Article

Resonant Auger spectroscopy at the L-2,L-3 shake-up thresholds as a probe of electron correlation effects in nickel

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Abstract

The excitation energy dependence of the three-hole satellites in the L3-M4,5M4,5 and L2-M4,5M4,5 Auger spectra of nickel metal has been measured using synchrotron radiation. The satellite behavior in the non-radiative emission spectra at the L3 and L2 thresholds is compared and the influence of the Coster-Kronig channel explored. The three-hole satellite intensity at the L3 Auger emission line reveals a peak structure at 5 eV above the L3 threshold attributed to resonant processes at the 2p53d9 shake-up threshold. This is discussed in connection with the 6-eV feature in the x-ray absorption spectrum.

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... Five peaks in the top diffractogram (x = 0.05) are indexed as fcc-NiC x structure (space group Fm-3m) with a lattice parameter of a = 3.610(1) Å. This lattice parameter is larger than that of fcc-Ni metal (3.524 Å) [19], but smaller than that of fcc-NiC (4.077 Å) [20]. Interpolation of these values yields an estimated phase composition of fcc-NiC x , where x = 0.23-0.30. ...
... For x = 0.05, the double-peak structure has essentially vanished in comparison to at x = 0.16 due to the superposition of the strong fcc contribution. (iv) The 6 eV feature [19,31] above the main 2p 3/2 peak is prominent in Ni metal x = 0.0 that is associated with electron correlation effects and narrow-band phenomena [32]. The intensity of the 6 eV feature is very low in the Ni 1−x C x films in comparison to Ni metal even at x = 0.05 due to more delocalized bands. ...
... Moreover, the 6 eV feature in the Ni XAS spectra that signifies electron correlation effects and narrow-band phenomena in metallic Ni [19,31] is washed out in the Ni 1−x C x samples due to the Ni 3d-C 2p orbital overlap that changes the properties of Ni already at very low carbon content. Thus, the spectral profiles of the Ni 1−x C x samples exhibit carbide signatures and exclude metallic nickel. ...
Article
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The crystal structure and chemical bonding of magnetron-sputtering deposited nickel carbide Ni 1−x C x (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-NiC y phase), instead of the expected rhombohedral-Ni 3 C. At low carbon content (4.9 at%), the thin film consists of hcp-NiC y nanocrystallites mixed with a smaller amount of fcc-NiC x . 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-NiC y 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-NiC y and fcc-NiC x nanodomain structures in an amorphous carbon-rich matrix. Raman spectra of carbon indicate dominant sp 2 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.
... Five peaks in the top diffractogram (x = 0.05) are indexed as fcc-NiC x structure (space group Fm-3m) with a lattice parameter of a = 3.610(1) Å. This lattice parameter is larger than that of fcc-Ni metal (3.524 Å) [19], but smaller than that of fcc-NiC (4.077 Å) [20]. Interpolation of these values yields an estimated phase composition of fcc-NiC x , where x = 0.23–0.30. ...
... For x = 0.05, the double-peak structure has essentially vanished in comparison to at x = 0.16 due to the superposition of the strong fcc contribution. (iv) The 6 eV feature [19, 31] above the main 2p 3/2 peak is prominent in Ni metal x = 0.0 that is associated with electron correlation Gaussian functions give the same trend as a comparison of the peak heights but yields a higher branching ratio for Ni metal than for the other samples. A lower 2p 3/2 /2p 1/2 branching ratio is an indication of higher ionicity (lower conductivity) for the highest carbon content333435. ...
... It can be assumed that chargetransfer occurs within the fcc-NiC x and hcp-NiC y nanocrystal carbide phases, but more significant across the carbide/matrix interface with the surrounding amorphous C-phase or between nanocrystals, that depends on the nanocrystalline size. Moreover, the 6 eV feature in the Ni XAS spectra that signifies electron correlation effects and narrow-band phenomena in metallic Ni [19, 31] is washed out in the Ni 1−x C x samples due to the Ni 3d-C 2p orbital overlap that changes the properties of Ni already at very low carbon content. Thus, the spectral profiles of the Ni 1−x C x samples exhibit carbide signatures and exclude metallic nickel. ...
... Multiplets observed in Auger spectra of Ni can be explained by taking the ground state of Ni as the superposition of d 8 , d 9 and d 10 configurations [21]. The observed features B, C, D in Ni L 3 M 45 M 45 Auger spectra (Fig. 2) can be attributed to 1 S, 1 G, 3 F terms respectively obtained theoretically using atomic calculations [9,22,23]. The atomic calculations also give 1 D and 3 P terms which are very close to 1 G term and are not resolved in our experiment. ...
... The atomic calculations also give 1 D and 3 P terms which are very close to 1 G term and are not resolved in our experiment. Feature A in Ni L 3 M 45 M 45 spectra corresponds to a satellite with d 7 4s 2 final state configuration which occurs only when the photon energy is high enough to ionize L 2 shell [22]. When L 2 and L 3 simultaneously ionized, hole in L 2 decays via a Coster-Cronig transition and creates an extra holes in L 3 shell which leads to L 3 M 45 M 45 Auger transition with 3 holes in the valence band. ...
... The spectra exhibit four features A, B, C and D as indicated in the figure. The features B, C and D may be respectively attributed to 1 S, 1 G and 3 F terms obtained from atomic calculations [5,6,7]. The feature A is satellite occurring due to the possible Koster Cronig transition from L 3 to L 2 shell giving rise to three hole final state. ...
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Fe1-xNix alloys have been prepared by arc melting method. This alloy system exhibits a transition from bcc to fcc structure at around 30% Ni concentration. In fcc region lattice parameter follows linear behaviour with concentration suggesting the formation of disordered alloys. Ni L23M45M45 Auger spectra of the alloys have been recorded at room temperature using monochromatic AlKα radiation as source of excitation. The spectra shift to lower kinetic energy with a decrease of Ni concentration in the alloys. The intensity of ³F feature decreases with a decrease of Ni concentration of the alloys suggesting charge transfer upon alloy formation.
... In this view, it is surprising that the calculations, which include only direct RIXS processes, capture both fluorescence and Raman behavior. This kind of Ramanto-fluorescence crossover is observed and discussed in resonant photoemission and resonant Auger spectroscopy [82][83][84][85][86] and has more recently been seen in RIXS [72,87]. The finite lifetime of the core hole allows below-threshold excitation, and, since the intermediate state is virtual, the energy loss depends only on the energy difference between the initial and final states. ...
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... The goal and topic of this critical review article is an improved understanding and systematization of how the underlying electronic structure and chemical bonding affects the macroscopic properties and how they can be tuned. Explaining the physical properties of MAX phases requires a thorough knowledge of orbital occupation and chemical bonding, as well as the role of phonons [15,16] and electron correlation effects [17,18]. By using bulk-sensitive and element-selective X-ray spectroscopy [19,20], it is possible to differentiate between the occupation of orbitals across and along the laminate basal plane in the interior of the MAX phases. ...
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... The goal and topic of this critical review article is an improved understanding and systematization of how the underlying electronic structure and chemical bonding affects the macroscopic properties and how they can be tuned. Explaining the physical properties of MAX phases requires a thorough knowledge of orbital occupation and chemical bonding, as well as the role of phonons [15,16] and electron correlation effects [17,18]. By using bulk-sensitive and element-selective X-ray spectroscopy [19,20], it is possible to differentiate between the occupation of orbitals across and along the laminate basal plane in the interior of the MAX phases. ...
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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 exhibits 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 material properties make it possible to tailor the characteristics of this class of materials by controlling the strengths of their chemical bonds.
... These multiple-excitation phenomena are studied by Ito et al. [148] for Brin organic solvents and by Magnuson et al. [149] for nickel metal. These more-than-one electron excitation signals are a source of spurious in the analysis of XAFS spectra [150]. ...
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1. Introduction 2. Basics for XAFS 3. Extreme conditions 4. Combination with scanning tunneling microscopes 5. Combination with optical luminescence 6. Combination with X-ray fluorescence 7. Photoconductive and electrochemical measurements 8. Total reflection XAFS 9. Electron and other secondary yield methods and their surface sensitivity 10. Strong field effects 11. Microscopy 12. EELS, ELNES, and EXELFS 13. EXEFS 14. DAFS 15. Theory and interpretation of XAFS spectra 16. Standardization 17. Instrumentation and spectrometer 18. Summary and addenda
... 24 The extrema α 2 and α 3 do not exactly coincide with the L 2 MM and the L 3 MM intensity maxima, which indicates a multiplet structure. 25 In the following we use the labels α σ i for electrons at the energies of α 2 and α 3 , excited with σ + and σ − polarized radiation, respectively. ...
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... Atomic nickel is a difficult sample to prepare in the gas phase due to the high temperatures required to vaporize the metal [29]. Despite experimental difficulties, the electronic structure and correlation effects in free nickel atoms were studied by resonant Auger spectroscopy [30,31], and the M 2,3 -shell Auger and autoionization spectra of free Ni atoms were also investigated [32]. The 3p photoelectron spectrum [33] and the 2p spectrum [34] of atomic Ni have been measured by using synchrotron radiation and atomic beam techniques. ...
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A variety of X-ray spectroscopies can be classified as “photon-in electron-out” techniques. Analogous to the “photon-in photon-out” methods discussed in Chap. 8, these electron-based methods involve measuring both the incident photon energy and the outgoing electron energy and in some cases the electron momentum and/or spin. Depending on the energy of the incoming photon, the type of electron analysis, and the experimental conditions, an inevitable slew of acronyms has been applied:
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Ni LVV Auger spectra, in coincidence with the corresponding 2p1/2, 2p3/2, and 6eV satellite photoelectrons, have been used to examine electron correlation and itinerance effects in Ni. In coincidence with the 2p3/2 core level, the Auger spectral shape is represented by localized 3d8 and itinerant valence final states with an additional 3d7 Auger shake-up contribution. The spectra in coincidence with the 6eV satellite probe the decay of localized 2p53d9 double hole states, leading to 3d7 final states. It is found that a fraction of the double hole states delocalize before the Auger decay. A similar delocalization is observed for the double hole states produced by the L2L3M45 Coster-Kronig process, and the delocalization rates have been determined.
Article
In order to test the presence of interatomic multi-atom resonant photoemission (MARPE) in 3d magnetic ultrathin films, 2p photoelectron emission of various ferromagnetic 3d metals was studied while the excitation energy was tuned around the L2,3 core level absorption edge of a different 3d metal. Both elements were in direct contact either as bilayer or as alloys to maximize this possible effect. Systems under study were Fe/Co, Fe/Ni, Fe30Ni70, Co, Co90Mn10, and Ni90Mn10, all grown as epitaxial films on Cu(001). No measurable change in intensity of the 2p photoemission intensities in normal emission for 45° incidence of more than 2.5–5% was found as a result of resonant excitation of neighboring atoms in any of these systems. We can thus exclude the presence of significant MARPE in these metallic systems in the present experimental geometry. This is further confirmed by the photon energy dependence of the linear magnetic dichroism in the Fe 2p photoemission of a Fe/Co film, which is not influenced by Co L2,3 edge resonant absorption.
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Unambiguous evidence for resonant photoemission in Ni is presented. Interference effects are identified at the 2p edges for the valence band and the 6 eV satellite. A rapid transition from a resonant Raman to an Auger-like regime shows that the core-excited states above threshold are not localized enough to significantly enhance the photoemission intensity, implying a large fraction of incoherent intensity. The results indicate that the appearance of interference effects does not require strong localization of the intermediate state.
Article
In this paper we present conclusive experimental evidence that the Auger satellite structure on the low-kinetic-energy side of the L3M45M45 Auger spectra in Cu and Zn is a direct result of the L2L3M45 Coster-Kronig transition preceding the Auger transition. The position of the satellite structure is compared with numerical calculations of the final state for the ionized atoms. The same Coster-Kronig process is shown to be responsible for the anomalous intensity ratio of the L2M45M45 to L3M45M45 Auger spectra. From this intensity ratio the Auger part of the L23 photoelectron linewidths can be determined and is shown to be in reasonable agreement with theoretical values.
Article
The construction of a new electron energy analyzer for photoelectron spectroscopy is described. The analyzer is a full hemisphere with a mean radius of 200mm. The spectrometer incorporates highly stable voltage supplies and is equipped with a multidetection system. The electron lens can be operated in different modes, optimizing transmission, spatial resolution or angular resolution. An angular resolution of better than 0.2° can be obtained. UV excited Xe5p spectra recorded in the gas phase show that the energy resolution is better than 2.7 meV at 2eV analyzer pass energy.
Article
We demonstrate the feasibility of Auger-photoelectron coincidence spectroscopy (APECS) and use this technique to study the Cu L23M45M45 Auger transitions. With APECS the Auger lines can be identified unambiguously and the Coster-Kronig-preceded Auger lines separated from the main L3M45M45 lines. The background due to scattered electrons is strongly reduced relative to that in conventional Auger or photoelectron spectroscopy. Some other interesting experiments that can be done with this technique are discussed.
Article
From an Auger study of dilute Ni alloys with electropositive metals it is concluded that multiplet splitting of the Ni ${d}^{8}$ configuration is important. It is shown that the ${d}^{8}$ ($^{3}F$) state is of sufficiently low energy to be strongly mixed in the Ni ground-state wave function whereas the other, mainly singlet, states are all well removed to higher energy. The relevance of multiplet splittings to polarity fluctuations and magnetism in transition metals and their alloys is discussed.
Article
Spin-polarized photoemission spectra have been measured on the ferromagnetic Ni(110) single crystal. Evidence for the Fano interference effect in the spin polarization of the 6-eV satellite of the valence band has been obtained. The results indicate that the interference effect between the direct 3d electron transition and the 3p core electron excitation followed by the MVV super-Coster-Kronig process to form the two-d-hole bound state is important to explain the behavior of the resonant 6-eV satellite. It is also found that the spin polarization is still large under an off-resonant condition, and this indicates that the direct 3d transition from the majority-spin state is effective to form the two-hole singlet bound state.
Article
In photoemission spectra of strongly correlated systems one usually observes a satellite structure below the main peak. Description of such satellite structures in the commonly used GW approximation has been found to be insufficient. To account for these satellite structures that originate from short-range correlations, we have developed a T-matrix formalism for performing ab initio calculations on real systems. The method is applied to Ni and we obtain a satellite structure below the Fermi level as well as a reduced exchange splitting. We also found a new interesting satellite structure above the Fermi level, which can be ascribed to particle-particle scattering.
Article
We report the observation of two resonance channels in the 2p resonant photoemission of ferromagnetic nickel using circularly polarized soft x rays. By identifying the local 3d8 and 3d7 configurations in the valence-band photoemission spectra, we are able to assign structures in 2p core-level-absorption and magnetic-circular-dichroism spectra to many-body 2p53d10 and 2p53d9 configurations as well as to a critical point in the band structure. The Ni data provide a critical test for theoretical models of x-ray absorption and magnetic-circular-dichroism spectroscopy of transition-metal magnetic materials. This work also demonstrates the unique possibilities provided by circularly polarized light for separating the Auger process from the resonant-photoemission process and unraveling the electronic structure.
Article
The LMM Auger spectra of Cu, Zn, Ga, and Ge are presented and discussed. Transition probability calculations are described and with these a clear assignment of the peaks can be made. It is further shown that from the L3M45M45 Auger lines the term splittings and the effective on-site electron-electron interaction can be determined. The latter is shown to be strongly reduced from the free-atom value. This has important consequences for the description of the band structure using one-electron theories. The satellite structure for Cu and Zn in the L3M45M45 region of the spectrum is shown to be a result of strong Coster-Kronig processes involving the L2 and L3 core levels.
Article
In this paper we present conclusive experimental evidence that the Auger satellite structure on the low-kinetic-energy side of the L3M45M45 Auger spectra in Cu and Zn is a direct result of the L2L3M45 Coster-Kronig transition preceding the Auger transition. The position of the satellite structure is compared with numerical calculations of the final state for the ionized atoms. The same Coster-Kronig process is shown to be responsible for the anomalous intensity ratio of the L2M45M45 to L3M45M45 Auger spectra. From this intensity ratio the Auger part of the L23 photoelectron linewidths can be determined and is shown to be in reasonable agreement with theoretical values.
Article
The L2M45M45 and L3M45M45 Auger spectra of clean metallic copper and zinc were measured. A theory was developed to predict the Auger energies. The theory employs experimental electron binding energies, which were also measured, two-electron integrals, and Hartree-Fock energies. It accounts for multiplet splitting in the d8 final state, predicting structure in excellent agreement with experiment in zinc and in very good agreement in copper. It also accounts for "static" atomic relaxation and for static extra-atomic relaxation (screening), which is related to the Friedel theory of alloys. The theory developed here predicts the Auger energies to within 1 eV in zinc and 2-3 eV in copper. Since atomic integrals were used, the success of the theory implies that an atomistic approach to Auger energies is valid for these metals. The magnitude of the extra-atomic relaxation energy (∼ 10 eV) suggests that it may be a crucial factor in Auger energy shifts arising from chemical environment or surface condition.
Article
High-resolution gold-valence-band photoemission spectra were obtained by the use of monochromatized Al Kα radiation and a single-crystal specimen. After background and scattering corrections were made, the results were compared directly with broadened theoretical density-of-states functions. The following conclusions were drawn: (i) Relativistic band-structure calculations are required to fit the spectrum. (ii) Both the Korringa-Kohn-Rostoker calculation of Connolly and Johnson and the relativistic-augmented-plane-wave calculation by Christensen and Seraphin give density-of-states results that (after broadening) follow the experimental curve closely. (iii) Of the theoretical functions available to date, those with full Slater exchange agree best with experiment (perhaps because of a cancellation of errors). Fractional (2/3 or 5/6) exchange gives d bands that are too wide. (iv) Eastman's 40.8-eV ultraviolet photoemission spectrum is similar to the x-ray spectrum, suggesting little dependence on photon energy above 40 eV. (v) Both (ii) and (iv) imply an absence of strong matrix-element modulation in the photoemission spectrum of gold.
Article
The Auger-emission process from solids can be very complex, with a variety of processes producing intensity in the final spectra. The L2,3-M4,5M4,5 (L2,3-MM) Auger spectra of the 3d transition metals, in particular, show many complicating effects. Auger photoelectron coincidence spectroscopy (APECS) is a technique that can be used to elucidate the source of this complexity. In the APECS experiment, Auger electrons are recorded only when the corresponding electron from the ionization event is also detected. In this way only those features that result from the particular initial ionization event in question are measured, thereby greatly reducing the complexity in the Auger spectra. Although a number of successful APECS studies have been made of the emission processes observed in the Auger lines of several individual 3d transition metals, none have yet studied trends across the series. In order to study some of these trends we have made the most systematic APECS study to date of the L2,3-MM Auger spectra of the metals Fe, Co, Ni, and Ga (in GaAs). The L2,3-MM lines were observed in coincidence with the 2p3/2 and 2p1/2 photoemission electrons in all of these materials. From these studies and the Cu coincidence (APECS) results of Haak and Sawatzky a number of trends are clear and these are reported and discussed with the view of aiding quantitative Auger electron spectroscopy. It has become clear that there is also a need for a consistent and clear nomenclature to describe and distinguish between the various processes which can lead to a common multiple-hole final state. A nomenclature is proposed that aids a clearer comparison and discussion of the contributions of the various processes to the total observed Auger line shape.
Article
The Ni L3-M4,5M4,5 Auger spectrum is shown to be free of any satellite structure when the ionizing photon energy is close to the ionization threshold. Making use of this observation, we extract the exact line shape of the satellite features appearing with higher ionizing energies. The dependence of the intensities of different features in the satellite reveals two distinctly different kinds of satellite structure to be present. The origin of these satellites is discussed.
Article
A satellite in the L3VV Auger spectrum in Ni is identified experimentally and interpreted as an L3M452-M454 transition, i.e., an LMM Auger transition in the presence of two spectator vacancies. Previously published valence-electron spectra, recorded close to the 3p resonance energy, are reconsidered and besides the well-known d8 double-hole satellite they are shown to reveal d7 and d6 multiple-hole states.
Article
The metallic renormalization of the LM45M45 Auger spectrum and in particular the L3M-MM45M45 Auger vacancy satellite spectrum is considered for Cu and Zn in terms of calculated one-, two-, and three-core-hole metallic shifts. Good agreement with experiment is obtained. Atomic calculations strongly support the interpretation given by Aksela and Sivonen for the recently observed satellite in Cu vapor, and furthermore it is shown that the same type of satellite has previously been observed, but not identified, in the spectrum from atomic Zn.
High resolution L3M4,5M4,5 Auger spectra of copper are compared with multiplet structure and transition rate calculations. The comparison reveals unexplained structure to lower energies which is attributed to Auger vacancy satellite lines.
Article
The analysis of x-ray absorption spectra to determine the electronic and magnetic structure of transition metal compounds is discussed. The models to describe the ground state of transition metal compounds (single-particle, impurity, crystal field) are introduced. Some basic aspects of the interaction of x-rays with matter are recapitulated and the description of x-ray absorption is separated into single-particle models for the 1s edges and multiplet models for the 2p edges. Magnetic circular dichroism is introduced and the six Thole sum rules are discussed. The complications and experimental problems of the sum rules are outlined. The last section briefly mentions some aspects of resonance studies, for which a detailed knowledge of x-ray absorption is crucial.
Article
Structural changes of elemental and binary thin-film layered crystals are investigated under coercive volume expansion using molecular-dynamics simulations. The results show that, although the crystalline lattice itself is stable against large volume expansion, it can be easily changed into a disordered structure when small anisotropic forces are locally applied. This type of lattice instability may be responsible for triggering the so-called solid-state amorphization. \textcopyright{} 1996 The American Physical Society.
Article
High resolution Cu L2,3 x-ray absorption spectra of bulk fcc Cu metal are compared with those of thin Cu layers in Cu/Fe multilayers. Comparison of the measured fine structure with that obtained from a fully relativistic first-principles calculation for fcc and bcc Cu reveals that Cu is bcc in Cu(3 Å)/Fe(10 Å) and fcc in Cu(10 Å)/Fe(3 Å) multilayers. This result indicates that the thicker layer simply acts as a template for the structure of the thinner layer. The excellent agreement between experimental and theoretical spectra also demonstrates the validity of the theoretical approach. The theoretical spectra are discussed in terms of their angular momentum composition and the energy dependence of the radial transition matrix elements. © 1996 The American Physical Society.
Article
Three-hole satellites (3d7 final-state configuration) in the nickel valence-band photoelectron spectrum have been identified at 13 and 18 eV binding energy with use of synchrotron radiation from the MAX storage ring. The three-hole satellites show resonances at photon energies close to the threshold for excitation of 3p53d9 core-hole shake-up states. The 13-eV satellite also shows a resonance directly at the 3p threshold. This is interpreted as an interference between the direct three-hole ionization and a shake-up transition in the Auger decay of the 3p hole. This shake-up process is also identified directly in the M2,3M4,5M4,5 Auger spectrum.
Article
Magnetic circular dichroism (MCD) has been observed at the L2,3 absorption edges of ferromagnetic nickel by use of circularly-polarized soft-x-ray synchrotron radiation. The MCD intensity ratio between the L2 and L3 edges is found to differ appreciably from that predicted by a simple exchange-split-valence-band model. Fine MCD features, imperceptible in the absorption spectra, are also observed, and a tentative interpretation is given. This work, demonstrating the feasibility of MCD measurements in the soft-x-ray region, provides a new approach to study 3d and 4f ferromagnetic systems with their respective dipole-permitted 2p-->3d and 3d-->4f transitions.
Article
The electronic state of ferromagnetic Ni and the expected magnetic circular dichroism (MCD) in Ni 2p→3d x-ray-absorption spectroscopy [2p (XAS)] are discussed from a viewpoint of 3d configuration interaction on the basis of the Anderson impurity model. The model includes multiplet effects arising from 3d-3d and 3d-2p electron interactions and a 3d interatomic exchange approximated by a molecular field acting on the 3d spin. By using commonly accepted values of the interaction strengths, it is shown that the ground state of a Ni atom in ferromagnetic Ni is expressed by a superposition of 3d10, 3d9, and 3d8 configurations with relative weights of 15%–20%, 60%–70%, and 15%–20%, respectively, and with an orbital-magnetic-moment contribution of ∼0.07μB to the total moment of 0.6μB. With these results, we can explain the recently observed MCD in Ni 2p XAS.
Article
A tight-binding analysis of soft-x-ray-absorption and magnetic-circular-dichroism (MCD) spectra on Ni at the 2{ital p}{r arrow}3{ital d} thresholds yields values for the valence spin-orbit parameter and exchange splitting which are, respectively, larger and smaller than the ground-state band-structure values by a factor of {similar to}2. The discrepancies are attributed to core-hole correlation effects. A feature that appears 4 eV above the main white lines, but only in the MCD spectrum, is also attributed to correlation effects.
Article
For narrow electronic bands in metals, we seek improvement over the local-density approximation (LDA) by including the on-site Coulomb interaction between localized electrons. For the 3d ferromagnetic series of Fe, Co, and Ni, by treating fluctuations to second order in the on-site interaction around the LDA solution, in comparison with experiment a distinct improvement over the conventional LDA is obtained for a number of properties: effective masses, x-ray photoemission spectra, and results derived from angle-resolved photoemission spectra, such as exchange splittings and quasiparticle bands. In addition, the predicted quasiparticle broadenings and satellite features, which are not present in standard LDA calculations, are in reasonable agreement with observation.
Article
The one-electron excitation spectra of ferromagnetic nickel have been obtained from a first-principles calculation of the self-energy operator within the so-called GW approximation. The dielectric matrix, needed to form the screened potential W, is computed within the random-phase approximation. The quasiparticle energies are in very good agreement with angle-resolved photoemission data. The bottom of the d band is raised by about 1 eV resulting in band narrowing as observed experimentally and the quasiparticle widths are also in favorable agreement with experiment. The exchange splittings, however, are the same for most cases as those given by the local-density approximation in density-functional theory. The satellite at 6 eV is not reproduced. Instead, we found a significant contribution to the spectral weight from quasiparticle peaks around that energy. We discuss the success and the shortcomings of the GW approximation in the light of our results.
Article
The soft-x-ray absorption and magnetic circular dichroism (MCD) cross sections at the L2 and L3 core-level edges of Ni and Fe have been calculated using a one-electron tight-binding band-structure approach. The tight-binding scheme is taken from the work of Papaconstantopoulos, supplemented with the inclusion of spin-orbit coupling in the d bands and fully relativistic dipole selection rules. In Ni, a fit to the various L2 and L3 intensity ratios can be achieved, but only with values of the d-band spin-orbit parameter xi and exchange parameter Deltaex at variance with the ground-state band-structure values. For Fe, there is no plausible value of xi capable of explaining the intensity ratios; also, the predicted substructure within the L2 and L3 white lines is not seen in experiment. These failures of the one-electron approach are qualitatively consistent with expected many-body electronic rearrangements associated with core-hole creation. Some discussion is offered on sum rules and on orbital versus spin magnetic moments.
Article
The observed enhancement in the 3d, 3p, and 3s photoemission structures at resonance with the 2p absorption edge of nickel is analyzed using a cluster calculation including multiplet structure. The result strongly supports the view of a localized electronic structure for nickel metal. It is found that the peak splitting in the 3s photoemission is due to d mixing, whereas the 3p photoemission shows the influence of both d mixing and electrostatic interaction.
Article
By photoabsorption in the Ar 2p range of Ar multilayer condensates, distinct contributions of surface and bulk excitations can be distinguished in the characteristic core resonances detected by partial-electron-yield near-edge x-ray-absorption fine-structure spectra. Compared to the corresponding bulk/gas-phase features, the surface excitations are shifted by ~0.5 eV towards lower/higher photon energy. Deexcitation of core-to-bound 4s resonances in these condensates leads to distinct spectator-shifted Auger features (2h1e final states). Decay of the 3d,5s resonances, however, is dominated by normal Auger processes to 2h states; 2h1e features are weak. This differs from the behavior of free atoms; it can be understood by the lowering of the ionization threshold to below the 3d,5s resonances by screening in the condensate and by efficient ionization of the core excitonic states during core lifetime, i.e., within a few femtoseconds. Detailed analysis reveals differences for the decay spectra of the lowest resonance at the surface and in the bulk, and shows that the screening energies for the various 2h1e states differ from those of 1h states, as well as among each other. Evidence for the existence of weak participator decay channels (1h final states) at certain photon energies is also found.
Article
Atomic C, N, and O chemisorbed on Ni(100) have been studied by x-ray-absorption spectroscopy. The atomic 2p orbitals are shown to form hybrid orbitals with the Ni 3d and 4sp bands. The spectral contributions from these hybrids are identified at the absorption threshold and in a region 6-12 eV above this. Between those regions, states derived from atomic 3p and higher np orbitals are observed. The threshold region shows vibrational and dynamical effects, which are discussed in connection with the corresponding photoemission spectra. The substrate Ni 2p3/2 x-ray-absorption spectrum is also presented. Its large similarity to the Ni 2p3/2 x-ray photoemission spectrum is discussed.
Article
Initiating Auger transitions using tunable monochromatic x rays from synchrotron, we show that the satellite intensities in L2M45M45 and L3M45M45 spectra of Cu and Zn increase with increasing photon energies up to about 200 eV above the thresholds. This indicates a pronounced influence of the history of the core-hole generation on Auger spectra, in sharp contrast to the universally accepted belief, and suggests a breakdown of the sudden approximation. Details of the photon energy dependence of the satellite intensity provide a new interpretation for the origin of the satellite.
Article
Results of an investigation of the discontinuity in the L2 level width and the L3-M45M45/L2-M45M45 Auger intensity ratio at Z=30. The afore-mentioned intensity ratio is found to undergo a sudden decrease at Z=30. Relative L2 and L3 level widths of Cu and Zn are derived from photoelectron spectra; while the L3 width increases from Cu to Zn, the L2 width of Cu is greater than that of Zn, contrary to the general trend. The above-mentioned discontinuity is traced to a discontinuity in the Coster-Kronig transition probability f sub 23 predicted in earlier calculations.
  • F M F De Groot
F. M. F. de Groot, J. Elec. Spec. 67, 529 (1994), and references therein.
  • N Mårtensson
  • R Nyholm
  • B Johansson
N. Mårtensson, R. Nyholm, and B. Johansson, Phys. Rev. B 30, 2245 (1984).
  • J Fuggle
  • P A Bennett
  • F U Hillebrecht
  • A Lenselink
  • G A Sawatzky
J. Fuggle, P. A. Bennett, F. U. Hillebrecht, A. Lenselink and G. A. Sawatzky, Phys. Rev. Lett. 49, 1787 (1982).
  • L I Yin
  • I Adler
  • M H Chen
  • B Crasemann
L. I. Yin, I. Adler, M. H. Chen, and B. Crasemann, Phys. Rev. A 7, 897 (1973).
  • T Jo
  • G A Sawatzky
T. Jo and G. A. Sawatzky, Phys. Rev. B 43, 8771 (1991).
  • E D Roberts
  • P Weightman
  • C E Johnson
E. D. Roberts, P. Weightman, and C. E. Johnson, J. Phys. C 8, L301 (1975).
  • E O F Zdansky
  • A Nilsson
  • H Tillborg
  • N Björneholm
  • J N Mårtensson
  • R Andersen
  • Nyholm
E. O. F. Zdansky, A. Nilsson, H. Tillborg, O Björneholm, N. Mårtensson, J. N. Andersen and R. Nyholm, Phys. Rev. B 48, 2632 (1993).
  • T. Jo