unlike the HF chemical etching of MAX phases, which results in MXenes, the electrochemical etching resulted in Carbide Derived Carbon (CDC). Here, I show the characterization of the produced CDC using several techniques such as XRD, TEM, Raman spectroscopy, and XPS. Electrochemical characterization was performed in the form of cyclic voltammetry, which sheds light on the etching mechanism.
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26.
  • Halim, Joseph, 1985- (författare)
  • Synthesis and transport properties of 2D transition metal carbides (MXenes)
  • 2018
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Since the isolation and characterization of graphene, there has been a growing interest in 2D materials owing to their unique properties compared to their 3D counterparts. Recently, a family of 2D materials of early transition metal carbides and nitrides, labelled MXenes, has been discovered (Ti2CTz, Ti3C2Tz, Mo2TiC2Tz, Ti3CNTz, Ta4C3Tz, Ti4N3Tz among many others), where T stands for surface-terminating groups (O, OH, and F). MXenes are mostly produced by selectively etching A layers (where A stands for group A elements, mostly groups 13 and 14) from the MAX phases. The latter are a family of layered ternary carbides and/or nitrides and have a general formula of Mn+1AXn (n = 1-3), where M is a transition metal and X is carbon and/or nitrogen. The produced MXenes have a conductive carbide core and a non-conductive O-, OH- and/or F-terminated surface, which allows them to work as electrodes for energy storage applications, such as Li-ion batteries and supercapacitors.Prior to this work, MXenes were produced in the form of flakes of lateral dimension of about 1 to 2 microns; such dimensions and form are not suitable for electronic characterization and applications. I have synthesized various MXenes (Ti3C2Tz, Ti2CTz and Nb2CTz) as epitaxial thin films, a more suitable form for electronic and photonic applications. These films were produced by HF, NH4HF2 or LiF + HCl etching of magnetron sputtered epitaxial Ti3AlC2, Ti2AlC, and Nb2AlC thin films. For transport properties of the Ti-based MXenes, Ti2CTz and Ti3C2Tz, changing n from 1 to 2 resulted in an increase in conductivity but had no effect on the transport mechanism (i.e. both Ti3C2Tx and Ti2CTx were metallic). In order to examine whether the electronic properties of MXenes differ when going from a few layers to a single flake, similar to graphene, the electrical characterization of a single Ti3C2Tz flake with a lateral size of about 10 μm was performed. These measurements, the first for MXene, demonstrated its metallic nature, along with determining the nature of the charge carriers and their mobility. This indicates that Ti3C2Tz is inherently of 2D nature independent of the number of stacked layers, unlike graphene, where the electronic properties change based on the number of stacked layers.Changing the transition metal from Ti to Nb, viz. comparing Ti2CTz and Nb2CTz thin films, the electronic properties and electronic conduction mechanism differ. Ti2CTz showed metallic-like behavior (resistivity increases with increasing temperature) unlike Nb2CTz where the conduction occurs via variable range hopping mechanism (VRH) - where resistivity decreases with increasing temperature.Furthermore, these studies show the synthesis of pure Mo2CTz in the form of single flakes and freestanding films made by filtering Mo2CTz colloidal suspensions. Electronic characterization of free-standing films made from delaminated Mo2CTz flakes was investigated, showing that a VRH mechanism prevails at low temperatures (7 to ≈ 60 K). Upon vacuum annealing, the room temperature, RT, conductivity of Mo2CTx increased by two orders of magnitude. The conduction mechanism was concluded to be VRH most likely dominated by hopping within each flake.Other Mo-based MXenes, Mo2TiC2Tz and Mo2Ti2C3Tz, showed VRH mechanism at low temperature. However, at higher temperatures up to RT, the transport mechanism was not clearly understood. Therefore, a part of this thesis was dedicated to further investigating the transport properties of Mo-based MXenes. This includes Mo2CTz, out-of-plane ordered Mo2TiC2Tz and Mo2Ti2C3Tz, and vacancy ordered Mo1.33CTz. Magneto-transport of free-standing thin films of the Mo-based MXenes were studied, showing that all Mo-based MXenes have two transport regimes: a VRH mechanism at lower temperatures and a thermally activated process at higher temperatures. All Mo-based MXenes except Mo1.33CTz show that the electrical transport is dominated by inter-flake transfer. As for Mo1.33CTz, the primary electrical transport mechanism is more likely to be intra-flake.The synthesis of vacancy ordered MXenes (Mo1.33CTz and W1.33CTz) raised the question of possible introduction of vacancies in all MXenes. Vacancy ordered MXenes are produced by selective etching of Al and (Sc or Y) atoms from the parent 3D MAX phases, such as (Mo2/3Sc1/3)2AlC, with in-plane chemical ordering of Mo and Sc. However, not all quaternary parent MAX phases form the in-plane chemical ordering of the two M metals; thus the synthesis of the vacancy-ordered MXenes is restricted to a very limited number of MAX phases. I present a new method to obtain MXene flakes with disordered vacancies that may be generalized to all quaternary MAX phases. As proof of concept, I chose Nb-C MXene, as this 2D material has shown promise in several applications, including energy storage, photothermal cell ablation and photocatalysts for hydrogen evolution. Starting from synthetizing (Nb2/3Sc1/3)2AlC quaternary solid solution and etching both the Sc and Al atoms resulted in Nb1.33C material with a large number of vacancies and vacancy clusters. This method may be applicable to other quaternary or higher MAX phases wherein one of the transition metals is more reactive than the other, and it could be of vital importance in applications such as catalysis and energy storage.  
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27.
  • Halim, Joseph, et al. (författare)
  • X-ray Photoelectron Spectroscopy Characterization of Two-Dimensional Titanium Metal Carbides (MXenes)
  • 2014
  • Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
    • Herein, we report X-ray Photoelectron Spectroscopy (XPS) analysis for cold pressed exfoliated 2D nanocrystals of transition metal carbides, MXenes. MXenes are a recently discovered family of 2D materials produced by selective chemical etching of the A element from MAX phases which are ternary metal carbides and nitrides. The latter has the formula of Mn+1AXn, where M is an early transition metal, A is an A-group element, and X is C and/or N. This study is a comparison between two MXenes, Ti3C2Tx and Ti2CTx, where Tx stands for surface termination groups such as –O, –OH, and –F. Ti3C2Tx and Ti2CTx were prepared by immersion of Ti3AlC2 and Ti2AlC powders in 50% conc. HF. A thorough XPS analysis was performed through peak fitting of high resolution XPS spectra and valence band, VB, spectra analysis. The effect of Ar sputtering as well as the number of layers n was the primarily interest of this study. According to the peak fitting analysis, both phases contain the following species, Ti–C, C–C, Ti–F, Ti–O and Ti–OH resulting in the following chemical formulas: Ti3C2(OH)x(O)y(F)z and Ti2C(OH)x(O)y(F)z. Comparing the VB spectra with the DOS calculations show the valance band spectra is actually a mixture of MXene with various terminations of OH, O and F. Before Ar+ sputtering both phases show a large percentage of fluorinated-TiO2 which is due to MXene surface oxidation as well as CHx, C-O and COO groups arising from either surface contaminations or due to drying the etched powders in ethanol after washing the powder of the HF acid. According to the VB spectra, it is shown that the fluorinated TiO2 is actually a mixture of anatase and rutile. The number of layers, n, also plays a role; the lower n, the more the MXene is prone to oxidation.
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28.
  • Ji, Fuxiang, 1991-, et al. (författare)
  • Remarkable Thermochromism in the Double Perovskite Cs2NaFeCl6
  • 2024
  • Ingår i: Advanced Optical Materials. - : John Wiley & Sons. - 2162-7568 .- 2195-1071. ; 12:8
  • Tidskriftsartikel (refereegranskat)abstract
    • Lead-free halide double perovskites (HDPs) have emerged as a new generation of thermochromic materials. However, further materials development and mechanistic understanding are required. Here, a highly stable HDP Cs2NaFeCl6 single crystal is synthesized, and its remarkable and fully reversible thermochromism with a wide color variation from light-yellow to black over a temperature range of 10 to 423 K is investigated. First-principles, density functional theory (DFT)-based calculations indicate that the thermochromism in Cs2NaFeCl6 is an effect of electron-phonon coupling. The temperature sensitivity of the bandgap in Cs2NaFeCl6 is up to 2.52 meVK(-1) based on the Varshni equation, which is significantly higher than that of lead halide perovskites and many conventional group-IV, III-V semiconductors. Meanwhile, this material shows excellent environmental, thermal, and thermochromic cycle stability. This work provides valuable insights into HDPs' thermochromism and sheds new light on developing efficient thermochromic materials.
  •  
29.
  • Karis, O., et al. (författare)
  • Observation of short- and long-range hybridization of a buried Cu monolayer in Ni
  • 2000
  • Ingår i: Physical Review B Condensed Matter. - 0163-1829 .- 1095-3795. ; 62:24, s. R16239-R16242
  • Tidskriftsartikel (refereegranskat)abstract
    • The electronic structure of a Cu monolayer buried in Ni fcc(100) is studied by means of x-ray emission and absorption spectroscopies in combination with first principles calculations. The local character of the x-ray probes allows us to investigate changes in the chemical interaction for these ultrathin film systems. In comparison to bulk Cu, the occupied d states of a buried Cu monolayer, as mapped in the x-ray emission spectrum, remain mostly unaltered. The absorption spectrum on the other hand shows that the empty states of the buried Cu monolayer are modified, and instead resemble the unoccupied electronic density of bulk Ni. These findings agree well with our first principle electronic structure calculations and the results are interpreted in terms of short- and long-range hybridization.
  •  
30.
  • Karis, O, et al. (författare)
  • Observation of short- and long-range hybridization of a buried Cu monolayer in Ni
  • 2000
  • Ingår i: PHYSICAL REVIEW B. - 0163-1829. ; 62:24, s. R16239-R16242
  • Tidskriftsartikel (refereegranskat)abstract
    • The electronic structure of a Cu monolayer buried in Ni fcc(100) is studied by means of x-ray emission and absorption spectroscopies in combination with first principles calculations. The local character of the x-ray probes allows us to investigate change
  •  
31.
  • Karis, O, et al. (författare)
  • Probing surface states of Cu/Ni thin films using x-ray absorption spectroscopy
  • 2001
  • Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 63:11
  • Tidskriftsartikel (refereegranskat)abstract
    • Surface and interface properties of Cu thin films (1–4 monolayers) deposited on Ni(100) have been extracted by means of x-ray absorption spectroscopy and analyzed in combination with ab initio density-functional calculations. An unoccupied Cu surface state is identified in an x-ray absorption spectra and studied as a function of film thickness. Experimental data is supported by calculations of the layer-resolved density of states and the results from this combined theoretical-experimental effort show that the surface state is almost entirely located on the atomic layer closest to the vacuum. Our results also indicate strong hybridization between unoccupied states at the Cu/Ni interface boundary.
  •  
32.
  • Kashiwaya, Shun, et al. (författare)
  • Synthesis of goldene comprising single-atom layer gold
  • 2024
  • Ingår i: Nature Synthesis. - : Nature Publishing Group. - 2731-0582.
  • Tidskriftsartikel (refereegranskat)abstract
    • The synthesis of monolayer gold has so far been limited to free-standingseveral-atoms-thick layers, or monolayers confned on or inside templates.Here we report the exfoliation of single-atom-thick gold achieved throughwet-chemically etching away Ti3C2 from nanolaminated Ti3AuC2, initiallyformed by substituting Si in Ti3SiC2 with Au. Ti3SiC2 is a renown MAX phase,where M is a transition metal, A is a group A element, and X is C or N. Ourdeveloped synthetic route is by a facile, scalable and hydrofuoric acid-freemethod. The two-dimensional layers are termed goldene. Goldene layerswith roughly 9% lattice contraction compared to bulk gold are observedby electron microscopy. While ab initio molecular dynamics simulationsshow that two-dimensional goldene is inherently stable, experiments showsome curling and agglomeration, which can be mitigated by surfactants.X-ray photoelectron spectroscopy reveals an Au 4f binding energy increaseof 0.88 eV. Prospects for preparing goldene from other non-van der WaalsAu-intercalated phases, including developing etching schemes,are presented.
  •  
33.
  • Kreutzer, Martin, et al. (författare)
  • Patent coronary artery and myocardial infarction in the era of primary angioplasty : assessment of an old problem in a new setting with data from the Swedish Coronary Angiography and Angioplasty Registry (SCAAR).
  • 2010
  • Ingår i: EuroIntervention. - 1969-6213. ; 6:5, s. 590-595
  • Tidskriftsartikel (refereegranskat)abstract
    • Aims: The purpose of this study was to evaluate factors that contribute to a patent IRA (infarct - related artery) and the prognostic impact of a patent IRA in patients with ST-elevation myocardial infarction.Methods and results: Using the Swedish angiography and angioplasty registry (SCAAR) we included all patients with STEMI and one-vessel coronary artery disease who underwent primary PCI of the culprit lesion only from May 2005 to December 2007. A patent IRA was found in 1,104 of 3,284 patients. Patients with an occluded IRA had significantly increased 7-day mortality (HR, 3.03, 95% CI 1.68-5.46, P<0.001). The incidence of an occluded IRA increased with higher age, in patients over 80 years of age (OR, 1.23, 95% CI; 0.92-1.64), lower in patients on lipid-lowering drugs (OR, 0.68, 95% CI; 0.54-0.86) and lower in patients pre-treated with heparin (OR 0.71, 95% CI; 0.60-0.83) or GPIIb/IIIa receptor blockade (OR 0.77, 95% CI; 0.61-0.97). Treatment with acetylsalicylic acid or clopidogrel had no effect on IRA patency.Conclusions: IRA patency was associated with a lower 7-day mortality. Older STEM I patients and patients not taking lipid-lowering drugs or pre-treated with heparin or GPIIb/IIIa receptor blockers seem to constitute risk groups for having an occluded IRA.
  •  
34.
  • Liljedahl, Magnus, et al. (författare)
  • Endothelial function in children with a history of premature prolonged rupture of membranes and bronchopulmonary dysplasia : a pilot study
  • 2008
  • Ingår i: Acta Paediatrica. - Oslo : Taylor & Francis. - 0803-5253 .- 1651-2227. ; 97:7, s. 909-914
  • Tidskriftsartikel (refereegranskat)abstract
    • Aim: To investigate vascular function in children with a neonatal history of generalised inflammation indicated by premature prolonged rupture of membranes (PPROM) and bronchopulmonary dysplasia (BPD).Methods: Children born at ≤ 30 weeks 1994–2000 were investigated at a present age of 6–12 years. Twenty-eight children participated and were divided into two groups with regard to BPD/no BPD (n = 15/13) and PPROM/no PPROM (n = 10/18). Vascular endothelial function was assessed by acetylcholine (ACh)-induced skin vasodilatation.Results: Maximum ACh-induced skin perfusion was statistically significantly lower in the PPROM group compared with the non-PPROM group (p = 0.045) after adjustment for confounders. We found no association between BPD and maximum ACh-induced skin perfusion (p = 0.404), after adjustment for confounders.Conclusion: A neonatal history of prolonged premature rupture of membranes was associated with later impairment of vascular endothelial function in childhood. This association was not observed with BPD. Some forms of perinatal inflammation may be associated with later cardiovascular function.
  •  
35.
  • Liljedahl Prytz, Karolina, 1976-, et al. (författare)
  • Antibiotic treatment with one single dose of gentamicin at admittance in addition to a beta-lactam antibiotic in the treatment of community-acquired bloodstream infection with sepsis
  • 2020
  • Ingår i: PLOS ONE. - : Public Library of Science. - 1932-6203. ; 15:7
  • Tidskriftsartikel (refereegranskat)abstract
    • Background: Combination therapy in the treatment of sepsis, especially the value of combining a beta-Lactam antibiotic with an aminoglycoside, has been discussed. This retrospective cohort study including patients with sepsis or septic shock aimed to investigate whether one single dose of gentamicin at admittance (SGA) added to beta-Lactam antibiotic could result in a lower risk of mortality than beta-Lactam monotherapy, without exposing the patient to the risk of nephrotoxicity.Methods and findings: All patients with positive blood cultures were evaluated for participation (n = 1318). After retrospective medical chart review, a group of patients with community-acquired sepsis with positive blood cultures who received beta-Lactam antibiotic with or without the addition of SGA (n = 399) were included for the analysis. Mean age was 74.6 yrs. (range 19-98) with 216 (54%) males. Sequential Organ Failure Assessment score (SOFA score) median was 3 (interquartile range [IQR] 2-5) and the median Charlson Comorbidity Index for the whole group was 2 (IQR 1-3). Sixty-seven (67) patients (17%) had septic shock. The 28-day mortality in the combination therapy group was 10% (20 of 197) and in the monotherapy group 22% (45 of 202), adjusted HR 3.5 (95% CI (1.9-6.2),p= < 0.001. No significant difference in incidence of acute kidney injury (AKI) was detected.Conclusion: This retrospective observational study including patients with community-acquired sepsis or septic shock and positive blood cultures, who meet Sepsis-3 criteria, shows that the addition of one single dose of gentamicin to beta-lactam treatment at admittance was associated with a decreased risk of mortality and was not associated with AKI. This antibiotic regime may be an alternative to broad-spectrum antibiotic treatment of community-acquired sepsis. Further prospective studies are warranted to confirm these results.
  •  
36.
  •  
37.
  • Magnuson, Martin, 1965- (författare)
  • An Electron Beam Heated Evaporation Source
  • 1994
  • Rapport (övrigt vetenskapligt/konstnärligt)abstract
    • An electron beam evaporator has been assembled, tested and used for deposition of thin nickel films. Flux and deposition rates has been measured with an oscillating quartz crystal monitor (QCM), an ion sensor wire, and visible deposition on a mirror on front of the evaporator. A thin nickel rod of 2 mm diameter was found to improve the pressure in comparison to a 6-mm nickel rod. The flux was typically 3-4 Angstroms per minute during the test, but other flux rates can easily be achieved by changing the filament current and the acceleration voltage.
  •  
38.
  • Magnuson, Martin, et al. (författare)
  • Anisotropy in the electronic structure of V2GeC investigated by soft x-ray emission spectroscopy and first-principles theory
  • 2008
  • Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 78:035117
  • Tidskriftsartikel (refereegranskat)abstract
    • Theanisotropy of the electronic structure of ternary nanolaminate V2GeC isinvestigated by bulk-sensitive soft x-ray emission spectroscopy. The measured polarization-dependentemission spectra of V L2,3, C K, Ge M1, and Ge M2,3 in V2GeCare compared with those from monocarbide VC and pure Ge.The experimental emission spectra are interpreted with calculated spectra usingab initio density-functional theory including dipole transition matrix elements. Differenttypes of covalent chemical bond regions are revealed: V 3d-C 2p bondingat −3.8  eV, Ge 4p-C 2p bonding at −6  eV, and Ge 4p-C 2s interaction mediatedvia the V 3d orbitals at −11  eV below the Fermi level.We find that the anisotropic effects are high for the4p valence states and the shallow 3d core levels ofGe, while relatively small anisotropy is detected for the V 3dstates. The macroscopic properties of the V2GeC nanolaminate result fromthe chemical bonds with the anisotropic pattern as shown inthis work.
  •  
39.
  • Magnuson, Martin, et al. (författare)
  • Bonding mechanism in the nitrides Ti2AlN and TiN: An experimental and theoretical investigation
  • 2007
  • Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 76:195127
  • Tidskriftsartikel (refereegranskat)abstract
    • Theelectronic structure of nanolaminate Ti2AlN and TiN thin films hasbeen investigated by bulk-sensitive soft x-ray emission spectroscopy. The measuredTi L2,3, N K, Al L1, and Al L2,3 emissionspectra are compared with calculated spectra using ab initio density-functionaltheory including dipole transition-matrix elements. Three different types of bondregions are identified; a relatively weak Ti  3d-Al  3p bonding between −1and −2  eV below the Fermi level, and Ti  3d-N  2p and Ti  3d-N  2sbondings which are deeper in energy observed at −4.8  eV and−15  eV below the Fermi level, respectively. A strongly modified spectralshape of 3s states of Al L2,3 emission from Ti2AlNin comparison with pure Al metal is found, which reflectsthe Ti  3d-Al  3p hybridization observed in the Al L1 emission. Thedifferences between the electronic and crystal structures of Ti2AlN andTiN are discussed in relation to the intercalated Al layersof the former compound and the change of the materialsproperties in comparison with the isostructural carbides.
  •  
40.
  • Magnuson, Martin, 1965-, et al. (författare)
  • Bonding Structures of ZrHx Thin Films by X-ray Spectroscopy
  • 2017
  • Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 121, s. 25750-25758
  • Tidskriftsartikel (refereegranskat)abstract
    • The variation in local atomic structure and chemical bonding of ZrHx (x=0.15, 0.30, 1.16) magnetron sputtered thin films are investigated by Zr K-edge (1s) X-ray absorption near-edge structure and extended X-ray absorption fine structure spectroscopies. A chemical shift of the Zr K-edge towards higher energy with increasing hydrogen content is observed due to charge-transfer and an ionic or polar covalent bonding component between the Zr 4d and the H 1s states with increasing valency for Zr. We find an increase in the Zr-Zr bond distance with increasing hydrogen content from 3.160 Å in the hexagonal closest-packed metal (a-phase) to 3.395 Å in the understoichiometric d-ZrHx film (CaF2-type structure) with x=1.16 that largely resembles that of bulk d-ZrH2. For yet lower hydrogen contents, the structures are mixed a- and d-phases, while sufficient hydrogen loading (x>1) yields a pure δ-phase that is understoichiometric, but thermodynamically stable. The change in the hydrogen content and strain is discussed in relation to the corresponding change of bond lengths, hybridizations, and trends in electrical resistivity.
  •  
41.
  • Magnuson, Martin, 1965-, et al. (författare)
  • Chemical bonding and electronic-structure in MAX phases as viewed by X-ray spectroscopy and density functional theory
  • 2017
  • Ingår i: Thin Solid Films. - : Elsevier. - 0040-6090 .- 1879-2731. ; 621, s. 108-130
  • Forskningsöversikt (refereegranskat)abstract
    • This is a critical review of MAX-phase carbides and nitrides from an electronic-structure and chemical bonding perspective. This large group of nanolaminated materials is of great scientific and technological interest and exhibit a combination of metallic and ceramic features. These properties are related to the special crystal structure and bonding characteristics with alternating strong M-C bonds in high-density MC slabs, and relatively weak M-A bonds between the slabs. Here, we review the trend and relationship between the chemical bonding, conductivity, elastic and magnetic properties of the MAX phases in comparison to the parent binary MX compounds with the underlying electronic structure probed by polarized X-ray spectroscopy. Spectroscopic studies constitute important tests of the results of state-of-the-art electronic structure density functional theory that is extensively discussed and are generally consistent. By replacing the elements on the M, A, or X-sites in the crystal structure, the corresponding changes in the conductivity, elasticity, magnetism and other materials properties makes it possible to tailor the characteristics of this class of materials by controlling the strengths of their chemical bonds.
  •  
42.
  • Magnuson, Martin, 1965-, et al. (författare)
  • Chemical bonding in carbide MXene nanosheets
  • 2018
  • Ingår i: Journal of Electron Spectroscopy and Related Phenomena. - : Elsevier. - 0368-2048 .- 1873-2526. ; 224, s. 27-32
  • Tidskriftsartikel (refereegranskat)abstract
    • tThe chemical bonding in the carbide core and the surface chemistry in a new group of transition-metalcarbides Tin+1Cn-Tx(n = 1,2) called MXenes have been investigated by surface-sensitive valence bandX-ray photoelectron spectroscopy. Changes in band structures of stacked nano sheets of different thick-nesses are analyzed in connection to known hybridization regions of TiC and TiO2that affect elastic andtransport properties. By employing high excitation energy, the photoelectron cross-section for the C 2s– Ti 3d hybridization region at the bottom of the valence band is enhanced. As shown in this work, theO 2p and F 2p bands strongly depend both on the bond lengths to the surface groups and the adsorptionsites. The effect of surface oxidation and Ar+sputtering on the electronic structure is also discussed.
  •  
43.
  • Magnuson, Martin, 1965-, et al. (författare)
  • ­Chemical Bonding in Epitaxial ZrB2 Studied by X-ray Spectroscopy
  • 2018
  • Ingår i: Thin Solid Films. - : Elsevier. - 0040-6090 .- 1879-2731. ; 649, s. 89-96
  • Tidskriftsartikel (refereegranskat)abstract
    • The chemical bonding in an epitaxial ZrB2 film is investigated by Zr K-edge (1s) X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopies and compared to the ZrB2 compound target from which the film was synthesized as well as a bulk α-Zr reference. Quantitative analysis of X-ray Photoelectron Spectroscopy spectra reveals at the surface: ~5% O in the epitaxial ZrB2 film, ~19% O in the ZrB2 compound target and ~22% O in the bulk α-Zr reference after completed sputter cleaning. For the ZrB2 compound target, X-ray diffraction (XRD) shows weak but visible   11, 111, and 220 peaks from monoclinic ZrO2 together with peaks from ZrB2 and where the intensity distribution for the ZrB2 peaks show a randomly oriented target material.  For the bulk α-Zr reference no peaks from any crystalline oxide were visible in the diffractogram recorded from the 0001-oriented metal. The Zr K-edge absorption from the two ZrB2 samples demonstrate more pronounced oscillations for the epitaxial ZrB2 film than in the bulk ZrB2 attributed to the high atomic ordering within the columns of the film. The XANES exhibits no pre-peak due to lack of p-d hybridization in ZrB2, but with a chemical shift towards higher energy of 4 eV in the film and 6 eV for the bulk compared to α-Zr (17.993 keV) from the charge-transfer from Zr to B. The 2 eV larger shift in bulk ZrB2 material suggests higher oxygen content than in the epitaxial film, which is supported by XPS. In EXAFS, the modelled cell-edge in ZrB2 is slightly smaller in the thin film (a=3.165 Å, c=3.520 Å) in comparison to the bulk target material (a=3.175 Å, c=3.540 Å) while in hexagonal closest-packed metal (α-phase, a=3.254 Å, c=5.147 Å). The modelled coordination numbers show that the EXAFS spectra of the epitaxial ZrB2 film is highly anisotropic with strong in-plane contribution, while the bulk target material is more isotropic. The Zr-B distance in the film of 2.539 Å is in agreement with the calculated value from XRD data of 2.542 Å. This is slightly shorter compared to that in the ZrB2 compound target 2.599 Å, supporting the XANES results of a higher atomic order within the columns of the film compared to bulk ZrB2.
  •  
44.
  • Magnuson, Martin, 1965-, et al. (författare)
  • Coherent and Incoherent Processes in resonant Photoemission
  • 1997
  • Ingår i: Advanced Light Source. - California, USA : Ernest Orlando Lawrence Berkeley National Laboratory, University of California Berkeley. ; 65:2, s. 159-167
  • Bokkapitel (populärvet., debatt m.m.)
  •  
45.
  • Magnuson, Martin, et al. (författare)
  • Competition between decay and dissociation of core-excited carbonyl sulfide studied by x-ray scattering
  • 1999
  • Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 59:6, s. 4281-4287
  • Tidskriftsartikel (refereegranskat)abstract
    • We show evidence of dissociation during resonant inelastic soft x-ray scattering Carbon and oxygen K-shell and sulfur L-shell resonant and nonresonant x-ray emission spectra were measured using monochromatic synchrotron radiation for excitation and ionization. After sulfur L-2,L-3-->pi*, sigma* excitation, atomic lines are observed in the emission spectra as a consequence of competition between de-excitation and dissociation. In contrast thr carbon and oxygen spectra show weaker line-shape variations and no atomic Lines. The spectra are compared to results from ab initio calculations. The discussion of the dissociation paths is based on calculated potential energy surfaces and atomic transition energies.
  •  
46.
  • Magnuson, Martin, 1965-, et al. (författare)
  • Compositional dependence of epitaxial Tin+1SiCn MAX-phase thin films grown from a Ti3SiC2 compound target
  • 2019
  • Ingår i: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films. - : American Institute of Physics (AIP). - 0734-2101 .- 1520-8559. ; 37:2
  • Tidskriftsartikel (refereegranskat)abstract
    • The authors investigate sputtering of a Ti3SiC2 compound target at temperatures ranging from RT (no applied external heating) to 970 °C as well as the influence of the sputtering power at 850 °C for the deposition of Ti3SiC2 films on Al2O3(0001) substrates. Elemental composition obtained from time-of-flight energy elastic recoil detection analysis shows an excess of carbon in all films, which is explained by differences in the angular distribution between C, Si, and Ti, where C scatters the least during sputtering. The oxygen content is 2.6 at. % in the film deposited at RT and decreases with increasing deposition temperature, showing that higher temperatures favor high purity films. Chemical bonding analysis by x-ray photoelectron spectroscopy shows C–Ti and Si–C bonding in the Ti3SiC2 films and Si–Si bonding in the Ti3SiC2 compound target. X-ray diffraction reveals that the phases Ti3SiC2, Ti4SiC3, and Ti7Si2C5 can be deposited from a Ti3SiC2 compound target at substrate temperatures above 850 °C and with the growth of TiC and the Nowotny phase Ti5Si3Cx at lower temperatures. High-resolution scanning transmission electron microscopy shows epitaxial growth of Ti3SiC2, Ti4SiC3, and Ti7Si2C5 on TiC at 970 °C. Four-point probe resistivity measurements give values in the range ∼120 to ∼450 μΩ cm and with the lowest values obtained for films containing Ti3SiC2, Ti4SiC3, and Ti7Si2C5.
  •  
47.
  • Magnuson, Martin, 1965-, et al. (författare)
  • Determination of the refractive index at soft X-ray resonances
  • 2004
  • Ingår i: Journal of Electron Spectroscopy and Related Phenomena. - : Elsevier. - 0368-2048 .- 1873-2526. ; 137, s. 519-522
  • Tidskriftsartikel (refereegranskat)abstract
    • The dispersive part of the refractive index, 1−δ, of vanadium is determined by measuring the angular dependence of the Bragg peak at the V L2,3 edge energy region using a Fe/V superlattice. This X-ray scattering technique provides access to the direct determination of the dispersive part of the refractive index across an absorption resonance and to the change of values from below unity to above unity. We demonstrate that previously tabulated values tend to underestimate the amplitude of the change in the real part of the refractive index. We also examine the need for applying absorption and polarization corrections.
  •  
48.
  • Magnuson, Martin, 1965-, et al. (författare)
  • Electronic properties and bonding in ZrHx thin films investigated by valence-bandx-ray photoelectron spectroscopy
  • 2017
  • Ingår i: Physical Review B Condensed Matter. - College Park, United States : American Physical Society. - 0163-1829 .- 1095-3795. ; 96:19
  • Tidskriftsartikel (refereegranskat)abstract
    • The electronic structure and chemical bonding in reactively magnetron sputtered ZrHx (x = 0.15, 0.30, 1.16)thin films with oxygen content as low as 0.2 at.% are investigated by 4d valence band, shallow 4p core-level,and 3d core-level x-ray photoelectron spectroscopy. With increasing hydrogen content, we observe significantreduction of the 4d valence states close to the Fermi level as a result of redistribution of intensity toward the H1s–Zr 4d hybridization region at ∼6 eV below the Fermi level. For low hydrogen content (x = 0.15, 0.30), thefilms consist of a superposition of hexagonal closest-packed metal (α phase) and understoichiometric δ-ZrHx(CaF2-type structure) phases, while for x = 1.16, the films form single-phase ZrHx that largely resembles thatof stoichiometric δ-ZrH2 phase. We show that the cubic δ-ZrHx phase is metastable as thin film up to x = 1.16,while for higher H contents the structure is predicted to be tetragonally distorted. For the investigated ZrH1.16film, we find chemical shifts of 0.68 and 0.51 eV toward higher binding energies for the Zr 4p3/2 and 3d5/2peak positions, respectively. Compared to the Zr metal binding energies of 27.26 and 178.87 eV, this signifiesa charge transfer from Zr to H atoms. The change in the electronic structure, spectral line shapes, and chemicalshifts as a function of hydrogen content is discussed in relation to the charge transfer from Zr to H that affectsthe conductivity by charge redistribution in the valence band.
  •  
49.
  • Magnuson, Martin, et al. (författare)
  • Electronic structure and chemical bonding anisotropy investigation of wurtzite AlN
  • 2009
  • Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 80, s. 155105-
  • Tidskriftsartikel (refereegranskat)abstract
    • The electronic structure and the anisotropy of the Al - N p and s chemical bonding of wurtzite AlN has been investigated by bulk-sensitive total fluorescence yield absorption and soft x-ray emission spectroscopies. The measured N K, Al L1, and Al L2,3 x-ray emission and N 1s x-ray absorption spectra are compared with calculated spectra using first principles density-functional theory including dipole transition matrix elements. The main N 2p - Al 3p hybridization regions are identified at -1.0 to -1.8 eV and -5.0 to -5.5 eV below the top of the valence band. In addition, N 2s - Al 3p and N 2s - Al 3s hybridization regions are found at the bottom of the valence band around -13.5 eV and -15 eV, respectively. A strongly modified spectral shape of Al 3s states in the Al L2,3 emission from AlN in comparison to Al metal is found, which is also reflected in the N 2p - Al 3p hybridization observed in the Al L1 emission. The differences between the electronic structure and chemical bonding of AlN and Al metal are discussed in relation to the position of the hybridization regions and the valence band edge influencing the magnitude of the large band gap.
  •  
50.
  • Magnuson, Martin, et al. (författare)
  • Electronic structure and chemical bonding in Ti2AlC investigated by soft x-ray emission spectroscopy
  • 2006
  • Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 74:195108
  • Tidskriftsartikel (refereegranskat)abstract
    • Theelectronic structure of the nanolaminated transition metal carbide Ti2AlC hasbeen investigated by bulk-sensitive soft x-ray emission spectroscopy. The measuredTi L, C K, and Al L emission spectra arecompared with calculated spectra using ab initio density-functional theory includingdipole matrix elements. The detailed investigation of the electronic structureand chemical bonding provides increased understanding of the physical propertiesof this type of nanolaminates. Three different types of bondregions are identified: The relatively weak Ti 3d–Al 3p bond1  eV below the Fermi level and the Ti 3d–C 2pand Ti 3d–C 2s bonds which are stronger and deeperin energy are observed around 2.5 and 10  eV below theFermi level, respectively. A strongly modified spectral shape of the3s final states in comparison to pure Al is detectedfor the intercalated Al monolayers indirectly reflecting the Ti 3d–Al3p hybridization. The differences between the electronic and crystal structuresof Ti2AlC, Ti3AlC2, and TiC are discussed in relation tothe number of Al layers per Ti layer in thetwo former systems and the corresponding change of the unusualmaterials properties.
  •  
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