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Magnuson, M., Halim, J. & Näslund, L.-Å. (2018). Chemical bonding in carbide MXene nanosheets. Journal of Electron Spectroscopy and Related Phenomena, 224, 27-32
Open this publication in new window or tab >>Chemical bonding in carbide MXene nanosheets
2018 (English)In: Journal of Electron Spectroscopy and Related Phenomena, ISSN 0368-2048, E-ISSN 1873-2526, Vol. 224, p. 27-32Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
Elsevier, 2018
Keywords
MXene, 2D materials, Valence band, X-ray photoelecton spectroscopy, XPS, Chemical bonding, Termination species
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:liu:diva-145690 (URN)10.1016/j.elspec.2017.09.006 (DOI)000428825400006 ()2-s2.0-85030792688 (Scopus ID)
Available from: 2018-03-16 Created: 2018-03-16 Last updated: 2018-06-04Bibliographically approved
Magnuson, M., Schmitt, T. & Duda, L. (2018). Polarization-dependent resonant inelastic X-ray scattering study atthe Cu L and O K-edges of YBa2Cu3O7-x. Journal of Electron Spectroscopy and Related Phenomena, 224, 38-44
Open this publication in new window or tab >>Polarization-dependent resonant inelastic X-ray scattering study atthe Cu L and O K-edges of YBa2Cu3O7-x
2018 (English)In: Journal of Electron Spectroscopy and Related Phenomena, ISSN 0368-2048, E-ISSN 1873-2526, Vol. 224, p. 38-44Article in journal (Refereed) Published
Abstract [en]

We present a study on the high-Tc superconductor (HTSC) YBa2Cu3O7-x(YBCO) using polarization-dependent X-ray absorption and resonant inelastic X-ray scattering. High-resolution measurementsusing synchrotron-radiation are compared with calculations using a quasi-atomic multiplet approachperformed at the Cu 2p3/2-edge of YBCO. We use a multiplet approach within the single impurity Ander-son model to reproduce and understand the character of the localized low-energy excitations in YBCO.We observe a distinct peak at about 0.5 eV in O K RIXS. This peak shows dependence on doping, incidentenergy, and momentum transfer that suggests that it has a different origin than the previously discussedcuprate bimagnons. Therefore, we assign it to bimagnon excitations within the Zhang Rice bands and/orthe Upper Hubbard bands, respectively.

Place, publisher, year, edition, pages
Elsevier, 2018
Keywords
H-Tc superconductors, YBCO, cuprates, RIXS
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:liu:diva-145691 (URN)10.1016/j.elspec.2017.07.005 (DOI)000428825400008 ()2-s2.0-85029521510 (Scopus ID)
Available from: 2018-03-16 Created: 2018-03-16 Last updated: 2018-06-04Bibliographically approved
Magnuson, M., Eriksson, F., Hultman, L. & Högberg, H. (2017). Bonding Structures of ZrHx Thin Films by X-ray Spectroscopy. The Journal of Physical Chemistry C, 121, 25750-25758
Open this publication in new window or tab >>Bonding Structures of ZrHx Thin Films by X-ray Spectroscopy
2017 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 121, p. 25750-25758Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2017
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:liu:diva-143207 (URN)10.1021/acs.jpcc.7b03223 (DOI)000416496200016 ()
Funder
Swedish Energy Agency, 43606-1Swedish Foundation for Strategic Research , FUNCASE [RMA11-0029]Carl Tryggers foundation , CTS16:303, CTS14:310
Note

Funding agencies: Swedish Government Strategic Research Area in Materials Science on Functiona

Available from: 2017-11-23 Created: 2017-11-23 Last updated: 2018-06-04
Olovsson, W., Alling, B. & Magnuson, M. (2016). Structure and Bonding in Amorphous Cr1−xCx Nanocomposite Thin Films: X‐ray Absorption Spectra and First-Principles Calculations. The Journal of Physical Chemistry C, 120(23), 12890-12899
Open this publication in new window or tab >>Structure and Bonding in Amorphous Cr1−xCx Nanocomposite Thin Films: X‐ray Absorption Spectra and First-Principles Calculations
2016 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 120, no 23, p. 12890-12899Article in journal (Refereed) Published
Abstract [en]

The local structure and chemical bonding in two-phase amorphous Cr1−xCx nanocomposite thin films are investigated by Cr K-edge (1s) X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopies in comparison to theory. By utilizing the computationally efficient stochastic quenching (SQ) technique, we reveal the complexity of different Cr-sites in the transition metal carbides, highlighting the need for large scale averaging to obtain theoretical XANES and EXAFS spectra for comparison with measurements. As shown in this work, it is advantageous to use ab initio theory as an assessment to correctly model and fit experimental spectra and investigate the trends of bond lengths and coordination numbers in complex amorphous materials. With sufficient total carbon content (≥30 at. %), we find that the short-range coordination in the amorphous carbide phase exhibit similarities to that of a Cr7C3 ± y structure, while excessive carbons assemble in the amorphous carbon phase.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2016
National Category
Inorganic Chemistry Theoretical Chemistry Condensed Matter Physics
Identifiers
urn:nbn:se:liu:diva-129386 (URN)10.1021/acs.jpcc.6b03608 (DOI)000378196200059 ()
Note

Funding agencies:We would like to thank the staff at MAX-lab for experimental support and U. Jansson and M. Andersson for providing the samples. This work was supported by the Swedish Research Council (VR) Linnaeus Grant LiLi-NFM, the FUNCASE project supported Swedish Strategic Research Foundation (SSF). W.O. acknowledges financial support from VR Grant No. 621-2011-4426, the Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University (Faculty Grant SFO-Mat-LiU No 2009 00971), Knut and Alice Wallenbergs Foundation project Strong Field Physics and New States of Matter 2014-2019 (COTXS). B.A. would like to thank E. Holmstrom and R. Lizarraga for support with the SQ method and acknowledges financial support by the Swedish Research Council (VR) through the young researcher Grant No. 621-2011-4417 and the international career Grant No. 330-2014-6336 and Marie Sklodowska Curie Actions, Cofund, Project INCA 600398. The calculations were performed using supercomputer resources provided by the Swedish National Infrastructure for Computing (SNIC) at the National Supercomputer Centre (NSC) and Center for Parallel Computing (PDC).

Available from: 2016-06-17 Created: 2016-06-17 Last updated: 2018-06-04Bibliographically approved
Furlan, A., Jansson, U., Lu, J., Hultman, L. & Magnuson, M. (2015). Structure and bonding in amorphous iron carbide thin films. Journal of Physics: Condensed Matter, 27(4), 045002
Open this publication in new window or tab >>Structure and bonding in amorphous iron carbide thin films
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2015 (English)In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 27, no 4, p. 045002-Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
Institute of Physics Publishing (IOPP), 2015
Keywords
iron carbide, thin film coatings, sputtering, synchrotron radiation, amorphous nanocomposites, TEM, RDF
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-113089 (URN)10.1088/0953-8984/27/4/045002 (DOI)000348493500002 ()25567721 (PubMedID)
Note

We would like to thank the staff at the MAX IV Laboratory for experimental support, and Jill Sundberg, UU, for help with the Raman measurements. The work was supported by the Swedish Research Council (VR) by project, and Linnaeus grants (VR 2008-6582). MM, UJ and JL also acknowledge the Swedish Foundation for Strategic Research Synergy Project FUNCASE (RMA11-0029).

Available from: 2015-01-08 Created: 2015-01-08 Last updated: 2018-06-04
Magnuson, M., Mattesini, M., Bugnet, M. & Eklund, P. (2015). The origin of anisotropy and high density of states in the electronic structure of Cr2GeC by means of polarized soft X-ray spectroscopy and ab initio calculations. Journal of Physics: Condensed Matter, 27(41), 415501-415509
Open this publication in new window or tab >>The origin of anisotropy and high density of states in the electronic structure of Cr2GeC by means of polarized soft X-ray spectroscopy and ab initio calculations
2015 (English)In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 27, no 41, p. 415501-415509Article in journal (Refereed) Published
Abstract [en]

The anisotropy in the electronic structure of the inherently nanolaminated ternary phase Cr2GeC is investigated by bulk-sensitive and element selective soft x-ray absorption/emission spectroscopy. The angle-resolved absorption/emission measurements reveal di erences between the in-plane and out-of-plane bonding at the (0001) interfaces of Cr2GeC. The Cr L2;3, C K, and Ge M1, M2;3 emission spectra are interpreted with rst-principles density-functional theory (DFT) including core-tovalence dipole transition matrix elements. For the Ge 4s states, the x-ray emission measurements reveal two orders of magnitude higher intensity at the Fermi level than DFT within the General Gradient Approximation (GGA) predicts. We provide direct evidence of anisotropy in the electronic structure and the orbital occupation that should a ect the thermal expansion coecient and transport properties. As shown in this work, hybridization and redistribution of intensity from the shallow 3d core levels to the 4s valence band explain the large Ge density of states at the Fermi level.

Place, publisher, year, edition, pages
Bristol, UK: Institute of Physics Publishing Ltd., 2015
Keywords
MAX-phases, spectroscopy, DFT, electronic structure
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:liu:diva-121642 (URN)10.1088/0953-8984/27/41/415501 (DOI)000362572100008 ()26414914 (PubMedID)
Available from: 2015-09-29 Created: 2015-09-29 Last updated: 2018-06-04Bibliographically approved
Furlan, A., Lu, J., Hultman, L., Jansson, U. & Magnuson, M. (2014). Crystallization characteristics and chemical bonding properties of nickel carbide thin film nanocomposites. Journal of Physics: Condensed Matter, 26(41), 415501-415512
Open this publication in new window or tab >>Crystallization characteristics and chemical bonding properties of nickel carbide thin film nanocomposites
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2014 (English)In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 26, no 41, p. 415501-415512Article in journal (Refereed) Published
Abstract [en]

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 about10–20 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 thatthe 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.

Place, publisher, year, edition, pages
Institute of Physics Publishing (IOPP), 2014
Keywords
Amorphous nanocomposite nickel carbide XRD TEM XAS SAED
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-110752 (URN)10.1088/0953-8984/26/41/415501 (DOI)000343423600004 ()25237716 (PubMedID)
Available from: 2014-09-20 Created: 2014-09-20 Last updated: 2018-06-04Bibliographically approved
Magnuson, M., Schmitt, T., Strocov, V., Schlappa, J., Kalabukhov, A. & Duda, L. (2014). Self-doping processes between planes and chains in the metal-to-superconductor transition of YBa2Cu3O6.9. Scientific Reports, 4(07017)
Open this publication in new window or tab >>Self-doping processes between planes and chains in the metal-to-superconductor transition of YBa2Cu3O6.9
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2014 (English)In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 4, no 07017Article in journal (Refereed) Published
Abstract [en]

The interplay between the quasi 1-dimensional CuO-chains and the 2-dimensional CuO2 planes ofYBa2Cu3O61x (YBCO) has been in focus for a long time. Although the CuO-chains are known to beimportant as charge reservoirs that enable superconductivity for a range of oxygen doping levels in YBCO,the understanding of the dynamics of its temperature-driven metal-superconductor transition (MST)remains a challenge. We present a combined study using x-ray absorption spectroscopy and resonantinelastic x-ray scattering (RIXS) revealing how a reconstruction of the apical O(4)-derived interplanarorbitals during theMSTof optimally dopedYBCOleads to substantial hole-transfer from the chains into theplanes, i.e. self-doping. Our ionic model calculations show that localized divalent charge-transferconfigurations are expected to be abundant in the chains of YBCO. While these indeed appear in the RIXSspectra from YBCO in the normal, metallic, state, they are largely suppressed in the superconducting stateand, instead, signatures of Cu trivalent charge-transfer configurations in the planes become enhanced. Inthe quest for understanding the fundamental mechanism for high-Tc-superconductivity (HTSC) inperovskite cuprate materials, the observation of such an interplanar self-doping process in YBCO opens aunique novel channel for studying the dynamics of HTSC.

Place, publisher, year, edition, pages
Nature Publishing Group, 2014
Keywords
Superconductor YBCO XAS RIXS spectroscopy synchrotron radiation superconductivity
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:liu:diva-111968 (URN)10.1038/srep07017 (DOI)000344760700007 ()25388860 (PubMedID)
Available from: 2014-11-12 Created: 2014-11-12 Last updated: 2018-09-18Bibliographically approved
Ritchie, A., Eger, S., Wright, C., Chelladurai, S., Borrowman, C., Olovsson, W., . . . Urquhart, S. (2014). Strain sensitivity in the nitrogen 1s NEXAFS spectra of gallium nitride. Applied Surface Science, 316, 232-236
Open this publication in new window or tab >>Strain sensitivity in the nitrogen 1s NEXAFS spectra of gallium nitride
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2014 (English)In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 316, p. 232-236Article in journal (Refereed) Published
Abstract [en]

The nitrogen 1s near edge X-ray absorption fine structure (NEXAFS) of gallium nitride (GaN) shows astrong natural linear dichroism that arises from its anisotropic wurtzite structure. An additional spectro-scopic variation arises from lattice strain in epitaxially grown GaN thin films. This variation is directlyproportional to the degree of strain for some spectroscopic features. This strain variation is interpretedwith the aid of density functional theory calculations.

Place, publisher, year, edition, pages
Elsevier, 2014
Keywords
GaN, Semiconductor strain, NEXAFS, XANES
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-109795 (URN)10.1016/j.apsusc.2014.07.070 (DOI)000343329100034 ()
Available from: 2014-08-28 Created: 2014-08-28 Last updated: 2018-06-04Bibliographically approved
Halim, J., Cook, K. M., Näslund, L.-Å., Magnuson, M., Hultman, L., Gogotsi, Y., . . . Barsoum, M. W. (2014). X-ray Photoelectron Spectroscopy Characterization of Two-Dimensional Titanium Metal Carbides (MXenes).
Open this publication in new window or tab >>X-ray Photoelectron Spectroscopy Characterization of Two-Dimensional Titanium Metal Carbides (MXenes)
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2014 (English)Manuscript (preprint) (Other academic)
Abstract [en]

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.

National Category
Physical Chemistry Chemical Sciences
Identifiers
urn:nbn:se:liu:diva-111127 (URN)
Available from: 2014-10-08 Created: 2014-10-08 Last updated: 2018-06-04Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-0317-0190

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