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The core and valence levels of β-PbO₂ have been studied using hard X-ray photoemission spectroscopy (hv = 6000 eV and 7700 eV). The Pb 4f core levels display an asymmetric lineshape which may be fitted with components associated with screened and unscreened final states. It is found that intrinsic final state screening is suppressed in the near-surface region. A shift in the O 1s binding energy due to recoil effects is observed under excitation at 7700 eV. It is shown that conduction band states have substantial 6s character and are selectively enhanced in hard X-ray photoemission spectra. However, the maximum amplitude in the Pb 6s partial density of states is found at the bottom of the valence band and the associated photoemission peak shows the most pronounced enhancement in intensity at high photon energy.

We report an extensive study on the intrinsic bulk electronic structure of the high-temperature superconductor CeFeAsO(0.89)F(0.11) and its parent compound CeFeAsO by soft and hard x-ray photoemissions, x-ray absorption, and soft x-ray emission spectroscopies. The complementary surface/bulk probing depth, and the elemental and chemical sensitivity of these techniques allow resolving the intrinsic electronic structure of each element and correlating it with the local structure, which has been probed by extended x-ray absorption fine-structure spectroscopy. The measurements indicate a predominant 4f(1) (i.e., Ce(3+)) initial-state configuration for cerium and an effective valence-band-to-4f charge-transfer screening of the core hole. The spectra also reveal the presence of a small Ce f(0) initial-state configuration, which we assign to the occurrence of an intermediate-valence state. The data reveal a reasonably good agreement with the partial density of states as obtained in standard density-functional calculations over a large energy range. Implications for the electronic structure of these materials are discussed.

The nature of electronic states at the Fermi energy in metallic β-Pb O2 has been identified by hard x-ray photoemission spectroscopy (HXPS) combined with x-ray emission spectroscopy and density-functional theory calculations. Pb 6s states are strongly enhanced in HXP spectra, allowing us to locate the Fermi level above the top of the valence band. The occupied conduction-band states have significant Pb 6s character, although the major 6s contribution to the density of states is found 9 eV below the Fermi energy. The enormous potential of HXPS for the study of s states in oxides is emphasized. © 2007 The American Physical Society.

We have performed hard-x-ray photoemission experiments at photon energy close to 6 keV on the ferromagnetic bilayered manganite La1.2Sr1.8Mn2O7 across its transition temperature T-C. Differences in both core level and valence band spectra have been observed as a function of temperature: We correlate the energy shift of the O 1s peak with a charge-transfer associated with the structural change taking place at the transition. A prominent shoulder on the low binding energy side of the Mn 2p core level that is observed below TC is tentatively ascribed to increased nonlocal screening in the ordered ferromagnetic phase.

We have performed hard-x-ray photoemission experiments at photon energy close to 6 keV on the ferromagnetic bilayered manganite La1.2Sr1.8Mn2O7 across its transition temperature T-C. Differences in both core level and valence band spectra have been observed as a function of temperature: We correlate the energy shift of the O 1s peak with a charge-transfer associated with the structural change taking place at the transition. A prominent shoulder on the low binding energy side of the Mn 2p core level that is observed below TC is tentatively ascribed to increased nonlocal screening in the ordered ferromagnetic phase.

We describe the design and the laboratory test of an electrostatic input lens developed for high energy (> 5 keV) and high resolution photoelectron spectrometers. The lens is part of a hemispherical electron energy analyzer and is designed to optimize the overall accepted solid angle, taking into account the constraints due to the acceptance of the hemispherical dispersing element. In particular, the lens can be operated with two different polarization schemes enabling to obtain high and constant linear magnification (M-1 = 12 and M-1 = 20) in a large interval of retarding factor ranging from an acceleration of 5 to a retardation of 600 (dynamical range of 3000) by the same mechanical layout. These features make such an electrostatic input element a considerable improvement in the technical challenge to perform high quality experiments in high energy photoemission. (c) 2005 Elsevier B.V. All rights reserved.

We present recent results obtained with a novel spectrometer developed within the EU project VOLPE (VOLume PhotoEmission from solids with synchrotron radiation), now operational at ESRF (Beamline ID 16), where we were able to achieve high energy resolution as well as good statistics photoemission spectra up to 6-8 keV of photoelectron kinetic energy. The spectrometer is a hemispherical deflector analyzer with electrostatic input lens and 2D position sensitive detector. Ag 3d, An 4f and valence band spectra have been measured from polycrystalline Ag and An, displaying an overall energy resolution (photons + analyzer) of about 71 meV at 6 keV, as measured at 18 K on the Fermi edge. The corresponding resolving power of 8 x 10(4) is one of the highest values achieved in photoemission measurements from solid samples. (c) 2005 Elsevier B.V. All rights reserved.

The status of the Volume PhotoEmission (VOLPE) project, now operational at ESRF, is reviewed. Commissioning phase and test experiments confirm that high energy resolution (71 meV at 5934 eV kinetic energy) with truly bulk sensitivity is achievable in Hard X-ray Photoelectron Spectroscopy (HAXPES) experiments. (c) 2005 Elsevier B.V. All rights reserved.

The instrument VOLPE (volume photoemission from solids) is an experimental setup dedicated to high energy photoemission (PE) experiments. The instrument is equipped with an electrostatic hemispherical spectrometer especially designed to analyze high energy electrons (up to 10 keV) with high resolving power. In order to attain an energy resolution of a few tens of millielectron volts, we designed and constructed a dedicated input lens system, high stability power supplies, and a low dark-count detector and readout electronics. The system has been tested and is now operational on the ID16 beamline at European Synchrotron Radiation Facility, where an optical layout has been developed to perform high energy, high resolution PE experiments. First results show an overall energy resolution (electron + photon) of 71+/-7 meV at 5934 eV. The effective attenuation length of the photoelectrons is estimated to be 5+/-0.5 nm at a kinetic energy of 5 keV. (C) 2005 American Institute of Physics.

We have determined the effective attenuation length of photoelectrons over the range of kinetic energies from 4 to 6 keV in Co, Cu, Ge, and Gd2O3. The intensity of the substrate (Si) and overlayer core level peaks was measured as a function of the thickness of the wedge-shaped overlayers. Experimental values vary between 45-50 angstrom at 4 keV and 60-65 angstrom at 6 keV in Co, Cu, and Ge. Smaller values (30 angstrom to 50 angstrom, respectively) are found in Gd2O3. Our results confirm that, for different classes of materials, high energy photoemission spectroscopy has the necessary depth sensitivity to go beyond surface analysis, yielding important information on the electronic properties of the bulk and of buried layers and interfaces.

We present high-resolution valence band and core level spectra of silver for photoelectron kinetic energies up to 8 keV. At these kinetic energies we estimate a surface contribution of less than 3%. Taking advantage of the favourable sp/d relative cross-sections, a comparison with the calculated density of states is presented. We observe an increasing photoemission intensity when approaching the Fermi level, which we assign to a free-electron-like character in the 5p-band, whereas the principal s-like contribution is located at the bottom of the d-band. The difference between measured and calculated values of the sp/d cross-section ratio is discussed.

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The time-energy dispersion (TED) characteristics of a spherical electrostatic mirror are used to design an unusual electron energy analyzer. It is shown that TED of a retarding spherical field in an electron mirror configuration is positive and it increases with the electron kinetic energy. This is due to an increasing penetration of electrons with high kinetic energy in the retarding field and provides the basis for developing a new type of time-of-flight spectrometer (TOF). Two limiting cases for the geometry of the proposed spectrometer are considered and for both of them the energy resolution of the TOF device depends on the combined time resolution of electron detector and readout electronics. In the case of a 10-cm inner sphere radius (22 cm outer sphere radius) for the electrostatic mirror, the spectrometer is expected to have an energy resolution of about 0.5 eV/ns and an acceptance solid angle of about 2.2 srad for electrons of 75 eV kinetic energy. A position sensitive detector allows retrieving the energy and the emission angle on the basis of the measured time-of-flight and detection point position. In the second case the inner sphere radius is 6 cm and the outer spherical segment has a radius of 120 cm. The energy resolution is expected to be about 160 meV/ns at the electron kinetic energy of 1 keV and the acceptance solid angle is 0.1 srad. In both cases changing the retarding potential can easily change the energy range within which the TOF analysis is performed. (C) 2003 Elsevier B.V. All rights reserved.

A novel apparatus devoted to time-resolved photoemission experiments in the sub-picosecond regime will be presented. The system is composed of a Ti:sapphire laser source and a time of flight (TOF) electron energy analyzer mounted in a UHV experimental chamber. The laser source is characterized by a pulse duration of 150 fs at a wavelength of 790 nm (1.57 eV) and operates at a repetition rate of 1 kHz. To perform photoemission measurements, UV radiation up to 6.28 eV is produced with sequential steps of frequency conversion by employing crystals with a second order nonlinearity. Photoelectrons are collected by a TOF spectrometer designed to analyze electrons from tenths of eV up to 5 eV. It can be operated in two different angular resolution modes switching on and off an electrostatic collection optics: the high angular resolution mode (Deltaalpha = +/-2.7degrees) and the low angular resolution mode (Deltaalpha = +/-5.6degrees). Single photon photoemission spectra from the Ag(100) clean surface have been recorded at room temperature using the fourth harmonic light (lambda = 200 nm and hv = 6.28 eV). The Fermi edge profile convoluted with a Gaussian-shaped energy transmission function of the TOF spectrometer sets an upper limit for the energy resolution which is about 65 meV (FWHM) at 2 eV of electron energy.

For the latest generation of SR sources, local bump orbit feedback systems are being developed for the improvement of the stability of the delivered radiation. The high brightness beamlines using undulator radiation are the most sensitive to electron beam oscillations. Therefore, Photon Beam Position Monitors (PBPM) are being built as detectors of beam movement and as references for feedback systems. The PBPM must not be destructive and has to be suitable for continuous usage. Usual storage ring configurations permit a significant part of the radiation coming from the upstream and downstream dipoles to be superimposed with the undulator radiation. A novel detector, based on spectroscopic techniques, has been developed at ELETTRA. It can be tuned on the working energy of the undulator from a few eV to some keV. A detailed description of the detector layout and its working principle is presented. Its performance with respect to the stability requirements of the beam of synchrotron radiation is also analysed. (C) 2002 Published by Elsevier Science B.V.

The latest generation SR sources have severe constraints for the stability of the delivered radiation. The high brightness beamlines using undulator radiation are most sensitive to electron beam oscillations. Therefore, photon beam position monitors for undulator radiation are being built as detectors of beam movement and as references for feedback systems. A significant part of the radiation coming from the upstream and downstream dipoles is superimposed on the undulator radiation. A novel detector, incorporating photoelectron analysers, has been developed at Elettra. It can be tuned to the working energy of the undulator from few eV to some keV, the active elements intercepting the tails of the photon distribution. A prototype has been developed for the vertical photon beam position monitoring, and a complete set of characterisation measurements has been performed down to the lowest photon energies of the undulator peak. A description of the detector and its features are presented along with the commissioning results. (C) 2001 Elsevier Science B.V. All rights reserved.