Koichi Izumi

Construction of a precision diffractometer for nuclear Bragg scattering at the Photon Factory

A versatile precision diffractometer for nuclear Bragg scattering was designed and constructed at the Photon Factory. Standardized component goniometers can be arranged to address various requirements of incident beam conditioning for nuclear Bragg scattering, including a high‐energy resolution monochromator with wide angular acceptance as well as a circularly polarized incident beam.

An X-Ray Phase Plate Using Bragg-Case Diffraction

An X-ray phase plate using two-beam Bragg case diffraction is proposed. The variation of the polarization state of the transmitted (forward-diffracted) beam through the incident angle was observed. Left-handed and right-handed circular polarizations whose degree of circular polarizations were ±0.90 were experimentally produced.

Nuclear Resonant scattering experiments with synchrotron radiation at KEK

Experiments of nuclear Resonant scattering carried out at PF and TRISTAN-AR of KEK are described, which include nuclear Bragg scattering in time domain as well as energy domain, time-resolved nuclear resonant forward scattering, and interferometric studies.

High-resolution measurements of nuclear Bragg scattering from a synthetic α-57Fe2O3 crystal

Nuclear Bragg scattering from a synthesized α-57Fe2O3 crystal was observed with 450 cps at beamline 16 of the Photon Factory. Mossbauer absorption spectra of the scattered beam were measured by oscillating the scatterer crystal while maintaining its Bragg condition. Time distribution of the scattered beam was measured with 300 ps resolution.

Evidence for a trimer in the √3 × √3 -Bi structure on the Si(111) surface by X-ray diffraction under the nearly normal incidence condition

The structure of the 3 x 3 structure on the Si(111) clean surface has been studied using X-ray diffraction under the nearly normal incidence condition. A thin substrate crystal, about 5 μm in thickness, was used to reduce the background scattering. From the analysis of the intensity distribution of diffraction patterns, evidence for a trimer of Bi atoms was obtained and the distance between Bi atoms forming the trimer was found to be 3.10±0.1 A.

Focusing Properties of a Linear-Phase Bragg-Fresnel Lens

Hard X-ray focusing by a linear phase Bragg-Fresnel crystal lens was performed with an efficiency close to 30%. The phase shift of an incident beam was controlled by deviating the crystal lens from the exact Bragg condition. Analytical expressions for the intensity and the image contrast at the focal point was presented.

Structural Investigation of Si(111)

The atomic structure of Si(111) √3×√3-In was investigated by low energy ion scattering spectroscopy with 1 keV He+ ions. Azimuthal angular distributions of scattered ions suggest that the In atoms are located in the three-fold sites on top of the second layer Si atoms. Comparing the experimental distribution as a function of the incident angle with the calculation using the Thomas-Fermi-Moliere potential taking of the thermal vibrations, the Debye temperature of the surface In atoms and the bond length between the In atom and the first layer Si atom were estimated.

\sqrt{3}\times \sqrt{3}

Interferometry of the nuclear Bragg scattered X-rays from 57Fe2O3 (777) with the optical path difference of 2.4 mm was reported. In order to carry out this measurement, a new X-ray interferometer of the wavefront-dividing type was designed and fabricated. The interference pattern was observed using this X-ray interferometer, since the temporal coherence length of the nuclear resonantly scattered X-rays is much longer than the optical path difference. From the visibility of the interference pattern, the vertical size of the X-ray source was estimated to be 50 µ m.

–In by Low-Energy Ion-Scattering Spectroscopy

High quality single crystals or thin films containing Mossbauer isotopes are the main x‐ray optical component for nuclear Bragg scattering (NBS) with synchrotron radiation. For this purpose, flux grown α‐57Fe2O3 (hematite) single crystals prepared in two growth runs have been characterized by plane wave x‐ray topography, which indicated the most suitable sample. Measurements of (111), (333), (555), (777), and (999) pure nuclear‐reflection profiles showed a good agreement of relative reflectivity with the values calculated from theory. At the beamline NE‐3, accumulation ring of TRISTAN, a Mossbauer event rate as high as 13 000 cps for (777) reflection was observed.

Interference of Nuclear Bragg Scattered X-Rays in X-Ray Interferometer with Large Optical Path Difference

We developed a micro-area X-ray diffraction system using a sub-µm X-ray beam of 10 keV energy that was produced by a phase zone plate made of tantalum. Using this system, we were able to measure the lattice strain distribution in InGaAsP metalorganic vapor phase epitaxial layers selectively grown on InP stripe regions a few µm in width between a pair of SiO2 mask stripes, with strain sensitivity of about 1×10-4. We found that the strain distribution in a 3-µm-wide stripe layer is almost completely uniform, while that in a 4-µm-wide layer is not.