Etsuo Arakawa

Polarization tunability and analysis for observing magnetic effects on BL39XU at SPring-8

Polarization tunability and analysis of X-rays is one of the most advancing features of third-generation synchrotron radiation sources. In order to apply such developments to the observation of magnetic effects, a diffractometer for X-ray magnetic absorption and scattering experiments was constructed on BL39XU at SPring-8. The efficiency of the apparatus is clearly demonstrated by several observations of the magnetic effects. In particular, a diamond phase plate plays an essential role in regulating both circular and linear polarization states.

High-speed x-ray reflectometory in multiwavelength-dispersive mode

The potential of a high speed x-ray reflectometer for time-resolved studies on the subsecond to millisecond timescales is demonstrated by recording x-ray reflection curves from a small area (1mm×10mm) of a 14.3nm thick gold film on a silicon substrate with data collection times of 0.05–1s. A horizontally convergent x-ray beam having a one-to-one correlation between ray direction and energy is produced by a curved crystal polychromator, and the beam is incident on and vertically reflected by a specimen placed at the focus. The x-ray reflectivity is measured as a function of the x-ray energy downstream of the focus using a one dimensional detector with no need for angle scan of the specimen and detector.

Development and Surface Evaluation of Large SiC X-Ray Mirrors for High-Brilliance Synchrotron Radiation.

Flat SiC mirrors coated with Pt, of which size are 800?50 mm2 and 1000?140 mm2 in area, are developed for high-brilliance synchrotron radiation. The large mirrors are well polished over the entire area from the viewpoint of surface roughness for application to the use for the synchrotron radiation beamline. The performance of the large mirror surface is evaluated by the measurements of not only reflectivity near the critical angle but also of the angle-resolved scattering (ARS) curve as a function of mirror surface position at several glancing angles with CuK? X-rays from a rotating target at the 30-m-long X-ray beamline facility of ISAS. By analyzing the ARS curves the power spectral density functions are derived as a function of the surface wave number. It is suggested that the large mirror may have a fractal surface finish like that of small mirrors. Evaluation of the longitudinal mirror curvature on the order of 10 km from the reflected beam profile width is also described. The results are compared with the measurements of the laser interferometers.

Real-time investigation of protein unfolding at an air-water interface at the 1 s time scale

Protein unfolding at an air–water interface is followed in real time by a recently developed simultaneous multiple-angle–wavelength-dispersive X-ray reflectometer with a time resolution of 1 s.

A simultaneous multiple angle-wavelength dispersive X-ray reflectometer using a bent-twisted polychromator crystal

Using a convergent X-ray beam having continuously varying energy and glancing angle as a function of direction, the whole profile of a specular X-ray reflectivity curve is measured with no need for any mechanical motion during the measurement.

Magnetostriction observed by X-ray diffraction in iron

A new technique to observe magnetostriction by X-ray diffraction was reported. We found that a symmetry part of the relative diffraction intensity change induced by applying magnetic field was proportional to a Bragg angle shift. It was a differential measurement on the rocking curve. The Bragg angle and its shift gave quantitative magnetostrictive coefficients. Sensitivity of the present method on the magnetostrictive coefficient for an iron specimen approached to 10/sup -7/.

Development and characterization of large x-ray mirrors for high-brilliance synchrotron radiation

Four kinds of large mirrors, which are 0.8 m SiC flat, 1 m SiC flat, and two 1 m Si cylindrical mirrors (coated with Pt or Ni), are developed for high brilliance synchrotron radiation with the cooperation of the suppliers. The reflectivity, surface finish, and surface figure are characterized by not only laser interferometers but also x-ray at ISAS 36 m long beamline.

A method for measuring the specular X-ray reflectivity with millisecond time resolution

A method for quick measurement of the specular X-ray reflectivity using a tapered undulator source is described. It uses a convergent X-ray beam with a one-to-one correspondence between X-ray energy and direction, which is produced by diffraction of a white X-ray beam at a curved silicon crystal. To increase the momentum transfer range, the sample is rotated 45? from the horizontal around the incident beam direction, so that both the X-ray energy and the incident angle change continuously with direction. The specularly reflected beam is observed with a two-dimensional detector. The X-ray reflectivity curve in a wide momentum transfer range can be observed in a single detector exposure with a time resolution in the millisecond range. Test measurements were done for a commercial silicon wafer and a gold thin film on silicon.

X-ray diffraction technique to observe magnetostriction and magnetization at coextensive volumes of iron

We present a new technique for observing both magnetostriction and magnetization as a function of applied magnetic field strength. They are simultaneously measured by the same X-ray probes with a goniometer at exactly coextensive specimen volumes. The measurements yield experimental magnetostriction curves during a cyclic magnetization process in iron (100) single-crystal specimen at room temperature. The technique is a new tool to investigate magnetic properties within X-ray extinction depth from the surface.

Grazing Incidence X-Ray Diffraction Study of Dimyristoylphosphatidic Acid Monolayers on Aqueous Subphases in the Presence of Calcium or Magnesium Ions

Focusing on the difference in the isotherms of dimyristoylphosphatidic acid (DMPA) monolayers on aqueous subphases in the presence of calcium and magnesium ions, the structures of the DMPA monolayer on the aqueous subphases were investigated by grazing incidence X-ray diffraction. We observed the reflections from the lattice of hydrocarbon chain packing of DMPA monolayers. It was found that the lattice spacings observed by X-ray diffraction in the presence of calcium ions are shorter than those in the presence of magnesium ions at every surface pressure measured. We discussed this result in terms of the hydration of these ions.