Search

The CeB6(001) single crystal used as a cathode in a low-emittance electron gun and operated at the free-electron laser facility SACLA was investigated using cathode lens electron microscopy combined with X-ray spectroscopy at SPring-8 synchrotron radiation facility. Multilateral analysis using thermionic emission electron microscopy, low-energy electron microscopy, ultraviolet and X-ray photoemission electron microscopy and hard X-ray photoemission spectroscopy revealed that the thermionic electrons are emitted strongly and evenly from the CeB6 surface after pre-activation treatment (annealing at 1500°C for >1 h) and that the thermionic emission intensity as well as elemental composition vary between the central area and the edge of the old CeB6 surface.

A wide-acceptance-angle spherical grid composed of numerous micro cylindrical holes was developed to be used for the retarding grid of a display-type retarding field analyzer (RFA) and to enhance the energy resolution (E/ΔE). Each cylindrical hole with a diameter of 50 µm and a depth of 80 µm is directed to the spherical center. The inner radius of the spherical grid is 40 mm. The holed area corresponds to an acceptance angle of ±52°. The E/ΔE of an RFA equipped with the developed holed grid was estimated to be 2000 from a measured Au 4f photoemission spectrum. A clear photoelectron hologram was observed in the Mo 4p core-level region of MoS2, indicating that the RFA with the holed grid is effective for photoelectron holography.

The CeB

Diamond has two crystallographically inequivalent sites in the unit cell. In doped diamond, dopant occupation in the two sites is expected to be equal. Nevertheless, preferential dopant occupation during growth under nonequilibrium conditions is of fundamental importance, for example, to enhance the properties of nitrogen-vacancy (N-V) centers; therefore, this is a promising candidate for a qubit. However, the lack of suitable experimental techniques has made it difficult to study the crystal- and chemical-site-resolved local structures of dopants. Here, we confirm the identity of two chemical sites with asymmetric dopant incorporation in the diamond structure, via the photoelectron holography (PEH) of heavily phosphorus (P)-doped diamond prepared by chemical vapor deposition. One is substitutionally incorporated P with preferential site occupations and the other can be attributed to a PV split vacancy complex with preferential orientation. The present study shows that PEH is a valuable technique to study the local structures around dopants with a resolution of crystallographically inequivalent but energetically equivalent sites/orientations. Such information provides strategies to improve the properties of dopant related-complexes in which alignment is crucial for sensing of magnetic field or quantum spin register using N-V centers in diamond.

An endstation dedicated to angle-resolved photoemission spectroscopy (ARPES) using a soft X-ray microbeam has been developed at the beamline BL25SU of SPring-8. To obtain a high photoemission intensity, this endstation is optimized for measurements under the condition of grazing beam incidence to a sample surface, where the glancing angle is 5° or smaller. A Wolter mirror is used for focusing the soft X-rays. Even at the glancing angle of 5°, the smallest beam spot still having a sufficient photon flux for ARPES is almost round on the sample surface and the FWHM diameter is ∼5 µm. There is no need to change the sample orientation for performing k x − k y mapping by virtue of the electron lens with a deflector of the photoelectron analyzer, which makes it possible to keep the irradiation area unchanged. A partially cleaved surface area as small as ∼20 µm was made on an Si(111) wafer and ARPES measurements were performed. The results are presented.

We investigate near-Fermi-energy (${E}_{F}$) element-specific electronic and spin states of ferromagnetic van der Waals (vdW) metal ${\mathrm{Fe}}_{5}\mathrm{Ge}{\mathrm{Te}}_{2}$. The soft x-ray angle-resolved photoemission spectroscopy (SX-ARPES) measurement provides spectroscopic evidence of localized Fe $3d$ band. We also find prominent hybridization between the localized Fe $3d$ band and the delocalized Ge/Te $p$ bands. This picture is strongly supported from direct observation of the remarkable spin polarization of the ligand $p$ bands near ${E}_{F}$, using x-ray magnetic circular dichroism (XMCD) measurements. The strength of XMCD signal from ligand element Te shows the highest value, as far as we recognize, among literature reporting finite XMCD signal for nonmagnetic element in any systems. Combining SX-ARPES and elemental selective XMCD measurements, we collectively point to an important role of giant spin polarization of the delocalized ligand Te states for realizing itinerant long-range ferromagnetism in ${\mathrm{Fe}}_{5}\mathrm{Ge}{\mathrm{Te}}_{2}$. Our finding provides a fundamental elemental selective viewpoint for understanding mechanism of itinerant ferromagnetism in low-dimensional compounds, which also leads to insight for designing exotic magnetic states by interfacial band engineering in heterostructures.

Insulator-to-metal transition in Ca$_{2}$RuO$_{4}$ has drawn keen attention because of its sensitivity to various stimulation and its potential controllability. Here, we report a direct observation of Fermi surface, which emerges upon introducing excess oxygen into an insulating Ca$_{2}$RuO$_{4}$, by using angle-resolved photoemission spectroscopy. Comparison between energy distribution curves shows that the Mott insulating gap is closed by eV-scale spectral-weight transfer with excess oxygen. Momentum-space mapping exhibits two square-shaped sheets of the Fermi surface. One is a hole-like $\alpha$ sheet around the corner of a tetragonal Brillouin zone, and the other is an electron-like $\beta$ sheet around the $\Gamma$ point. The electron occupancies of the $\alpha$ and $\beta$ bands are determined to be $n_{\alpha}=1.6$ and $n_{\beta}=0.6$, respectively. Our result indicates that the insulator-to-metal transition occurs selectively in $d_{xz}$ and $d_{yz}$ bands and not yet in $d_{xy}$ band. This orbital selectivity is most likely explained in terms of the energy level of $d_{xy}$, which is deeper for Ca$_{2}$RuO$_{4+\delta}$ than for Ca$_{1.8}$Sr$_{0.2}$RuO$_{4}$. Consequently, we found substantial differences from the Fermi surface of other ruthenates, shedding light on a unique role of excess oxygen among the metallization methods of Ca$_{2}$RuO$_{4}$., Comment: 9 pages, 6 figures

Using a well-focused soft X-ray synchrotron radiation beam, angle-resolved photoelectron spectroscopy was applied to a full-Heusler-type Co$_2$MnGe alloy to elucidate its bulk band structure. A large parabolic band at the Brillouin zone center and several bands that cross the Fermi level near the Brillouin zone boundary were identified in line with the results from first-principles calculations. These Fermi level crossings are ascribed to majority spin bands that are responsible for electron transport with extremely high spin polarization especially along the direction being perpendicular to the interface of magneto-resistive devices. The spectroscopy confirms there is no contribution of the minority spin bands to the Fermi surface, signifying half-metallicity for the alloy. Furthermore, two topological Weyl cones with band crossing points were identified around the $X$ point, yielding the conclusion that Co$_2$MnGe could exhibit topologically meaningful behavior such as large anomalous Hall and Nernst effects driven by the Berry flux in its half-metallic band structure., 6 pages, 4 figures; Supplementary Information: 5 pages, 3 figures

A large anomalous Hall effect (AHE) has been observed in ferromagnetic ${\mathrm{Fe}}_{3}{\mathrm{Sn}}_{2}$ with breathing kagome bilayers. To understand the underlying mechanism for this, we investigate the electronic structure of ${\mathrm{Fe}}_{3}{\mathrm{Sn}}_{2}$ by angle-resolved photoemission spectroscopy (ARPES). In particular, we use both vacuum ultraviolet light (VUV) and soft x ray (SX), which allow surface-sensitive and relatively bulk-sensitive measurements, respectively, and distinguish bulk states from surface states, which should be unlikely related to the AHE. While VUV-ARPES observes two-dimensional bands mostly due to surface states, SX-ARPES reveals three-dimensional band dispersions with a periodicity of the rhombohedral unit cell in the bulk. Our data show a good consistency with a theoretical calculation based on density functional theory, suggesting a possibility that ${\mathrm{Fe}}_{3}{\mathrm{Sn}}_{2}$ is a magnetic Weyl semimetal.

Unconventional features of relativistic Dirac/Weyl quasi-particles in topological materials are most evidently manifested in the 2D quantum Hall effect (QHE), whose variety is further enriched by their spin and/or valley polarization. Although its extension to three dimensions has been long-sought and inspired theoretical proposals, material candidates have been lacking. Here we have discovered valley-contrasting spin-polarized Dirac fermions in a multilayer form in bulk antiferromagnet BaMnSb$_2$, where the out-of-plane Zeeman-type spin splitting is induced by the in-plane inversion symmetry breaking and spin-orbit coupling (SOC) in the distorted Sb square net. Furthermore, we have observed well-defined quantized Hall plateaus together with vanishing interlayer conductivity at low temperatures as a hallmark of the half-integer QHE in a bulk form. The Hall conductance of each layer is found to be nearly quantized to $2(N+1/2)e^2/h$ with $N$ being the Landau index, which is consistent with two spin-polarized Dirac valleys protected by the strong spin-valley coupling., 14 pages, 4 figures. Accepted in Phys. Rev. B (Rapid Communication)

Spectro-photoelectron holography method combined with first-principles simulations determined the local three-dimensional atomic structures of arsenic (As) atoms doped into a silicon (Si) crystal. As 3d core level photoelectron spectroscopy demonstrated the presence of three types of As atoms, denoted as BEH, BEM, and BEL. The As atoms of BEH corresponded to electrically active As occupying substitutional sites, while those of BEM corresponded to electrically inactive As embedded in the As n V (n = 2–4) type clusters, and those of BEL were assigned to electrically inactive As in locally disordered structures.

The atomic scale characterization of dopant atoms in semiconductor devices to establish correlations with the electrical activation of these atoms is essential to the advancement of contemporary semiconductor process technology. Spectro-photoelectron holography combined with first-principles simulations can determine the local three-dimensional atomic structures of dopant elements, which in turn affect their electronic states. In the work reported herein, this technique was used to examine arsenic (As) atoms doped into a silicon (Si) crystal. As 3d core level photoelectron spectroscopy demonstrated the presence of three types of As atoms at a total concentration of approximately 1020 cm–3, denoted as BEH, BEM, and BEL. On the basis of Hall effect measurements, the BEH atoms corresponded to electrically active As occupying substitutional sites and exhibiting larger thermal fluctuations than the Si atoms, while the BEM atoms corresponded to electrically inactive As embedded in the AsnV (n = 2–4) type cluste...

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 YbB 12 and tetragonal SmCu 2 Si 2 . 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.

Recent discovery of both gapped and gapless topological phases in weakly correlated electron systems has introduced various relativistic particles and a number of exotic phenomena in condensed matter physics. The Weyl fermion is a prominent example of three dimensional (3D), gapless topological excitation, which has been experimentally identified in inversion symmetry breaking semimetals. However, their realization in spontaneously time reversal symmetry (TRS) breaking magnetically ordered states of correlated materials has so far remained hypothetical. Here, we report a set of experimental evidence for elusive magnetic Weyl fermions in Mn$_3$Sn, a non-collinear antiferromagnet that exhibits a large anomalous Hall effect even at room temperature. Detailed comparison between our angle resolved photoemission spectroscopy (ARPES) measurements and density functional theory (DFT) calculations reveals significant bandwidth renormalization and damping effects due to the strong correlation among Mn 3$d$ electrons. Moreover, our transport measurements have unveiled strong evidence for the chiral anomaly of Weyl fermions, namely, the emergence of positive magnetoconductance only in the presence of parallel electric and magnetic fields. The magnetic Weyl fermions of Mn$_3$Sn have a significant technological potential, since a weak field ($\sim$ 10 mT) is adequate for controlling the distribution of Weyl points and the large fictitious field ($\sim$ a few 100 T) in the momentum space. Our discovery thus lays the foundation for a new field of science and technology involving the magnetic Weyl excitations of strongly correlated electron systems., 43 pages, 12 figures

Mixed-anion perovskites such as oxynitrides, oxyfluorides, and oxyhydrides have flexibility in their anion arrangements, which potentially enables functional material design based on coordination chemistry. However, difficulty in the control of the anion arrangement has prevented the realization of this concept. In this study, we demonstrate strain engineering of the anion arrangement in epitaxial thin films of the Ca1–xSrxTaO2N perovskite oxynitrides. Under compressive epitaxial strain, the axial sites in TaO4N2 octahedra tend to be occupied by nitrogen rather than oxygen, which was revealed by N and O K-edge linearly polarized X-ray absorption near-edge structure (LP-XANES) and scanning transmission electron microscopy combined with electron energy loss spectroscopy. Furthermore, detailed analysis of the LP-XANES indicated that the high occupancy of nitrogen at the axial sites is due to the partial formation of a metastable trans-type anion configuration. These results are expected to serve as a guide f...

Resonant photoelectron spectroscopy at the Co and Mn $2p$ core absorption edges of half-metallic ${\mathrm{Co}}_{2}\mathrm{MnGe}$ has been performed to determine the element-specific density of states (DOS). A significant contribution of the Mn $3d$ partial DOS near the Fermi level $({E}_{\mathrm{F}})$ was clarified by measurement at the Mn $2p$ absorption edge. Further analysis by first-principles calculation revealed that it has ${t}_{2\mathrm{g}}$ symmetry, which must be responsible for the electrical conductivity along the line perpendicular to the film plane. The dominant normal Auger contribution observed at the Co $2p$ absorption edge indicates delocalization of photoexcited Co $3d$ electrons. The difference in the degrees of localization of the Mn $3d$ and Co $3d$ electrons in ${\mathrm{Co}}_{2}\mathrm{MnGe}$ is explained by the first-principles calculation. Our findings of the element-/orbital-specific electronic states near ${E}_{\mathrm{F}}$ will pave the way for future interface design of magnetic tunneling junctions to overcome the temperature-induced reduction of the magnetoresistance.

Doping is an important technology for modern science. For example, to create a semiconductor device, a circuit is formed by controlling carriers by doping. It is important to search for appropriate conditions since the carrier emission from dopant differs depending on the doping conditions. The atomic arrangement around the dopant differs depending on the conditions. Therefore, it has been desired to observe the atomic arrangement around the dopant, but it has been difficult with conventional measurement methods. The atomic resolution holography such as photoelectron holography, x-ray fluorescence holography, neutron holography, which are methods that can measure the three-dimensional (3D) atomic arrangement of the dopant. Among them, photoelectron holography can measure the atomic structure of each dopant depending on the chemical state. We have built photoelectron holography apparatuses at BL25SU in SPring-8. We also developed a software platform 3D-AIR-IMAGE for data processing, simulation of photoelectron holograms, and 3D atomic image reconstruction.

A large anomalous Hall effect (AHE) has been observed in ferromagnetic Fe3Sn2 with breathing kagome bilayers. To understand the underlying mechanism for this, we investigate the electronic structure of Fe3Sn2 by angle-resolved photoemission spectroscopy (ARPES). In particular, we use both vacuum ultraviolet light (VUV) and soft x ray (SX), which allow surface-sensitive and relatively bulk-sensitive measurements, respectively, and distinguish bulk states from surface states, which should be unlikely related to the AHE. While VUV-ARPES observes two-dimensional bands mostly due to surface states, SX-ARPES reveals three-dimensional band dispersions with a periodicity of the rhombohedral unit cell in the bulk. Our data show a good consistency with a theoretical calculation based on density functional theory, suggesting a possibility that Fe3Sn2 is a magnetic Weyl semimetal.

We use bulk-sensitive soft X-ray angle-resolved photoemission spectroscopy and investigate bulk electronic structures of Ce monopnictides (CeX; X=P, As, Sb and Bi). By exploiting a paradigmatic study of the band structures as a function of their spin-orbit coupling (SOC), we draw the topological phase diagram of CeX and unambiguously reveal the topological phase transition from a trivial to a nontrivial regime in going from CeP to CeBi induced by the band inversion. The underlying mechanism of the topological phase transition is elucidated in terms of SOC in concert with their semimetallic band structures. Our comprehensive observations provide a new insight into the band topology hidden in the bulk of solid states., Comment: 5 pages, 4 figures

Soft X-ray micro-ARPES measurements have successfully been applied to band mapping of the strongly correlated metallic V2O3., Soft X-ray angle-resolved photoemission has been performed for metallic V2O3. By combining a microfocus beam (40 µm × 65 µm) and micro-positioning techniques with a long-working-distance microscope, it has been possible to observe band dispersions from tiny cleavage surfaces with a typical size of several tens of µm. The photoemission spectra show a clear position dependence, reflecting the morphology of the cleaved sample surface. By selecting high-quality flat regions on the sample surface, it has been possible to perform band mapping using both photon-energy and polar-angle dependences, opening the door to three-dimensional angle-resolved photoemission spectroscopy for typical three-dimensional correlated materials where large cleavage planes are rarely obtained.

The proverbial ``canary in a coal mine'' is truly a thing of the past; nowadays zinc oxide is a key material in solid-state gas sensors, yet the mechanism by which doping can improve its performance is not fully understood. The authors use two-dimensional photoelectron diffraction to study thin films of tungsten-doped ZnO, and find clear evidence for substitution of segregated W atoms into Zn sites in the subsurface layer, which drastically improves the sensing response. This insight into the surface's structure-function relationship suggests how best to prepare these films for this important application.

The mechanism of dense vertically aligned carbon nanotube growth achieved by a recently developed thermal chemical vapor deposition method was studied using synchrotron radiation spectroscopic techniques., The mechanism of the one-order-of-magnitude increase in the density of vertically aligned carbon nanotubes (CNTs) achieved by a recently developed thermal chemical vapor deposition process was studied using synchrotron radiation spectroscopic techniques. In the developed process, a Ti film is used as the underlayer for an Fe catalyst film. A characteristic point of this process is that C2H2 feeding for the catalyst starts at a low temperature of 450°C, whereas conventional feeding temperatures are ∼800°C. Photoemission spectroscopy using soft and hard X-rays revealed that the Ti underlayer reduced the initially oxidized Fe layer at 450°C. A photoemission intensity analysis also suggested that the oxidized Ti layer at 450°C behaved as a support for nanoparticle formation of the reduced Fe, which is required for dense CNT growth. In fact, a CNT growth experiment, where the catalyst chemical state was monitored in situ by X-ray absorption spectroscopy, showed that the reduced Fe yielded a CNT forest at 450°C. Contrarily, an Fe layer without the Ti underlayer did not yield such a CNT forest at 450°C. Photoemission electron microscopy showed that catalyst annealing at the conventional feeding temperature of 800°C caused excess catalyst agglomeration, which should lead to sparse CNTs. In conclusion, in the developed growth process, the low-temperature catalyst activation by the Ti underlayer before the excess Fe agglomeration realised the CNT densification.

The observation of one-dimensional N2 inside single-walled carbon nanotubes raises the questions, how are the N2 molecules formed and how do they manage to make their way to this peculiar place? We have used N15 and C13 isotope labeled acetonitrile during the synthesis of single-walled carbon nanotubes to investigate this process. The isotope shifts of phonons and vibrons are observed by Raman spectroscopy and X-ray absorption. We identify the catalytic decomposition of acetonitrile as the initial step in the reaction pathway to single-walled carbon nanotubes containing encapsulated N2.

The angular distributions of photoelectrons and Auger electrons from single crystal surfaces show characteristic diffraction patterns, which contain information on the local atomic structures surrounding the emitter atoms. Using computational reconstruction processes on the diffraction patterns enables us to determine the local atomic structures of, for example, dopants, catalytic active sites, and surface/interface structures. This method has become known as "photoelectron holography (PEH)". Several advanced photoelectron analyzers for PEH are now available at beamlines at SPring-8, the world's largest synchrotron radiation facility. Recently, the use of micron-sized photon beams, as well as pump-and-probe time-resolved techniques has become possible with relatively high energy resolution. Here, the experimental apparatus and some representative applications are introduced.

Carbon-based materials, such as carbon nanotubes and graphene nanoribbons, have been studied as interconnect materials because of their lower resistivity, higher thermal conductivity, and intrinsically higher current carrying capacity compared to Cu. We have succeeded in growing networked-nanographite (NNG) films on dielectric layers without any metal catalysts, and fabricated NNG wires as the first step toward multi-layer graphene interconnects. In this study, we investigated the electrical properties and reliability, such as current tolerance and thermal stability, of these NNG wires. In addition, we investigated the mechanism of resistivity decreases in NNG. Our results show that the NNG wires can sustain a higher current density than Cu wires. However, their resistivity gradually decreases due to thermal stress. Raman and X-ray photoelectron spectroscopy revealed that the decrease in resistivity can be attributed to an increase in sp2 bonding corresponding to the formation of a graphene sheet. It is important to clarify the mechanism of the decrease in resistivity, not only to improve thermal stability but also to obtain lower resistivity in carbon interconnects.

We have studied the orientational order in films of vertically aligned single walled carbon nanotubes, by means of resonant Raman spectroscopy, resonant X-ray absorption, and direct imaging. These methods investigate the hierarchical morphology at different length scales. Here, we discuss the systematic comparison of orientational order as function of wavelength in films with different inherent morphologies and provide thus a basis to quantitatively evaluate and compare the different experimental approaches.

The unexpected presence of a linear arrangement of co-axially oriented N2 molecules inside aligned single-walled carbon nanotubes is revealed by high resolution near-edge X-ray absorption spectroscopy. The encapsulated N2 molecules exhibit free stretching vibrations with a long electronic lifetime of the X-ray-excited anti-bonding π∗ states. Molecular dynamics simulations confirm that narrow-diameter nanotubes (d

Using the high-brilliance synchrotron radiation at super photon ring 8 (SPring-8) we determined the electron escape depths in approximately 1-nm-thick low-temperature oxide layers, which were formed on Si(1 1 1) at 300 ◦ C using three kinds of atomic oxygen, and that in approximately 1-nm-thick thermally grown oxide layer formed in 1 Torr dry oxygen at 900 ◦ C by measuring Si 2p photoelectron spectra at the photon energy of 1050 eV. The results indicated that the electron escape depths in the three kinds of low-temperature oxide layers were 13–21% smaller than that in the thermally grown oxide layer. Furthermore, the electron escape depth in the thermally grown oxide layer, whose thickness was close to that of the structural transition layer, was 19% smaller than that in bulk SiO 2. © 2005 Elsevier B.V. All rights reserved.

The angle-resolved Si 2p photoelectron spectra arising from the transition layers formed on both sides of the SiO2/Si(100) interface covered with more than one SiO2 monolayer, which is device grade, were measured with the probing depth of nearly 2 nm. The novel analytical procedure of these spectra is developed by considering that one SiO2 monolayer, two compositional transition layers (CTLs), and one Si monolayer on Si substrate surface are continuously connected with each other. It was found for the interface formed in dry O2 at 900 {degree sign}C that two CTLs constitute the first and second CTLs. The first CTL formed at the interface consists mainly of Si1+, Si2+, and Si0 and the second CTL formed on the first CTL consists mainly of Si3+ and Si4+. Influences of oxidation temperature, annealing in forming gas on the chemical structures of transition layers formed on both sides of the interface are also discussed.

High resolution photoelectron spectroscopy is utilized to investigate degradation of rubber-to-brass adhesion by thermal aging. Special attention is given to the role of water in the environment surrounding brass-embedded rubber so that three aging processes are employed; hydrothermal aging, moist-heat aging and dry-heat aging. All aging processes lead to the decrease in the amount of S at the rubber/brass interface. This desulfurization accompanies the decrease in the ratio of CuxS (x ≃ 2) to CuS, i.e., CuxS/CuS, and the increase in the amount of ZnO, Zn(OH)2 and ZnS, all of which are key factors for degradation of adhesion. The changes in the chemical composition are enhanced by water in the surrounding environment during the aging treatments, indicating that the water molecules accelerate degradation of rubber-to-brass adhesion.

We have examined the local 3d electronic structures of Co-Au multinuclear complexes with the medicinal molecules D-penicillaminate (D-pen) [Co{Au(PPh3)(D-pen)}2]ClO4 and [Co3{Au3(tdme)(D-pen)3}2] by Co L_2,3-edge soft X-ray absorption (XAS) spectroscopy, where PPh3 denotes triphenylphosphine and tdme stands for 1,1,1-tris[(diphenylphosphino)methyl]ethane. The Co L_2,3-edge XAS spectra indicate the localized ionic 3d electronic states in both materials. The experimental spectra are well explained by spectral simulation for a localized Co ion under ligand fields with the full multiplet theory, which verifies that the ions are in the low-spin Co3+ state in the former compound and in the high-spin Co2+ state in the latter., Comment: 7 pages, 5 figures. To be published in J. Phys. Soc. Jpn

Substantial upgrades have been made to the beamline BL25SU at SPring-8 for soft X-ray imaging and spectroscopy of solid-state materials. The upgraded beamline consists of two branches: a micro-beam branch with high energy resolution, and a nano-beam branch with small angular divergence. The beamline has been available for use since October 2014, following a half year commissioning period. We present here the beamline performance parameters, including resolving power, photon flux, and focused beam size, which are consistent with designed specifications.

The present status and the recent progress of pump-probe time-resolved photoemission electron microscopy at SPring-8 are introduced. Combining the variety of bunch operation modes available at the SPring-8 storage ring with ultra-short excitation sources including pulsed magnetic fields, electric fields and lasers, the element-specific time evolution of materials in response to the excitation can be observed with spatial and temporal resolutions of (50–300) nm and (40–100) ps, respectively, with repetition frequencies of up to 42 MHz. By using the magnetic circular dichroism effect, the domain motion of sub-micron sized magnetic areas can be observed. The time evolution of electronic structures in local areas can also be studied. The experimental setups and representative activities are described.

Soft-x-ray-excited angle-resolved photoelectron spectroscopy studies on silicon dioxide films formed utilizing oxygen radicals (ORs) and oxygen molecules (OMs) with or without forming gas annealing (FGA) are reported. The SiO2/Si interface structure formed utilizing ORs were only slightly influenced by FGA. On the other hand, although the thickness of oxide film formed utilizing OMs is weakly influenced by FGA, the FGA-induced nearly 10% decrease in the amounts of Si1+, Si2+, and Si3+ formed utilizing OMs were found. Therefore, the interface structure formed utilizing OMs is influenced by FGA.

A soft X-ray angle-resolved photoemission system applicable to 100 µm crystals has been developed., A system for angle-resolved photoemission spectroscopy (ARPES) of small single crystals with sizes down to 100 µm has been developed. Soft X-ray synchrotron radiation with a spot size of ∼40 µm × 65 µm at the sample position is used for the excitation. Using this system an ARPES measurement has been performed on a Si crystal of size 120 µm × 100 µm × 80 µm. The crystal was properly oriented on a sample stage by measuring the Laue spots. The crystal was cleaved in situ with a microcleaver at 100 K. The cleaved surface was adjusted to the beam spot using an optical microscope. Consequently, clear band dispersions along the Γ–X direction reflecting the bulk electronic states were observed with a photon energy of 879 eV.

Soft-x-ray-excited angle-resolved photoelectron spectroscopy studies on silicon dioxide films formed using oxygen radicals (OR) versus oxygen molecules (OM) are reported. Most of intermediate oxidation states of Si, so called suboxides, consisting of Si3+, Si2+, and Si1+ are localized at and near the SiO2/Si interfaces. The suboxides formed utilizing OM are located extremely close to the interfaces, while suboxides formed utilizing OR are located not only at the interface but also in the Si substrate. This implies the penetration of a part of OR into the Si substrate to form Si1+ and to relax the interfacial stress. Intermediate chemical bonding states of Si are formed in Si substrate closer to the interface as compared with those formed utilizing OM. This implies that the interfacial stress in the former is smaller than that in the latter.

The epitaxial silicon oxynitride (SiON) layer grown on a 6H-SiC(0001) surface is studied with core level photoemission spectroscopy. Si 2p spectra show three spectral components other than the bulk one. Chemical shifts and emission angle dependence of these components are well explained within a framework of a determined structure model of the SiON layer.