Binding Energy Region Research Articles

Quasiparticle energy bands of transition-metal oxides within a model GW scheme

We calculate the quasiparticle band structure of NiO and ${\mathrm{CaCuO}}_{2}$ by using a model self-energy correction which approximates closely the GW method of Hedin. We obtain energy gaps and magnetic moments in agreement with experiment. For NiO, our results agree with integrated and angle-resolved photoemission experiments in the low binding energy region. The spectral distributions of O 2p and Ni 3d states are discussed, in relationship with the available experimental data. Our results demonstrate that the addition of self-energy corrections to local-spin-density band calculations provides a meaningful description of many aspects of the electronic states of transition-metal oxides. As expected, the satellite structures observed in photoemission experiments are not found in our calculations.

Composition dependent electronic structure effects in Nd1−x Sr x TiO3

The development of the electronic structure in Nd1−x Sr x TiO3 as a function of x was investigated using resonant photoelectron spectroscopy. Attention is focussed indication of changes in the Ti 3d-O2p hybridization and on electron-electron correlation effects evident in the Ti 3d intensity within ∼ 3 eV of the Fermi level (E F). The energetic position of the Ti 3d intensity signals the importance of electron correlation effects. The total intensity in this region is found to correlate linearly with composition and changes in the spectral structure are discussed in terms of the one-electron spectral function. For x < 0.25 (insulating or semiconducting compositions), only incoherent intensity associated with the lower Hubbard band is present. Additional intensity, attributed to a coherent quasiparticle contribution, appears at the composition of the metal-insulator transition, x < 0.25. Ti 3d intensity also occurs in the higher binding energy region of the predominantly O 2p band due to Ti 3d O-2p hybridization. Composition-dependent changes in this region are analyzed to determine changes in the Ti 3d-O2p hybridization with composition and structure.

Core-to-Rydberg excitations and their Auger decay in the HCl and DCl molecules.

The resonant Auger electron spectra of the HCl and DCl molecules have been measured at the first core-to-Rydberg resonances. The low binding energy region of the spectra has been decomposed into transitions to different bound states and their vibrational progressions. Several transitions have been assigned using the strict spectator model. The total ion yield spectrum of HCl in the energy region of the core-to-Rydberg resonances has been recorded and its assignment refined with the help of the Auger electron and chlorine 2{ital p} photoelectron spectra. {copyright} {ital 1996 The American Physical Society.}

In-situ characterization of doping-effect on electronic structure of epitaxial films of infinite layer SrCuO2

Change of electronic structure of infinite-layer SrCuO2 epitaxial film with both hole-and electron-doping has been studied byin-situ photoemission spectroscopy. In both of the cases, semiconducting gap in the vicinity of the stoichiometric compound has been vanished by “light-doping”. By further introductions of carriers, monotonous shifts of corebinding energies have been observed; the shift toward lower binding-energy region by the hole-doping, and that toward higher side by the electron-doping. Total amount of the shift over the whole range of the doping was much smaller than the semiconducting gap. For the metallic regions, comparison between the energy-shift observed and that expected by a calculation under local-density-approximation is discussed.

Core level photoelectron spectroscopy on the lanthanide-induced hydrolysis of DNA

The electronic structures of the complexes of diphenyl phosphate (DPP), a model compound of DNA, with lanthanide ions have been investigated to shed light on the mechanism of the cerium (IV)-induced nonenzymatic hydrolysis of DNA. Binding energies of the P 2p core level of DPP were 134.2 eV for the complexes with La(III), Eu(III), and Lu(III), and was 134.4 eV for the Ce(IV) complex, when the metal/DPP molar ratio was 1:1. When the molar ratio was increased, only Ce(IV), the most active metal ion for DNA hydrolysis, showed a chemical shift of ∼0.5 eV toward the higher binding energy region. The chemical shift of ∼0.5 eV toward the higher binding energy region. The chemical shift was due to the systematic increase in the intensity of the higher binding energy component. The observed change in the electronic structure of the DPP-Ce(IV) complex may be related to the superb ability of Ce(IV) for the hydrolysis of DNA.

Auger electron–ion coincidence experiment on nitric oxide molecule excited by electron impact

The fragmentation of nitric oxide by electron impact is studied via Auger electron–ion coincidence experiments. The kinetic energy releases of the different fragments have been measured in the 39–70 eV binding energy region of the dication. The experimental data confirm that the three lower lying states of NO2+ are bound states, while all the other states in the studied region are repulsive ones. Experimental evidence is provided that all the repulsive states up to 54 eV binding energy dissociate to the lowest dissociation limit and that dissociative channels leading to the formation of N2+ and O2+ are populated at 62 eV binding energy. The experimental results are compared with previous experimental data obtained with different techniques and with the more recent theoretical predictions.

Effect of hole doping on the electronic structure of Nd1-xSrxTiO3.

Photoelectron spectroscopy has been employed to follow the development of the electronic structure in ${\mathrm{Nd}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Sr}}_{\mathit{x}}$${\mathrm{TiO}}_{3}$ as a function of x. Resonant effects at the Ti 3p threshold were used to highlight Ti 3d contributions in the valence bands. Particular attention is focused on Ti 3d intensity within \ensuremath{\sim}3 eV of the Fermi level (${\mathit{E}}_{\mathit{F}}$). The total intensity in this region is found to correlate linearly with composition, as expected. Changes in the shape of this spectral structure are discussed in terms of the one-electron spectral function. For x0.25 (insulating or semiconducting compositions), only incoherent intensity associated with the lower Hubbard band is present. Additional intensity, attributed to a coherent quasiparticle contribution, appears at the composition of the metal-insulator transition x\ensuremath{\sim}0.25. The relative intensities of these two components are determined as a function of x. Ti 3d intensity also occurs in the higher binding-energy region of the predominantly O 2p band due to Ti 3d--O 2p hybridization. Composition-dependent changes in this region are analyzed in order to determine changes in the Ti 3d--O 2p hybridization with composition and structure.

An experimental study of the valence shell photoelectron spectrum of hydrogen sulphide

The complete valence shell photoelectron spectrum of hydrogen sulphide has been studied in the 10 to 25 eV binding energy region using He I, He II and synchroton radiation. Using monochromated synchroton radiation, photoelectron angular distributions and branching ratios have been determined in the 14 to 120 eV photon energy range. The results suggest that most of the prominent inner valence features should be associated with ionisation from the 4a1 molecular orbital. High resolution spectra have been obtained over a similar binding energy range using He I and He II excitation. Several narrow photoelectron bands have been observed in the region between 22.5 and 24.5 eV, and are associated with vibrational progressions belonging to two different electronic states. The He I excited spectrum has allowed a detailed analysis to be made of the vibrational and rotational fine structure exhibited in the photoelectron bands associated with ionisation from the 2b1 and the 5a1 orbitals. For the A 2A1 state, comparisons are made with the rovibronic structure predicted by Duxbury et al.

Resonant photoemission study ofK-derived valence-band states in K X C60

The electronic structure of K-doped C60 was investigated by photoemission (PE) and X-ray absorption near-edge structure (XANES) studies at the C-1s and K-2p thresholds. In addition, information on the local K-derived partial density of states in superconducting K3C60 was obtained by resonant PE at the K-2p1/2 threshold. The experimental observations support a complete charge transfer from K to C60 and we clearly observe a finite density of states atEF. From resonant PE, occupied states with K-p, d character could be identified in the binding-energy region from 1.5 to 8 eV below, but not directly at the Fermi level. This partial-density-of-states structure agrees well with the results of our band-structure calculations based on the local-density approximation.

Superconducting energy gap in Bi2Sr2CaCu2O8 observed by high-resolution photoemission spectroscopy

A high-energy resolved low-temperature photoemission spectrometer of angle-integrated mode was constructed to study the detailed electronic structure near the Fermi level of novel materials, in particular, cuprate high-Tc superconductors. Photoemission measurement with this spectrometer on a Bi2Sr2CaCu2O8 polycrystal clearly showed a transfer of spectral weight from the vicinity of the Fermi level to the higher binding-energy region below the superconducting transition temperature, indicating opening of the superconducting gap. Numerical simulation for both normal and superconducting states showed that the superconducting gap parameter (Δ) of 18 meV with dx 2−y 2 symmetry gives a most reasonable fitting.

X-Ray photoelectron spectra of some bioinorganic complexes of the rare earths with N-acetylalanine

X-Ray photoelectron spectra of some bioinorganic complexes of La, Ce, Pr, Nd, Sm and Eu with N-acetylalanine have been measured and the 3d52 and 3d32 main peaks and their satellites have also been assigned. The spin—orbit splitting between the 3d52 and 3d32 core-level of the rare earth ion in these complexes becomes slightly larger than that of the free rare earth atom due to the effect of the crystal field. The satellite for the 3d main peaks of La in the solid state complex are in higher binding energy region and may be attributable to the L → 4ƒ charge-transfer shake-up process. The satellites for the 3d main peaks of Ce, Pr, Nd, Sm and Eu are in the lower binding energy region and may be attributable to the 4ƒ→L charge-transfer shake-down process.

Surface segregation of PdAg membranes upon hydrogen permeation

PdAg membranes are permeable to hydrogen. Hydrogen treatment results in a small chemical shift (±0.1–0.2 eV) of Pd 3d core level but no change in the Ag3d level. A new valence band in the binding energy region of 7–9 eV corresponding to the interaction between H 1s and Pd4d appears on a hydrogen permeated membrane surface. Quantitative XPS analysis reveals that Pd segregates at the membrane surface toward the high hydrogen pressure side while Ag segregation occurs at the surface on the low hydrogen pressure side after hydrogen permeation. Both surface segregations are explained based on an MTCIP-1A (modern thermodynamic calculation of interface properties — first approximation) approach. It is concluded that hydrogen chemisorption induces palladium segregation on the PdAg membrane surface.

Angle-resolved-photoemission study of the electronic structure of Gd(0001).

The electronic structure of thick (g300 \AA{}) single-crystal Gd(0001) layers on W(110) has been studied by angle-resolved-photoelectron spectroscopy. Photoemission spectra measured with photon energies between 30 and 60 eV show intense 4f emission at 8.3-eV binding energy and 5d 6s\char21{}derived valence-band states within 4 eV from the Fermi level. No other structure is observed in the 5\char21{}11-eV binding-energy region. The valence-band spectra show a surface state at \ensuremath{\Gamma}\ifmmode\bar\else\textasciimacron\fi{} near the Fermi level and other higher-binding-energy features possibly related to states localized near the surface.

XPS and BIS studies of CePd 2Al 3

Electronic structures of CePd 2Al 3, PrPd 2Al 3 and SmPd 2Al 3 are studied by X-ray photoemission (XPS) and inverse photoemission (BIS) spectroscopy. The rare earth atom 3d XPS spectra have shown a prominent spin-orbit doublet (3d 94f n) with a shoulder in the smaller binding energy ( E B ) region which is ascribable to the 3d 94f n+1 state. Hybridization between the 4f and conduction electron states is, however, very small. The 5d band crosses the Fermi level ( E F ).

Photoemission Study of the Electronic Structure of the Ferromagnetic Cr1-δTe System

The electronic structure of Cr1-δTe (δ=0.05, 0.25, 0.375) has been studied by photoemission spectroscopy. Structures near the Fermi level are qualitatively explained by the density of states (DOS) given by band-structure calculations, but significant discrepancies exist in the higher binding energy region. Configuration-interaction cluster-model calculations have been performed and the overall experimental features have been explained, indicating significant electron correlation effects in these compounds.

Electronic structure of metal chalcogen cubane clusters: photoelectron spectroscopic, electrochemical, and theoretical studies of [(.eta.-C5H4Me)TiS]4, [(.eta.-C5H4Me)VS]4, [(.eta.-C5H5)CrO]4, [(.eta.-C5H4Me)CrO]4, [(.eta.-C5H4Me)CrS]4, [(.eta.-C5H4Me)CrSe]4, [(.eta.-C5H4-iso-Pr)MoS]4, and [(.eta.-C5H4-iso-Pr)MoSe

He I and He II spectra of [(eta-C5H4iPr)MoS]4, [(eta-C5H4iPr)MoSe]4, [(eta-C5H4Me)CrS]4, [(eta-C5H4Me)CrSe]4, [(eta-C5H4Me)TiS]4, [(eta-C5H4Me)VS]4, [(eta-C5H5)CrO]4, and [(eta-C5H4Me)CrO]4 are presented. The photoelectron spectrum of [(eta-C5H4iPr)MoS]4 has been measured using synchrotron radiation over the photon energy range 21-80 eV. Relative partial photoionization cross section and photoelectron branching ratio data are presented for the first six valence bands (binding energy 5.0-10.5 eV). The cross sections of the d bands show a p --> d giant resonance in the photon energy range 39-60 eV. Intensity variations are interpreted in terms of the atomic orbital contributions to the molecular orbitals from which ionization is occurring. Similarities are observed between the low binding energy (4.8-7.5 eV) regions of the spectra of the sulfur and selenium derivatives of the group 6 elements and are interpreted in terms of ionization from molecular orbitals, composed largely of metal d-orbitals, delocalized over the metal tetrahedron. The molecular ion state ordering 2T2 < 2E < 2A1 is observed, the 2T2 and 2E states showing Jahn-Teller splitting. The a1 and e orbitals are metal-metal bonding whereas the t2 orbitals are nonbonding. Subsequent bands are assigned to cyclopentadienyl pi-orbitals and to metal-chalcogen bonding orbitals. The spectrum of [(eta-C5H4Me)VS]4 is consistent with an a(1)2e4t2(2) ground-state configuration for the metal-based orbitals, ionization from these three orbitals being easily identified. The ground state of [(eta-C5H4Me)TiS]4 cannot be unambiguously assigned from the PE spectrum. The d band region of the [(eta-C5H5)CrO]4 and [(eta-C5H4Me)CrO]4 Spectra shows fewer features. In these cases the metal d electrons are localized on the Cr ions, and the diamagnetism shown at low temperatures is the result of weak antiferromagnetic coupling. Cyclic voltammetry studies on [(eta-C5H4iPr)MoS]4, [(eta-C5H4iPr)MoSe]4, [(eta-C5H4Me)CrS]4, [(eta-C5H4Me)CrSe]4, [(eta-C5H4Me)VS]4, and [(eta-C5H4Me)CrO]4 reveal two reversible oxidations for all of the compounds except [(eta-C5H4Me)CrO]4, which can sustain only one reversible oxidation, consistent with a smaller degree of metal d electron delocalization. Ultraviolet and visible spectroscopy data are presented for [(eta-C5H4iPr)MoS]4, [(eta-C5H4iPr)MoS]4+, [(eta-C5H4Me)CrS]4, and [(eta-C5H4Me)CrS]4+, in which the presence of a band in the spectra of the cations which is not observed in the spectra of the neutral molecules is attributed to a 2A1 <-- 2T2 transition.

Anisotropy of the electronic states around Cu in Bi 2Sr 2CaCu 2O 8+x

The polarized x-ray Cu Kβ 2,5 emission bands of Bi 2Sr 2CaCu 2O 8+x single crystals were measured. They reveal the anisotropy of the p-partial density of states (PDOS) around copper. Pure polarization components of the Cu Kβ 2,5 x-ray emission band, corresponding to the states perpendicular and parallel to c, are given. The valence states oriented parallel to the CuO 2 plane are situated in the high binding energy region of the PDOS.

Vibrationally resolved threshold photoemission of N 2 and CO at the N and C K-edges

Zero-kinetic-energy photoelectron spectroscopy was used to measure the Franck—Condon factors for the carbon and nitrogen K-shell ionized states in N 2 and CO. Corresponding features in the two spectra showed nearly identical energy spacings, both below and above the ionization threshold, as predicted by the equivalent-core model. The equilibrium bond length, R e, for the CO C-1s −1 state was determined to be 1.077±0.005 Å, and R e for the N 2 N-1s −1 state was found to be 1.077±0.010 Å, changes of −0.051 Å for CO and −0.020 Å for N 2 from their ground-state equilibrium bond lengths. The two-electron states corresponding to 1s −1 val −1π* were examined in the binding energy region predicted by Green function calculations. Two-electron states absent in the X-ray photoemission spectrum are present in both molecules and show evidence of vibrational structure.

Surface characterization of activated charcoal by X-ray photoelectron spectroscopy (XPS): correlation with phenobarbital adsorption data.

X-ray photoelectron spectroscopy (XPS) was used to identify the functional states of carbon existing on the surfaces of various activated charcoals. The relative percentages of carbon, oxygen, and detectable trace elements comprising the activated charcoal surfaces were determined. Analysis of the carbon core-electron binding energy region revealed the existence of one hydrocarbon state (C-H, C-C are indistinguishable) and three oxygen-containing functional states. These states were hydroxyls or ethers (C-O), carbonyls (C = O), and carboxylic acids or esters (O-C = O). The C-O functional state contributed approximately 60-70% to the total percentage of oxygen-containing states. A very good correlation existed between the apparent areas occupied on the adsorbent surface per phenobarbital molecule and the relative percentages of the C-O functional state. Previously reported heat of displacement results for phenobarbital adsorption are now explained since the C-O state appears to be the primary site involved in the binding of phenobarbital by the activated charcoals.

Electronic structure and orientation of anthracene on Ag(111)

Spectroscopic techniques based on photoabsorption and photoemission, i.e. near edge X-ray absorption fine structure (NEXAFS) and angular-resolved photoemission (ARUPS) using synchrotron radiation, as well as inverse photoemission (IPES) have been employed to obtain information on the molecular orientation and electronic structure of thin films of anthracene adsorbed on Ag(111) surfaces. By measuring the polarisation dependence of the (Cls →π∗) transitions in the NEXAFS spectra, we find a parallel orientation of the molecular plane with respect to the substrate. The angular behaviour of the adsorbate-induced photoemission bands corroborates this result, and additionally a complete mapping of the valence levels and an improved assignment for the bands extended over a large binding energy region emerges. The unoccupied π ∗ levels levels have been studied by inverse photoemission and have been compared with MO calculations, as well as with electron transmission gas phase measurements (ETS). A well ordered (4 × 4) structure is observed in LEED investigations.