Yasushi Kagoshima

We have improved the performance of a previously reported multilayer zone plate by reducing its outermost zone width, using the same multilayer materials (MoSi2 and Si) and fabrication technique. The focusing performance was evaluated at the BL24XU of SPring-8 using 20-keV X-rays. The line spread function (LSF) in the focal plane was measured using a dark-field knife-edge scan method, and the point spread function was obtained from the LSF through a tomographic reconstruction principle. The spatial resolution was estimated to be 30 nm, which is in relatively good agreement with the calculated diffraction-limited value of 25 nm, while the measured diffraction efficiency of the + 1st order was 24%.

Multilayer zone plate (MZP) technology for hard X-ray focusing was upgraded and its focusing performance was evaluated using 20-keV X-rays at the synchrotron beamline (BL24XU) of SPring-8. The MZP consists of MoSi2 and Si layers alternately deposited on a glass fiber by magnetron sputtering so that all zone boundaries satisfy the Fresnel zone configuration. The focused beam was evaluated using knife-edge scanning in which the measured intensity distribution is identical to the line spread function (LSF) in the focal plane. The focused beamsize of about 30 nm was estimated by oscillation peaks observed in the measured LSF according to Rayleigh's criterion.

A total-reflection zone plate (TRZP), which is a reflective grating that generates a line focus of hard X-rays, was developed. Newly designed TRZPs, introducing a laminar grating concept, were fabricated with various zone parameters. The focusing performances with regard to the beam size and the diffraction efficiency were evaluated using synchrotron radiation X-rays of 10 keV energy. Although the beam sizes measured are insufficient in comparison with the ideal value, the maximum diffraction efficiency, measured at 20%, exceeds the limitations of conventional TRZPs based on a binary grating.

We have developed a four-dimensional (4D) x-ray microcomputed tomography (CT) system that can obtain time-lapse CT volumes in real time. The system consists of a high-speed sample rotation system and a high-frame-rate x-ray imager, which are installed at a synchrotron radiation x-ray beamline. As a result of system optimization and introduction of a "zoom resolution" procedure, a real-time 4D CT movie with a frame rate of 30 was obtained with a voxel size of 2.5 μm using 10 keV x-rays. © Published under licence by IOP Publishing Ltd.

We designed point focusing total-reflection zone plates (TRZPs): a double linear type TRZP in Kirkpatrick-Baez arrangement, a conical TRZP, and an open conical TRZP. In this paper, we show detail characteristics of the open conical TRZP, which is the most promising candidate for practical use, and evaluate the effect of fabrication error and misalignment on focused beam profiles by calculation.

A circular type multilayer Laue lens (MLL) has been designed and fabricated. A graded-thickness multilayer was deposited on a tapered wire core by using a magnetron sputtering system. A combination of MoSi2 and Si was chosen as the multilayer materials owing to its superior properties of high diffraction efficiency and relatively sharp interfaces between layers. Optical properties of the circular type MLL were measured at BL24XU of SPring-8 with 20-keV x-rays. It was confirmed that only the +first-order diffraction was focused in the focal point owing to the wedged zone structure. Measured +first-order diffraction efficiency of the multilayer part was as high as 52%. Applying the circular type MLL to scanning transmission microscopy, a 50-nm line and space of a test chart was resolved.

A multilayer Laue lens (MLL) made from MoSi2/Si has been fabricated aiming at a sub-10-nm spatial resolution for hard x-ray microscopy. A multilayer of 1000 alternating MoSi2 and Si layers with a layer thickness gradually increasing from 5 nm to 316 nm according to the Fresnel lens structure was deposited on a silicon substrate using DC magnetron sputtering, and then the substrate was diced, polished and thinned. The multilayer total thickness was about 10 mu m. Optical properties were measured at the SPring-8 beamline BL24XU using 20-keV x-rays. While observing changes in far-field diffraction patterns by changing the tilt angle of the MLL, a dynamical diffraction effect of the MLL was visually confirmed. The achieved line focusing size was 13.1 nm, which is the best ever reported by using an MLL. The maximum local diffraction efficiency was measured to be 62%. Further, two MLLs were arranged in the KB configuration and applied to scanning transmission microscopy.

X-ray nanofocusing devices are capable of focusing X-rays down to sizes of about 10 nm. We have developed a new nanofocusing device, known as total-reflection zone plates (TRZPs), for focusing high-brilliance synchrotron radiation in the hard x-ray region. This device consists of a reflective zone pattern on a flat substrate. It has the potential to focus hard x-rays down to sub-10-nm dimensions. Furthermore, it is considerably easier to fabricate than other hard x-ray nanofocusing devices since it is used with a very small grazing incidence angle. We have focused 10-keV x-rays to sub-15 nm dimensions using a TRZP that was fabricated by conventional electron-beam lithography. In addition, we present designs for more efficient devices that have a target focus size of 5 nm. We propose and discuss a new approach for achieving point focusing with nanometer dimensions.

To develop a multilayer Laue lens (MLL), we fabricated depth-graded Mo/Si and MoSi2/Si multilayers with each boundary according to the Fresnel zone configuration. The multilayers were deposited by magnetron sputtering. From the result of SEM image analysis of the multilayer cross sections, MoSi2/Si multilayer had smaller layer-thickness errors than Mo/Si multilayer. In addition, from the result of the focusing test by using 20-keV X-rays, the measured beam size of MoSi2/Si MLL had a small blurring from the diffraction limited beam size. These results suggest that MoSi2/Si multilayer is better suited than Mo/Si multilayer for use as an MLL in hard x-ray nanofocusing.

A new total reflection double-slit for hard X-ray region was developed. It consists of Au narrow stripes deposited on a SiO2 substrate and can function equivalently as a conventional Young's interferometer by operating with a small grazing incident angle. The Young's interferometer using the total reflection double-slit was constructed at Hyogo-ID BL of SPring-8, and the spatial coherence at 10 keV X-rays was evaluated by analyzing the interference fringes.

A multilayer Laue lens (MLL) as a hard X-ray focusing device has been designed and fabricated. Mo/Si and MoSi2/Si were chosen to form the multilayers owing to their superior properties of high diffraction efficiency and relatively sharp interface between layers. DC magnetron sputtering system was used for deposition of the multilayers. The optical properties of the MLL were measured at BL24XU of SPring-8 with 20-keV X-rays. To confirm the dynamical diffraction effect, far-field diffraction images were taken at various incidence angles and depths. The resultant intensity distributions showed similar structure to those expected by calculations. Further, an almost diffraction-limited beam size of around 30 nm was obtained.

Fast X-ray computed tomography (CT) system with sub-second order measurement for single CT acquisition has been developed. The system, consisting of a high-speed sample rotation stage and a high-speed X-ray camera, is constructed at synchrotron radiation beamline in order to utilize fully intense X-rays. A time-resolving CT movie (i.e. 4D CT) can be available by operating the fast CT system continuously. Real-time observation of water absorbing process of super-absorbent polymer (SAP) has been successfully performed with the 4D CT operation.

A new apparatus has been constructed for hard x-ray micro-imaging and microdiffraction experiments at BL24XU of the SPring-8. The new apparatus can be used as a scanning microscope mainly for mapping measurements of trace elements, a microdiffractometer with either a theta-2theta arrangement or an IP detector and an imaging microscope. As its optical devise, two phase zone plates made of tantalum can be mounted on each precision stage. In the scanning microscope and the microdiffraction experiments, a sub-mum beam are available with the photon flux of similar to10(9) photons/sec at 10 keV. The imaging microscope, making structures visible as fine as 60-nm line-and-space pattern at 10 keV, is used for Zernike's phase-contrast microscopy to visualize transparent specimens, microtomography achieving a 0.6-mum spatial resolution and micro-interferometry enabling the phase measurement with a few hundred-nm spatial resolution. In this paper, the details of the apparatus are described and some experimental topics are presented.

We have developed a high-resolution x-ray microdiffraction system at the BL24XU of the SPring-8. This system uses a focused beam produced by using a zone plate combined with a narrow slit. The size of the focused beam is 0.32 mum vertically and 1.3 mum horizontally and the angular divergence in the horizontal direction is about 70 prad at a photon energy of 15 keV. This low-divergence microbeam enables us to perform high-resolution x-ray microdiffraction experiments using a precise theta-2theta goniometer with sub-100-nm-resolved XYZ sample positioning stages. We demonstrate that the spatial non-uniformity of the strain and the period in InGaAsP multi-quantum-well structures, fabricated by selective metalorganic-vapor-phase epitaxy, can be measured with sufficient accuracy using this system.

We have demonstrated to form an x-ray microbeam with a narrow angular divergence in both vertical and horizontal polarization directions of synchrotron radiation x-rays by the use of successive asymmetric Bragg reflections. Using the highly parallel x-ray microbeam thus obtained, we are able to analyze the local minute strain of less than 10^<-5> in semiconductor materials and devices. A series of x-ray rocking curves have been obtained by scanning the sample against the x-ray microbeam. Variations of the reflection peak intensity, angular shift value and/or half widths inform us how strain is distributed in the materials with high spatial resolution. In addition, reciprocal space maps have been drawn with an analyzer crystal put behind the sample on the x-ray path. From those data, strain distribution can be analyzed in terms of both lattice tilt variation and lattice parameter variation independently. Strain near Si-oxide film edges on Si substrate or that in silicon-on-insulator (SOI) crystals or other semiconducting materials has been measured. The results of reciprocal space maps have shown that the strain in the bonded SOI layers is mainly due to the lattice tilt variation rather than the lattice parameter variation.

A hard X-ray transmission imaging microscope has been in use at the beamline BL24XU of SPring-8. It makes use of a phase zone plate made of tantalum as its X-ray lens, and is capable of imaging the structure as fine as 125-nm line-and-space pattern. The Zernike's phase-contrast method has been implemented to the microscope with phase plates made of gold. The photon energy was tuned to 12 keV just above the L-3 absorption edge of gold (11.9 keV) in order to increase the image contrast. Polystyrene micro particles as transparent specimens were imaged clearly in the opposite image contrast with phase plates to shift the phase of the central order spectra in the back focal plane of the objective by one-quarter and three-quarters of a period, while the absorption contrast image showed little image contrast. Performance of the newly developed phase zone plate has been tested and it was confirmed that the structure as fine as 60-nm line-and-space pattern was able to be imaged.

Using a highly parallel x-ray microbeam with a narrow angular divergence in both the vertical and the horizontal polarization directions of synchrotron radiation, we have demonstrated local minute strains of less than 10(-5) in semiconductor materials and devices. Xray rocking curve maps have been obtained by scanning the sample against the x-ray microbeam. In addition, reciprocal space maps have also been obtained by adding an analyser crystal behind the sample. From those data, strain distribution can be analysed in terms of both lattice tilt variation and lattice parameter variation. Strain near SiO2/Si film edges and in silicon-on-insulator (SOI) crystals has been measured. The strain in the bonded SOI layers is found to be mainly due to the lattice tilt variation rather than the lattice parameter variation.

Utilizing synchrotron radiation from SPring-8, an X-ray microbeam with a narrow energy bandwidth and a small angular divergence has been developed. Using the X-ray microbeam, we have demonstrated to measure very local and minute lattice strain in various semiconducting materials after some wafer preparation processes or device fabrication processes. Local strain in a Si crystal around the SiO_2/Si film edges and that in top Si layers of silicon-on-insulator (SOI) crystals are discussed as sample materials.

We are investigating clinical potentiality of refraction imaging using Synchrotron Radiation. In this study, we set up the distance 10, 5 and 0.1 m between sample and cooled CCD. The scattered X-Ray was prominently decreased and contrast was improved. The spatial resolution was evaluated 36-micrometer using test-chart at 80 mrem radiation dose. We got the X-Ray image of human skull phantom (same dose) and hand one (about 20 mrem). The image quality of those were much improved compared with clinical X-Ray images at same radiation dose. This is a evidence of clinical potentiality of simple imaging using Synchrotron Radiation.

We have obtained the x-ray phase contrast images of the activated carbon/carbon (AC/C) composite used as electrodes in an electric double-layer capacitor (EDLC). To improve the spatial resolution, the beam size of x-ray transmitted from a sample were expanded by using asymmetric Bragg diffraction (asymmetric factor b) of analyzer crystal. Since the analyzer crystals were placed in (+, -) arrangements in both vertical and horizontal directions, the total magnification factor was 1/b(2) for each direction. By using the 511 asymmetric Bragg diffraction of Si (100) analyzer with an asymmetric factor of 0.207, we could obtain the magnification factor of about 23.3. We applied this optical system to the AC/C composite. The phase contrast image corresponding to the carbon particles with the diameter of about 10 mu m could be detected with the spatial resolution of 5 mu m. Furthermore, we also obtained realtime images of bubble formation and movement during the overcharging of an EDLC with the time resolution of 30 frames number per second.

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 I tun 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 similar to4 X 10(8) photons/s. A system for a scanning x-ray microscope has been constructed and the transmission and/or fluorescence microscopy has also been performed.

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.

Since the synchrotron X-rays are intense enough even after the sequential expansion of the X-ray beam by successive asymmetric Bragg reflections, Live refraction images of internal structure for biological materials can be seen on an X-ray image sensor. Video images of some living insects or a frog or a mouse show clearly their internal structures of the body, for instance, cellular structures in a lung.

Phase-contrast x-ray microscopy has been performed using a point focus x-ray source. The method is essentially the projection microscopy, but the contrast enhancement due to the refraction is obtained by taking a certain sample-detector distance large enough to spatially resolve phase gradients in the x-ray beam. The spatial resolution was measured to be 2.5 mum in horizontal and 2.2 mum in vertical directions. A phase contrast image of a glass tube was taken, and the contrast enhancement was clearly observed in boundary regions. The phase contrast images of a butterfly and a mosquito were also taken. It was confirmed that this method was useful to observe samples composed of light elements such as insects.