2p X-ray Absorption Spectroscopy Spectra Research Articles

Disorder and mixed valence properties of Sr2FeMoO6 studied by photoelectron diffraction and x-ray absorption spectroscopy

A single crystal of the double peroviskite Sr2FeMoO6 has been prepared and was studied by using two-dimensional photoelectron diffraction (2DPED) and x-ray absorption spectroscopy (XAS). We found clear evidence for disorder of Fe3+/Mo5+ by 2DPED experiments, supporting a disorder picture for Sr2FeMoO6. On the other hand, Fe 2p XAS spectra suggested the existence of Fe2+ components (i.e. the mixed valence states) at the surface, but it was suppressed in the bulk. It seems that this fact has complicated a controversy so far concerning the reduction of saturation magnetization of this material.

Experimental evidence for mixed-valent Cr ions in half-metallic CrO2: Temperature-dependent XMCD study

By employing soft X-ray magnetic circular dichroism (XMCD) and soft X-ray absorption spectroscopy (XAS), we have investigated the temperature (T)-dependent valence and spin states of Cr ions in half-metallic ferromagnet CrO2 nanorod powder. The lineshape-analysis of both the Cr 2p XAS and XMCD spectra of CrO2 reveals that the Cr ions in bulk CrO2 have both Cr4+t2g2↑ and Cr3+t2g3↑ valence configurations. This work provides the direct experimental evidence for the Cr3+-Cr4+ mixed-valent states in bulk CrO2(Cr3.8+), demonstrating that the half-metallic ferromagnetism in CrO2 originates from the double-exchange interaction. The T-dependent intensity variation of the Cr 2p XMCD spectrum agrees well with the bulk magnetization M(T) and the Curie temperature, indicating that the measured Cr 2p XMCD data represent the intrinsic bulk ferromagnetism in CrO2, and support the above finding of the XMCD lineshape analysis.

Resonant photoemission and X-ray absorption spectroscopies of lithiated magnetite thin film

Resonant photoemission spectroscopy (RPES) and X-ray absorption spectroscopy (XAS) were used to investigate the effect of lithiation on the electronic structure of Fe3O4 thin film relevant to the operation mechanism of nanoionic devices to enable magnetic property tuning. Comparison of the Fe 2p XAS spectrum for lithiated Fe3O4 (Li–Fe3O4) with that for pristine Fe3O4 clearly demonstrated that the number of Fe2+ ions at octahedral B sites is increased by lithiation. The valence band RPES spectra of Li–Fe3O4 further showed that lithiation increases the density of states near the Fermi level originating Fe2+ ions at octahedral B sites. These findings agree well with the observed decrease in the saturation magnetization in the magnetization–magnetic field (M–H) loop of Li–Fe3O4 thin film, indicating that minority spins (down spins) increase (i.e., total spins decrease) due to lithiation. The variation in the number of Fe2+ ions at B sites is suggested to be an underlying operating mechanism of a nanoionics-based magnetic property tuning device.

Pd층의 두께 변화에 따른 [Co/Pd] 다층박막의 연엑스선 방사광 분광 연구

We have investigated the electronic structures of intermetallic multilayer (ML) films of [Co(2A)/Pd(xA)] (x: the thickness of the Pd sublayer; x = 1 A, 3 A, 5 A, 7 A, 9 A) by employing soft X-ray absorption spectroscopy (XAS) and soft X-ray magnetic circular dichroism (XMCD). Both Co 2p XAS and XMCD spectra are found to be similar to one another, as well as to those of Co metal, providing evidence for the metallic bonding of Co ions in [Co/Pd] ML films. By analyzing the measured Co 2p XMCD spectra, we have determined the orbital magnetic moments and the spin magnetic moments of Co ions in [Co(2A)/Pd(xA)] ML films. Based on this analysis, we have found that the orbital magnetic moments are enhanced greatly when x increases from 1 A to 3 A, and then do not change much for x ≥ 3 A. This finding suggests that the interface spin-orbit coupling plays an important role in determining the perpendicular magnetic anisotropy in [Co/Pd] ML films.

Soft X-ray absorption spectroscopy study of multiferroic Bi-substituted Ba1−x Bi x Ti0.9Fe0.1O3

The electronic structures of multiferroic oxides of Ba(1-x)Bi(x)Ti(0.9)Fe(0.1)O(3) (0 < x < 0.12) have been investigated by employing photoemission spectroscopy and soft x-ray absorption spectroscopy (XAS). The measured Fe and Ti 2p XAS spectra show that Ti ions are in the Ti4+ states for all x and that Fe ions are Fe2+-Fe3+ mixed-valent for x > 0. The valence states of Fe ions are found to be nearly trivalent for x=0, and decreases with increasing x from being nearly trivalent (v(Fe)~ 3) for x=0 to v(Fe)~ 2.6 for x=0.12. The valence states of both Ti and Ba ions do not change for all x < 0.12. Based on the obtained valence states of Fe ions, the electronic and magnetic properties of Ba(1-x)Bi(x)Ti(0.9)Fe(0.1)O(3) are explored.

An in situ resonant photoemission and x-ray absorption study of the BiFeO3 thin film

Multiferroic bismuth ferrite (BiFeO3) thin films were prepared using the pulsed laser deposition (PLD) technique. The electronic structure of the film was studied in situ using photoemission spectroscopy (PES) and x-ray absorption spectroscopy (XAS). Both the Fe 2p PES and XAS spectra show that the Fe ions were initially in a+3 valence state. The Fe 2p and O K edge XAS spectra indicate that the oxygen octahedral crystal ligand field divides the unoccupied Fe 3d state into t2g↓and eg↓states. Valence band Fe 2p–3d resonant photoemission results indicate that hybridization between Fe 3d and O 2p plays an important role in the multiferroic properties of BiFeO3 thin films.

Electronic structure of V2O3 thin film prepared by RF magnetron sputtering using oxygen radical and V-metal

We have prepared V2O3 thin films on Al2O3 (0001) substrate by RF magnetron sputtering using oxygen radical and V-metal target, and studied their electronic structures by X-ray absorption spectroscopy (XAS) and X-ray photoemission spectroscopy (XPS). The as-deposited V2O3 thin films deposited at 600 °C exhibits high crystallization by oxygen radical irradiation during deposition. The electrical resistivity decreases with increasing deposition temperature, and this result is due to decreasing electron scattering. The crystal field splitting (10Dq) of the V2O3 thin film estimated from the fitting of the V 2p XAS spectrum is larger than that of the bulk crystal. In the XPS spectrum of the valence band region, the density of state (DOS) of the orbital in the V 3d state increases at around the Fermi level. These results contribute to the lattice distortion between the thin film and the substrate.

철원소를 함유한 분자기반 생체물질 나노입자들의 연 x선 방사광 분광 연구

이 연구에서는 헬리코박터 파이로리 페리틴, 헴, <TEX>$NaM[Fe(CN)_6]{\cdot}H_2O$</TEX> 프러시안 블루(M=Co, Ni) 등의 분자기반 생체물질 나노입자들의 전자 구조를 연구하기 위하여 방사광을 광원으로 사용한 연 x선 광흡수 분광(soft x-ray absorption spectroscopy: XAS)과 연 x선 자기 원편광 이색성(soft x-ray magnetic circular dichroism: XMCD) 분광법 실험을 수행하였다. 이 연구로부터 페리틴 나노 입자들을 구성하고 있는 Fe 이온들은 모두 거의 3가 (<TEX>$Fe^{3+}$</TEX>)의 원자가 상태에 있으며, 프러시안 블루 나노 입자들 내의 Fe 이온들은 <TEX>$Fe^{2+}-Fe^{3+}$</TEX>의 혼합원자가 상태에 있다는 것을 알 수 있었다. 또한 페리틴 내의 <TEX>$Fe^{3+}$</TEX> 이온들은 한 종류의 대칭성을 가진 국소 구조를 가지며, Fe 이온들의 자기모멘트는 모두 한 방향으로 정렬되어 있다는 사실을 발견하였다. 그리고 프러시안 블루 나노 입자들의 Fe 이온의 국소적 결합은 주로 <TEX>$(CN)^-$</TEX> 리건드와의 결합에 의하여 결정된다는 것을 분광학적으로 알 수 있었다. By employing soft x-ray absorption spectroscopy (XAS) and soft x-ray magnetic circular dichroism (XMCD), the electronic structures of molecule-based nano bioparticles, such as Helicobacter pylori ferritin (H. pylori ferritin), Heme, <TEX>$NaM[Fe(CN)_6]{\cdot}H_2O$</TEX>-type Prussian Blue (M=Co, Ni) analogue, have been investigated. The measured Fe 2p XAS spectra reveal that Fe ions are trivalent (<TEX>$Fe^{3+}$</TEX>) in H. pylori ferritins, while they are in the <TEX>$Fe^{2+}-Fe^{3+}$</TEX> mixed-valent states in <TEX>$NaM[Fe(CN)_6]{\cdot}H_2O$</TEX> Prussian Blue analogues (M=Co, Ni). According to the Fe 2p XMCD spectrum of high-state H. pylori ferritin, all the <TEX>$Fe^{3+}$</TEX> ions have the same local symmetry and their magnetic moments are aligned in the same direction. It is also found that the Fe 3d orbitals in <TEX>$NaM[Fe(CN)_6]{\cdot}H_2O$</TEX> have a strong covalent bonding to <TEX>$(CN)^-$</TEX> ligands, but with a very weak bonding to the 2p orbitals of O ligands.

방사광을 이용한 FeV2O4스피넬 산화물의 덩치상태와 분말상태의 전자구조 차이 연구

연 x선 광흡수 분광법(soft x-ray absorption spectroscopy: XAS)과 연 x선 자기 원편광 이색성(soft x-ray magnetic circular dichroism: XMCD)을 이용하여 스피넬 준강자성 산화물인 <TEX>$FeV_2O_4$</TEX>의 전자 구조를 연구하였다. Fe 2p XAS와 V 2p XAS 측정으로 부터 <TEX>$FeV_2O_4$</TEX>에서 Fe 이온과 V이온의 고유한 원자가는 각각 약 <TEX>$Fe^{2.3+}$</TEX>의 혼합원자가 상태와 약 <TEX>$V^{3+}$</TEX>의 상태임을 알 수 있었다. 실험적으로 측정된 Fe 2p XMCD의 신호는 거의 <TEX>$Fe^{2+}$</TEX> 상태에서 기인하였으며, <TEX>$Fe^{3+}$</TEX> 상태는 Fe 2p XMCD의 신호에 거의 기여하지 않는다는 사실이 발견되었다. 그러므로 <TEX>$FeV_2O_4$</TEX>의 자성 특성을 결정함에 있어서 자기적으로 정렬된 <TEX>$Fe^{2+}$</TEX> 상태 이온들이 중요한 역할을 한다고 생각된다. The electronic structure of ferrimagnetic spinel oxide of <TEX>$FeV_2O_4$</TEX> has been investigated by employing soft x-ray absorption spectroscopy (XAS) and soft x-ray magnetic circular dichroism (XMCD). The Fe 2p and V 2p XAS spectra show that the valence states of Fe and V ions are <TEX>${\sim}Fe^{2.3+}$</TEX> mixed-valent states and <TEX>${\sim}V^{3+}$</TEX> states, respectively. In Fe 2p XMCD spectra, finite XMCD signals are observed for divalent <TEX>$Fe^{2+}$</TEX> states only, but not for <TEX>$Fe^{3+}$</TEX> states. This finding indicates that the magnetic moments of <TEX>$Fe^{2+}$</TEX> ions are ordered ferromagnetically but that those of <TEX>$Fe^{3+}$</TEX> ions are cancelled, implying that <TEX>$Fe^{2+}$</TEX> ions play an important role in determining magnetic properties of <TEX>$FeV_2O_4$</TEX>.

High resolution photoemission and x-ray absorption spectroscopy of a lepidocrocite-like TiO2 nanosheet on Pt(110) (1 × 2)

The electronic structure of TiO(2) nanosheets on the Pt(110)-(1 × 2) surface has been investigated by using high resolution photoemission spectroscopy and x-ray absorption spectroscopy (XAS). The Ti 2p XAS spectra of the deposited TiO(2) films have been theoretically evaluated and, from the comparison with the experimental data, the assignment to a lepidocrocite-like structure is confirmed. Coexistence of TiO(2) islands with PtO(2) stripes for incomplete nanosheets is confirmed by high resolution photoemission data. The location of the valence and conduction band edges of the nanosheet has been experimentally determined allowing us to describe in details subtle electronic effects due to the interface with the substrate. The locations of the valence band maximum and the leading peak in the O 1s XAS spectrum indicate a band gap similar to anatase but with the Fermi level closer to mid-gap than found for bulk, n-type TiO(2).

Temperature-dependent magnetic circular dichroism study of ferromagnetic double perovskite La2MnNiO6

The temperature-dependent electronic structure of ferromagnetic double perovskite La2MnNiO6 has been investigated by employing soft x-ray magnetic circular dichroism (XMCD) and soft x-ray absorption spectroscopy (XAS). The measured 2p XAS spectra for Mn and Ni ions at low temperature show that most of Mn ions are formally tetravalent (3d3) and that Ni ions are divalent (3d8). The measured Ni 2p core-level x-ray photoemission spectroscopy spectrum also supports the divalent states of Ni ions. With increasing temperature, the measured XMCD intensity decreases, in agreement with its high Curie temperature. The line shapes of both XMCD and XAS spectra do not change with temperature, suggesting that the valence states of La2MnNiO6 do not change with temperature.

Soft x-ray synchrotron radiation spectroscopy study of SrMn1−xRuxO3 perovskites (≤x≤1)

The electronic structures of SrMn1−xRuxO3 (0≤x≤1) have been investigated by employing soft x-ray absorption spectroscopy (XAS). The measured Mn 2p XAS spectra for SrMn1−xRuxO3 show that the valence states of Mn ions change monotonically from Mn4+ for x=0 to ∼Mn3+ for x=0.8, suggesting that the valence states of the substituted Ru ions are higher than 4+. The Ru 3p XAS spectra of SrMn1−xRuxO3 show the existence of pentavalent Ru5+ ions for the low x value. The measured O 1s XAS spectra also support these findings.

Reinvestigation of the Fe, Cu and Cr valences in (FeCu)Cr2S4 spinels

AbstractThe valence states of Fe, Cu, and Cr ions in single crystalline Fe1–x Cux Cr2S4 have been studied using X‐ray photoelectron spectroscopy (XPS), X‐ray absorption spectroscopy (XAS) and X‐ray magnetic circular dichroism (XMCD). XPS measurements of compositions x = 0.2, 0.5, 0.6, and 0.9 indicate that the Cu and Cr ions remain mainly in the same valence state over the whole substitution range. XAS, XPS and XMCD investigations of Fe0.5Cu0.5Cr2S4 reveal a sample and preparation dependence of the Cu and Fe spectra. The comparison of the Cu 2p XAS spectrum with a literature measurement shows a change in the amount of Cu2+ explained by the appearance of an additional Cu2+ phase, possibly due to oxidation on the surface. XAS, XPS and XMCD spectra of Fe show a Fe3+ impurity phase present in air‐treated Fe0.5Cu0.5Cr2S4, especially in powdered samples. The lines related to trivalent Fe are found to disappear completely after cleaning the samples in‐situ and only the lines attributed to divalent Fe remain. Since many experimental methods rely on powdered samples and measure in air or in low vacuum, these findings provide an explanation for the differing results concerning the Fe valence obtained by these methods. (© 2009 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Synchrotron-Radiation Study of Valence States and Electronic Structures of $\hbox{AgNi}_{1-{\rm x}}\hbox{Co}_{\rm x}\hbox{O}_{2}$ Delafossite Oxides

The electronic structures of AgNi <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</sub> Co <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> (0 les x les 1) delafossite oxides have been investigated by employing photoemission spectroscopy (PES) and X-ray absorption spectroscopy (XAS) in the soft X-ray regime of synchrotron radiation. The Ag 3d core-level PES spectra shift toward the higher binding energy with increasing x, in agreement with the metallic nature for low values of x and the insulating nature for high values of x in AgNi <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</sub> Co <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> . Further, the Ag 3d core-level PES spectra become more asymmetric with decreasing x, which reflects the larger number of electron-hole pairs in the Ni-rich regime. Valence-band PES spectra reveal that the band width of the occupied Ni 3d states is broader than that of the Co 3d states, implying the larger Ni 3d-O 2p hybridization than the Co 3d-O 2p hybridization. The Co and Ni 2p XAS spectra show that Co ions are in the low-spin Co <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> states for all x, while Ni ions are in the Ni <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2+</sup> -Ni <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> mixed-valent states. The Ni <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> component increases with x.

Hybridization between the conduction band and3dorbitals in the oxide-based diluted magnetic semiconductorIn2−xVxO3

The electronic structure of In2-xVxO3 (x=0.08) has been investigated by photoemission spectroscopy and x-ray absorption spectroscopy (XAS). The V 2p core-level photoemission and XAS spectra reveale ...

Co oxidation accompanied by degradation of Pt–Co alloy cathode catalysts in polymer electrolyte fuel cells

The electronic structure of Co ions in Pt(3)Co alloy cathode catalysts for polymer electrolyte fuel cells (PEFCs) under different operation conditions has been investigated using X-ray absorption spectroscopy (XAS). The line shapes of the Co 2p XAS spectra indicate that the Co atoms in the cathode layer are predominantly metallic in all cells, and the spectrum of the first-operated cell is the most metallic among them. The Co 2p XAS spectra slightly change depending on the operation conditions, and the differences in the spectra can be explained by the presence of cobalt oxides. Decomposition analysis of the Co 2p XAS spectra reveals that the operation of Pt-Co PEFCs yields trivalently oxidised cobalt in the cathode layer.

Soft X-ray Absorption and Photoemission Studies of Ferromagnetic Mn-Implanted 3C-SiC

We have performed X-ray photoemission spectroscopy (XPS), X-ray absorption spectroscopy (XAS), and resonant photoemission spectroscopy (RPES) measurements of Mn-implanted 3C-SiC (3C-SiC:Mn) and carbon-incorporated Mn5Si2 (Mn5Si2:C). The Mn 2p core-level XPS and XAS spectra of 3C-SiC:Mn and Mn5Si2:C were similar to each other and showed “intermediate” behaviors between the localized and itinerant Mn 3d states. The intensity at the Fermi level was found to be suppressed in 3C-SiC:Mn compared with Mn5Si2:C. These observations are consistent with the formation of Mn5Si2:C clusters in the 3C-SiC host, as observed in a recent transmission electron microscopy study.

Formation and Characterization of Manganese Silicide on Si(111) and Si(100) Substrates

The electronic structure of the interface formation at Mn/Si at room temperature (RT) and the growth of manganese silicide were studied by using photoemission spectroscopy (PES) and X-ray absorption spectroscopy (XAS) with synchrotron radiation. The Mn coverage dependence of the Si 2p and the Mn 3p core-level spectra revealed that the growth of Mn on Si(111)-7 × 7 at RT started in a layer-by-layer growth at a coverage of less than 0.5 ML (monolayer). Mn 2p XAS spectra also showed no reaction between Mn and Si at RT. Three thin manganese silicide samples were prepared by using solid phase epitaxy at 610 ◦C (MSS), reactive deposition epitaxy at 290 ◦C for Si(111) and at 350 ◦C for Si(100) (MSR) and post annealing the MSR sample at 610 ◦C (MSP) on the Si(111) and the Si(100) substrates. The LOW ENERGY ELECTRON DIFFRACTION (LEED) pattern and the fine structure in the Mn 2p XAS spectra showed that the phases of the MSS, the MSR, and the MSP samples were the same. Emissions at the Fermi energy in the valence-band (VB) PES spectra and the line shape of Si 2p core-level photoemission spectra also showed the formation of metallic MnSi.

Study of the growth of NiO on highly oriented pyrolytic graphite by X-ray absorption spectroscopy

In this work, we present a X-ray absorption spectroscopy (XAS) study of the growth of NiO on highly oriented pyrolytic graphite (HOPG). NiO has been grown by reactive evaporation of metallic Ni in an oxygen atmosphere (2 × 10 −5 Torr) at room temperature. We paid special attention to the study of the early stages of growth. Both, Ni 2p and O 1s core-level XAS spectra were measured. For large NiO coverages, the spectra resemble that of a NiO single crystal, thus indicating the formation of a stoichiometric NiO thin film on the HOPG substrate. The Ni 2p XAS spectra remain similar during the whole growth process, indicating that Ni atoms are present in the high spin Ni 2+ form, as supported by multiplet calculations. In contrast, for low coverages the line-shape of the O 1s XAS spectra differ strongly from that of bulk NiO. Cluster calculations of the spectra in octahedral and pyramidal symmetries support the formation of nanometric planar NiO islands at the graphite steps as previously observed by atomic force microscopy (AFM) in this system.

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.