2p X-ray Absorption Spectroscopy Spectra Research Articles

Electronic structures of [formula omitted] delafossite oxides

Electronic structures of AgNi 1 - x Co x O 2 ( 0 ⩽ x ⩽ 1 ) delafossite oxides have been investigated by using photoemission spectroscopy (PES) and soft X-ray absorption spectroscopy (XAS). T 2p XAS ( T = Co , Ni) spectra of AgNi 1 - x Co x O 2 show that the valence states of Co ions are trivalent and do not change with x . In contrast, Ni ions are in the Ni 2 + – Ni 3 + mixed-valent states and the trivalent component increases with increasing x . This finding suggests that the metallic nature of AgNi 1 - x Co x O 2 for low values of x arises from the divalent Ni ions. The valence-band PES study of AgNi 1 - x Co x O 2 reveals that the Ni 3d states are more metallic like than the Co 3d states.

Combined X-ray Absorption Spectroscopy and Density Functional Theory Examination of Ferrocene-Labeled Peptides

A combination of soft X-ray absorption spectroscopy (XAS) measurements and StoBe density functional theory (DFT) calculations has been used to study the electronic structures of the ferrocene-labeled peptides Fc-Pro(n)-OBz (n = 1-4). Excellent agreement between the measured and the simulated data is observed in all cases, and the origin of all major spectral features was assigned. The breaking of the degeneracy of the ferrocene 3e(2u)-like unoccupied molecular orbital under the influence of a substituent attached to a Cp ring was observed experimentally. The influence of the bonding environment on the O 1s and N 1s XAS spectra was examined. A corrected assignment of one of the major features in the Fe 2p XAS spectra of ferrocene is proposed and supported by the DFT simulations, as well as the measured spectra.

Photoemission spectroscopy and x-ray absorption spectroscopy study of delafossite AgTO2 (T=Fe,Co,Ni)

Electronic structures of delafossite AgTO2 (T=Fe,Co,Ni) have been investigated by using photoemission spectroscopy (PES) and x-ray absorption spectroscopy (XAS). The T 2p XAS spectra of AgTO2 show that Fe and Co ions are in the trivalent states but that Ni ions are mainly in the divalent states, suggesting that the metallic nature of AgNiO2 arises from hole carriers due to divalent Ni ions. The valence-band PES study of AgTO2 (T=Co,Ni) reveals that T 3d states are located close to EF and that the Ni 3d band is more metalliclike than the Co 3d band.

Electronic structure of La0.7Ce0.3MnO3 thin film

AbstractThe electronic structure of epitaxial thin films of La0.7Ce0.3MnO3 (LCeMO) has been investigated using photoemission spectroscopy (PES) and X‐ray absorption spectroscopy (XAS). The measured valence‐band PES, Ce 3d PES, and Ce 3d XAS spectra for LCeMO consistently indicate that the localized Ce 4f orbitals are almost unoccupied so that the Ce valence is nearly tetravalent. The Mn 2p XAS spectrum suggests Mn2+ and Mn3+ mixed‐valent states of Mn ions in LCeMO. The LSDA + U calculation agrees better with the measured PES/XAS spectra than the LSDA calculation (U: the on‐site Coulomb interaction). (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Photoemission and x-ray absorption spectroscopy study of electron-doped colossal magnetoresistive manganiteLa0.7Ce0.3MnO3films

The electronic structure of La0.7Ce0.3MnO3 (LCeMO) thin film has been investigated using photoemission spectroscopy (PES) and x-ray absorption spectroscopy (XAS). The Ce 3d core-level PES and XAS spectra of LCeMO are very similar to those of CeO2, indicating that Ce ions are far from being trivalent. A very weak 4f resonance is observed around the Ce 4d $\to$ 4f absorption edge, suggesting that the localized Ce 4f states are almost empty in the ground state. The Mn 2p XAS spectrum reveals the existence of the Mn(2+) multiplet feature, confirming the Mn(2+)-Mn(3+) mixed-valent states of Mn ions in LCeMO. The measured Mn 3d PES/XAS spectra for LCeMO agrees reasonably well with the calculated Mn 3d PDOS using the LSDA+U method. The LSDA+U calculation predicts a half-metallic ground state for LCeMO.

PES and XAS studies of Mn12-Ac molecular magnet

Abstract The electronic structure of Mn12-Ac has been investigated using photoemission spectroscopy (PES) and X-ray absorption spectroscopy (XAS). The PES spectrum indicates that Mn 3d states are located near the top of the valence band, and the Mn 2p XAS spectrum provides clear evidence for the Mn3+–Mn4+ mixed-valent states.

Crystal-Field Effects at the TiO2−SiO2 Interface As Observed by X-ray Absorption Spectroscopy

The electronic structure of the TiO2−SiO2 interface has been investigated using X-ray absorption spectroscopy (XAS). TiO2 overlayers have been grown on two substrates, amorphous SiO2 and highly oriented pyrolytic graphite (for comparison), by evaporation of Ti in an oxygen atmosphere at room temperature. The evaporation rate was low enough to allow a detailed study of the early stages of growth, i.e., the submonolayer regime (θ < 1). The Ti 2p XAS spectra of the TiO2 overlayers have been measured for different coverages. The spectra corresponding to the submonolayer regime show an unusual shape not reported up to now. A comparison with existing atomic multiplet calculations indicates a significant decrease of the crystal field (≈0.7 eV) as compared with bulk TiO2 (≈1.7 eV) due to strong electronic interactions at the interface. The presence of the SiO2 substrate and the covalent character of the Si−O bonds lowers the crystal field of the TiO2 overlayer at the interface. In contrast, the graphite substrate...

Cu 2p X-ray absorption and Cu 2p–3d resonant photoemission spectroscopy of LaCuO3

Abstract In order to study the effect of intercluster interaction on the high-energy spectroscopy of formally Cu3+ oxides, we have performed X-ray absorption spectroscopy (XAS) and Cu 2p–3d resonant photoemission spectroscopy (RPES) studies of rhombohedrally distorted LaCuO3. In the Cu 2p XAS spectrum, the Cu 2p3/2 main peak is split into two structures, indicating that the interaction between the CuO6 octahedral clusters is strong. The valence-band RPES spectrum shows an enhanced satellite structure at ∼12.5 eV, similar to that of Cu2+ oxides for the incident photon energies which create intermediate states well screened by the intercluster interaction. For the incident photon energy for the poorly screened intermediate state, the enhanced satellite structure becomes broad and has a maximum at ∼13 eV.

Possibility for an intermediate-spin ground state in the charge-transfer material SrCoO3.

We discuss the possibility of an intermediate-spin ground state for a ${\mathit{d}}^{5}$ (${\mathit{d}}^{6}$) system. The intermediate-spin state is stabilized by the relative stability of the ligand hole state that it hybridizes with. Using atomic multiplet calculations we showed that an intermediate-spin ground state is possible for ${\mathrm{Co}}^{4+}$ (${\mathit{d}}^{5}$) when the ${\mathit{d}}^{6}$L state dominates the ground state. From a comparison of the experimental Co 2p x-ray absorption spectroscopy spectrum with the calculated one we assume an intermediate-spin ground state for ${\mathrm{SrCoO}}_{3}$. The intermediate-spin ground state is a highly symmetrical state with high-spin Co ${\mathit{d}}^{6}$ ions on each site. Each oxygen then contributes 1/3 hole which is antiferromagnetically coupled to both neighboring Co ions. In this way the itinerant oxygen holes couple the high-spin Co ${\mathit{d}}^{6}$ ions ferromagnetically. With this model of oxygen holes that introduce ferromagnetic correlations we can also explain the spin-glass behavior for slightly doped ${\mathrm{LaCoO}}_{3}$.

Photoemission and Absorption Spectroscopy of Mn2Sb, MnAlGe, Mn2As, Cr2As and Fe2As

Electronic structures of ferri-, ferro- and antiferromagnetic Cu 2 Sb type intermetallic compounds have been studied by ultraviolet and X-ray photoemission spectroscopy (UPS, XPS) as well as by X-ray absorption spectroscopy (XAS). The different spectral features in the core level XPS and the 2p XAS spectra of these materials are discussed by considering the non-equivalent sites of the transition metal atom, M(I) and M(II). The valence band photoemission spectra are also discussed in comparison with the results of recent band calculations.