| 1. |
- Mathieu, C., et al.
(författare)
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Nitrogen 1s NEXAFS and XPS spectroscopy of NH3-saturated Si(001)-2x1: Theoretical predictions and experimental observations at 300 K
- 2009
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Ingår i: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 79:20
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Tidskriftsartikel (refereegranskat)abstract
- In the light of hybrid functional density-functional theory calculations of the core-excited and core-ionized states, this paper discusses original N 1s x-ray photoemission spectroscopy (XPS) and near-edge x-ray absorption fine-structure (NEXAFS) experimental data on the single-domain (vicinal) Si(001)-2x1 surface saturated by NH3 at 300 K. The theoretical approach enables to discuss the vibrational shape of the N 1s XPS spectrum and quantifies the binding-energy splitting due to intrarow and inter-row hydrogen bondings between amine pairs. The observed N 1s NEXAFS peaks are interpreted through the analysis of the contour maps of the antibonding Kohn-Sham orbitals of the NH2 adsorbate and through the Delta Kohn-Sham calculation of the transition energies, laying a theoretical basis for a discussion of the adsorbate spatial orientation. Finally, suggestions are given for future directions of research to get a further knowledge of a system that has potential applications as a template for molecular layer deposition and supramolecular assembly.
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| 2. |
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| 3. |
- Vonau, F, et al.
(författare)
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Branched Substituents Generate Improved Supramolecular Ordering in Physisorbed Molecular Assemblies
- 2009
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Ingår i: JOURNAL OF PHYSICAL CHEMISTRY C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 113:12, s. 4955-4959
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Tidskriftsartikel (refereegranskat)abstract
- We present an experimental study supported by molecular simulations of the influence of the shape of alkyl side groups on the interactions and self-organization of supramolecular assemblies, built from bis-ureasubstituted toluene molecules deposited on Au(111) surfaces. In particular, we demonstrate the crucial importance of the presence of branched alkyl groups (i.e., ethylhexyl) that allow two adjacent supramolecular polymers to arrange closer to each other, leading to the formation of molecular "zippers". Thus, steric constraints at the level of individual molecules can generate improved Ordering between neighboring supramolecular polymers interacting with a planar substrate.
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| 4. |
- Azad, A.K., et al.
(författare)
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Structural and magnetic properties of LaFe0.5Cr0.5O3 studied by neutron diffraction, electron diffraction and magnetometry
- 2005
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Ingår i: Materials Research Bulletin. - 0025-5408. ; 40(10), s. 1633-1644
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Tidskriftsartikel (refereegranskat)abstract
- The structural and magnetic properties of the perovskite type compound LaFe0.5Cr0.5O3 have been studied by temperature dependent neutron powder diffraction and magnetization measurements. Rietveld refinement of the neutron diffraction data shows that the compound crystallizes in an orthorhombic perovskite structure with a random positioning of the Fe and Cr cations at the B sublattice. The magnetic structure at 10 K is a collinear antiferromagnetic one with the magnetic moment per site being equal to 2.79(4) mu(B). Magnetisation measurements confirm the overall antiferromagnetic behaviour. Moreover, it indicates a weak uncompensated magnetic moment close to the transition temperature T-N approximate to 265 K. This moment can be described by a magnetic cluster state, which remains up to 550 K. Electron diffraction patterns along with high-resolution transmission electron microscopy images reveal that the crystallites are composed by domains of different orientation, which share the same cubic perovskite sub-cell reflections. (C) 2005 Elsevier Ltd. All rights reserved
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| 5. |
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| 6. |
- Gisselbrecht, Mathieu, et al.
(författare)
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Photon energy dependence of fragmentation of small argon clusters
- 2005
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 123:19
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Tidskriftsartikel (refereegranskat)abstract
- Photofragmentation of small argon clusters with size below ten atoms is reported. In this size range significant modifications from the electronic properties and geometry take place. When tuning the photon energy through the argon 2p edge, the fragmentation pattern is changed. Specifically, cation dimer production is enhanced at the 2p(3/2)-> 4s resonance, while above the 2p edge almost complete atomization is observed. In both cases, the widths of the peaks in the mass spectra indicate that a large amount of kinetic energy is imparted to the fragment due to the formation of multiply charged clusters. A model based on "Coulomb explosion"-charge separation, simply resulting in a complete atomization of the cluster with no dependence on the photon energy-is insufficient to explain the observed photofragmentation of small clusters.
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| 7. |
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| 9. |
- Lindgren, Andreas, et al.
(författare)
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Molecular alignment of ammonia studied by electron-ion-ion coincidence spectroscopy
- 2005
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 122:11
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Tidskriftsartikel (refereegranskat)abstract
- Electron-ion-ion coincidence measurements carried out at discrete resonances near the N 1s threshold in ammonia are reported. The measured coincidence spectra show clear alignment of the molecule upon resonant core-electron excitation. The coincidence data are analyzed to extract information about the molecule in the excited state by simulating the alignment and the dissociation processes. Dynamic changes in molecular geometry are found as the photon energy is scanned through the N 1s -> 4a(1) resonance, whereas for the N 1s -> 2e state the geometry and kinetic energy released upon dissociation remain unchanged. The alignment of the core-excited molecules is found to be preserved even in two-step dissociation processes.
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| 10. |
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| 11. |
- Tseggai, M., et al.
(författare)
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Effects of magnesium substitution on the magnetic properties of Nd0.7Sr0.3MnO3
- 2005
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Ingår i: Journal of Solid State Chemistry. - : Elsevier BV. - 0022-4596 .- 1095-726X. ; 178:4, s. 1203-1211
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Tidskriftsartikel (refereegranskat)abstract
- Effects of magnesium substitution on the magnetic properties of Nd0.7Sr0.3MnO3 have been investigated by neutron powder diffraction and magnetization measurements on polycrystalline samples of composition Nd0.7Sr0.3MnO3, Nd0.6Mg0.1Sr0.3MnO3, Nd0.6Mg0.1Sr0.3Mn0.9Mg0.1O3, and Nd0.6Mg0.1Sr0.3Mn0.8Mg0.2O3. The pristine compound Nd0.7Sr0.3MnO3 is ferromagnetic with a transition temperature occurring at about 210 K. Increasing the Mg-substitution causes weakened ferromagnetic interaction and a great reduction in the magnetic moment of Mn. The Rietveld analyses of the neutron powder diffraction (NPD) data at 1.5 K for the samples with Mg concentration, y=0.0 and 0.1, show ferromagnetic Mn moments of 3.44(4) and 3.14(4) μB, respectively, which order along the [001] direction. Below 20 K the Mn moments of these samples become canted giving an antiferromagnetic component along the [010] direction of about 0.4 μB at 1.5 K. The analyses also show ferromagnetic polarization along [001] of the Nd moments below 50 K, with a magnitude of almost 1 μB at 1.5 K for both samples. In the samples with Mg substitution of 0.2 and 0.3 only short range magnetic order occurs and the magnitude of the ferromagnetic Mn moments is about 1.6 μB at 1.5 K for both samples. Furthermore, the low-temperature NPD patterns show an additional very broad and diffuse feature resulting from short range antiferromagnetic ordering of the Nd moments.
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| 12. |
- Ye, F, et al.
(författare)
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Electronic Self-Organization in the Single-Layer Manganite Pr1-xCa1+xMnO4
- 2009
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 103:16
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Tidskriftsartikel (refereegranskat)abstract
- We use neutron scattering to investigate the doping evolution of the magnetic correlations in the single-layer manganite Pr1-xCa1-xMnO4, away from the x = 0.5 composition where the CE-type commensurate antiferromagnetic (AF) structure is stable. We find that short-range incommensurate spin correlations develop as the system is electron doped (x < 0.5), which coexist with the CE-type AF order. This suggests that electron doping in this system induces an inhomogeneous electronic self-organization, where commensurate AF patches with x = 0.5 are separated by electron-rich domain walls with short-range magnetic correlations. This behavior is strikingly different than for the perovskite Pr1-xCaxMnO3, where the long-range CE-type commensurate AF structure is stable over a wide range of electron or hole doping around x = 0.5.
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