Mari Mizusawa

X-ray Diffraction Imaging of Anatase and Rutile

Both anatase and rutile are well-known as stable phases of TiO(2). In real-life samples, TiO(2) is most likely to be a mixture of those phases rather than pure anatase and rutile, and therefore quantitative analysis is extremely important. It is basically possible to determine the average ratio by X-ray diffraction (XRD) using differences in the crystal structure, but it is not easy to do so when attempting mapping by point-by-point scanning. The present paper describes the successful application of newly developed projection-type XRD imaging, which is an extremely rapid and highly efficient method.

Evaluation of high-resolution X-ray absorption and emission spectroscopy for the chemical speciation of binary titanium compounds.

For the chemical speciation of binary compounds of tri- and tetravalent titanium, high-resolution X-ray absorption and emission spectra were recorded in different energy regimes in order to evaluate and to qualify both near-edge X-ray absorption fine structure (NEXAFS or XANES) spectroscopy and wavelength-dispersive X-ray emission spectroscopy (WDXES) as spectroscopic methods for this analytical task. A high resolving power in the excitation channel was ensured by use of monochromatic synchrotron radiation provided by BESSY II, where the soft X-ray emission spectra were recorded as well. In the hard X-ray range, emission measurements were performed at SPring-8. For a comparison of the information gained from the various methods, the titanium compounds were classified according to the bonded titaniums oxidation state. Thus, it was possible to distinguish between inner atomic effects due to different oxidation states and external effects related to the respective ligand and the surrounding structure. It becomes evident, that certain compounds, while hardly distinguishable in their Ti-K XANES spectra, still show significant differences in their emission characteristics. On the other hand, some compounds with little difference in their emission spectra are easily distinguished by their NEXAFS structures. Only the combined use of the complementary methods both in the soft and the hard X-ray range allows for a reliable speciation of tri- and tetravalent titanium compounds.

X-ray reflection tomography: a new tool for surface imaging.

We report here a novel technique of surface imaging by X-ray reflection tomography utilizing an ordinary laboratory X-ray source. The technique utilizes the line projection, at different rotation angles, of the reflected beam from a highly reflecting patterned sample at grazing incidence. Filtered back-projection algorithm is applied to the line projection data to reconstruct an image of the pattern on the sample surface. Spatial resolution currently obtained is ~1.6 mm. Nonetheless, we have achieved high correlation between the original image and the reconstructed image. This work is the first step in future efforts of nondestructive X-ray imaging for buried surfaces and interfaces.

Instrumentation for X-ray reflectivity in micro area: present status and future outlook

X-ray reflectivity is sensitive to slight structural changes along the depth of layered materials in the order of sub-nanometers or even smaller. This property is extremely promising for the observation of buried interfaces, but the conventional X-ray reflectivity technique unfortunately lacks spatial resolution. The method looks at quite a large area, typically mm2~ cm2of the sample, and this often makes it difficult to analyze realistic problems in modern nano sciences and technologies. The present article discusses instrumentation for upgrading the X-ray reflectivity technique to give it a much higher spatial resolution. Recent preliminary results with high-energy white X-rays are reported.

In-situ X-ray reflectivity measurement of polyvinyl acetate thin films during glass transition

Thin films quite often have different properties from the bulk. In the case of polyvinyl acetate, it is known that glass transition takes place at around room temperature (~30 o C), and the thermal expansion coefficient is well determined for the bulk. However, with a ~0.1 micron thin film, such measurements are not generally easy. The present paper reports the results of in-situ X-ray reflectometry, which is extremely sensitive to slight changes in layer thickness. It was found that thickness increases from 968 to 985 A when the temperature is scanned from 10 to 55 o C, but the slope changes from 0.22 to 0.72 A/ o C at around 35 o C. As the thickness change is due to thermal expansion, it is possible to discuss the mechanical properties below and above the transition temperature.

Fast X‐Ray Fluorescence Camera Combined with Wide Band Pass Monochromatic Synchrotron Beam

A double W/B4C multilayer monochromator (2d=50.4A) was commissioned for non‐scanning X‐ray fluorescence (XRF) imaging experiments. The combination of a brilliant multi‐pole wiggler source and the present wide band pass monochromator permits 1.2 × 1013 photons/sec at the sample position for 8.04 keV X‐rays. Energy resolution ΔE and ΔE/E are 300∼500 eV and ∼5%, respectively. The exit beam height is constant for X‐ray energy ranging from 5.5 to 13.0 keV. Indirect cooling of the 1st multilayer works successfully. In addition, a new fast CCD camera was developed for quick readout and transfer of the image data. It was found that the typical exposure time for one XRF image with 1000 × 1000 pixels is 0.03∼1 sec. This permits in‐situ movie recording for the distribution of elements.

Density Gradient of a Mirror-Polished Rutile (110) Surface: X-ray Reflectivity Evaluation

A realistic rutile (110) surface was studied by means of grazing-incidence X-ray reflectivity measurement using 16.0 keV monochromatic synchrotron radiation. The data were analyzed by considering the density gradient, rather than employing conventional models based on the assumption of uniform layers. It was demonstrated that the low-density layer of approximately 4 nm has several parts, i.e., a Gaussian-like gradient part, an almost linear gradient part and a transition region. The effect of annealing on the density profile is also discussed.

Magnetic Field Dependence of the Canted Spin Moment around the Interface between Ferromagnetic Ni and Antiferromagnetic FeMn Revealed by the Polarized Neutron Reflectivity

Photon Factory and Condensed Matter Research Center, Institute of Materials Structure Science, High Energy Accelerator Research Organization, Tsukuba, Ibaraki 305-0801, Japan Research Center for Neutron Science and Technology, Comprehensive Research Organization for Science and Society, Tokai, Ibaraki 319-1106, Japan Quantum Beam Science Center, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195, Japan

Realtime X-ray reflectometry to see changes at buried interfaces

X-ray reflectometry is powerful in determining internal structure of multilayered thin films, such as thickness and density of each layer, as well as the roughness of surface and interfaces [1]. The measurement requires some precise angular scans near the critical angle with monochromatic parallel X-rays, and therefore it has not been thought that the technique is basically suitable to see changes. However, even without any angular scans, it is possible to obtain essentially the same data by using wide angular dispersion of the incident X-ray beam. The principle is basically known as Naudons pioneering concept [2]. The system has been improved further by employing a monochroator, which was not used by Naudon’s work. A multilayer monochromator was placed at very narrow limited space between a rotating anode X-ray source and the sample stage [3]. Use of a fast Si strip detector also contributed to improve the time-resolution. One can obtain an X-ray reflectivity curve with 4.5 decades even in 1 sec. It is possible to measure the curve down to 10-6, if 20 sec accumulation is allowed. Another advantage of the present instrument is fairly wide angular divergence, which ensures simultaneous data collection for 2 deg range. One of our recent successful applications of this method is the measurement of thermal expansion factor of the polymer thin film. It was also possible to see melting and freezing surfaces. In the presentation, such practical application will be demonstrated, in addition to the detailed description of our instruments.

XAFS imaging of Tsukuba gabbroic rocks: area analysis of chemical composition and local structure.

Gabbroic rocks were collected at Mount Tsukuba in Japan, and their XAFS images were studied using a projection-type X-ray fluorescence (XRF) microscope, which is a powerful new tool recently developed for extremely rapid imaging. The instrument employs a grazing-incidence arrangement in order that primary X-rays illuminate the whole sample surface, as well as parallel-beam optics and an extremely close geometry in order to detect XRF by a high-performance X-ray CCD system with 1024 x 1024 pixels. The XRF image indicated that black amphibole and white feldspar, both of which are typical mineral textures of the rock, contain iron. The origin has been suggested to be several small yellowish-brown minerals contained there. The XAFS imaging has been carried out by repeating the exposure of XRF images during the energy scan of the primary X-rays. It has been found that the structure is qualitatively close to that of olivine, and the main differences found in both areas can be explained as a difference in iron and magnesium concentration, i.e. the mixed ratio of forsterite (Mg(2)SiO(4)) and fayalite (Fe(2)SiO(4)). The feasibility of the present XAFS imaging method has been demonstrated for realistic inhomogeneous minerals.