3d Core-level Photoemission Spectra Research Articles

Structure and properties of mixed valent CeFe2Al8

Temperature dependent magnetic, electrical transport and thermal properties of polycrystalline orthorhombic CeFe2Al8intermetallic compound have been studied along with its isostructural La counterpart, LaFe2Al8. For the cerium compound, low fielddcmagnetization exhibits an antiferromagnetic like ordering (TN) ∼ 4 K. The main feature of the magnetic susceptibility plot is a broad hump spanning a large temperature range, indicating mixed valence of Ce in the compound, in good agreement with reported literature. However, contrary to the reported observations we find that the mixed valence state is very robust and was evident even up to very high magnetic fields (> 2 T). Further, in this work we report 3d core level photoemission spectra of cerium in CeFe2Al8, to understand the valence state of cerium ions in this system. Additionally, from resistivity measurements it is found that, CeFe2Al8is metallic with no indication of any anomaly, till the lowest temperature of measurement. Specific heat measurements show very low value of heat capacity and electronic contribution. The isostructural La analogue, LaFe2Al8compound shows broadness in susceptibility with maxima around 44 K which may be attributed to ordering of Fe moments. The comparison of Ce and La compounds brings out the role of Fe magnetic moments which may be responsible for competing with cerium moments and resulting in the dilution of long-range magnetic order, also contributing to magnetic frustration in CeFe2Al8.

Observation of the 4f ground-state symmetry in strongly correlated cubic Pr compounds probed by linearly polarized 3d core-level photoemission spectroscopy

We report the core-level photoemission study of cubic PrBe13, PrIr2Zn20 and PrB6 using linearly polarized hard X-ray. We have successfully observed linear dichroism (LD) in Pr3+ 3d core-level photoemission spectra reflecting the 4f ground-state symmetry for all the compounds. The observed LDs and polarization-dependent spectra are reproduced by ionic-model calculations including the full multiplet theory and the local crystalline electric field (CEF) splitting. We have confirmed that LDs in Pr3+ 3d core-level photoemission spectra are able to determine unambiguously the Pr3+ 4f ground-state symmetry.

Linear dichroism in 3d core-level and 4f valence-band photoemission spectra of strongly correlated rare-earth compounds

We have revealed that anisotropic 4f charge distributions caused by the crystalline electric field are responsible for linear dichroism (LD) in 3d core-level photoemission spectra of rare earth compounds. Indeed, we have successfully observed the intrinsic LD for cubic YbB12 and tetragonal SmCu2Si2. We have also performed polarization-dependent 4f photoemission in a valence-band region. The observed LDs in the experimental 4f spectra are reduced from those predicted from the theoretical simulations for the localized ions.

Electronic structures of organic salt DMTSA-BF4 using photoelectron spectromicroscopy

Abstract The electronic structures of organic salt DMTSA-BF 4 , where DMTSA is 2,3-dimethyltetraseleno-anthracene, have been studied with photoelectron spectromicroscopy at various photon energies. The atomic orbital characters of the spectral features observed in the valence band region were determined from the photon energy dependence of the photoionization cross-section. The features between ∼1 and ∼4 eV are predominantly derived from both Se 4p and C 2p states. The features at ∼6 eV, between ∼7 and ∼10 eV, and between ∼10 and ∼20 eV are predominantly derived from Se 4p, C 2p, and Se 4s and/or C 2s states, respectively. The F 2p states originating from the counter anion BF 4 are located at ∼8 eV. By comparing the Se 3d core-level photoemission spectra between DMTSA-BF 4 and DMTSA, it is suggested that DMTSA-BF 4 has a mixed valence state.

Absence of long-range ordered reconstruction on the GaAs(311)A surface

We have investigated the decapped GaAs(311)A surface using both scanning tunneling microscopy and synchrotron-radiation photoemission. While our data are in broad agreement with the structural model of GaAs(311)A proposed in a recent study [Wassermeier et al., Phys. Rev. B 51, 14 721 (1995)], we find considerable differences in the surface order. In particular, the As dimer rows are unbroken over much shorter length scales and are highly kinked. We observe a correspondingly lower degree of anisotropy in the surface roughness than that previously reported. An (8\ifmmode\times\else\texttimes\fi{}1) reconstruction was not observed. An analysis of As 3d and Ga 3d core-level photoemission spectra suggests that surface As atoms are in only one bonding configuration while surface Ga adopts two different bonding states. We discuss possible origins for the core-level spectra surface components.

Evidence for three surface components in the 3d core-level photoemission spectra of Ge(100)-(2 x 1) surface.

The 3d surface core-level shifts of the clean Ge(100)(2\ifmmode\times\else\texttimes\fi{}1) surface have been investigated at 300 K by photoemission. A previously unobserved (to our knowledge) shifted component at about +0.19 eV relative to the bulk emission has been clearly identified and associated with dimer down-atom emission. The binding energy difference of 0.72 eV between dimer down-atom and dimer up-atom 3d core levels, consistent with a charge transfer similar to that occurring in the Si(100)-(2\ifmmode\times\else\texttimes\fi{}1) surface, supports the so-called ionic model of the Ge(100)-(2\ifmmode\times\else\texttimes\fi{}1) buckled-dimer reconstruction. \textcopyright{} 1996 The American Physical Society.

3d core-level photoemission spectra of intermetallic Yb compounds.

The Yb 3d core-level photoemission spectra of trivalent YbAs, mixed-valence ${\mathrm{YbAl}}_{3}$, and divalent ${\mathrm{YbPb}}_{3}$ were measured with a Si K\ensuremath{\alpha} x-ray source. Significant intensities of divalent peaks were observed even for trivalent YbAs and mixed-valence ${\mathrm{YbAl}}_{3}$. This is probably due to the divalent surface layers, which makes difficult the estimation of the 4f hybridization strength from the 3d core-level spectra. The 4d core-level and the 4f spectra are consistent with this interpretation.

Homogeneous intermediate valence of Sm on Al(111).

Ordered and disordered monolayers and submonolayers of Sm were formed on Al(111). The ordered monolayer has the structure Al(2\ifmmode\times\else\texttimes\fi{}2)Sm. Valence-band and Sm 3d core-level photoemission spectra were taken using Al K\ensuremath{\alpha} radiation. The data show that the 3d core spectrum is a true replicate spectrum and allows a measurement of the valence. Sm in ordered overlayers always exhibited a valence of 3, whereas in disordered overlayers the Sm atom presented a valence of 2.4 at very low coverage, rising to a value of 2.8 at multilayer coverage. It is argued that the measured valence for the disordered submonolayer is site independent and homogeneous. The interaction with the aluminum substrate is sufficient to promote intermediate valence in the isolated adsorbed Sm atom, leading to a valence of 2.4.

ESCA studies of some mixed-valence rare-earth intermetallics

ESCA (or XPS) studies of some rare-earth intermetallics were carried out using ESCA (3) Mark II and ‘ESCALAB’ machines from V G Scientific. The mixed valence nature of EuCu2Si2 and EuNi2P2 intermetallic compounds has been established. The 3d core-level photoemission spectra of Eu in EuCu2Si2 and EuNi2P2 exhibit two sets of structures corresponding to two different valence states of the rare-earth ions. Each of these sets shows simple spin-orbit splitting. The replicate splitting measured by us agrees well with those calculated by Herbst and Wilkins. The 3d core-level photoemission spectra of Eu is free from the multiplet splitting and satellite structure. The importance of 3d core-level photoemission studies in the understanding of valence fluctuation phenomenon has been emphasized.