Nobuhiro Yasui

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.

Development of Phase‐Separated Scintillators with Light‐Guiding Properties

Alkali halide systems that function as phase-separated scintillators (PSSs) with light-guiding properties are sucessfully created. Furthermore, it is the matrix phases of the PSSs which display the light-guiding properties. CsI-NaCl:Tl is a practical material pair because of its high pixel light output and good spatial resolution.

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.

Characterization of high-density patterned media fabricated by a new anodizing process

Patterned media with dots of 65nm period (153Gdots∕in.2) and 25nm period (1.03Tdots∕in.2) fabricated by a new anodizing process were investigated. Write/read characteristics were successfully measured with a specific patterned marker providing an accessing method to the narrow patterned area of 10×10μm2. The read-back signals were obtained by a spin stand with a flying head and a static tester with a contact head. Although 1 dot resolution was not achieved in the flying write/read measurement for the media with 25nm period (1.03Tdots∕in.2), it was achieved in the contact write/read measurement.

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.

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.