S. Ueda

Performance of a very high resolution soft x-ray beamline BL25SU with a twin-helical undulator at SPring-8

We report on the excellent performance of a newly constructed soft x-ray helical undulator beamline BL25SU of SPring-8 for photon energies 500–1800 eV. The full beamline was designed to perform very high resolution soft x-ray spectroscopy of solids with using high brilliance, highly circularly polarized undulator radiation. The grazing incidence monochromator employs varied-line-spacing plane gratings which operate in convergent light from a spherical mirror and focuses monochromatic light onto the exit slit. A resolving power in excess of 15 000 was measured at 540 and 870 eV for a grating with a central groove density of 600 lines/mm from the photoemission spectra of Au. A resolving power of more than 20 000 is estimated near 870 eV for a grating with a central groove density of 1000 lines/mm. A photon flux of more than 1×1011 photons/s/100 mA/0.02% b.w. is supplied onto the sample between 500 and 1800 eV with very low amount of higher-order light. The low heat load from the twin-helical undulator gives...

Twin helical undulator beamline for soft X-ray spectroscopy at SPring-8

A very high resolution soft X-ray beamline, BL25SU, has been designed and is under construction at SPring-8. Completely right or left circularly polarized light is supplied on a common axis of a newly designed twin helical undulator. A helicity modulation up to 10 Hz can be performed using five kicker magnets. The fundamental radiation covers the region 0.5-3 keV. Higher-order radiation is rather weak on the axis. A monochromator with varied-line-spacing plane gratings is installed to cover the region below 1.5 keV. A very high resolution beyond 10(4) is expected for the whole energy region.

Soft X-ray beamline for spectroscopy of solids at SPring-8

The performance of the first soft X-ray beamline BL25SU at SPring-8 is described. A grating monochromator is found to realize very good energy resolution. This is demonstrated by the experimental photoabsorption spectra of the Ar 2p(∼250 eV) and N2 1 s (∼400 eV) edges, which show the quality competitive to or better than the best results reported to date. In addition, the excellent performance is augmented by the high photon flux of about 1011 photons/s100 mA−10.02%−1 b.w., low degree of higher order light (less than 1%) and high circular polarization at the experimental stations.

Magnetic circular dichroism in Mn 2p core absorption of Ga1−xMnxAs

Abstract We have measured the magnetic circular dichroism in the Mn 2p core absorption of ferromagnetic diluted magnetic semiconductor Ga 1− x Mn x As with x =0.025 in the Faraday configuration. The electronic structure parameters for Mn in Ga 1− x Mn x As are obtained by fitting the experimental spectra on the basis of the cluster model calculation with considering the configuration interaction. The Mn 3d-As 4p hybridization and the negative weak p–d exchange constant are estimated.

Local magnetic states in La1−xSrxMnO3 and Nd1−xSrxMnO3

Abstract Local magnetic state of Mn atoms in ferromagnetic perovskite-type manganites is investigated with magnetic circular dichroism (MCD) of Mn 2p core-level absorption (XAS). Small but clear differences in XAS and MCD spectra are found between La 0.84 Sr 0.16 MnO 3 and Nd 0.53 Sr 0.47 MnO 3 . The electronic states of Mn atoms, especially the local spin and orbital states are discussed.

High resolution Ce 3d–4f resonant photoemission study of CeNiSn and CePdSn

Abstract We have measured Ce 3d resonant photoemission spectra of CeNiSn and CePdSn with high resolution of E/ΔE∼4000. Although the Ce valences are close to 3+ for both compounds, the Ce 3d resonant spectra show stronger f1 final states near the Fermi level compared with Ce 4d resonant spectra. Calculations based on the single impurity model give consistent spectral functions to the experimental results. The valence band states except for the Ce 4f states in the bulk are essentially the same as those in the surface and consistent with the result of a band-structure calculation.

ELECTRONIC STRUCTURES OF ND1-XSRXMNO3, LA1-XSRXMNO3 AND LA1-X CAXMNO3 STUDIED BY PHOTOEMISSION AND INVERSE PHOTOEMISSION SPECTROSCOPY

Abstract We have investigated the electronic structures of perovskite manganese oxides, Nd0.5Sr0.5MnO3, (Nd0.062Sm0.938)0.5Sr0.5MnO3, La0.84Sr0.16MnO3 and La0.7Ca0.3MnO3, by X-ray photoemission (XPS) and X-ray bremsstrahlung isochromat spectroscopy in addition to vacuum ultraviolet inverse photoemission. It is found that the VUV-IPES spectra seem to be well explained by the band-structure calculation. Mn 3p-3d resonance photoemission measurements have also been performed, where the contributions of the occupied Mn 3d states are extracted. We observed hybridization between the Mn 3d and O 2p states from the Mn 2p and 3p spectra of all samples, and the Mn spin state from the Mn 3s XPS spectra of Nd0.5Sr0.5MnO3 and (Nd0.062Sm0.938)0.5Sr0.5MnO3.

High resolution photoemission study of CeRu2Si2

Abstract High resolution Ce 4d → 4f resonance photoemission study was done for CeRu2Si2. The Ce 4f spectrum has shown two prominent peaks around 0.3 and 2.5 eV. The 0.3 eV peak has clearly shown an additional structure closer to the Fermi level, whose intensity decreases at higher temperatures. This intensity reduction is ascribed to the tail of the Kondo resonance peak.

Cytochrome P450 Monooxygenase CYP716A141 is a Unique b-Amyrin C-16b Oxidase Involved in Triterpenoid Saponin Biosynthesis in Platycodon grandiflorus

The roots of Platycodon grandiflorus are widely used as a crude drug. The active components include a variety of triterpenoid saponins. Recent studies have revealed that Cyt P450 monooxygenases (P450s) function as triterpene oxidases in triterpenoid saponin biosynthesis in many plant species. However, there have been no reports regarding triterpene oxidases in P. grandiflorus. In this study, we performed transcriptome analysis of three different P. grandiflorus tissues (roots, leaves and petals) using RNA sequencing (RNA-Seq) technology. We cloned six P450 genes that were highly expressed in roots, and classified them as belonging to the CYP716A, CYP716D and CYP72A subfamilies. We heterologously expressed these P450s in an engineered yeast strain that produces β-amyrin, one of the most common triterpenes in plants. Two of the CYP716A subfamily P450s catalyzed oxidation reactions of the β-amyrin skeleton. One of these P450s, CYP716A140v2, catalyzed a three-step oxidation reaction at C-28 on β-amyrin to produce oleanolic acid, a reaction performed by CYP716A subfamily P450s in a variety of plant species. The other P450, CYP716A141, catalyzed the hydroxylation of β-amyrin at C-16β. This reaction is unique among triterpene oxidases isolated to date. These results enhance our knowledge of functional variation among CYP716A subfamily enzymes involved in triterpenoid biosynthesis, and provide novel molecular tools for use in synthetic biology to produce triterpenoid saponins with pre-defined structures.

Bulk-sensitive high-resolution ce 3d–4f resonance photoemission study of CeNiSn and CePdSn

Abstract High-resolution Ce 3d–4f resonance photoemission (RPES) spectra highly reflecting bulk 4f states have been measured for a Kondo semiconductor CeNiSn and its reference material CePdSn. An intensity of f 0 final states is markedly weaker for CeNiSn than for CePdSn. We also report on photon-energy dependence of the RPES spectra. Comparison between the RPES spectra of CeNiSn and La 3d–4f RPES spectra of LaNiSn shows that the rare-earth 5d enhancement is significantly weaker than Ce 4f resonance enhancement. The high-resolution 3d–4f RPES spectra clarify the difference of the bulk electronic states near the Fermi level between CeNiSn and CePdSn.