Toru Den

Electrodeposition of (001) oriented CoPt L10 columns into anodic alumina films

Anodic alumina films are known to have perpendicular holes normal to the film surface. This character is favorable to perpendicular magnetic recording and patterned media. L10-ordered CoPt columns are filled into anodic alumina nanoholes by an electrodeposition method and a subsequent thermal annealing process. Two kinds of metal (W and Pt) were used as underlayers at the bottom of nanoholes, which acts as electrode layer for electrodeposition. We show that while the embedded L10-ordered CoPt columns have random c-axis orientations for W underlayer samples, the c-axis orientation can be controlled by using the underlayer with Pt(001) surface. This orientation controlled sample has a perpendicular anisotropy with Hc=7.4 kOe, and Mr/Ms=0.96. This approach has the potential to become one of the important methods for the fabrication of recording media with ultrahigh areal density.

Two-dimensional grating-based X-ray phase-contrast imaging using Fourier transform phase retrieval

We demonstrate a single shot two-dimensional grating-based X-ray phase-contrast imaging using a synchrotron radiation source. A checkerboard designed phase grating for π phase modulation at 17 keV and 35 keV, and a lattice-shaped amplitude grating with a high aspect ratio to shield X-rays up to 35 keV were fabricated. A Fourier analysis of Moiré fringe generated by the gratings was introduced to obtain the two-dimensional differential phase-contrast image with a single exposure. The results show that soft tissues and cartilages of a chicken wing sample are clearly seen with differential phase variation in two-dimensional directions. Using this method not only the whole of an object but also only an inner part of the object can be imaged.

Two-dimensional gratings-based phase-contrast imaging using a conventional x-ray tube

A Talbot-Lau interferometer using two-dimensional gratings and a conventional x-ray tube has been used to investigate a phase-contrast imaging technique that is sensitive to phase gradients in two orthogonal directions. Fourier analysis of Moiré fringe patterns was introduced to obtain differential phase images and scattering images from a single exposure. Two-dimensional structures of plastic phantoms and characteristic features of soft tissue were clearly obtained at 17.5 keV. The phase-stepping technique was also examined to investigate the spatial resolution of different phase retrieval methods. In the presented setup we found that the choice of phase retrieval method made little difference in image blur, and a large effective source size was found to give a high intensity in the image plane.

Submicron-diameter phase-separated scintillator fibers for high-resolution X-ray imaging

We demonstrated micrometer-scale resolution X-ray imaging by using phase-separated scintillator fibers. Hexagonally well-aligned 680-nm-diameter GdAlO3(GAP):Ce3+ scintillator fibers surrounded with α-Al2O3 were fabricated from directionally solidified eutectics. The GAP:Ce3+ fibers convert X-rays to lights and emitted lights are confined and transported along the fiber direction by a total reflection mode. High-resolution X-ray image of a gold grating phantom with a 4 μm aperture, corresponding to a bundle of 12 fibers, was achieved even with a 150 -μm-thick scintillator. These scintillator fibers overcome resolution reduction caused by light scattering and almost reach the resolution limit of the material nature itself.

Phase-Separated CsI-NaCl Scintillator With Optical Guiding Function

We demonstrate a new scintillator material that has a one-dimensional eutectic structure and optical light-guiding properties. Our light propagation calculations predicted that a structure where high refractive index luminescence cylinders are embedded in a matrix should show effective light-guiding properties. An inverse structure where a high refractive index luminescence matrix contains low refractive index cylinders was also predicted to possess light-guiding properties. A CsI-NaCl:Tl eutectic phase, which contained NaCl cylinders in a CsI matrix, was grown by a one-dimensional solidification method. This material showed high spatial resolution because of the difference in the refractive indices of NaCl and CsI.

Perpendicular recording media using phase-separated AlSi films

We have developed perpendicular recording media with nanosized cylindrical Co particles. The diameter and period of these particles are less than 10 and 12 nm, respectively. Al cylinders were grown in an a-Si matrix during AlSi film deposition due to the eutectic phase separation. The Al cylinders can be removed by chemical etching to form nanoporous templates. The pores were filled with Co by electrodeposition method via a metal underlayer as an electrode. These films show perpendicular anisotropy with Hc of 4.1 kOe.

New phase retrieval method for single-shot x-ray Talbot imaging using windowed Fourier transform

We propose a new phase retrieval technique using a windowed Fourier transform (WFT) method for fringe pattern analysis to obtain a high-resolution phase map. The WFT method has been studied to improve the noise robustness of FT methods. In our proposed technique, an extra step is added to isolate the WFT spectrum containing phase information from other spectra, which is effective when a narrow window function is used for the high-resolution phase map. We demonstrate phase retrieval along both x- and y-axes from a two-dimensional fringe pattern obtained by X-ray Talbot imaging. Differential phase maps in high resolution with effective noise reduction are retrieved by the proposed method.

High-refractive-index CuI waveguide with aligned cylindrical micropores for high-resolution X-ray imaging

We have fabricated porous CuI crystals and used them as scintillator plates for high-resolution X-ray imaging by combining the properties of high-refractive-index light waveguide and scintillation. Porous CuI crystals containing aligned cylindrical micropores with pore volumes of 6% and 30% were fabricated by leaching directionally solidified CuI/NaCl and CuI/KCl eutectic crystals. The continuous cylindrical pores, which had a smooth surface, extended inward from the front to the back surface of the CuI crystal; therefore, light is confined in the CuI matrix with high refractive index (n ≈ 2.35) and transported along the pore direction by a total reflection mode. High-resolution X-ray imaging was demonstrated by using a 30% pore volume CuI crystal for an X-ray resolution chart and the 10 lp/mm pattern was clearly resolved.

Sparse phase-stepping in two-dimensional x-ray phase contrast imaging

We have developed a sparse phase-stepping (SPS) method for x-ray Talbot-Lau interferometry, which first constructs a SPS intensity pattern of fewer images than the conventional phase-stepping (PS) method and then fills the data gap with neighboring pixels for phase retrieval. The SPS method is highly beneficial in practice since the fundamental difference in spatial resolution between the SPS and PS methods becomes negligible due to the blur caused by an interferometer. The concept of the SPS method has been proved by the experiment using a small effective source size. Furthermore, the experiment using a large effective source size has verified that in practical situations the SPS method can reduce the required number of images for phase retrieval and still offer the retrieved images with as high a spatial resolution as the PS method.

Single-shot X-ray phase-contrast imaging using two-dimensional gratings

We developed a two-dimensional gratings-based X-ray interferometer that requires only a single exposure for clinical radiography. The interferometer consisted of a checkerboard phase grating for π phase modulation and a latticed amplitude grating. Using a synchrotron radiation source, the phase grating modulates the X-rays and generates a self-image, transformed to a moire fringe by the amplitude grating. To allow use of a conventional X-ray tube, the latticed source grating was installed downstream from the X-ray tube. Differential phase-contrast and scattering images in two orthogonal directions were obtained by Fourier analysis of the single moire fringe image and an absorption image. Results show that characteristic features of soft tissue in two orthogonal directions were clearly shown in the differential phase-contrast images.