Seishi Kikuta

Study on the Si(111) √3×√3-Ag Surface Structure by X-Ray Diffraction

The surface structure of Si(111) √3×√3-Ag has been analyzed from the X-ray intensity versus energy curves measured both for the integral- and fractional-order spots. A modified trimer model with three Ag atoms in the √3×√3 unit cell is proposed, in which triangles made of Ag atoms are chained in a honeycomb arrangement. The distances between the nearest neighbor Ag atoms are about twice the van der Waals radius. The height of the Ag layer measured from the ideal first Si layer is 2.9±0.1 A. The center of each triangle coincides with the position of the honeycomb protrusion observed by scanning tunneling microscopy.

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.

Measurements on Local Variations in Spacing and Orientation of the Lattice Plane of Silicon Single Crystals by X-Ray Double-Crystal Topography

A method of measuring the local variations in the spacing and the orientation of a lattice plane in a single crystal is reported. The angular positions of diffraction peak at each point of the specimen are measured at four incident azimuths making 90° to each other by a double-crystal spectrometer. This method is applied to two specimens of silicon single crystals doped with arsenic and containing oxygen respectively. The growth striations observed in the two specimens are for the most part due to the variation in lattice spacing. The intensity contrast extended in the long range is due to misorientation.

X-ray monochromator with an energy resolution of 8×10−9 at 14.41 keV

An ultrahigh-resolution x-ray crystal monochromator providing a 120 μeV bandwidth at 14.41 keV is presented. The design, which uses four independent silicon crystals and has an output beam parallel to the incident beam, may be generalized to arbitrary energies. Fluxes of 1.3×106 photons/s (1.0×107 photons/s) in bandwidths of 120±15 μeV (140±15 μeV) were measured. The performance of the monochromator, including the preservation of coherence through it, was verified by measurement of a 9.6±2.0% enhancement in the coincidence rate (i.e., γ(2)−1=0.096±0.020) in an intensity correlation experiment.

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.

Surface structure analysis of Si(111)√3 × √3-Bi by X-ray diffraction — Approach to the solution of the phase problem

Abstract X-ray intensity versus energy ( I - E ) curves of the integral-order rods have been observed for the Si(111) 3 × 3 −Bi structure under nearly normal incidence condition, and the 3-dimensional structure of the surface has been analyzed by utilizing the interference effect between the X-rays diffracted from the surface atoms and the bulk crystal around the Bragg points, which gives information on the positions of the surface atoms, especially of the heavy atoms with respect to the bulk crystal. Bi atoms, forming a trimer with an interatomic distance of 3.08±0.08 A , are bonded to the first-layer Si atoms by means of the dangling bonds, and the displacements of the first- and second-layer Si atoms from their ideal positions are less than 0.15 A. The spacing between the Bi layer and the ideal first Si layer is 2.68±0.02 A . A Si adatom layer making a honeycomb structure exists 0.80±0.20 A above the Bi layer. The model in which the center of the trimer is on the second-layer Si atoms rather than on the fourth-layer Si atoms is favored.

A study of the Si(111)3×3-Ag surface by transmission X-ray diffraction and X-ray diffraction topography

Abstract The adsorption site of Ag atoms with respect to the unreconstructed Si crystal was uniquely determined using transmission X-ray diffraction. The result is consistent with one of the two honeycomb-chained triangle models previously proposed by the authors using reflection X-ray diffraction. Next, the reconstruction of Si was analyzed; an Si trimer layer is about 0.8 A below the Ag layer, and at least two double layers of Si are reconstructed, having the component of the honeycomb arrangement. Finally, the capability of surface X-ray diffraction topography was shown by observing the integral-order spot near the Bragg point.

A possible use of the soft X-ray standing wave method for surface and interface structure analysis

Abstract The standing wave method in the soft X-ray region is described, in which the incident photon energy is scanned and Auger electrons from the sample crystal are detected in a UHV chamber. A preliminary application to the Si(111) (7×7) surface shows that this method will be a promising tool for surface and interface structure analysis of semiconductors.

Perfect crystal X-ray phase retarders

Abstract X-ray phase retarders of perfect crystals are discussed on the basis of a dynamic theory of diffraction. Although all conceivable diffraction geometries can be used for a phase retarder, transmission of less absorptive crystals in both Laue and Bragg geometries as well as reflection and transmission of absorptive crystals in Laue geometry give practical solutions for circularly polarized X-ray generation with synchrotron radiation (SR). Some SR beamline optics using these phase retarders are presented.

Generation and Application of Ultrahigh Monochromatic X-ray Using High-Quality 57FeBO3 Single Crystal

Ultrahigh monochromatic 14.4 keV X-rays with a narrow bandwidth of 15.4 neV were generated successfully with a high counting rate of 12,000 counts/s at the undulator beamline (BL11XU) of SPring-8. It was achieved by combining an intense X-ray from the third generation synchrotron radiation facility SPring-8 and pure nuclear Bragg scattering of a very high-quality 57FeBO3 perfect single crystal at the Neel temperature. We describe the detailed study of the beam characteristics and some performance test experiments of energy-domain synchrotron radiation Mossbauer spectroscopy, including a high-pressure experiment using a diamond anvil cel.