Toru Asahi

Structural and optical properties of poly lactic acids

Fibrous and crystal structures of a helical polymer, poly‐L‐lactic acid (PLLA), were analyzed by using x‐ray diffraction experiments. It was confirmed that the molecular residues were arranged on a nonintegral 10/3 helix as De Santis and Kovacs [Biopolymers 6, 299 (1968)] reported. The atomic positions in a monomeric unit, which were proposed by Hoogsteen, Postema, Pennings, ten Brinke, and Zugenmaier [Macromolecules 23, 634 (1990)], were validated. However, the previous reports on the positions of the two helical chains were found to be in error. The correct positions were determined. The second helical chain shifts from the base center by 0.45, 0.25, and 0.61 A along a, b, and c axes. Besides, the second chain rotates by 2.46° with respect to the first. Distribution function of the crystallites in various drawn fibers were determined as a function of spiral angle. Optical gyrations of PLLA and poly‐D‐lactic acid fibers were successfully measured by using high accuracy universal polarimeter, as functions of temperature and drawing ratio. By using x‐ray data of the change of the fibrous structure by drawing treatments, the gyration tensor components of PLLA could be calculated. It is of great interest that gyration tensor component g33 along the helical axis is extremely large, ∼(3.85±0.69)×10−2, which corresponds to a rotatory power of (9.2±1.7)×103°/mm, about two orders of magnitude larger than those of ordinary crystals. This is the first experimental evidence that helical polymers will produce enormous optical activity in the solid state. Helical polymers will be important for the elucidation of gyro‐optical properties of solids and promising for new optical applications utilizing their large optical activity.

Self-Assembly of Quantum Dots and Carbon Nanotubes for Ultrasensitive DNA and Antigen Detection

A highly selective, ultrasensitive, fluorescence detection method for DNA and antigen based on self-assembly of multiwalled carbon nanotubes (CNTs) and CdSe quantum dots (QDs) via oligonucleotide hybridization is reported. Mercaptoalkyloligonucleotide molecules bind to the quantum dots, while amineoalkyloligonucleotides bind to CNTs with -COCl surface groups. QDs and CNTs further assemble into nanohybrids through DNA hybridization in the presence of target complementary oligonucleotides. The method is achieved with good repeatability with the detection limit of 0.2 pM DNA molecules and 0.01 nM antigen molecules. This novel detection system can also be used for multicomponent detection and antigen-antibody immunoreaction. The novel system has great potential in applications such as ultrasensitive pathogen DNA or antigen or antibody detection, molecular imaging, and photoelectrical biosensors.

Newly developed SmCo5 thin film with perpendicular magnetic anisotropy

A sputter-deposited SmCo5 thin film with perpendicular magnetic anisotropy has been developed. The Sm?Co film, composed of [Co (0.41?nm)/Sm (0.31?nm)]35, was prepared by sputtering on a Cu (100?nm)/glass substrate at various substrate temperatures. The coercivity was found to increase rapidly at 325?345?C and to be much greater in the direction perpendicular to the film surface than in the film plane. By using in-plane x-ray diffractometry, reflection peaks of the Sm?Co film deposited at 325?345?C were confirmed to originate from the SmCo5 phase, and the film showed a preferred orientation of the c-axis in the direction perpendicular to the film surface. The Co/Sm laminate structure deposited on the Cu seedlayer at an appropriate substrate temperature was found to be the key to promoting crystallization of the SmCo5 with its c-axis oriented perpendicular to the film surface.

Thin films of SmCo5 with very high perpendicular magnetic anisotropy

Thin films of SmCo5 with extraordinarily high perpendicular magnetic anisotropy were prepared by introducing a Cu∕Ti dual underlayer and controlling the substrate temperature during the sputter deposition. Under optimized conditions, the magnetic anisotropy constant reached 4.0×107erg∕cm3, and the coercivity and the remanence ratio in the direction perpendicular to the film surface were 12.0kOe and unity, respectively. The high perpendicular magnetic anisotropy is attributed to the high degree of preferred orientation of the c axis; the full width at half maximum in the rocking curve of SmCo5(002) reflection was 3.1°.

Transparent, tough collagen laminates prepared by oriented flow casting, multi-cyclic vitrification and chemical cross-linking.

The lamellar architecture found in many natural fibrous tissues has a significant bearing on their specific functions. However, current engineered tissues have simultaneously no realistic structures and no adequate functions. This study demonstrates a two-step process for obtaining structurally mimicking laminates in natural fibrous tissues with good optical and mechanical characters from purified-clinically-safe collagen molecules. Stacked lamella structures can be created by repeating flow casting, with the controlling parallel/orthogonal directionalities of each thin single-layer (2-5 μm in thickness). The transparency of laminates is successfully improved by a unique multi-cyclic vitrification with chemical cross-linking. The directionalities of optical and mechanical functions in laminates are strongly related with the preferential collagen alignments in the laminates. The tensile strength of laminates is extremely higher than any other engineered materials as well as native cornea, which exhibit an orthogonal laminated collagen structure and a good optical transmission.

Novel soft magnetic underlayer for double-Layered perpendicular magnetic recording media: electroless-deposited films of CoNiFe-based alloy

We present a novel fabrication process for a soft magnetic underlayer of a CoNiFe-based alloy for a double-layered perpendicular magnetic recording medium using electroless deposition. The electroless-deposited CoNiFeP film is focused on as the soft magnetic underlayer. The CoNiFeP soft magnetic underlayer was fabricated on a 2.5-in glass disk with a Ni/Ti seed layer and the substrate was rotated in an electroless deposition bath under a magnetic field applied. The CoNiFeP underlayer as deposited was flattened using a chemical mechanical polishing, and the film thickness thereby became about 1 /spl mu/m. The in-plane coercivity and saturation magnetic flux density of the CoNiFeP underlayer were less than 2 Oe and more than 12 kG, respectively. The magnetic domain observation revealed that the CoNiFeP underlayer electroless deposited under the magnetic field applied and the substrate rotated exhibited no marked domain boundary, vanishing a spike noise in read-write experiments. A double-layered perpendicular magnetic recording medium with the electroless-deposited CoNiFeP film showed a sufficient overwrite performance and high signal-to-noise ratio as compared with a typical soft magnetic underlayer fabricated using sputtering.

Effect of underlayers on magnetic properties of Co/Pd multilayer perpendicular magnetic recording media

Abstract Amorphous C and Si films were sputter-deposited as underlayers of Co/Pd multilayer perpendicular magnetic recording media. The magnetic properties of the media were significantly affected by the underlayer thickness; namely, the values of coercivity H c and nucleation field − H n increased and the value of α decreased with merely increasing the thickness of C or Si underlayer, where α is the derivative of M – H loop at the value of coercivity. The coercivity was not always affected by magnetic anisotropy constant K u for the Co/Pd media. In read–write experiments, the higher S/N ratio was obtained for the media with the thicker C or Si underlayer, which exhibited low α and high H c . In the time decay experiments of magnetization, the Co/Pd multilayer media with C or Si underlayer possessed good thermal stability. This study demonstrated that the introduction of C or Si underlayer greatly improves magnetic properties, read–write characteristics, and thermal stability of Co/Pd multilayer perpendicular magnetic recording media.

Microstructure and magnetic properties of Co/Pd multilayered thin films with C or Si seedlayer

Microstructure and magnetic properties of sputter deposited Co/Pd multilayered perpendicular magnetization films with amorphous C or Si seedlayer were investigated. The angstrom scale surface roughness of the seedlayer causes fine crystal grains to form in the Co/Pd multilayer and to decrease the extent of intergranular exchange coupling, while it obstructs the formation of a regular interface between Co and Pd layers. The Si seedlayer, which exhibits a surface roughness lower than the C seedlayer, yields Co/Pd multilayered films with the lowest intergranular exchange coupling and the highest coercivity. The improvement in magnetic properties of the Co/Pd film with Si seedlayer is attributable mainly to the formation of Pd2Si at the interface between the Co/Pd layer and the Si seedlayer. The Pd2Si provides suitable nucleation sites for the grain growth of Co/Pd multilayered film that can be utilized as a perpendicular magnetic recording medium.

Microstructure and magnetic properties of a Co/Pd multilayer on a controlled Pd/Si seed layer for double-layered perpendicular magnetic recording media

A 10 nm Pd/Si dual thin film was developed as a seed layer for a Co/Pd multilayer in double-layered perpendicular magnetic recording media. The Pd/Si seed layer, sputter deposited under Ar sputtering gas containing N2 and postannealed at 400 °C, markedly reduced intergranular exchange coupling of the Co/Pd multilayered film, resulting in a decrease in both the slope parameter, defined as 4π(dM/dH)H=Hc, and the magnetic cluster size. Consequently, medium noise was essentially reduced, thereby improving the signal-to-noise ratio of the Co/Pd recording media on a CoZrNb soft magnetic underlayer. The addition of N2 gas effectively decreased the grain size of Pd in the seed layer. A Pd/Si seed layer prepared with both processes exhibited a granular structure of fine Pd-rich grains surrounded by a Si-rich amorphous region, which provided nucleation sites for the growth of well-separated Co/Pd multilayered grains.

SmCo/sub 5/-based thin films with high magnetic anisotropy for perpendicular magnetic recording

An investigation was carried out on the effects of the addition of Cu and the thickness of the SmCo/sub 5/-based thin film with perpendicular magnetic anisotropy upon its magnetic properties, with the aim of reducing the Cu/Ti underlayer thickness. As a result, the Cu/Ti underlayer thickness necessary to obtain the squareness ratio of unity was successfully reduced from 125 to 50 nm. Moreover, for the SmCo/sub 5/ double-layered perpendicular magnetic recording media with a CoZrNb soft magnetic underlayer, the Cu/Ti underlayer thickness was further reduced to 35 nm. However, the magnetic cluster size and the values of coercivity and saturation field of the SmCo/sub 5/ media were found to be too large. Thus, we recognized the need for adjusting the cluster size and the magnetic properties to appropriate values, and also the need for investigating the possibility of using this material as patterned media or thermally assisted recording media.