| 1. |
- Wessley, O, et al.
(författare)
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Final state effects in the X-ray absorption spectra of La0.7Sr0.3MnO3
- 2004
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Ingår i: Journal of Magnetism and Magnetic Materials. - : Elsevier BV. - 0304-8853. ; 272-276:3, s. 1780-1781
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Tidskriftsartikel (refereegranskat)abstract
- We present a comparison of theoretical calculations of the electronic structure of La0.7Sr0.3MnO3 with measurements of the unoccupied local density of states for Mn obtained from X-ray absorption spectroscopy (XAS). We compare two different theoretical calculations of the Mn XAS spectra, one based on the local spin density approximation (LSDA) and the other one based on an atomic Hartree–Fock calculation for the Mn ions. In the atomic calculation the solid state effects are introduced through a cubic crystal field where the crystal field strength is obtained from the LSDA calculation. It is found that the atomic calculations agree better with experimental data.
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| 2. |
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| 3. |
- Karis, O, et al.
(författare)
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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
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| 4. |
- Karis, O, et al.
(författare)
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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.
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| 5. |
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| 6. |
- Arvanitis, D, et al.
(författare)
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Magnetic X-ray circular dichroism on in situ grown 3d magnetic thin films on surfaces
- 2001
-
Ingår i: JOURNAL OF SYNCHROTRON RADIATION. - : MUNKSGAARD INT PUBL LTD. - 0909-0495. ; 8, s. 120-124
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Tidskriftsartikel (refereegranskat)abstract
- Epitaxic thin and ultrathin films on surfaces allow crystallographic phases that do not occur naturally in the bulk to be stabilized. They also offer new possibilities for an improved understanding of soft X-ray photoabsorption in magnetic systems. Data c
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| 7. |
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| 8. |
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| 9. |
- Eyrich, C., et al.
(författare)
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Effects of substitution on the exchange stiffness and magnetization of Co films
- 2014
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 90:23, s. 235408-
-
Tidskriftsartikel (refereegranskat)abstract
- An antiferromagnetically coupled FM/NM/FM (FM = ferromagnet, NM = normal metal) trilayer structure responds to an external magnetic field by the formation of a magnetic-moment spring within the FM layers. We show that the exchange stiffness (A ex) of an FM layer can be determined by fitting the field-dependent magnetization, M(H), of the FM/NM/FM trilayer to a micromagnetic model. Using this method, we have measured the exchange stiffness of thin-film Co alloyed with Cr, Fe, Ni, Pd, Pt, and Ru. The results show that the rate at which a substituent element reduces the exchange stiffness is not directly related to its effect on the magnetization of the alloy. The observed trends have been understood by material-specific modeling based on density functional theory within the local density approximation. The stiffness measurements are in agreement with Brillouin light scattering carried out on thicker Co films.
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| 10. |
- Eyrich, C., et al.
(författare)
-
Exchange stiffness in thin film Co alloys
- 2012
-
Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 111:7, s. 07C919-
-
Tidskriftsartikel (refereegranskat)abstract
- The exchange stiffness (A(ex)) is one of the key parameters controlling magnetization reversal in magnetic materials. We used a method based on the spin spiral formation in two ferromagnetic films antiferromagnetically coupled across a non-magnetic spacer layer and Brillouin scattering to measure A(ex) for a series of Co1-delta X delta (X=Cr, Ni, Ru, Pd, Pt) thin film alloys. The results show that A(ex) of Co alloys does not necessarily scale with M-s; A(ex) approximately decreases at the rate of 1.1%, 1.5%, 2.1%, 3.5%, and 5.6%, while M-s decreases at the rate of 1.1%, 0.5%, 1.1%, 3.7%, and 2.5% per addition of 1 at% of Pt, Ni, Pd, Cr, and Ru, respectively.
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| 11. |
- Fohlisch, A, et al.
(författare)
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Beyond the chemical shift: Vibrationally resolved core-level photoelectron spectra of adsorbed CO
- 1998
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Ingår i: PHYSICAL REVIEW LETTERS. - : AMERICAN PHYSICAL SOC. - 0031-9007. ; 81:8, s. 1730-1733
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Vibrational fine structure has been observed in the Cls and O1s photoelectron lines of CO adsorbed on Ni(100). This allows a detailed separation of vibrational and electronic contributions to the line profile. The main line is found to represent the fully
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| 12. |
- Fohlisch, A, et al.
(författare)
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Franck-Condon breakdown in core-level photoelectron spectroscopy of chemisorbed CO
- 1999
-
Ingår i: CHEMICAL PHYSICS LETTERS. - : ELSEVIER SCIENCE BV. - 0009-2614. ; 315:3-4, s. 194-200
-
Tidskriftsartikel (refereegranskat)abstract
- The photon energy dependence of the vibrational fine structure in the Cls and Ols X-ray photoelectron main lines of chemisorbed CO on Ni(100) and Ru(0001) has been measured from 6 to 150 eV above the core-level thresholds. Significant deviations from the
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| 13. |
- Fohlisch, A, et al.
(författare)
-
Ground-state interpretation of x-ray emission spectroscopy on adsorbates: CO adsorbed on Cu(100)
- 2000
-
Ingår i: PHYSICAL REVIEW B. - : AMERICAN PHYSICAL SOC. - 0163-1829. ; 61:23, s. 16229-16240
-
Tidskriftsartikel (refereegranskat)abstract
- The application of resonant inelastic x-ray scattering and resonantly excited x-ray emission to adsorbates has evolved into a powerful technique to investigate the valence electronic structure of adsorbates in an atom-specific and orbital-symmetry-selecti
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| 14. |
- Fohlisch, A, et al.
(författare)
-
How carbon monoxide adsorbs in different sites
- 2000
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Ingår i: PHYSICAL REVIEW LETTERS. - : AMERICAN PHYSICAL SOC. - 0031-9007. ; 85:15, s. 3309-3312
-
Tidskriftsartikel (refereegranskat)abstract
- The interplay between the electronic and the geometric structure of adsorbates is of fundamental importance for the understanding of many surface phenomena. Using x-ray emission spectroscopy and ab initio cluster calculations, this issue has been investig
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| 15. |
- Fohlisch, A, et al.
(författare)
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The bonding of CO to metal surfaces
- 2000
-
Ingår i: JOURNAL OF CHEMICAL PHYSICS. - : AMER INST PHYSICS. - 0021-9606. ; 112:4, s. 1946-1958
-
Tidskriftsartikel (refereegranskat)abstract
- The atom and symmetry specific properties of x-ray emission spectroscopy have been applied to the investigation of CO adsorbed on Ni(100) and Cu(100) surfaces. In comparison to ab initio electronic structure calculations, obtained in density functional th
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| 16. |
- Fohlisch, A, et al.
(författare)
-
Vibrational fine structure in core level photoelectron lines of adsorbed molecules: System dependent effects
- 1999
-
Ingår i: JOURNAL OF ELECTRON SPECTROSCOPY AND RELATED PHENOMENA. - : ELSEVIER SCIENCE BV. - 0368-2048. ; 103, s. 303-308
-
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- System dependent effects in resolving vibrational fine structure in the corn-level lines of adsorbates are discussed. The example is carbon monoxide on transition metals. The importance of dynamic metallic screening is exemplified and the role of shake-up
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| 17. |
- Girt, Erol, et al.
(författare)
-
A method for measuring exchange stiffness in ferromagnetic films
- 2011
-
Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 109:7, s. 07B765-
-
Tidskriftsartikel (refereegranskat)abstract
- An exchange stiffness, A(ex), in ferromagnetic films is obtained by fitting the M(H) dependence of two ferromagnetic layers antiferromagnetically coupled across a nonmagnetic spacer layer with a simple micromagnetic model. In epitaxial and textured structures this method allows measuring A(ex) between the crystallographic planes perpendicular to the growth direction of ferromagnetic films. Our results show that A(ex) between [0001] planes in textured Co grains is 1.54 +/- 0.12 x 10(-11) J/m.
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| 18. |
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| 19. |
- Gorgoi, M, et al.
(författare)
-
The high kinetic energy photoelectron spectroscopy facility at BESSY progress and first results
- 2009
-
Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 601:1-2, s. 48-53
-
Tidskriftsartikel (refereegranskat)abstract
- Photoelectron spectroscopy at high kinetic energy is a research field that receives an increasing interest due to the possibility of studying bulk properties of materials and deeply buried interfaces. Recently the high kinetic energy electron (HIKE) spectroscopy facility at BESSY in Berlin has become operative at the bending magnet beamline KMC-1. The first results show very good performance. Electron spectra have been recorded using X-ray energies from 2 keV up to 12 keV. Using back-scattering conditions in the crystal monochromator, very high-resolution has been achieved for photon energies around 2, 6 and 8 keV. In the latter case, spectra with a resolving power from the monochromator of >= 80 000 have been achieved and it has been possible to perform electron spectroscopy with resolving power of >= 60 000, yielding a total instrument resolution of about 150 meV as determined directly from spectra. This paper describes the facility and reports some of the first results. (C) 2009 Elsevier B.V. All rights reserved.
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| 20. |
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| 21. |
- Hahlin, A, et al.
(författare)
-
Ultrathin Co films on flat and stepped Cu(111) surfaces: Determination of per atom orbital and spin moments
- 2002
-
Ingår i: Applied Physics Reviews. - : AIP Publishing. - 1931-9401. ; 91:10, s. 6881-6883
-
Tidskriftsartikel (refereegranskat)abstract
- We have used the x-ray magnetic circular dichroism technique to characterize ultrathin Co films deposited on flat and vicinal Cu(111) single crystal surfaces. All films were prepared and characterized in situ, in ultrahigh vacuum. Similar to other investigators we report a 40% increase of the ratio m(l)/m(s) (orbital to spin moment) of ultrathin Co on both flat and vicinal Cu(111). In addition, an apparently correlated enhancement of both the orbital and spin moments is observed for Co on vicinal Cu(111). This finding is in contrast to what has earlier been reported for a similar system, Co on vicinal Cu(100). (C) 2002 American Institute of Physics.
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| 22. |
- Hahlin, A, et al.
(författare)
-
Ultrathin Co films on flat and vicinal Cu(111) surfaces: per atom determination of orbital and spin moments
- 2003
-
Ingår i: Journal of Physics: Condensed Matter. - : IOP Publishing. - 0953-8984. ; 15:5, s. 573-586
-
Konferensbidrag (refereegranskat)abstract
- We have performed x-ray magnetic circular dichroism, x-ray resonant magnetic scattering and scanning tunnelling microscopy measurements on ultrathin Co films deposited on flat and vicinal Cu(111). The range of film thickness varies between one and 25 monolayers. For the vicinal Cu(111), Co deposition below one monolayer leads to the formation of elongated islands preferentially oriented along the step edges. These islands extend over lateral length scales of up to several thousand angstroms. For the thicker films we still observe that the vicinal surface leads to the occurrence of a preferential uniaxial growth direction. No such preferential growth direction can be identified for the flat surface. In correlation to the Co growth we observe an increase of both the orbital and the spin moment per Co atom on vicinal Cu(111) of about 25% versus what was observed for Co on flat Cu(111). This enhancement is observed in both the x-ray absorption and the reflectivity measurements. Similar to what was earlier reported for Co on Cu(100) we also observe for the case Co on Cu(111) an increase in the ratio m(l)/m(s), (orbital to spin moments) of 40% for thin Co films. In contrast to what has been reported for Co films on flat and vicinal Cu(100) we do not observe any major variations in the occupancy of the Co 3d states for Co grown on the vicinal Cu(111) surface.
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| 23. |
- Hasselstrom, J, et al.
(författare)
-
Ammonia adsorbed on Cu(110): An angle resolved x-ray spectroscopic and ab initio study
- 1999
-
Ingår i: JOURNAL OF CHEMICAL PHYSICS. - : AMER INST PHYSICS. - 0021-9606. ; 110:10, s. 4880-4890
-
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- We present a study of a monolayer of ammonia (NH3) adsorbed on Cu(110) using core level spectroscopies in combination with ab initio calculations based on density functional theory. In particular, x-ray emission spectroscopy has been applied, providing an
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| 24. |
- Hasselstrom, J, et al.
(författare)
-
The adsorption structure of glycine adsorbed on Cu(110); comparison with formate and acetate/Cu(110)
- 1998
-
Ingår i: SURFACE SCIENCE. - : ELSEVIER SCIENCE BV. - 0039-6028. ; 407:1-3, s. 221-236
-
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- The molecular orientation of an ordered monolayer of glycine adsorbed on Cu(110) has been studied using X-ray Photoelectron Spectroscopy (XPS), Near Edge X-ray Absorption Fine Structure (NEXAFS), X-ray Photoelectron Diffraction (XPD), Low-Energy Electron
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| 25. |
|
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| 26. |
- Hunter Dunn, Jonathan, et al.
(författare)
-
Elliptically polarised soft X-rays produced using a local bump in MAX II characterisation of the degree of polarisation
- 2004
-
Ingår i: AIP Conference Proceedings. - : AIP. - 1551-7616 .- 0094-243X. ; 705, s. 65-68
-
Konferensbidrag (refereegranskat)abstract
- MAX-lab has introduced a local perturbation to the electron orbit of the MAX II storage ring, providing users at the SX700 monochromator beam line, D1011, with elliptically polarised soft X-rays. This is achieved by using corrector magnets to send the electron orbit on an ascending or descending trajectory through the dipole magnet source. This simple "bump" approach has many advantages over and above insertion device based solutions. To illustrate the potential of the approach, the degree of circular polarisation, Pc, has both been calculated and measured. The calculation was made by applying the Stokes formalism to the intensities given by the standard dipole emission formula. Experimentally Pc was characterised using X-ray magnetic circular dichroism measurements. In such experiments magnetic contrast scales directly proportional to Pc. Using a 25 atomic layer bcc Fe film deposited on the Cu(100) surface as a calibration standard the spin moment, ms, was determined. By comparing the values of ms obtained here with those reported earlier, the degree of circular polarisation could be estimated. At ~715 eV the calculated and measured values of Pc are 0.93 and 0.85, respectively
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| 27. |
- Jana, Somnath, et al.
(författare)
-
Analysis of the linear relationship between asymmetry and magnetic moment at the M edge of 3d transition metals
- 2020
-
Ingår i: Physical Review Research. - : American Physical Society. - 2643-1564. ; 2:1
-
Tidskriftsartikel (refereegranskat)abstract
- The magneto-optical response of Fe and Ni during ultrafast demagnetization is studied experimentally and theoretically. We have performed pump-probe experiments in the transverse magneto-optical Kerr effect (T-MOKE) geometry using photon energies that cover the M absorption edges of Fe and Ni between 40 and 72 eV. The magnetic asymmetry was obtained by forming the difference of reflected intensities obtained for two opposite orientations of the sample magnetization. Density functional theory (DFT) was used to calculate the magneto-optical response of different magnetic configurations, representing different types of excitations: long wavelength magnons, short wavelength magnons, and Stoner excitations. In the case of Fe, we find that the calculated asymmetry is strongly dependent on the specific type of magnetic excitation. Our modeling also reveals that during remagnetization Fe is, to a reasonable approximation, described by magnons, even though small nonlinear contributions could indicate some degree of Stoner excitations as well. In contrast, we find that the calculated asymmetry in Ni is rather insensitive to the type of magnetic excitations. However, there is a weak nonlinearity in the relation between asymmetry and the off-diagonal component of the dielectric tensor, which does not originate from the modifications of the electronic structure. Our experimental and theoretical results thus emphasize the need to consider a coupling between asymmetry and magnetization that may be more complex than a simple linear relationship. This insight is crucial for the microscopic interpretation of ultrafast magnetization experiments.
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| 28. |
- Kadas, Krisztina, et al.
(författare)
-
Structural properties of amorphous metal carbides : Theory and experiment
- 2012
-
Ingår i: Acta Materialia. - : Elsevier BV. - 1359-6454 .- 1873-2453. ; 60:12, s. 4720-4728
-
Tidskriftsartikel (refereegranskat)abstract
- By means of theoretical modeling and experimental synthesis and characterization, we investigate the structural properties of amorphous Zr-Si-C. Two chemical compositions are selected: Zr0.31Si0.29C0.40 and Zr0.60Si0.33C0.07. Amorphous structures are generated in the theoretical part of our work by the stochastic quenching (SQ) method, and detailed comparison is made regarding the structure and density of the experimentally synthesized films. These films are analyzed experimentally using X-ray absorption spectroscopy, transmission electron microscopy and X-ray diffraction. Our results demonstrate a remarkable agreement between theory and experiment concerning bond distances and atomic coordination of this complex amorphous metal carbide. The demonstrated power of the SQ method opens up avenues for theoretical predictions of amorphous materials in general.
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| 29. |
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| 30. |
- Karis, O., et al.
(författare)
-
High-kinetic-energy photoemission spectroscopy of Ni at 1s: 6-eV satellite at 4 eV
- 2008
-
Ingår i: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121 .- 1550-235X. ; 78:23, s. 3-3
-
Tidskriftsartikel (refereegranskat)abstract
- Electron correlations are responsible for many profound phenomena in solid-state physics. A classical example is the 6-eV satellite in the photoelectron spectrum of Ni. Until now the satellite structure has only been investigated at the L shell and more shallow levels. Here we report a high-kinetic-energy photoemission spectroscopy (HIKE) investigation of Ni metal. We present 1s and 2p photoelectron spectra, obtained using excitation energies up to 12.6 keV. Our investigation demonstrates that the energy position of the satellite relative to the main line is different for the 1s and the 2p levels. In combination with electronic structure calculations, we show that this energy shift is attributed to unique differences in the core-valence coupling for the K and L-2,L-3 shells in 3d transition metals, resulting in different screening of the core holes.
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| 31. |
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| 32. |
- 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.
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| 33. |
- Karis, O, et al.
(författare)
-
One-step and two-step description of deexcitation processes in weakly interacting systems
- 1996
-
Ingår i: PHYSICAL REVIEW LETTERS. - : AMER INST PHYSICS. ; 76:8, s. 1380-1383
-
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- The origin of one- and two-step behavior of core-hole decay processes is identified in connection with high resolution autoionization spectra for Ar/Pt(111). The spectra simultaneously show features of the two types (resonant Raman vs Auger-like behavior)
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| 34. |
- Karis, O, et al.
(författare)
-
The bonding of simple carboxylic acids on Cu(110)
- 2000
-
Ingår i: JOURNAL OF CHEMICAL PHYSICS. - : AMER INST PHYSICS. - 0021-9606. ; 112:18, s. 8146-8155
-
Tidskriftsartikel (refereegranskat)abstract
- We present a study of the bonding of formate (HCOO) and acetate (CH3COO) chemisorbed on Cu(110) using core level spectroscopies in combination with theoretical calculations. For the first time, we apply x-ray emission spectroscopy (XES) to these systems.
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| 35. |
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| 36. |
- Locht, Inka L. M., 1986-, et al.
(författare)
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Magnetic asymmetry around the 3p absorption edge in Fe and Ni
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- This work is a joint theoretical and experimental study of the relation between the magneto- optical response of a material in the sub-picosecond timescale and its instantaneous magnetisation. We perform pump-probe experiments in the transverse magneto-optical Kerr effect (T-MOKE) geometry. We measure the magnetic asymmetry of elemental Fe and Ni before and after the laser pulse. The observed differences between the magnetic asymmetry curves for various photon energies suggest that the relation between asymmetry and sample magnetization is more complex than a simple proportionality. Further insight is obtained by means of theoretical simulations based on density-functional theory. Our calculations show that non-linear effects in the asymmetry are most prominent at energies corresponding to the absorption edge and that the proportionality is recovered outside of this region. In conclusion, our experimental and theoretical results emphasize the need of including the complex relation between asymmetry and magnetization in the interpretation of ultrafast magnetization experiments in terms of microscopic properties.
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| 37. |
- Magnuson, Martin, 1965-, et al.
(författare)
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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.)
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| 38. |
- Martensson, N, et al.
(författare)
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Coherent and incoherent processes in resonant photoemission
- 1997
-
Ingår i: APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING. - 0947-8396. ; 65:2, s. 159-167
-
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- The basis for resonant photoemission is discussed in connection with data for a physisorption system, Ar/Pt(111) and a 3d transition metal, Ni(100). For Ar/Pt(111) the quasi-localized character of the intermediate state leads to two types of features in t
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| 39. |
- Martensson, N, et al.
(författare)
-
Resonant processes in the soft X-ray regime
- 1999
-
Ingår i: JOURNAL OF ELECTRON SPECTROSCOPY AND RELATED PHENOMENA. - : ELSEVIER SCIENCE BV. - 0368-2048. ; 100, s. 379-393
-
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- The phenomenon of resonant excitation of X-ray and electron emission spectra is discussed. The basic phenomena are demonstrated for Ni metal. The importance of the localization of the intermediate state is discussed in connection with spectra for adsorbed
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| 40. |
- MAXWELL, AJ, et al.
(författare)
-
C-60 ON AL(111) - COVALENT BONDING AND SURFACE RECONSTRUCTION
- 1995
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Ingår i: PHYSICAL REVIEW B-CONDENSED MATTER. - : AMER INST PHYSICS. ; 52:8
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- We present photoemission and C 1s photoabsorption data for an annealed monolayer C-60/Al(111), which show that a strong covalent bond is formed between the C-60 molecules and the substrate. Low-energy electron-diffraction and scanning tunneling microscopy
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| 41. |
- Mazumdar, Dipanjan, et al.
(författare)
-
The valence band electronic structure of rhombohedral-like and tetragonal-like BiFeO3 thin films from hard X-ray photoelectron spectroscopy and first-principles theory
- 2016
-
Ingår i: Journal of Electron Spectroscopy and Related Phenomena. - : Elsevier BV. - 0368-2048 .- 1873-2526. ; 208, s. 63-66
-
Tidskriftsartikel (refereegranskat)abstract
- Abstract We investigate the electronic structure of rhombohedral-like (R) and tetragonal-like (T) BiFeO3 thin films using high energy X-ray photoelectron spectroscopy and first-principles electronic structure calculations. By exploiting the relative elemental cross sections to selectively probe the elemental composition of the valence band, we identify a strong Bi 6p contribution at the top of the valence band in both phases, overlapping in energy range with the O 2p states; this assignment is confirmed by our electronic structure calculations. We find that the measured occupied Bi 6p signal lies closer to the top of the valence band in the T phase than in the R phase, which we attribute, using our electronic structure calculations, to lower Bi–O hybridization in the T phase. We note, however, that our calculations of the corresponding densities of states underestimate the difference between the phases, suggesting that matrix element effects resulting from the different effective symmetries also contribute. Our results shed light on the chemical nature of the stereochemically active Bi lone pairs, which are responsible for the large ferroelectric polarization of BiFeO3.
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| 42. |
- Nilsson, A, et al.
(författare)
-
An atom-specific look at the surface chemical bond
- 1997
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Ingår i: PHYSICAL REVIEW LETTERS. - : AMER INST PHYSICS. - 0031-9007. ; 78:14, s. 2847-2850
-
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- High resolution x-ray emission spectroscopy is shown to reveal unprecedented details of the chemical bond formed between a molecule and a transition metal surface. An atom and symmetry projected view of the bonding orbitals is obtained. We find that all o
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| 43. |
- Nilsson, A, et al.
(författare)
-
Local probing of the surface chemical bond using X-ray emission spectroscopy
- 1997
-
Ingår i: APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING. - : SPRINGER VERLAG. - 0947-8396. ; 65:2, s. 147-154
-
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- X-ray emission spectroscopy applied to adsorbate systems is shown to reveal new details of the chemical bond formed at surfaces. An atom and symmetry projected view of the bonding orbitals is obtained. We will present recent studies of N-2 and CO on Ni(10
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| 44. |
- Nilsson, A, et al.
(författare)
-
Probing chemical bonding in adsorbates using X-ray emission spectroscopy
- 2000
-
Ingår i: JOURNAL OF ELECTRON SPECTROSCOPY AND RELATED PHENOMENA. - : ELSEVIER SCIENCE BV. - 0368-2048. ; 110:1-3, s. 15-39
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Tidskriftsartikel (refereegranskat)abstract
- When a molecule is adsorbed on a metal surface by chemical bonding new electronic states are formed. The direct observation and identification of these states has been an experimental challenge. Their signature is often obscured by bulk substrate states.
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| 45. |
- Nyberg, M, et al.
(författare)
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The electronic structure and surface chemistry of glycine adsorbed on Cu(110)
- 2000
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Ingår i: JOURNAL OF CHEMICAL PHYSICS. - : AMER INST PHYSICS. - 0021-9606. ; 112:12, s. 5420-5427
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Tidskriftsartikel (refereegranskat)abstract
- We present a combined density functional theory and x-ray emission spectroscopy study of the bonding and chemistry of glycine (NH2CH2COOH) chemisorbed on Cu(110). The amino acid deprotonates upon adsorption. The adsorbate exhibits a rich surface chemistry
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| 46. |
- Panda, Swarup K., et al.
(författare)
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High photon energy spectroscopy of NiO : Experiment and theory
- 2016
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Ingår i: PHYSICAL REVIEW B. - 2469-9950. ; 93:23
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Tidskriftsartikel (refereegranskat)abstract
- We have revisited the valence band electronic structure of NiO by means of hard x-ray photoemission spectroscopy (HAXPES) together with theoretical calculations using both the GW method and the local density approximation + dynamical mean-field theory (LDA+DMFT) approaches. The effective impurity problem in DMFT is solved through the exact diagonalization (ED) method. We show that the LDA+DMFT method in conjunction with the standard fully localized limit (FLL) and around mean field (AMF) double-counting alone cannot explain all the observed structures in the HAXPES spectra. GW corrections are required for the O bands and Ni-s and p derived states to properly position their binding energies. Our results establish that a combination of the GW and DMFT methods is necessary for correctly describing the electronic structure of NiO in a proper ab initio framework. We also demonstrate that the inclusion of photoionization cross section is crucial to interpret the HAXPES spectra of NiO. We argue that our conclusions are general and that the here suggested approach is appropriate for any complex transition metal oxide.
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| 47. |
- Persson, Petter, et al.
(författare)
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N1s x-ray Absorption Study of the Bonding Interaction of Bi-Isonicotinic Acid on Rutile TiO2 (110)
- 2000
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 112:9, s. 3945-3948
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Tidskriftsartikel (refereegranskat)abstract
- N1s x-ray absorption spectra of bi-isonicotinic acid (2,28-bipyridine–4,48-dicarboxylic acid! on rutile TiO2(110) have been studied experimentally and quantum chemically. Differences between multilayer and monolayer spectra are explained by the adsorbate bonding to the substrate. A connection to the electronic coupling in dye-sensitized electrochemical devices is made.
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| 48. |
- Phuyal, Dibya, 1985-, et al.
(författare)
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Electronic Structure of Two-Dimensional Lead(II) Iodide Perovskites : An Experimental and Theoretical Study
- 2018
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Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 0897-4756 .- 1520-5002. ; 30:15, s. 4959-4967
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Tidskriftsartikel (refereegranskat)abstract
- Layered two-dimensional (2D) hybrid organic-inorganic perovskites (HOP) are promising materials for light-harvesting applications because of their chemical stability, wide flexibility in composition and dimensionality, and increases in photovoltaic power conversion efficiencies. Three 2D lead iodide perovskites were studied through various X-ray spectroscopic techniques to derive detailed electronic structures and band energetics profiles at a titania interface. Core-level and valence band photoelectron spectra of HOP were analyzed to resolve the electronic structure changes due to the reduced dimensionality of inorganic layers. The results show orbital narrowing when comparing the HOP, the layered precursor PbI2, and the conventional 3D (CH3NH3)PbI3 such that different localizations of band edge states and narrow band states are unambiguously due to the decrease in dimensionality of the layered HOPs. Support from density functional theory calculations provide further details on the interaction and band gap variations of the electronic structure. We observed an interlayer distance dependent dispersion in the near band edge electronic states. The results show how tuning the interlayer distance between the inorganic layers affects the electronic properties and provides important design principles for control of the interlayer charge transport properties, such as the change in effective charge masses as a function of the organic cation length. The results of these findings can be used to tune layered materials for optimal functionality and new applications.
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| 49. |
- Phuyal, Dibya, et al.
(författare)
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The electronic structure and band interface of cesium bismuth iodide on a titania heterostructure using hard X-ray spectroscopy
- 2018
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Ingår i: Journal of Materials Chemistry A. - : Royal Society of Chemistry (RSC). - 2050-7488 .- 2050-7496. ; 6:20, s. 9498-9505
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Tidskriftsartikel (refereegranskat)abstract
- Bismuth halide compounds as a non-toxic alternative are increasingly investigated because of their potential in optoelectronic devices and their rich structural chemistry. Hard X-ray spectroscopy was applied to the ternary bismuth halide Cs3Bi2I9 and its related precursors BiI3 and CsI to understand its electronic structure at an atomic level. We specifically investigated the core levels and valence band using X-ray photoemission spectroscopy (PES), high-resolution X-ray absorption (HERFD-XAS), and resonant inelastic X-ray scattering (RIXS) to get insight into the chemistry and the band edge properties of the two bismuth compounds. Using these element specific X-ray techniques, our experimental electronic structures show that the primary differences between the two bismuth samples are the position of the iodine states in the valence and conduction bands and the degree of hybridization with bismuth lone pair (6s(2)) states. The crystal structure of the two layered quasi-perovskite compounds plays a minor role in modifying the overall electronic structure, with variations in bismuth lone pair states and iodine band edge states. Density Functional Theory (DFT) calculations are used to compare with experimental data. The results demonstrate the effectiveness of hard X-ray spectroscopies to identify element specific bulk electronic structures and their use in optoelectronic devices.
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| 50. |
- Phuyal, Dibya, et al.
(författare)
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The origin of low bandgap and ferroelectricity of a co-doped BaTiO3
- 2018
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Ingår i: Europhysics letters. - : IOP Publishing. - 0295-5075 .- 1286-4854. ; 124:2
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Tidskriftsartikel (refereegranskat)abstract
- We recently demonstrated the lowest bandgap bulk ferroelectric material, BaTi1-x(Mn1/2Nb1/2)xO3, a promising candidate material for visible light absorption in opto- electronic devices. Using a combination of x-ray spectroscopies and density functional theory (DFT) calculations, we here elucidate this compound’s electronic structure and the modifications induced by Mn doping. In particular, we are able to rationalize how this compound retains its ferroelectricity even through a significant reduction of the optical gap upon Mn doping. The local electronic structure and atomic coordination are investigated using x-ray absorption at the Ti K, Mn K, and O K edges, which suggests only small distortions to the parent tetragonal ferroelectric system, BaTiO3, thereby providing a clue to the substantial retention of ferroelectricity in spite of doping. Features at the Ti K edge, which are sensitive to local symmetry and an indication of Ti off-centering within the Ti-O6 octahedra, show modest changes with doping and strongly corroborates with our measured polarization values. Resonant photoelectron spectroscopy results suggest the origin of the reduction of the bandgap in terms of newly created Mn d bands that hybridize with O 2p states. X-ray absorption spectra at the O K-edge provide evidence for new states below the conduction band of the parent compound, illustrating additional contributions facilitating bandgap reduction.
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