Kazushi Yokoyama

Hyogo beamline at SPring-8: multiple station beamline with the TROIKA concept

Abstract The Hyogo beamline has been constructed as the first contract beamline at SPring-8. It has three experimental hutches and their corresponding three monochromators. Two upstream transparent monochromators enable us to perform three experiments for different purposes simultaneously. Employing a figure-8 undulator, horizontally or vertically polarized X-rays can be obtained in a wide energy range. Rocking curves of the monochromators were almost identical to theoretical ones.

PHASE-CONTRAST X-RAY IMAGING USING BOTH VERTICALLY AND HORIZONTALLY EXPANDED SYNCHROTRON RADIATION X-RAYS WITH ASYMMETRIC BRAGG REFLECTION

Results of phase-contrast X-ray imaging are presented. The optical system employed consisted of a successive arrangement of horizontal and vertical (+, -) double crystals taking asymmetric Bragg reflection with an asymmetry factor of ~0.2. The original beam size was thus expanded in both directions and the field of view actually obtained was ~5×5 mm2. Boundary structures in samples were clearly observed with much higher contrast than those obtained in conventional absorption-contrast imaging. Since this method works in real time, it will provide a new X-ray imaging diagnosis technique for in situ observation over a large area of the samples.

Formation of Parallel X-Ray Microbeam and Its Application

We have developed a parallel X-ray microbeam of 7×5 µm2 in size with a small angular divergence, which aims high-resolution strain measurements in a very local area. The microbeam has been formed by compressing and collimating the X-rays from a third-generation undulator source using successive asymmetric reflections. Using this beam, we have evaluated the strain induced by field oxidation in silicon wafers by rocking curve measurements. We have observed that the lattice constant in the Si region near the oxide film edge is contracted and that in the SiO2/Si region is extended. The difference between these lattice constants is as small as about Δd/d~±5×10-6.

High-resolution microbeam x-ray diffractometry applied to InGaAsP/InP layers grown by narrow-stripe selective metal-organic vapor phase epitaxy

We measure the diffraction peaks of InGaAsP selective metal-organic vapor-phase epitaxial layers on 1.7-μm-wide InP stripe regions between a pair of SiO2 mask stripes. This is achieved by using an x-ray microbeam with low angular divergence and a narrow energy bandwidth that was produced through two-dimensional condensation of undulator radiation x rays from a synchrotron light source using successive asymmetric diffraction. The lattice strain is investigated by changing the SiO2 mask width from 4 to 40 μm. The rocking curves reveal clear peak shifts in the InGaAsP layers from the higher angle side to the lower angle side of the InP substrate peaks as the mask width increases.

New design concept of multilayer supermirrors for hard x-ray optics

It is important to enhance the reflectivity of multilayer supermirrors in 10-100 keV region used for hard x-ray optical systems. For this purpose design methods of multilayer supermirrors have been investigated at the grazing angle of 0.3 degrees by means of the x-ray etalon or phase matching configuration. It means that the 1st and higher order Bragg reflections emanated from different periodic lengths cooperatively enhance the reflectivity at energy bands concerned. The x-ray etalons method is useful for multi-band mirror with the band width of 5 keV or so, but becomes a bit difficult to make the energy band wider connecting gaps between isolated bands. Because heavy oscillation of reflectivity curve occurs due to adjacent destructive and constructive interference. The phase matching method is useful to get smooth reflectivity in the broad energy band and is possible to enhance the 2nd order Bragg reflection in higher energy region. We present the design of hard x-ray telescope sensitive in 25-40 keV region by means of multi-block supermirrors of Pt/C multilayers. The effective area was obtained to be more than 100 cm2.

Crystallinity estimation of thin silicon-on-insulator layers by means of diffractometry using a highly parallel X-ray microbeam

An X-ray microbeam with a small angular divergence and a narrow energy bandwidth has been produced at BL24XU at SPring-8. The beam size was measured to be 3.1 microm and 1.6 microm in the horizontal and vertical directions, respectively, and the horizontal angular divergence was 4.0 arcsec. Using this microbeam the crystallinity estimation of thin layers on silicon-on-insulator (SOI) wafers is demonstrated. In reciprocal-space maps the lattice tilt variations were 80 arcsec and more than 220 arcsec in the SOI layers on bonded and SIMOX wafers, respectively. In equi-tilt maps, the typical equi-tilt areas of the SOI layers were 7 microm and 4 microm in size on the bonded and SIMOX wafers, respectively.

Focusing properties of tantalum phase zone plate and its application to hard x-ray microscope

A phase zone plate made of tantalum has been designed and fabricated for focusing hard x-rays. It is designed to optically match to the undulator radiation of the BL24XU at the SPring-8. Its focusing properties were measured. The focused beam size smaller than 1 μm was obtained at the photon energy of 10 keV. The diffraction efficiency was measured around 10 keV and the maximum efficiency of 20.7% was obtained at 9.8 keV. Photon flux was estimated to be ∼4×108 photons/s. A system for a scanning x-ray microscope has been constructed and the transmission and/or fluorescence microscopy has also been performed.

Formation and Growth Mechanism of Calcium Carbonate Nanoparticles via a Bubbling Method

The mechanism of formation and growth of calcium carbonate (CaCO3) nanoparticles by bubbling carbon dioxide in aqueous suspensions of calcium hydroxide was investigated using time-resolved in situ synchrotron small-angle X-ray scattering (SAXS) and transmission electron microscopey (TEM). In situ SAXS showed a significant change in the particles size in the primary reaction. This suggests that the nucleus forms CaCO3 at in this period. After the nucleation, the crystal grow with the reaction time to yield 40 nm CaCO3 nanoparticles. TEM showed fibrous or chain-like intermediates formed by aggregation of fine particles of CaCO3 as calcite. We propose that CaCO3 crystal nuclei generated in the primary reaction grow to yield fibrous or chain-like CaCO3 which then separates into individual particles to form CaCO3 nanoparticles.

Estimation of bonded silicon-on-insulator wafers by means of diffractometry using a parallel X-ray microbeam

Crystallinity of bonded silicon-on-insulator (SOI) wafers has been investigated by means of diffractometry using a parallel X-ray microbeam. Peak shifts and extended tails were observed in the rocking curves of the SOI layer. Further, reciprocal lattice maps revealed that the SOI lattice planes were tilt dispersively within about 100 μrad. The typical sizes of the grains are ranging from a few μm to a several tens μm. The inferiority of the thin SOI crystal may arise from the extended force of buried oxide layer.

Real-time phase-contrast x-ray imaging using two-dimensionally expanded synchrotron radiation x-rays at the BL24XU (Hyogo-BL) of the SPring-8

Phase-contrast x-ray imaging has been studied for materials, biological and medical sciences at the Hyogo-prefectural beamline (BL24XU) of the SPring-8. Its optical system consists of a successive arrangement of horizontal and vertical (+, −) silicon double crystals taking asymmetric Bragg reflection. A living insect and a frog were observed in real time at the photon energy of 15 keV. Boundary structures in samples were clearly observed with much higher contrast than those obtained in absorption-contrast imaging. The beamline BL24XU, optical system and experimental results are described.