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We report the direct evidence of valence fluctuation in the thermoelectric material Yb3Si5 by using synchrotron X-ray photoemission spectroscopy. The Yb 3d core level photoemission spectrum of a Yb3Si5 single crystal shows clear separation of the Yb2+ peak and Yb3+ multiplet peaks. From the spectral weight of each component, the mean valence of Yb ions is estimated to be +2.67 at 20 K. Furthermore, a Kondo resonance peak just below the Fermi energy is also observed by high-resolution soft X-ray photoemission spectroscopy, suggesting the valence fluctuating state in Yb3Si5.

An experimental and computational investigation of the space-charge effects occurring in ultrafast photoelectron spectroscopy from the gas phase is presented. The target sample CF$_3$I is excited by ultrashort (100 fs) far-ultraviolet radiation pulses produced by a free-electron laser. The modification of the energy distribution of the photoelectrons, i.e. the shift and broadening of the spectral structures, is monitored as a function of the pulse intensity. The experimental results are compared with computational simulations which employ a Barnes-Hut algorithm to calculate the effect of individual Coulomb forces acting among the particles. In the presented model, a survey spectrum acquired at low radiation fluence is used to determine the initial energy distribution of the electrons after the photoemission event. The spectrum modified by the space-charge effects is then reproduced by $N$-body calculations that simulate the dynamics of the photoelectrons subject to the individual mutual Coulomb repulsion and to the attractive force of the positive ions. The employed numerical method accounts for the space-charge effects on the energy distribution and allows to reproduce the complete photoelectron spectrum and not just a specific photoemission structure. The simulations also provide information on the time evolution of the space-charge effects on the picosecond scale. Differences with the case of photoemission from solid samples are highlighted and discussed. The presented simulation procedure, although it omits the analysis of angular distribution, constitutes an effective simplified model that allows to predict and account for space-charge effects on the photoelectron energy spectrum in time-resolved photoemission experiments with high-intensity pulsed sources., 21 pages, 5 figures, 1 table

Differences in postcollision interaction (PCI) effects on Kr L_{3}M_{4,5}M_{4,5} Auger electron spectra were observed, depending on whether the initial photoionization occurred slightly above the K threshold or slightly above the L_{3} threshold. For the former, KL fluorescence emission most likely happens and then Auger processes due to the L_{3} hole follow. The time delay due to fluorescence causes a reduced shift of the Auger peak and tailing toward lower energy, since the Auger overtaking of the photoelectron happens later in time and at a location farther away from the ionic core, compared to the case for the simple one-step L_{3}M_{4,5}M_{4,5} Auger decay after L-shell photoionization. Time-dependent theory for PCI in multistep processes agrees well with experiment, illustrating the effect as an internal clock for the time-sequence of the dynamical process.

International audience; We have recently initiated hard x-ray photoelectron spectroscopy experiments on heavy atoms and heavy-element containing molecules in gas phase by using synchrotron radiation up to 35 keV at SPring-8 undulator beamlines. We have successfully measured deep inner-shell photoelectron spectra, as well as L-MM and M-NN Auger electron spectra excited below and above the K-edge of heavy elements. Target specimens utilized for the preliminary experiments are Ar, Kr and Xe atoms, and also iodine in iodomethane (CH 3 I) and trifluoroiodomethane (CF 3 I) molecules, respectively. We show some selected results on the extracted core-hole lifetime broadenings for the iodine 1s core level of the CH 3 I molecule and also for the Xe 2s, 2p core levels, to compare with theoretical values. The L-MM Auger electron spectra of Kr recorded at 13 and 16.6 keV excitation energies are also shown as typical examples, and the spectrum measured above the K-edge, i.e. 14.327 keV, is analyzed based on theoretical calculations using the Hartree-Fock method. As a result, we give a tentative assignment for the double-core-hole hyper-satellite LL-LMM Auger transitions of the Kr atom.

Carbon 1s photoelectron angular distributions of an iodomethane molecule were measured relative to the recoil-frame determined by the momentum correlation between I+ and CH3+ at photoelectron energies of 3, 6.1, and 12 eV. The energy dependent behavior of the recoil-frame photoelectron angular distributions is reproduced reasonably well by the time-dependent density functional theory with B-spline methods. We discuss potential applications of the fully differential photoelectron angular distribution measurements in the molecular frame to three-dimensional molecular structural determinations identifying the directions and lengths of the bonds.

International audience; Hard X-ray electron spectroscopic study of iodine 1s and 2s photoionization of iodomethane (CH3I) and trifluoroiodomethane (CF3I) molecules is presented. The experiment was carried out at the SPring-8 synchrotron radiation facility in Japan. The results are analyzed with the aid of relativistic molecular and atomic calculations. It is shown that charge redistribution within the molecule is experimentally observable even for very deep levels and is a function of the number of electron vacancies. We also show that the analysis of Auger spectra subsequent to hard X-ray photoionization can be used to provide insight into charge distribution in molecules and highlight the necessity of quantum electrodynamics corrections in the prediction of core shell binding energies in molecules that contain heavy atoms.

We have applied a recently developed scanning soft x-ray spectromicroscope to characterize the buried multi-layered micro-structure by means of microprobe x-ray fluorescence (μXRF) analyses. We could successfully visualize single element maps of O and Fe contained in a buried 500-μm square test-pattern made of SiO2 and Ni81Fe19 (permalloy) beneath 30-nm thick Au coating. For their chemical-state analyses, we measured O Kα and Fe Lα x-rays emitted from the buried micro-structure using a soft x-ray microprobe to explore the x-ray absorption spectroscopy (XAS) spectra of O and Fe contained in a local area by partial fluorescence yield spectroscopy.

In this work, X-ray absorption spectroscopy (XAS) and site-selective X-ray emission spectroscopy (XES) were used to measure the oxygen K-edge (OC=O,1s and OCO−,1s) of oxalic acid, with theoretical calculations performed to reproduce the spectra observed. Structure sampling of a cluster model was performed using an ab initio molecular dynamics trajectory. Relative XES intensities from core-hole excited state dynamics simulations were calculated using density functional theory (DFT). It was found that the theoretical X-ray absorption and emission spectra well reproduced the experimental spectra and showed a resonant effect between COOH functional groups which is absent in monocarboxylic acids.

We study the electronic structure of HgBa_{2}Ca_{2}Cu_{3}O_{8+δ} (Hg1223; T_{c}=134 K) using photoemission spectroscopy (PES) and x-ray absorption spectroscopy (XAS). Resonant valence band PES across the O K edge and Cu L edge identifies correlation satellites originating in O 2p and Cu 3d two-hole final states, respectively. Analyses using the experimental O 2p and Cu 3d partial density of states show quantitatively different on-site Coulomb energy for the Cu site (U_{dd}=6.5±0.5 eV) and O site (U_{pp}=1.0±0.5 eV). Cu_{2}O_{7}-cluster calculations with nonlocal screening explain the Cu 2p core level PES and Cu L-edge XAS spectra, confirm the U_{dd} and U_{pp} values, and provide evidence for the Zhang-Rice singlet state in Hg1223. In contrast to other hole-doped cuprates and 3d-transition metal oxides, the present results indicate weakly correlated oxygen holes in Hg1223.

A photoemission electron microscope (PEEM) system has been newly installed at the soft X-ray undulator beamline (BL17SU) of SPring-8 to realize time-resolved nanospectroscopy for the local transient electronic structures of advanced materials. This PEEM is a versatile machine composed of an electrostatic lens system and is intended for use in specific experiments such as time-resolved measurements. Pump–probe measurements in tandem with a femtosecond pulsed-laser system and an X-ray chopper are now readily available.

The hydration structure of trimethylamine N-oxide (TMAO) in aqueous solutions has been investigated by means of soft X-ray spectroscopy and chemometric analysis. Soft X-ray absorption spectra in the O 1s region have a concentration-dependent shoulder at 533 eV, which is assigned to the 6a1 resonance of TMAO. Soft X-ray emission spectra acquired at this resonance comprise both TMAO and water components, with a prominent peak at 525.6 eV which is assigned to the emission caused by the 5e to O 1s transition. An apparent inverse concentration dependence of around 523 eV suggests that the electronic structure of water is modified by the strong interaction with TMAO. Such an effect has been included in the quantitative spectral analysis, called the classical least squares regression method, to obtain information on the hydration structure of the system. The analysis indicates that nine or more water molecules interact with a TMAO molecule. The present method offers a useful technique for probing the solvation structure around the solute which interacts strongly with the solvent.

Transition metal compounds often undergo spin-charge-orbital ordering due to strong electron-electron correlations. In contrast, low-dimensional materials can exhibit a Peierls transition arising from low-energy electron-phonon-coupling-induced structural instabilities. We study the electronic structure of the tunnel framework compound K2Cr8O16, which exhibits a temperature-dependent (T-dependent) paramagnetic-to-ferromagnetic- metal transition at T-C = 180 K and transforms into a ferromagnetic insulator below T-MI = 95 K. We observe clear T-dependent dynamic valence (charge) fluctuations from above T-C to T-MI, which effectively get pinned to an average nominal valence of Cr+3.75 (Cr4+:Cr3+ states in a 3:1 ratio) in the ferromagnetic-insulating phase. High-resolution laser photoemission shows a T-dependent BCS-type energy gap, with 2G(0) similar to 3.5(k(B)T(MI)) similar to 35 meV. First-principles band-structure calculations, using the experimentally estimated on-site Coulomb energy of U similar to 4 eV, establish the necessity of strong correlations and finite structural distortions for driving the metal-insulator transition. In spite of the strong correlations, the nonintegral occupancy (2.25 d-electrons/Cr) and the half-metallic ferromagnetism in the t(2g) up-spin band favor a low-energy Peierls metal-insulator transition.

We have studied the electronic structure of bulk single crystals and epitaxial films of magnetite Fe$_3$O$_4$. Fe $2p$ core-level spectra show clear differences between hard x-ray (HAX-) and soft x-ray (SX-) photoemission spectroscopy (PES), indicative of surface effects. The bulk-sensitive spectra exhibit temperature ($T$)-dependent charge excitations across the Verwey transition at $T_V$=122 K, which is missing in the surface-sensitive spectra. An extended impurity Anderson model full-multiplet analysis reveals roles of the three distinct Fe-species (A-Fe$^{3+}$, B-Fe$^{2+}$, B-Fe$^{3+}$) below $T_V$ for the Fe $2p$ spectra, and its $T-$dependent evolution. The Fe $2p$ HAXPES spectra show a clear magnetic circular dichroism (MCD) in the metallic phase of magnetized 100-nm-thick films. The model calculations also reproduce the MCD and identify the magnetically distinct sites associated with the charge excitations. Valence band HAXPES shows finite density of states at $E_F$ for the polaronic metal with remnant order above $T_V$, and a clear gap formation below $T_V$. The results indicate that the Verwey transition is driven by changes in the strongly correlated and magnetically active B-Fe$^{2+}$ and B-Fe$^{3+}$ electronic states, consistent with resistivity and bulk-sensitive optical spectra., Comment: 5 pages, 4 figures Accepted in Physical Review Letters

We have measured the relative intensities of double-spectator type resonant Auger (RA) transitions leading to the Ne + [2 p 3 ]3 p 2 final ionic states from the [1 s 2 p ]( 3 P)3 p 2 1 P doubly excited state of Ne, where square brackets indicate hole states, as a function of excitation photon energy. The intensity curve measured across the double excitation resonance, which locates at 902.45 eV, was analyzed based on the theory of radiationless resonant Raman scattering. We present, for the first time, the results which have manifested the characteristic behaviour of the Auger resonant Raman effect on the double-spectator type RA transition associated with the [1 s 2 p ]3 p 2 multiply-excited intermediate state. The resonance energy and natural width of the doubly excited state determined by the Fano profile fitting to the absorption spectrum have been validated through the measurement with constant-ionic-state scan for these double-spectator type RA decay channels.

We have investigated the lowest-energy satellite bands accompanying the F 1s mainline of SiF4 molecule using angle-resolved photoelectron spectroscopy and separated the contributions from the direct shake-up and the conjugate shake-up. The direct shake-up satellites are resonantly enhanced by the shape resonance at the same kinetic energy as that of the mainline: the anisotropy parameter β of the direct shake-up satellites drops in the vicinity of the shape resonance as for the mainline. The intensity of the conjugate shake-up satellites decreases monotonically with the increase in the photon energy: their β value also varies monotonically as a function of the energy.

The measurements combining K β resonant x-ray emission and partial fluorescence yield spectroscopy were performed for Fe metal, Fe 2 O 3 and Fe 3 O 4 near K absorption edge. Spin states of these materials are studied systematically with considering the origins of the K β' line and of the pre-edge peak. Theoretical calculations for the cluster model of Fe 2 O 3 were performed and reproduce well the experimental emission spectra. Resonant Raman scattering effect both in the absorption edge and in the pre-edge regions was observed and compared with the theory. Chemical effects between metal and its oxides were also discussed.

High-resolution resonant inelastic x-ray scattering (RIXS) and low-energy photoemission spectra of oxygen molecules have been measured for investigating the electronic structure of Rydberg states in the O 1s → σ* energy region. The electronic characteristics of each Rydberg state have been successfully observed, and new assignments are made for several states. The RIXS spectra clearly show that vibrational excitation is very sensitive to the electronic characteristics because of Rydberg-valence mixing and vibronic coupling in O2. This observation constitutes direct experimental evidence that the Rydberg-valence mixing characteristic depends on the vibrational excitation near the avoided crossing of potential surfaces. We also measured the photoemission spectra of metastable oxygen atoms (O*) from O2 excited to 1s → Rydberg states. The broadening of the 4p Rydberg states of O* has been found with isotropic behavior, implying that excited oxygen molecules undergo dissociation with a lifetime of the order of 10 fs in 1s → Rydberg states.

The absolute flux, polarization properties, and spatial dependence of the intensity of figure-8-undulator radiation were measured by a gas-scattering method. Absolute-flux measurements were in good agreement with calculated values and the angular divergence measured at 6.6 keV was also close to expected value. Polarization measurements showed oscillations of the degree of linear polarization which varied with photon energy, indicating that both horizontal and vertical polarizations were included. In addition, the polarization plane was found to rotate when the vertical observation angle was changed. These polarization characteristics are not observed in other conventional-undulator radiation and thus unique to figure-8-undulator radiation.

We performed temperature dependent x-ray linear dichroism (XLD) experiments on an iron pnictide system, $\mathrm{Ba}({\mathrm{Fe}}_{1\ensuremath{-}x}{\mathrm{Co}}_{x}{)}_{2}{\mathrm{As}}_{2}$ with $x=0.00$, 0.05, 0.08, and 0.10 to experimentally verify the existence of orbital ordering (OO). Substantial XLD was observed in polarization dependent x-ray absorption spectra of Fe $L$ edges. By exploiting the difference in the temperature dependent behaviors, OO, and structure contributions to XLD could be clearly separated. The observed OO signal indicates different occupation numbers for ${d}_{yz}$ and ${d}_{zx}$ orbitals and supports the existence of ferro-OO. The results are also consistent with the theoretical prediction. Moreover, we find substantial OO signal well above the structural and magnetic transition temperatures, which suggests the existence of strong OO fluctuations up to high temperatures.

${\mathrm{CuFeO}}_{2}$ is one of the multiferroic materials and is the first case that the electric polarization is not explained by the magnetostriction model or the spin-current model. We have studied this material using soft x-ray resonant diffraction and found that superlattice reflection 0 $1\ensuremath{-}2q$ 0 appears in the ferroelectric and incommensurate magnetic ordered phase at the Fe ${L}_{2,3}$ absorption edges and moreover that the rotation of the x-ray polarization such as from $\ensuremath{\sigma}$ to $\ensuremath{\pi}$ or from $\ensuremath{\pi}$ to $\ensuremath{\sigma}$ is allowed at this reflection. These findings definitely provide direct evidence that the $3d$ ${t}_{2g\ensuremath{\downarrow}}$ orbital state of Fe ions has a long-range order in the ferroelectric state. The spin-orbit interaction in Fe ions plays a crucial role to the ferroelectricity in ${\mathrm{CuFeO}}_{2}$, coupling two nontrivial spin and orbital orders, both of which break the crystal symmetry.

We use hard x-ray photoemission spectroscopy (HAXPES) to investigate the electronic structure of YbAl 2 , for which the Yb valence has not been consistently reported to date. The bulk sensitivity and the analytical simplicity provided by the Yb 3 d core-level HAXPES allow a reliable determination of the mean valence of Yb ions. For YbAl 2 , it is evaluated to be +2.20, which remains nearly unchanged below 300 K. The Kondo resonance peak with an extremely high Kondo temperature (above 2000 K) is clearly identified in the valence-band spectra. The results indicate that a coherent Kondo state can be robust even in a nearly divalent system.

We study the surface and bulk electronic structure of the room-temperature ferromagnet $\mathrm{Co}\ensuremath{\mathbin:}{\mathrm{TiO}}_{2}$ anatase films using soft- and hard-x-ray photoemission spectroscopy with probe sensitivities of $\ensuremath{\sim}1$ and $\ensuremath{\sim}10\text{ }\text{ }\mathrm{nm}$, respectively. We obtain direct evidence of metallic ${\mathrm{Ti}}^{3+}$ states in the bulk, which get suppressed to give a surface semiconductor, thus indicating the difference in electronic structure between surface and bulk. X-ray absorption and resonant photoemission spectroscopy reveal ${\mathrm{Ti}}^{3+}$ electrons at the Fermi level (${E}_{F}$) and high-spin ${\mathrm{Co}}^{2+}$ electrons occurring away from ${E}_{F}$. The results show the importance of the charge neutrality condition: ${\mathrm{Co}}^{2+}+V_{\mathrm{O}}{}^{2\ensuremath{-}}+2{\mathrm{Ti}}^{4+}\ensuremath{\leftrightarrow}{\mathrm{Co}}^{2+}+2{\mathrm{Ti}}^{3+}$ (${V}_{\mathrm{O}}$ is oxygen vacancy), which gives rise to the elusive Ti $3d$ carriers mediating ferromagnetism via the Co $3d--\mathrm{O}$ $2p--\mathrm{Ti}$ $3d$ exchange interaction pathway of the occupied orbitals.

High-resolution soft X-ray photoelectron spectra of liquid water (H(2)O and D(2)O) were measured using a liquid beam photoelectron spectrometer. The 1a(1) (O1s) band and the lowest valence 1b(1) band had single peaks, which is not consistent with the split 1b(1)→ 1a(1) of the X-ray emission band of liquid water if the splitting is assumed to originate from level shifts in two different hydrogen bonding structures. The second valence 3a(1) band of liquid water exhibited a flat top implying that two bands exist underneath a broad feature, which is similar to the case of the 3a(1) band of amorphous ice. The energy splitting between the two 3a(1) bands is estimated to be 1.38 eV (H(2)O) and 1.39 eV (D(2)O). Ab initio calculations suggest that the large splitting of the 3a(1) band is characteristic of water molecules that function as both proton donor and acceptor. The overall result is consistent with the conventional model of a tetrahedral hydrogen-bonding network in liquid water.

We investigate the electronic structure of Chromium Nitride (CrN) across the first-order magneto-structural transition at T_N ~ 286 K. Resonant photoemission spectroscopy shows a gap in the 3d partial density of states at the Fermi level and an On-site Coulomb energy U ~ 4.5 eV, indicating strong electron-electron correlations. Bulk-sensitive high resolution (6 meV) laser photoemission reveals a clear Fermi edge indicating an antiferromagnetic metal below T_N. Hard x-ray Cr 2p core-level spectra show T-dependent changes across T_N which originate from screening due to coherent states as substantiated by cluster model calculations using the experimentally observed U. The electrical resistivity confirms an insulator above T_N (E_g ~ 70 meV) which becomes a disordered metal below T_N. The results indicate CrN transforms from a correlated insulator to an antiferromagnetic metal, coupled to the magneto-structural transition., Submitted to Physical Review Letters (February 2010) 11 pages, 3 figures in the main text, 1 Supplementary Information

Epitaxial ultrathin Fe films on fcc Cu(001) exhibit a spin spiral (SS), in contrast to the ferromagnetism of bulk bcc Fe. We study the in-plane (IP) and out-of-plane (OP) Fermi surfaces (FSs) of the SS in 8 monolayer Fe/Cu(001) films using energy-dependent soft-x-ray momentum-resolved photoemission spectroscopy. We show that the SS originates in nested regions confined to OP FSs, which are drastically modified compared to IP FSs. From precise reciprocal-space maps in successive zones, we obtain the associated real space compressive strain of 1.5+/-0.5% along c axis. An autocorrelation analysis quantifies the incommensurate ordering vector q=(2pi/a)(0,0, approximately 0.86), favoring a SS and consistent with magneto-optic Kerr effect experiments. The results reveal the importance of IP and OP FS mapping for ultrathin films.

Enantiomers, or stereoisomers, have crystal structures that are mirror images of each other and are thus handed, like our right and left hands. The physical properties of enantiomers are identical except for optical activity, which rotates linearly polarized light by equal amounts but in opposite directions. While conventional x-ray Bragg diffraction can determine crystal structures, it does not distinguish between right- and left-handed crystals. We show resonant Bragg diffraction using circularly polarized x rays reveals the handedness of crystals by coupling x-ray helicity to a crystal screw axis. The intensity of resonantly allowed reflection of alpha-quartz is well described by an admixture of a parity-even and a parity-odd process. Our results are of general importance and demonstrate a new method to directly study chiral motifs in structures that include biomaterials, liquid crystals, magnets, multiferroics, etc.

High energy resolution photoelectron spectroscopy of conduction electrons in the vicinity of the Fermi-edge in Al and Au at the excitation energy of 880 and 7940 eV was carried out using synchrotron radiation. For the excitation energy of 7940 eV, the observed Fermi energy of Al shows a remarkable shift to higher binding energy as compared with that of Au, with accompanying broadening. This is due to the recoil effect of the emitted photoelectrons. The observed spectra are well reproduced by a simple model of Bloch electrons based on the isotropic Debye model., Comment: 5 pages, 2 figures

Interatomic Coulombic decay (ICD) from an Auger-final dicationic state is observed in the Ar dimer. A $2p$ inner-shell vacancy created by photoionization is replaced with $3s$ and $3p$ vacancies via intra-atomic Auger decay. The Auger-final dicationic state is subject to ICD in which one of the $3p$ electrons in the same Ar atom fills the $3s$ vacancy while one of the $3p$ electrons from the neighboring Ar atom is emitted as an ICD electron. This ICD process is unambiguously identified by electron-ion-ion coincidence spectroscopy in which the kinetic energy of the ICD electron and the kinetic energy release between ${\mathrm{Ar}}^{+}$ and ${\mathrm{Ar}}^{2+}$ are measured in coincidence.

We present a precise measurement of the photoexcited F K alpha satellite intensity's evolution for NaF from [1s2p] double excitation threshold to saturation. A direct comparison between the observed evolution and the x-ray absorption spectrum was successfully made, and the contribution of multielectron transitions to the absorption spectrum was clearly resolved for the first time. A resonance-like feature observed in the near-threshold evolution is attributed to the [1s2p]3p(2) resonant double excitation as confirmed by calculations.

Time-resolved hard x-ray photoelectron spectroscopy (trHAXPES) is established using the x-ray free-electron laser SACLA. The technique extends time-resolved photoemission into the hard x-ray regime and, as a core-level spectroscopy, combines element and atomic-site specificity and sensitivity to the chemical environment with femtosecond time resolution and bulk (sub-surface) sensitivity. The viability of trHAXPES using 8 keV x-ray free-electron-laser radiation is demonstrated by a systematic investigation of probe and pump pulse-induced vacuum space-charge effects on the V 1s emission of VO2 and the Ti 1s emission of SrTiO3. The time and excitation energy dependencies of the measured spectral shifts and broadenings are compared to the results of N-body numerical simulations and simple analytic (mean-field) models. Good agreement between the experimental and calculated results is obtained. In particular, the characteristic temporal evolution of the pump pulse-induced spectral shift is shown to provide an effective means to determine the temporal overlap of pump and probe pulses. trHAXPES opens a new avenue in the study of ultrafast atomic-site specific electron and chemical dynamics in materials and at buried interfaces.

The streaming potentials of liquid beams of aqueous NaCl, NaBr, and NaI solutions are measured using soft X-ray, He(I), and laser multiphoton ionization photoelectron spectroscopy. Gaseous molecules are ionized in the vicinity of liquid beams and the photoelectron energy shifts are measured as a function of the distance between the ionization point and the liquid beam. The streaming potentials change their polarity with concentration of electrolytes, from which the singular points of concentration eliminating the streaming potentials are determined. The streaming currents measured in air also vanish at these concentrations. The electron binding energies of liquid water and I(-), Br(-), and Cl(-) anions are revisited and determined more accurately than in previous studies.

Amorphous carbon nanorods were synthesized from hollow multiwalled carbon nanotubes (MWCNTs) by low-energy Ar ion irradiation at room temperature. The obtained nanorods were investigated by Raman spectroscopy, transmission electron microscopy (TEM), soft X-ray photoelectron spectroscopy (XPS), and soft X-ray absorption spectroscopy (XAS). It was found that the diameter of the MWCNTs significantly increased with increasing the fluence. Finally, the original hollow structure and the graphite (002) TEM diffraction spots of MWCNTs completely disappeared and a broadening of Raman spectra occurred, indicating the amorphization of MWCNTs. The increase in the diameter by the irradiation can be explained by the bending and the randomization of the broken carbon hexagonal networks, and the accumulation of knocked-on atoms. The XPS and XAS measurements also support the formation of amorphous carbon nanorods.

Controlling defect structure in multiwalled carbon nanotube (MWCNT) is essential to realization of MWCNT devices. Here, we show that the diagram of the Raman intensity ratio of the G to D peaks and the G peak width can reveal two damaging stages of MWCNT films. In a transition period, additional peaks appeared in the X-ray absorption spectra, thereby indicating some significant change in the electronic structure. Also, a remarkable increase occurred in the diameter of the MWCNTs in the latter stage, suggesting the formation of dislocation dipoles which may relate to the change in the properties of field-emission devices.

We report on the soft X-ray photoemission and absorption spectroscopy of Ag 2 NiO 2 and Ag 2 MnO 2 , which consist of alternate stacks of (Ag 2 ) + and ( M O 2 ) - layers. The core-level photoemission and absorption spectra indicate mainly trivalent Ni 3+ in Ag 2 NiO 2 , and trivalent Mn 3+ with an admixture of Mn 2+ states in Ag 2 MnO 2 . The M 2 p –3 d resonant photoemission clearly shows that the density of states at the Fermi level includes the M 3 d character in both compounds. The results indicate that the Ni 3 d and Mn 3 d states at the Fermi level are responsible for the significant mass enhancement of carriers, as seen in the transport properties of Ag 2 NiO 2 and Ag 2 MnO 2 .

Spin domains in bulk NiO have been observed by photoemission electron microscopy combined with X-ray magnetic linear dichroism (XMLD) using s - and p -polarized light. The azimuthal angle dependence of domain contrast at Ni L 2 -edge XMLD has been analyzed with a NiO 6 cluster model taking into account crystal symmetry and multiplet splitting. The complete assignment of spin domains has been achieved. The results evoke the reconsideration of the domain assignment and XMLD studies based on the existing atomic multiplet theory.

Inner-shell ionization of an isolated atom typically leads to Auger decay. In an environment, for example, a liquid or a van der Waals bonded system, this process will be modified, and becomes part of a complex cascade of relaxation steps. Understanding these steps is important, as they determine the production of slow electrons and singly charged radicals, the most abundant products in radiation chemistry. In this communication, we present experimental evidence for a so-far unobserved, but potentially very important step in such relaxation cascades: Multiply charged ionic states after Auger decay may partially be neutralized by electron transfer, simultaneously evoking the creation of a low-energy free electron (electron transfer-mediated decay). This process is effective even after Auger decay into the dicationic ground state. In our experiment, we observe the decay of Ne[2+] produced after Ne 1s photoionization in Ne–Kr mixed clusters., 安定なイオンが周囲の原子の電子をキャッチ＆リリース！ --X線照射による生体分子損傷の機構解明に貢献--. 京都大学プレスリリース. 2017-02-01.