BUNSEKI KAGAKU Abstracts

Vol. 55 No. 6

June, 2006

Accounts

Observation of Chemical Changes at the Atomic Level

Kazuo Yasuda¹, Toshie Yaguchi², Kuniyasu Nakamura², Yoshihiro Hirano³ and Kichinosuke Hirokawa⁴

(Received 7 December 2005, Accepted 25 February 2006)

It is said that a 0.1 portion of an atom or a 0.01 portion of a molecule can be detected with a newly developed method. However, the above values were employing a signal-to-noise ratio. We are measuring the numbers of shadows of objects, it is so-called signal, not the object, itself, at present. It is required to observe and measure the numbers of the object, itself, and discuss the signal-to-noise ratio in the observation. The concept of the present methodology is based on millions or billions of atoms, but observations or measurements at the atomic level are different using the above concept. The measurement of a group consisting of 100~1000 atoms should be applied to another concept different from the existing one. The vaporization, reaction, phase transfer and observation of the detection limit in an alloy were studied by using a high-resolution electron microscope. It is thought that these three processes in the former are basically continuous phenomena, but it was found that they are intermittent phenomena. The key point in the above mentioned phenomena is the fact that it is related to the activity coefficient of the analyte atom in a binary alloy. Interactions between an analyte atom and co-existing or surrounding atoms occur as intermittent phenomena, like a geyser, so to say. This interaction is different from a conjugate bond between two kinds of atoms, and is recognized in the properties of an alloy. Upon observing to detection limit, a covering phenomenon over the analyte atom by sputtered surround atoms interferes with the radiation signal from the analyte. It can be said that the method of counting numbers of atoms is reliable compared with measuring the signal-to-noise ratio in this experiment.

Keywords : activity coefficient; atomic absorption; detection limit; high-resolution electron microscope; interaction; stepwise vaporization; stepwise chemical reaction; stepwise phase transfer.

Direct Observation of Specific Intermolecular Forces in Functional Molecules by Atomic Force Microscopy

Shinpei Kado¹ and Keiichi Kimura¹

(Received 7 December 2005, Accepted 19 January 2006)

It has been reported in the recent decade that molecular interactions in a variety of molecular pairs can be measured directly by using atomic force microscopy (AFM) as a highly sensitive and precise force sensor. The target molecules are immobilized covalently on AFM probe tips and substrates by utilizing self-assembled monolayers of thiol and organosilane derivatives. The AFM technique can be applied to novel analytical methods based on mechanochemical measurements of specific molecular interactions. In the present study, we directly measured the specific intermolecular forces for several functional molecules by AFM using the probe tip and substrate modified chemically with them. The target molecules used were crown ether and urea derivatives, which are host molecules possessing the abilities of cation-binding and hydrogen bonding, respectively, for analytical applications, and a photochromic spirobenzopyran derivative for a photochemical study. We demonstrated direct observations of the rupture forces of specific interactions based on their functionalities at a molecular level and an evaluation of the single forces. A promising application of the AFM methodology is also described, aiming at the development of an analytical method, such as a high-resolution chemical mapping based on direct AFM detection of a specific molecular interaction force.

Keywords : atomic force microscopy; adhesion force; specific intermolecular force; single force.

Study on Microstructures of Advanced Metallic Materials by Small-Angle X-Ray and Neutron Scattering

Masato Ohnuma¹ and Jun-ichi Suzuki²

(Received 16 December 2005, Accepted 24 February 2006)

The microstructures of metal-nonmetal nano-granular soft magnetic films, precipitation hardened stainless steel and Al-Mg-Si alloys, have been studied by small-angle X-ray/neutron scattering (SAXS/SANS). Quantitative evaluation of average scale of their microstructures in nanometer scale has been accomplished by SAXS and SANS. Using this information, the contribution of the microstructures to the magnetic and mechanical properties are discussed in this paper.

Keywords : average size; nanogranular films; nano precipitates; soft magnetic; precipitation hardening.

Research Papers

Three-Dimensional Visualization of Nuclear Densities by MEM Analysis from Time-of-Flight Neutron Powder Diffraction Data

Fujio Izumi¹ and Yukihiko Kawamura¹

(Received 9 December 2005, Accepted 26 January 2006)

We established a method for determining the three-dimensional distribution of nuclear densities from time-of-flight (TOF) neutron powder diffraction data measured with multiple detector banks. At first, the observed crystal-structure factors {Fo(h)} and standard deviations of |Fo(h)|'s estimated after Rietveld analysis using GSAS are output in text files, *.mem, with a file converter, Alchemy. After combining reflection data [hkl, Fo(h), s{|Fo(hK)|}] in the *.mem files, so as to minimize the extinction effect in reflections with large interplanar spacings, they are analyzed by a maximum-entropy method program, PRIMA, to determine the nuclear densities in the unit cell. The resulting nuclear-density distribution is visualized in three dimensions with VEND. Such a procedure enabled us to visualize nuclear densities in Ni from TOF neutron powder diffraction data.

Keywords : neutron powder diffraction; maximum-entropy method; 3D visualization.

Accurate Analysis and Visualization of Crystal Structure of Synthetic Zeolite-A by X-Ray Powder Diffractometry

Takayuki Konya¹, Tetsuya Ozawa¹, Go Fujinawa¹, Atsuko Oono² and Toshihiro Nakamura²

(Received 9 December 2005, Accepted 16 February 2006)

The crystal structure (Na₉₆A_l96Si₉₆O₃₈₄·183.7H₂O) and the phase content of synthetic zeolite-A were determined by X-ray powder diffraction data using the Rietveld method. The result of a Rietveld refinement for a structure determination gave R_wp=9.42% and S=1.52. The electron density image, calculated with the maximum-entropy method, proved the reliablity of the refined crystal structure. The content of zeolite-A calculated by a scale factor obtained by the Rietveld refinement was 74.8 mass%, which was identical to the value of 74.3 mass% by Vonk's crystallinity analysis. The residue of zeolite-A might be an amorphous or amorphous-like phase. The number of bond water calculated by the Rietveld refinement was 184, the same as that of thermogravimetry.

Keywords : zeolite; powder X-ray diffraction; Rietveld method; maximum-entropy method.

Application of In-Plane X-Ray Diffraction Technique for Residual Stress Measurement of TiN Film/WC-Co Alloy

Shigeki Takago¹, Haruyuki Yasui¹, Kaoru Awazu¹, Toshihiko Sasaki², Yukio Hirose² and Kenji Sakurai³

(Received 12 December 2005, Accepted 28 April 2006)

An in-plane X-ray diffraction technique was used to measure the residual stress of a CVD (chemical vapor deposition) TiN-coated WC-Co alloy. We could obtain the diffraction pattern from a thin film layer, eliminating that of the substrate. In the case of a conventional X-ray diffractometer, the X-ray penetration depth is about few mm. However, for a grazing incidence beam it is only 0.2 mm. Depth profiles of residual stress in TiN film layer were evaluated by the present method and the conventional sin2y technique. We concluded that the in-plane diffraction technique enables us to determine the residual stress in a CVD-TiN film having an oriented texture. It was found that the residual tensile stress generated a mismatch of the coefficient of thermal expansion between the film and the substrate.

Keywords : X-ray diffraction; in-plane diffraction; TiN film; chemical vapor deposition; residual stress; tungsten carbide-cobaltite.

Thermal Unfolding Process of Proteins Depending on Structural Hierarchy Clarified by Wide-Angle X-Ray Scattering at a Third Generation Synchrotron Source

Masaharu Koizumi¹, Mitsuhiro Hirai¹ and Katsuaki Inoue²

(Received 15 December 2005, Accepted 2 March 2006)

As is well known, α-lactalbumin (α-LA) and hen egg-white lysozyme (HEWL) are homologous with each other and closely similar in their ternary structures. On the other hand, their unfolding-folding processes were clarified to show different thermodynamic characteristics; however, the details of how such a difference relates to their structural transitions have not been clarified. In this report, based on an X-ray solution scattering method, we discuss the difference between the characteristics in the thermal structural transitions of α-LA and HEWL in solution at pH 7. A small-angle X-ray scattering (SAXS) method using a synchrotron radiation (SR) source was used for analyzing the protein structures in solutions, especially for studies of protein folding. For a long time the SR-SAXS method had provided us with low-resolution structural information, such as the radius of gyration obtained from SAXS data at a small-angle region. In the present study we observed the structural transitions of the above proteins in the wide-distance range from 2.5Å to 200Å, and analyzed the characteristics of the structural transition processes of the proteins, depending on all hierarchical structures (quaternary and ternary structures, domain structures and secondary structures). By using the method of SR-WAXS data analysis described in this report, we were able to analyze quantitatively and respectively the structural changes in a protein unfolding-refolding process, depending on different hierarchical structure levels and the structural transition cooperativeness between those structure levels, local structural changes, and so on. We show the recent development of an X-ray solution scattering method with significant improvements of the experimental resolutions in both time and space due to the use of third-generation SR sources, such as SPring-8 in Japan.

Keywords : synchrotron radiation; wide-angle X-ray scattering; protein; folding; hierarchal structure.

Atomic-Scale Structure Investigation of CeO₂/YSZ/Si Hetero-Interface by High Resolution Analytical Electron Microscope

Takanori Kiguchi¹, Naoki Wakiya², Nobuyasu Mizutani³ and Kazuo Shinozaki²

(Received 15 December 2005, Accepted 15 March 2006)

The interface structure and the chemical state on the orientation of a CeO₂/YSZ (yttria stabilized zirconia)/Si and YSZ/CeO₂/Si hetero structure have been considered using a high-resolution transmission electron microscope (HRETM) equipped with an analytical setup. Although both films showed a columnar structure, they had different orientations. In the YSZ/CeO₂/Si hetero structure, the CeO₂ layer has a (111) orientation without any in-plane orientation. TEM-EELS (electron energy loss spectroscopy) and TEM-EDS (energy dispersive X-ray spectroscopy) analyses showed that there were reacted interface layers due to a reduction of the CeO₂ layer and the oxidation of the Si substrate. In the CeO₂/YSZ/Si hetero structure, the CeO₂ layer preferentially had a 001 orientation. The quality of the 001 orientation was increased on an ultra-thin YSZ layer. The interface of CeO₂/YSZ (thick) has a semi-coherent interface with misfit dislocations. The interface of CeO₂/YSZ (thin) has been ambiguous due to a disordered structure of the YSZ layer. A TEM-EDS analysis showed that there was only a reacted interface layer due to oxidation of the Si substrate. This means that a thin YSZ layer effects the passivation layer for the reduction of a thermodynamically unstable CeO₂ layer against Si, as well as an epitaxy transmission from the Si substrate into the CeO₂ layer.

Keywords : TEM; CeO₂; YSZ; interface layer; epitaxy.

Development of Confocal 3D Micro XRF Spectrometer and Its Application to Rice Grain

Kazuhiko Nakano^1,2 and Kouichi Tsuji^1,2

(Received 22 December 2005, Accepted 4 April 2006)

A new 3D-micro XRF instrument based on confocal set-up using two polycapillary X-ray lenses was developed and applied to rice-grain. The depth resolution of the confocal 3D-XRF spectrometer, which was evaluated by 10 µm thick Au foil, was approximately 90 µm. It was confirmed that the background intensity was reduced by applying polycapillary half lens. In the confocal set-up, 3D-elemental mapping of major elements in the rice grain was performed non-destructively at ambient air pressure. Two-dimensional elemental maps for K, Ca and Fe were obtained at different depths (200, 400 and 500 µm from the surface) in the embryo of the rice grain. Major elements, such as K, Ca and Fe, in the rice grain showed different mapping images in the different layers, respectively.

Keywords : confocal 3D-micro XRF; polycapillary X-ray lens; depth resolution; rice grain; 3D-analysis.

Measurement of K Series of X-Ray Fluorescence Spectra of Ce and Gd by High Energy X-Ray from Synchrotron Radiation Source

Masaaki Harada¹, Masahiko Shoji², Hiroshi Kawata³ and Kenji Sakurai²

(Received 24 January 2006, Accepted 15 April 2006)

The high-energy X-ray fluorescence method has provided information of lanthanides in bulk samples without any interference of coexisting transition metals. In this study, the Kβ X-ray fluorescence spectra of Ce and Gd were measured with high-energy X-rays from a synchrotron-radiation source. The energy-dispersive spectra of Ce were measured with a Ge solid-state detector and analog/digital electronics for signal processing. It was shown that the intensities of the Kβ X-ray fluorescence spectra varied with the electronics used for signal processing and the experimental conditions (fluorescent intensity). This result should be noted for analytical applications using spectral intensities. To obtain higher energy-resolution spectra, a wavelength-dispersive measurement with a crystal monochromator and an imaging plate was also investigated. The five Kβ peaks of Gd (Kβ₃, Kβ₁, Kβ₅, Kβ₂, KO_2,3) were separately observed with 70 keV X-ray excitation, and the energy resolution was estimated to be about 60 eV at Gd Kβ₁ (48.7 keV) when the IP was read out with a 100 µm resolution. The energy resolution is yet to be improved by a higher resolution IP read-out or CCD camera system. It is expected that this high-energy X-ray fluorescence spectroscopy will be useful for the analysis of many kinds of lanthanide compounds and materials in the near future. Measurements of other lanthanide's Kβ spectra are now under investigation.

Keywords : high-energy X-ray fluorescence; Kβ spectra; synchrotron radiation; cerium; gadolinium.

Technical Papers

Measurment of Incident Beam Angular Dependence of X-Ray Luminescence Intensity and Possibility of New Atom Resolved Holography

Kouichi Hayashi¹, Tetsutaro Hayashi², Toetsu Shishido¹, Eiichiro Matsubara³, Hisao Makino⁴ and Takafumi Yao⁵

(Received 19 December 2005, Accepted 25 February 2006)

An X-ray excited optical luminescence phenomenon was used for atom resolved X-ray holography. In this study, we measured the incident-beam angular dependence of the X-ray luminescence intensity from a ZnO/MgO/Al₂O₃ film. The observed pattern corresponded to the hologram of an Al₂O₃ substrate, differently from the Zn Ka X-ray fluorescence hologram. This result shows the possibility of the hologram measurement of light elements whose X-ray fluorescence is hardly detectable in air.

Keywords : X-ray fluorescence holography; X-ray luminescence; X-ray excited optical luminescence; local structure; ZnO; sapphire.

Notes

Pavel Karimov^1,2, Ernst Z. Kurmaev² and Jun Kawai¹

(Received 12 December 2005, Accepted 29 March 2006)

A numerical simulation was performed to check the aptitude of low-Z materials, like carbon and boron, to be used as cladding layers in planar X-ray waveguides with a beryllium core. For a particular incident beam-energy value, an optimization technique based on a genetic algorithm was used to find the waveguide layer thicknesses, which provided the highest electric field intensity resonant enhancement in the core layer. The results of C/Be/C and B/Be/B waveguide simulations for incident beam energies from 10 to 15 keV were compared with the results obtained for Mo/Be/Mo waveguides. This comparison showed that waveguides with low-Z cladding layers should provide a guided beam of high intensity.

Keywords : planar waveguide; X-ray optics; genetic algorithm.

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