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We present experimental and theoretical results for the surface core-level binding-energy shifts of Al(100), representative of an sp metal, and Cu(100), representative of a transition metal. Our analysis of these results leads to a unified interpretation for the different behavior of sp and transition metals. The d-electron contribution to smaller surface core-level binding energies is elucidated.
No full textWe present experimental and theoretical results for the surface core-level binding-energy shifts of Al(100), representative of an sp metal, and Cu(100), representative of a transition metal. Our analysis of these results leads to a unified interpretation for the different behavior of sp and transition metals. The d-electron contribution to smaller surface core-level binding energies is elucidated
FINAL-STATE EFFECTS FOR THE CORE-LEVEL XPS SPECTRA OF NIO
No full textIonization of the Ni 3s core level in NiO has been studied using ab initio wavefunctions for an NiO6 cluster model. Three important final state effects are studied: (I ) ligand to Ni 3d charge transfer; (2) exchange coupling of the ionized core level within the open 3d shell; and (3) atomic correlation effects among the metal 3s, 3p, and 3d shells. Analysis of the cluster wave-functions shows that these mechanisms are strongly coupled and must be treated on an equal footing. The ligand to metal charge transfer is often fractional, i.e. intermediate between 0 and 1
Core binding-energies for clusters deposited on different insulating substrates - ESCA spectra and theoretical electronic-structure studie
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Chemisorption of CO on defect sites of MgO
No full textChemisorption of a CO molecule on regular and defect sites of the MgO(100) surface has been investigated by means of cluster model calculations. At all sites studied, CO bonds at the cation with the C atom closest to the surface. The bonding is considerably larger at a three-coordinated corner site than for a regular five-coordinated surface site. A blueshift in the C-O stretching frequency, ωe, of adsorbed CO compared to free CO is found; the shift is much higher for a corner than for a surface site because of the larger local electric field for low-coordinated cations. Both the bond strength and the ω shift are largely due to electrostatic effects and not to the formation of a dative σ-bond with the surface. Surface relaxation effects have also been considered. © 1992
Loss structures in the photoemission spectra of MnO: A careful analysis of peak intensities
No full textA careful and rigorous analysis of the intensities of several features of the Mn 3s x-ray photoemission spectra of MnO, including the satellites at 20-30 eV below the main exchange split peaks is carried out. The previous interpretation of the 20-30 eV satellite is that they arose from electron correlation effects relative to the near degeneracy of the atomic levels. Our work shows that loss processes must also be taken into account. In particular, it is shown that only about 60% of the broad 20-30 eV satellite is due to near degeneracy correlation effects, while a contribution from the shakeup and plasmon loss structures constitutes the remaining 40% of the intensities of this featur
A PROPER ANDERSON-HAMILTONIAN TREATMENT OF THE 3S PHOTOELECTRON-SPECTRA OF MnO, FeO, CoO AND NiO
No full textX-ray photoelectron spectra of the 3s core lines of NiO, CoO, FeO and MnO obtained on high-quality single crystals are interpreted on the basis of an impurity-cluster configuration-interaction model where the exchange and the intra-atomic M-shell charge redistribution energies are evaluated ab initio, Good agreement between the experimental and calculated binding energies and the intensity of the spectral components is obtained. These results clarify the interplay among the charge transfer, exchange and intra-atomic charge redistribution effects on the spectral structure
STUDIES OF THE CU-O BOND IN CUPRIC OXIDE BY X-RAY PHOTOELECTRON-SPECTROSCOPY AND ABINITIO ELECTRONIC-STRUCTURE MODELS
No full textX-ray photoemission spectroscopy (XPS) and ab initio molecular orbital cluster model wavefunctions are used in a combined study of the electronic structure of CuO. High-resolution XPS spectra for single-crystal CuO identify and clarify several features of the core and valence level spectra. The molecular orbital cluster wavefunctions show that there is a significant covalent contribution to the ionic Cu-O bond. For the copper core hole final states, the states where the core hole is screened by charge transfer from O2p to Cud lie at lower binding energy than the states where charge transfer does not screen the core hole. The multiplet splitting of the higher binding energy 2p-hole states is large (ca. 3 eV)
Mechanisms responsible for chemical shifts of core-level binding energies and their relationship to chemical bonding
No full textA comprehensive review of different mechanisms which contribute to the chemical shifts of core-level binding energies, BEs, is made. A principle focus is on showing how the mechanisms can be used to relate the BE shifts to features of the chemical bonding and chemical interactions in the studied system. Several initial state mechanisms are identified; while some are well. known, the importance of others has been only recognized fairly recently. A theoretical framework is presented which places the analysis and interpretation of these BE shifts on a firm foundation. A rigorous definition and distinction of initial and final state effects is presented. This definition is applied to show that initial state effects are often the dominant factors for the chemical BE shifts. It is also shown that, in many cases, theoretical approaches involving the use of constrained variations can permit a clear and definitive separation of the contributions of the different mechanisms. Several representative applications to the analysis and interpretation of core-level BE shifts are described which show how the theoretical methods of analysis can be used to identify the mechanisms important for the BE shifts. Often more than one mechanism makes an important contribution to the shifts and it is common that the contributions will be canceling. When all of the relevant mechanisms are taken into account in the analysis of the BE shifts, these shifts do provide valuable information about the chemical bonding and electronic structure of the materials being studied. The mechanisms presented and the theoretical frameworks described provide a unified view of BE chemical shifts
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