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We present an experimental study of the electronic structure of MnSi. Using x-ray absorption spectroscopy (XAS), x-ray photoemission, and x-ray fluorescence, we provide experimental evidence that MnSi has a mixed valence ground state. We show that self-consistent local density approximation supercell calculations cannot replicate the XAS spectra of MnSi, while a good match is achieved within the atomic multiplet theory assuming a mixed valence ground state. We discuss the role of the electron-electron interactions in this compound and estimate that the valence fluctuations are suppressed by a factor of 2.5, which means that the Coulomb repulsion is not negligible.

Photoemission and x-ray absorption measurements have been performed on Er5Ir4Si10, a compound that exhibits an incommensurate charge-density-wave formation below 155 K. The resonant photoemission and x-ray absorption measurements performed across the Er N54 and Er M5 edge identify the Er 4f multiplet lines, the 4f occupancy and the character of the states close to the Fermi edge.

Quantum Efficiency (QE) measurements of single photon photoemission from a Cu(111) single crystal and a Cu polycrystal photocathodes, irradiated by 150 fs-6.28 eV laser pulses, are reported over a broad range of incidence angle, both in s and p polarizations. The maximum QE (\simeq 4\times10^{-4}) for polycrystalline Cu is obtained in p polarization at an angle of incidence {\theta} = 65deg. We observe a QE enhancement in p polarization which can not be explained in terms of optical absorption, a phenomenon known as vectorial photoelectric effect. Issues concerning surface roughness and symmetry considerations are addressed. An explanation in terms of non local conductivity tensor is proposed., Comment: 3 pages, 3 figures

Core level and valence band photoemission measurements combined with near edge x-ray absorption fine structure measurements were performed on a single C(70) layer adsorbed on polycrystalline Al (1 ML-C(70)/Al) (ML-monolayer), pure and doped with sodium atoms. The data obtained from the pure ML chemisorbed on Al surface show a semiconducting behavior of the system, which is characterized by a covalent bond between the adsorbate and the substrate. The same data show also that the C(70) molecules tend to orient themselves with the C(5v) axis perpendicular to the surface in analogy to what observed for 1 ML-C(70)/Cu(111). By doping the sample with sodium atoms a charge transfer from the alkali atoms to the lowest unoccupied molecular orbital (LUMO) of the C(70) molecules takes place, as underlined by the gradual increasing intensity of the C(70) LUMO peak as a function of doping. Nevertheless, no metallic phases are observed for any doping step.

Nonlinear photoemission from a silver single crystal is investigated by femtosecond laser pulses in a perturbative regime. A clear observation of above-threshold photoemission in solids is reported for the first time. The ratio between the three-photon above-threshold and the two-photon Fermi edges is found to be 10^{-4}. This value constitutes the only available benchmark for theories aimed at understanding the mechanism responsible for above-threshold photoemission in solids., Comment: 5 pages, 4 figures

The origin of the ferromagnetic insulating (FMI) phase observed at low temperature in a large variety of manganites is addressed by using x-ray absorption spectroscopy. The variations in the Mn ${L}_{2,3}$ and O $K$-edge x-ray absorption and circular dichroism spectra as a function of temperature are consistent with a carrier localization and localized lattice distortions associated with this phase.

We observe, with angle-resolved photoemission, a dramatic change in the electronic structure of two C60 monolayers, deposited, respectively, on Ag (111) and (100) substrates, and similarly doped with potassium to half filling of the C60 lowest unoccupied molecular orbital. The Fermi surface symmetry, the bandwidth, and the curvature of the dispersion at Gamma point are different. Orientations of the C60 molecules on the two substrates are known to be the main structural difference between the two monolayers, and we present new band-structure calculations for some of these orientations. We conclude that orientations play a key role in the electronic structure of fullerides.

BACH, the new soft x‐ray beamline for polarization dependent experiments at the Italian synchrotron radiation facility ELETTRA, has been commissioned, characterized and opened to external users. Based on two APPLE II undulators, it covers an energy range between 35 eV and 1600 eV with the control of the light polarization. The monochromator works either in high resolution or high flux mode. Resolving powers of 16000 at 50 eV, 12000 at 90 eV, more than 12000 at 400 eV, 15000 at 534 eV and 6600 at 867 eV have been achieved with the three high resolution gratings. The resolving powers of the high flux grating, which covers the 290 – 1600 eV range, have been measured reaching 7000 at 400 eV and 2200 at 867 eV. The fluxes, in the high resolution mode, range between 4⋅1011 photons/s at 125 eV and 2⋅1010 photons/s at about 1100 eV. Using the high flux grating with the best resolution achievable 1.7⋅1011 photons/s impinge on the sample at 900 eV. Two branches are installed after the monochromator allowing the set‐up of two different experimental stations. One of them, besides several facilities for surface preparation and analysis, hosts a compact inelastic soft x‐ray spectrometer (ComIXS) dedicated to x‐ray emission experiments exploiting the small spot (10 μm in the vertical direction) on the sample. The other branch hosts a liquid helium cryostat equipped with a superconducting coil to perform absorption and transmission experiments with temperatures down to 2 K and magnetic field up to ±7 T.

Photoemission from image potential states on Ag(100) is investigated using angle resolved multiphoton photoemission induced by 150 fs laser pulses. For the first time we demonstrate that image potential states populated by indirect transitions can be observed with light polarized parallel to the plane of incidence and light polarized normal to the plane of incidence. The latter is a process normally forbidden by the dipole transition selection rules. These findings are related to the creation of a hot-electron population whose properties largely remains to be understood.

To accommodate increasing interest in soft x‐ray inelastic scattering, a new spectrometer has been designed, constructed and commissioned at Elettra. This instrument uses as the dispersive element one of two interchangeable Variable Line Spacing (VLS) spherical gratings. The energy scan is performed by a 7 cm linear translation of a back illuminated CCD which also collects the zero order light, facilitating alignment and calibration. The two gratings have the same radius of curvature while the groove densities and the groove density variations differ by a factor four. Thus the energies focused by the gratings at a particular position differ by a factor of four. The total length of the instrument is 60 cm, the energy range covered is roughly 25–1000 eV and the expected resolving power ranges from 1000 to 5000. The spectrometer is now operating on the beamline Bach. It takes advantage of the small size of the photon spot in the experimental chamber and of the possibility to control the polarization of the incoming radiation. The small spot constitutes the virtual entrance slit, and the spectrometer collects the photons emitted in a solid angle of about 30×10 mrad2. The instrument, named ComIXS (Compact Inelastic X‐ray Spectrometer), has been routinely operating since October 2002. Several experiments have already been carried out, and some results illustrating the characteristics of the instrument are described. The manufacture and testing of the blaze gratings are also discussed.

The resonant photoemission of Cd0.82Mn0.18Te single crystals has been studied in the vicinity of the Mn 2p --> 3d absorption threshold. A clear resonant behavior is detected for valence band states at the Mn 2p --> 3d absorption threshold, while a weak normal Auger emission is singled out in the valence band region for photon energies well above the main absorption edge. Resonant Raman-Auger and normal Auger emissions are found to coexist above the absorption edge. This effect is ascribed to the presence of a manifold of localized states arising from the Mn 2p --> 3d Coulomb and exchange interaction, which prevents the delocalization in the intermediate state of the autoionization process and favors the Raman-Auger process. (C) 2004 Elsevier B.V. All rights reserved.

Resonant photoemission at the Mn 2p --> 3d absorption threshold is used to probe the distribution of the Mn spectral weight in the valence band of Mn thin layers grown onto the CdTe (1 1 0) surface. It is shown that at the early stages of the evaporation process, a Cd-Mn-Te surface alloy is formed, even at room temperature. The Mn 3d spectral weight in the valence band, which is enhanced across the resonance, is quite similar to that observed for Cd1-xMnx Te single crystals. At larger Mn coverages, the growth of a metallic Mn phase on top of the Mn-Cd-Te surface alloy is detected both at resonance and by collecting Mn 2p core level photoemission data. (C) 2004 Elsevier B.V. All rights reserved.

This letter reports the experimental evidence of a 2.3 eV blue shift of the plasmon loss lines observed in the x‐ray photoelectron spectra of an ultrathin Si layer equivalent to 1.5×1015 at./cm2 deposited onto a randomly oriented Al2O3 single crystal. The plasmon line shifts, which is roughly proportional to the deposited Si(mass)−2/3, are attributed to quantum confinement effects in agreement with electron energy loss measurements performed on nanosized Si particles.

This article reports ab initio Fermi surfaces and conduction-band calculations of both stoichiometric and oxygen-reduced ${\mathrm{MoO}}_{3}.$ The data, based on a TB-LMTO approach in LDA, provide a convincing and detailed interpretation of the one-electron removal XPS valence bands, where a clear energy gap is observed for the stoichiometric samples, whereas a significant emission at the Fermi edge is measured for the oxygen reduced system. In addition, the electrical conductivity, as deduced from the shape of the calculated Fermi surface, is confined in the xz plane of the crystal, as required for Luttinger-liquid behavior. These results, when compared to the conduction mechanism observed in the blue bronze ${\mathrm{K}}_{0.3}{\mathrm{MoO}}_{3},$ clearly suggest that oxygen reduction and doping can bring to very different processes for the electronic transport.

We describe the design of a proposed source of ultra‐fast synchrotron radiation x‐ray pulses based on a recirculating superconducting linac, with an integrated array of ultrafast laser systems. The source produces x‐ray pulses with duration of 10–50 fs at a 10 kHz repetition rate, with tunability from EUV to hard x‐ray regimes, and optimized for the study of ultra‐fast dynamics. A high‐brightness rf photocathode provides electron bunches. An injector linac accelerates the beam to the 100 MeV range, and is followed by four passes through a 700 MeV recirculating linac. Ultrafast hard x‐ray pulses are obtained by a combination of electron bunch manipulation, transverse temporal correlation of the electrons, and x‐ray pulse compression. EUV and soft x‐ray pulses as short as 10 fs are generated in a harmonic‐cascade free electron laser scheme. We describe the facility major systems and peformance.

Resonant photoemission spectroscopy data from ${\mathrm{Cd}}_{1\ensuremath{-}x}{\mathrm{Mn}}_{x}\mathrm{Te}$ single crystals are presented. A strong resonant behavior, related to the Raman-Auger decay channel arising from the creation of the Mn $2p$ core hole, is detected for states in the valence-band region at the Mn $2\stackrel{\ensuremath{\rightarrow}}{p}3d$ absorption threshold. The transition from the resonating Raman-Auger to the weak, normal Auger emission is shown to occur well above the main absorption edge. This effect is ascribed to the presence of a manifold of localized states arising from the Mn $2\stackrel{\ensuremath{\rightarrow}}{p}3d$ Coulomb and exchange interaction, which prevents the delocalization in the intermediate state of the autoionization process.

C 60 fullerides are challenging systems because both the electron-phonon and electron-electron interactions are large on the energy scale of the expected narrow band width. We report angle-resolved photoemission data on the band dispersion for an alkali-doped C 60 monolayer and a detailed comparison with theory. Compared to the maximum bare theoretical band width of 170 meV, the observed 100-meV dispersion is within the range of renormalization by electron-phonon coupling. This dispersion is only a fraction of the integrated peak width, revealing the importance of many-body effects. Additionally, measurements on the Fermi surface indicate the robustness of the Luttinger theorem even for materials with strong interactions.

The intrinsic linewidth of Ag(100) electronic image-potential states versus the momentum parallel to the surface has been obtained from line-shape analysis of high-resolution angle-resolved two-photon photoemission spectra. For the n = 1 state, the measured intrinsic linewidths have been observed to increase from 14 meV at normal emission (k∥=0) to 70 meV at k∥=0.18 A - 1 . This finding, when compared to the significantly lower inverse lifetime broadening measured on Cu(100), opens the question of the interplay between collective particle effects and nonlocal mechanisms associated with the image-potential electrons decay dynamics. In addition, the effective electron masses for the n = 1 and n=2 states, observed in our experiments along the ΓM and rX directions of the surface Brillouin zone, improve the agreement between the measured values and the theoretical predictions.

International audience; Molecular chemistry allows to synthesize new magnetic systems with controlled properties such as size, magnetization or anisotropy. The theoretical study of the magnetic properties of small molecules (from 2 to 10 metallic cations per molecule) predicts that the magnetization at saturation of each ion does not reach the expected value for uncoupled ions when the magnetic interaction is antiferromagnetic...

Raman spectra of single-wall carbon nanotubes (CNTs) either in the form of micrometer sized bundles or thin layers prepared by dilution and sonication of powders have been compared. We have been able to collect the Raman spectrum of nanotube bundles that are not in touch with the substrate, and therefore not affected by interactions with the substrate surface. This spectrum resulted to be similar to that of the precursor nanotube powders, whereas relevant changes in the Raman spectrum are detected when the diluted powders form very thin layers on either metallic or insulating surfaces, as probed by confocal microraman imaging on well defined areas of the CNTs layers. In the case of thin layers, the intensity of the Raman D band, detected between 1 320 and 1 340 cm-1 and ascribed to disorder effects, is strongly enhanced. This enhancement occurs independently on the kind of substrate.

Resonant photoemission spectroscopy data from Cd1-xMnxTe single crystals are presented. A strong resonant behavior, related to the Raman-Auger decay channel arising from the creation of the Mn 2p core hole, is detected for states in the valence-band region at the Mn 2p-->3d absorption threshold. The transition from the resonating Raman-Auger to the weak, normal Auger emission is shown to occur well above the main absorption edge. This effect is ascribed to the presence of a manifold of localized states arising from the Mn 2p-->3d Coulomb and exchange interaction, which prevents the delocalization in the intermediate state of the autoionization process.

A sum rule is derived that relates the exchange coupling between core and open valence shell electrons in correlated systems to the main and satellite features of their complex photoemission spectra. The principle focus of our analysis is on the photoionization of the metal $2s$ and $3s$ shells in ionic transition-metal compounds. In spite of charge-transfer and near-degeneracy effects, which may induce a considerable redistribution of the spectral weight among a manifold of configurations, this rule points out that the exchange splitting evaluated with the sum rule is equal to the value obtained with the ground-state exchange integral for the material. Application of the sum rule to ${\mathrm{MnF}}_{2}$ and NiO shows that the exchange integral given by the sum rule is very close to that calculated for the free ion; this shows the dominant ionic character of these materials. Deviations of the sum rule for ${\mathrm{MnF}}_{2}$ from the ionic exchange interaction are taken as evidence that satellite structure present in the photoemission spectra may not have been identified.

The interplay between the resonant Raman and the Auger-like regime across the Cu 2p→3d absorption threshold was investigated. The resonant photoemission experiment performed on CuGeO 3 unambiguously shows that a fraction of primary electrons is contributing to the interfering resonant Raman emission even when the noninterfering Cu L 3 M 4 , 5 M 4 , 5 Auger emission is clearly detectable. At the 2p→3d resonance the autoionization channel prevails over the direct photoemission channel and, in agreement with the Fano theory, a high q value (9′2) was extracted from the data by properly tracking the weak resonant emission above the absorption threshold.

Molecular chemistry allows to synthesize new magnetic systems with controlled properties such as size, magnetization or anisotropy. The theoretical study of the magnetic properties of small molecules (from 2 to 10 metallic cations per molecule) predicts that the magnetization at saturation of each ion does not reach the expected value for uncoupled ions when the magnetic interaction is antiferromagnetic. The quantum origin of this effect is due to the linear combination of several spin states building the wave function of the ground state and clusters of finite size and of finite spin value exhibit this property. When single crystals are available, spin densities on each atom can be experimentally given by Polarized Neutron Diffraction (PND) experiments. In the case of bimetallic MnCu powdered samples, we will show that X-ray Magnetic Circular Dichroism (XMCD) spectroscopy can be used to follow the evolution of the spin distribution on the MnII and CuII sites when passing from a dinuclear MnCu unit to a one dimensional (MnCu) n compound.

Pump and probe electron photoemission, induced by 150 fs–790 nm laser pulses on polycrystalline molybdenum, is used to investigate the non-linear photoemissive regime. The analysis of these experimental data evidences third and fourth order thermally assisted currents that contribute to the electron yield. In addition, partial yield measurements at very low pulse intensities confirm the above analysis, evidencing a change in the logarithmic slope as predicted by the theory.

LBNL is pursuing design studies and the scientific program for a facility dedicated to the production of x-ray pulses with ultra-short time duration, for application in dynamical studies of processes in physics, biology, and chemistry. The proposed x-ray facility has the short x-ray pulse length ({approx}60 fs FWHM) necessary to study very fast dynamics, high flux (up to approximately 10E11 photons/sec/0.1 percentBW) to study weakly scattering systems, and tuneability over 1-12 keV photon energy. The hard x-ray photon production section of the machine accommodates seven 2-m long undulators. Design studies for longer wavelength sources, using high-gain harmonic generation, are in progress. The x-ray pulse repetition rate of 10 kHz is matched to studies of dynamical processes (initiated by ultra-short laser pulses) that typically have a long recovery time or are not generally cyclic or reversible and need time to allow relaxation, replacement, or flow of the sample. The technique for producing ultra-short x-ray pulses uses relatively long electron bunches to minimize high-peak-current collective effects, and the ultimate x-ray duration is achieved by a combination of bunch manipulation and optical compression. Synchronization of x-ray pulses to sample excitation signals is expected to be of order 50 - 100 fs. Techniques formore » making use of the recirculating geometry to provide beam-based signals from early passes through the machine are being studied.« less

A new experimental station for soft x-ray microscopy is under construction at BACH beamline, at Elettra Synchrotron Radiation Facility (Italy). This station will be devoted both to scanning transmission x-ray microscopy (STXM) and photoemission microscopy (SPEM), with spatial resolution of about 50 nm. A Fresnel Zone Plate (FZP) will provide the micro-focusing of the beam delivered by the monochromator of BACH. The photon beam features are high resolving power (30000-5000 in the 40-1500 eV range), high flux (more than 1011 photons/s after the exit slit) and the possibility to select the light polarization. The experimental chamber will host several photon and electron detectors which should provide spatially resolved information of the bulk and surface composition. The expected acquisition times are of the order of the seconds for STXM and less than 1 minute for SPEM. The branch line hosting this station will start from the exit slit of the BACH monochromator. A toroidal mirror will focus the exit slit-spot on a pinhole which will be the source for the following FZP. With a 10x10 micrometers 2 pinhole it will be possible to obtain a spot of about 50x50 nm2 with enough flux (from 108 to 109 ph/sec) to perform microscopic experiments with polarized radiation. In this paper we present the optical scheme of the instrument as well as the foreseen performances in terms of resolution and flux.© (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The temperature dependence of the surface resistivity for a metallic ${\mathrm{K}}_{3}{\mathrm{C}}_{60}$ ordered film in the nonsuperconducting state has been obtained by reflection electron energy loss spectroscopy. We demonstrate that the normal state electronic and transport properties of the top molecular layer of ${\mathrm{K}}_{3}{\mathrm{C}}_{60}$ are similar to the corresponding properties measured with bulk sensitive techniques. These observations strengthen and give a general character to the experimental results obtained with surface sensitive techniques on fullerene compounds. In addition, the transport properties may deviate from the Fermi-liquid behavior above 500 K.

Physical Review Letters

A beamline for advanced dichroism (BACH), to perform light polarization dependent experiments in the 35–1600 eV photon energy range is under construction at the ELETTRA Synchrotron Radiation Source in Trieste, Italy. The radiation source, based on two APPLE-II helical undulators, is designed for high photon flux and high resolving powers. The photons dispersion system is based on a Padmore variable angle spherical grating monochromator with a typical resolving power of 20 000–6000, 20 000–6000, and 15 000–5000 in the energy ranges 35–200 eV, 200–500 eV, and 500–1600 eV, respectively. Two separate branches after the monochromator allow setting two independent experimental chambers. The photon flux in the experimental chamber(s), calculated at the best resolutions achievable and with the aperture of the slits set at 10 μm, is expected to be above 1011 photons’s with linearly or circularly polarized light. In addition, a fourth grating operates in the 400–1600 eV range to provide a higher flux, 1012 photons’...

Here we report the general layout of the beamline and concentrate our attention on the characteristics of the optical elements as well as on the optical performances (monochromator's resolving powers and efficiencies, flux and spot dimensions) of the beamline.

The normal state temperature dependence of a metallic K3C60 phase pure film has been investigated by means of core levels and valence band photoemission, carbon K edge x-ray absorption, and electron energy loss spectroscopies and compared with that of a Mott–Hubbard insulating K4C60 film. The anomalous temperature behavior of K3C60, in the range 30 K–600 K, can be consistently interpreted considering the presence of orientational disorder of the C60 molecules together with the inhomogeneity of the conduction electron distribution at the molecular level. In particular, the changes observed in the photoemission spectra near the Fermi level, are consistent with the behavior predicted for strongly correlated metallic systems in presence of disorder. Also in the case of K4C60 we observe anomalies in the temperature dependence of core levels photoemission data. These anomalies can be explained with the freezing of the molecular motions at low temperature and point to large thermal fluctuations of the alkali ato...

Ab initio theoretical results for the 2p- and 3p-hole states of an Mn(2+) ion are reported in order to determine the importance of atomic contributions to the photoelectron spectra of bulk MnO. A combined treatment of relativity and electron correlation reveals important physical effects that have been neglected in virtually all previous work. The many-body and relativistic effects included in the atomic model are able, without any ad hoc empirical parameters, to explain most of the features of the MnO photoelectron spectra. In particular, it is not necessary to invoke charge transfer to explain the complex p-level spectra.

Cu‐nuclear quadrupole resonance (NQR) frequency and relaxation rates measurements in CuO, in the vicinity of the antiferromagnetic ordering temperature TN, are presented. As T→T+N divergent behaviors of the relaxation rates T−11,2 and an anomalous decrease in the NQR frequency are observed. These effects are discussed in light of the temperature dependence expected for conventional one‐dimensional Heisenberg paramagnet and some anomalies are interpreted as possible results of valence fluctuations in the CuO bond character.

Resonant photoemission experiments at the Co 3p-->3d absorption threshold are used to identify the correlated satellites in the one-electron removal spectrum of the valence band of the two-dimensional Ising antiferromagnet K2CoF4. In addition, x-ray photoelectron spectra of the core levels, interpreted by a configuration-interaction impurity-cluster model, are reported. The estimated charge transfer Delta and the Mott-Hubbard U charge fluctuations pose K2CoF4 in the Mott-Hubbard region of the Zaanen-Sawatzky-Allen diagram. The values of Delta and U are also used to estimate the superexchange parameter J by considering a metal-ligand-metal three-center model. The results for K2CoF4 are compared to those obtained for CoO and the effect of Delta on the photoemission spectral features and on the magnitude of J are discussed.

It is shown that electron correlation among Cu d -electrons explains the photoemission data of CuGeO 3 and is responsible for the insulating behaviour and of the observed complex satellite structures. The analysis and interpretation of the experiments require the use of a multi-band Hamiltonian which explicitly includes both on site electron correlation and a detailed description of the single-particle band states.

The absorption coefficient of CuGeO3 was measured in the energy range of 1-4 eV, in a temperature interval between 300 and 20 K, for light polarized along the b and c crystal axes. A weak absorption band at 1.7 eV is attributed to copper d-d transitions partially allowed by electron-phonon interactions; this is followed by a region of transparency leading to a strong exponential edge above 3 eV, which is identified with the onset of charge-transfer transitions.

A high resolution X-ray photoemission, XPS, study of PbMg 1 3 Nb 2 3 O 3 is reported. The binding energy of the Pb core lines are consistent with a formal valence of 2+, while a valence of 5+ is found for Nb. In addition, on the basis of present data, the existence of different coordination sites for Pb, Nb and Mg is discarded. Finally, within the limit of the present experimental conditions, domains with non-homogeneous electrostatic charges, as proposed by some structural models, are not observed. Instead, the XPS results are consistent with a random distribution of Nb and Mg ions on the cationic site.

X-ray photoelectron spectroscopy of pure and K chemisorbed VxOy/TiO2 powders are reported. Core-line and valence band spectra suggest the presence of vanadium open shell ions on the pure VxOy/TiO2 interface, whereas potassium vanadate seems to form after K chemisorption. That results in the presence of a significant amount of gap states, with vanadium character, just above the O2p band edge, for the pure VxOy/TiO2 powder, while K chemisorption, reducing significantly the open shell vanadium ions, quenches the gap emission in the XPS valence band spectra.

We report about very high-quality epitaxial NiO films grown on a Fe(0 0 1) passivated surface. X-ray magnetic linear dichroism at the Ni L 2 absorption edge has been applied to investigate the magnetic anisotropy in the NiO layer. We find that very thin NiO films (7–20 atomic layers) develop an in-plane uniaxial magnetic anisotropy, whose axis is found to be perpendicular to the Fe substrate magnetization M . This behaviour is in contrast with what observed in the specular Fe/NiO(0 0 1) interface, where the coupling is parallel.

Coal and oil combustion produces fly ash particulates whose dispersion into the environment represents one of the major sources of pollution.

X-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.

The X-Ray Photoemission (XP) core level spectra of transition metal (TM) compounds have been intensively investigated with the aim to obtain appropriate parameters to characterise their electronic properties 1–15. In particular, the charge transfer (CT) energy, A, which describes the charge fluctuation from the ligand to the metal according to the mechanism d n → d n+1 L and the Mott-Hubbard energy U, which accounts for the electronic charge fluctuation between two transition metal ions in the crystal lattice, \( d_i^nd_j^n \to d_i^{n - 1}d_j^{n + 1} \) are basic concepts to understand the electronic correlations of TM compounds 7–9.

X-ray-photoelectron spectroscopy (XPS) and optical measurements have been performed to investigate the structure of electronic states in yttrium-stabilized zirconia. From reflectivity observations, the spectral behavior of the dielectric function, of the energy loss, and of the effective electron number in the range 3--30 eV were obtained for single crystals with an yttria content of 12 and 24 mol %. This information, combined with binding-energy spectra from XPS, was used to infer the structure of valence and conduction states and to discuss the nature of the main optical transitions, also in connection with available theoretical data.