Masamitsu Watanabe

Spectrometer for polarized soft X-ray Raman scattering

An experimental system for polarized soft X-ray Raman scattering spectroscopy has been constructed. The soft X-ray spectrometer is based on the Rowland circle geometry with a holographic spherical grating. Three types of gratings are used to cover the energy range from 18 eV to 1200 eV. According to a ray-trace simulation, the resolution is expected to be 200 meV at 700 eV by using a 10 micro m slit width. The polarized and depolarized soft X-ray Raman scattering spectra can be measured by rotating the soft X-ray spectrometer around the axis of the incident beam. Preliminary measurements of polarized and depolarized spectra were accomplished at undulator beamline BL-2C of the Photon Factory.

DESIGN OF A FLAT FIELD SPECTROMETER FOR SOFT X-RAY EMISSION SPECTROSCOPY

A spectrometer for soft X-ray emission spectroscopy was designed and constructed. The aims of this spectrometer are high detection efficiency and realizing the energy resolution of 1000 (E/ΔE) in a compact size. To satisfy these requirements, a flat field spectrometer with a varied line spacing grating and a CCD detector was chosen. Furthermore, the configuration without the entrance slit was employed. For compact flat field spectrometers, the spectral dispersion on the detector is sometimes smaller than the spatial resolution of existing detectors restricting maximum energy resolution. The spectral dispersion on the detector was optimized to balance with the spatial resolution of CCD. Optical performance was tested with a ray-tracing program. The spectrometer covers 250–900 eV, with two gratings. Taking into account the spatial resolution of a CCD detector, the maximum energy resolution of the spectrometer is estimated to be about 1000 (E/ΔE) for the beam size of 10 μm. Using the constructed spectrometer, test experiments were performed at the beamline BL27SU in SPring-8.

Magnetism and metal-insulator transition in III-V based diluted magnetic semiconductors

Abstract We report experiments on the magnetism and the transport in III–V based diluted magnetic semiconductors (Ga,Mn)As and (In,Mn)As. Heat treatment (annealing) at comparatively low temperatures (slightly above the growth temperature) is unexpectedly found to be effective to improve the ferromagnetism and the metallic conduction. IR optical conductivity measurements and soft X-ray absorption spectroscopy reveal that the double exchange model is a convenient picture to describe the ferromagnetism. The transport in the vicinity of metal–insulator critical point was studied in detail by using the low-temperature annealing method.

Soft X-ray emission spectroscopy of early transition metal compounds

Abstract Soft X-ray emission studies for several early transition metal compounds, such as Sc, Ti and V compounds, have been studied. Raman scattering was found at the 2p→3d excitation in the transition metal compounds. The elementary excitation of the Raman spectrum is mainly elucidated by the d–d transition within the 3d bands, as well as the interband transition from the O 2p valence band to the conduction band, which consists mainly of transition metal 3d states. The charge transfer transition due to the localized electron picture is dominant in the soft X-ray spectra of Sc compounds. Raman scattering is a powerful tool in the study of the electronic structure of transition metal compounds.

Performance of a varied-space plane-grating monochromator

A new grazing incidence soft x-ray monochromator has been commissioned on the undulator beamline BL-2 of the Photon Factory. The monochromator has been designed to meet the demands for high-resolution soft x-ray spectroscopy. The monochromator has employed a varied space plane grating and a configuration with sagittal focusing and converging beam to satisfy the requirement. According to analytical estimation and ray tracing simulation, the high resolving power beyond 10000 can be obtained over the full energy range from 250 to 1400 eV. Preliminary experiments have been done on three points concerning the resolving power, photon flux, and spot size. The results have showed the typical resolving power from 7500 to 10000, the absolute photon flux ofthe order of lOb photons/s/300mA/O.02%BW, and the spot size ofO.1(V) x 0.9(11) 2FW at the sample position.

High resolution soft X-ray absorption spectroscopy for the chemical state analysis of Mn

Abstract Mn L 2,3 X-ray absorption spectra of various manganese compounds were measured using a synchrotron radiation facility. Very high-resolution spectra were obtained. Sharp lines, which were not found before, were observed, and reproducibility was checked using a different beam line in the synchrotron radiation facility. Difference in spectral line shape was observed as the difference of quantum yield method. An unknown sample was measured and the specimen was concluded to be a mixture of two different oxidation states of Mn. The effects on the change of spectral profiles are discussed.

Resonant Soft X-Ray Emission Spectroscopy of NiO across the Ni L2,3 Thresholds.

We study the electronic structure of NiO using resonant soft X-ray emission spectroscopy across the Ni L 2,3 thresholds. We observe inelastic (Raman) features within 10 eV of the elastic peak energ...

Electronic Structure of B-2p State in AlB2 Single Crystal: Direct Observation of pσ and pπ Density of States

X-ray emission (XES) and absorption (XAS) spectra near the B- K edge were measured on single-crystalline AlB 2 compound which is an isostructural diboride of superconducting MgB 2 . The partial den...

Probing oxygen and nitrogen bonding sites in chitosan by X-ray emission

Abstract We present X-ray fluorescence measurements of biopolymer chitosan [C 6 H 11 NO 4 ] n and chitosan cross-linked with ethylene glycol diglycidyl ether (EGDE). Changes in the fine structure of resonantly excited O Kα X-ray emission spectra (XES) of unmodified chitosan are attributed to the excitation of non-equivalent oxygen sites belonging to –OH, –O– functional groups. The comparison of the nonresonant nitrogen Kα XES of unmodified chitosan cross-linked with EGDE does not show any differences, which excludes the model of chemical structure according to which EGDE is linked to chitosan via the amine group.

Polarization dependence of the soft X-ray raman scattering at the L edge of TiO2

Abstract Polarization dependence of the soft X-ray Raman scattering was investigated at the Ti 2p absorption edge of TiO2. Strong Raman scattering features appear about 14 eV below elastic peaks with strong polarization dependence. These Raman scattering structures are charge transfer excitations to the antibonding state between 3d 1 L and 3d0 states, because they are enhanced when the incident photon energies are tuned at satellite structures of Ti 2p absorption spectrum. Broad Raman scattering structures are found between 3 eV and 10 eV below elastic peaks. They show weak polarization dependence and are assigned to be nonbonding type charge transfer excitations.