Shinjiro Hayakawa

A SCANNING TRANSMISSION X-RAY MICROSCOPE FOR MATERIALS SCIENCE SPECTROMICROSCOPY AT THE ADVANCED LIGHT SOURCE

Design and performance of a scanning transmission x-ray microscope (STXM) at the Advanced Light Source is described. This instrument makes use of a high brightness undulator beamline and extends the STXM technique to new areas of research. After 2.5 years of development it is now an operational tool for research in polymer science, environmental chemistry, and magnetic materials.

Removal of hydrogen sulfide using crushed oyster shell from pore water to remediate organically enriched coastal marine sediments.

Hydrogen sulfide is highly toxic and fatal to benthic organisms as well as causing depletion of dissolved oxygen and generating blue tide in eutrophic coastal seas. The purposes of this study are to reveal adsorption characteristics of hydrogen sulfide onto crushed oyster shell, and to evaluate removal efficiency of hydrogen sulfide from pore water in organically enriched sediments using container experiment in order to develop a coastal sediment amendment. The crushed oyster shell was mainly composed of CaCO(3) with calcite and CaO crystal phase. The batch experiment showed removal kinetics of hydrogen sulfide can be expressed as the first order equation and Langmuir plot fitted well in describing the adsorption behavior with the adsorption maximum at 12 mg-S g(-1). The container experiments suggested the oyster shell adsorbs hydrogen sulfide in pore water effectively and reduces oxygen consumption in the overlying water. Furthermore, oxidation-reduction potential of the sediment was higher with addition of crushed oyster shell than the control without oyster shell. Thus, it is concluded that crushed oyster shell can be an effective amendment to remediate organically enriched sediments in eutrophic coastal seas.

Analysis of trace Co in synthetic diamonds using synchrotron radiation excited X-ray fluorescence analysis

Abstract Synchrotron radiation excited X-ray fluorescence analysis was utilized for characterization of trace impurities in synthetic diamonds. Advantage of the energy tunability was fully utilized to evaluate the attenuation of X-rays through the sample, and the absorption corrected X-ray fluorescence yield was utilized for quantitative analysis. Diamonds grown with several types of metallic solvents were investigated, and quantitative analysis of trace Co was carried out. It was found that Co prefers to be dissolved into {1 1 1} growth sector and that Co concentration in the {1 1 1} growth sector decreases one order of magnitude with the existence of Ni in the solvent. XANES spectra of dissolved Co shows characteristic pre-edge feature similar to that reported with the dissolved Ni. Experimental results suggest that both Ni and Co occupy in the similar site in the diamond lattice and that Ni is easier to be dissolved into diamonds.

Construction and Commissioning of BL37XU at SPring-8

Trace element analysis beamline (BL37XU) at SPring‐8 was designed for application to various X‐ray fluorescence analyses such as XRF imaging, XAFS, TXRF and XRF holography. The beamline has of two branches, one being a SPring‐8 standard undulator‐beamline optics branch (Branch A) and the other a high‐energy branch (Branch B). In the experimental hutches, several kinds of experimental device are equipped. The end‐stations have been opened to public use since November 2002, and various experiments have been carried out.

A numerical simulation of total reflection X-ray photoelectron spectroscopy (TRXPS)

Abstract Numerical simulations of “total reflection X-ray photoelectron spectroscopy (TRXPS)” are presented. Monochromatized X-rays impinge on a specular sample with a glancing angle smaller than the critical angle of total reflection. Under this condition, the X-rays cannot penetrate deeper than the evanescent length, usually 20–40 A depending on the sample material, the wavelength of the X-rays, and the incident angle. The intensity of X-rays in the evanescent region can be as much as four times stronger than the incident X-ray intensity because of the standing-wave formation on the surface. Therefore, the photoelectron signal of atoms in the surface region is intensified. As a consequence, TRXPS is an even more powerful tool for the study of surface chemistry and physics than ordinary X-ray photoelectron spectroscopy (XPS). Moreover the signal to background ratio is improved at least twice if compared with that of the ordinary XPS because the number of inelastically scattered photoelectrons is reduced.

Fluorescence x‐ray absorption fine structure measurements using a synchrotron radiation x‐ray microprobe

X‐ray absorption fine structure (XAFS) measurements in regions less than 20 μm in diameter were realized using an x‐ray microprobe employing the fluorescence detection method. To realize an energy tunable intense small x‐ray beam, an ellipsoidal mirror was used as the synchrotron radiation focusing element combined with a double‐crystal monochromator. Distortion of a XAFS spectrum due to the self‐absorption effect is discussed in detail. The degree of the distortion was experimentally evaluated from the measurement of the x‐ray fluorescence intensity as a function of takeoff angle, and the distortion was significantly reduced with the small takeoff angle detection geometry. Utilizing this technique, reliable XAFS spectra were obtained from a rock sample containing several minerals.

Combined adsorption and oxidation mechanisms of hydrogen sulfide on granulated coal ash

Hydrogen sulfide is highly toxic to benthic organisms and may cause blue tide with depletion of dissolved oxygen in water column due to its oxidation. The purpose of this study is to reveal the combined adsorption and oxidation mechanisms of hydrogen sulfide on granulated coal ash that is a byproduct from coal electric power stations to apply the material as an adsorbent for hydrogen sulfide in natural fields. Sulfur species were identified in both liquid and solid phases to discuss removal mechanisms of the hydrogen sulfide with the granulated coal ash. Batch experiments revealed that hydrogen sulfide decreased significantly by addition of the granulated coal ash and simultaneously the sulfate ion concentration increased. X-ray absorption fine structure analyses showed hydrogen sulfide was adsorbed onto the granulated coal ash and successively oxidized by manganese oxide (III) contained in the material. The oxidation reaction of hydrogen sulfide was coupling with reduction of manganese oxide. On the other hand, iron containing in the granulated coal ash was not involved in hydrogen sulfide oxidation, because the major species of iron in the granulated coal ash was ferrous iron that is not easily reduced by hydrogen sulfide.

TOTAL REFLECTION X-RAY PHOTOELECTRON SPECTROSCOPY

Abstract We have measured x-ray photoelectron spectra of Au Si wafer and SiO 2 Si wafer using grazing incidence x-rays. The spectral profiles have drastically changed backgrounds with the change of angle of incidence just above and below the critical angle of x-ray total reflection. The background intensity was reduced to less than 1 2 when the glancing angle of the incident x-ray beam was just below the critical angle compared with just above the critical angle. The excitation x-rays were those from a synchrotron radiation source. Four incident x-ray energies were selected between 2000 and 3000 eV. The electron energy analyzer was a concentric hemisphere analyzer. The samples were a Si wafer as received and a Au evaporated Si wafer. The XPS signal from an oxide layer on the Si wafer surface was observed to be enhanced when the incident x-rays were totally reflected.

Development of scanning X-ray microscopes for materials science spectromicroscopy at the Advanced Light Source

The development of two zone-plate microscopes for X-ray spectroscopic analysis of materials is described. This pair of instruments will provide imaging NEXAFS analysis of samples in transmission at atmospheric pressure and imaging XPS and NEXAFS analysis of sample surfaces in a UHV environment.

Depth selective X-ray absorption fine structure spectrometry

Abstract Depth selective X-ray absorption fine structure (XAFS) spectrometry is proposed. Recording both the total electron yield (TEY) and the X-ray fluorescence yield (XFY) XAFS concurrently, makes it possible to obtain surface (10–100 A) and bulk chemical information on powder samples. An example is presented for X-ray fluorescent powder sample.