Yoshimitsu Kobayashi

High-Density Pulse Width Modulation Recording and Rewritable Capability in GeSbTe Phase-Change System Using Visible Laser Beam at Low Linear Velocity

Write and erase characteristics at low linear velocity in GeSbTe phase-change optical disks have been studied using 488 nm and 680 nm visible lasers. Good characteristics, which are carrier-to-noise ratio (CNR) of more than 50 dB and erasability of more than 25 dB, were obtained by optimizing the composition of GeSbTe and the layer structure. However, smaller erase power margin has been observed in comparison with the case of using a 780 nm laser. From transmission electron microscope (TEM) observation and numerical simulation, it is explained that these phenomena are mainly due to the difference in the temperature profile arising from the beam profile. For pulth width modulation (PWM) recording using a 680 nm laser, the resolution has been improved by 25% in comparison with the case of a 780 nm laser. Furthermore, a clear eye pattern of the eight-to-fourteen modulation (EFM) signal was observed at the 3 T mark length of 0.65 µm. Crosstalk of less than -26 dB was obtained even at 1.0 µm track pitch. In the overwrite cycle test using a 680 nm laser, no degradation of CNR up to 10000 cycles was observed.

TeSeF films by TeSe‐SeF6/Ar reactive sputtering for ablative optical recording

A TeSeF film with fine polycrystalline structure with a grain size of less than about 1000 A had desirable properties as a recording layer for an ablative write‐once medium. Low media noise, and uniform and regular pit shape were achieved. The TeSeF film was prepared by reactive sputtering of TeSe in a gaseous mixture of Ar and SeF6. The fluorine‐doping effect on the crystallinity of TeSe alloy films and a reactive sputtering process with TeSe alloy target in a gaseous mixture of SeF6 and Ar were studied. With SeF6 flow, polycrystalline films with a large grain size of more than a few thousand A became amorphous in an as‐deposited state. After annealing below 100 °C, the amorphous films became fine polycrystalline with a 500–1000 A grain size. This crystallinity change was due to 20–30 at. % of fluorine incorporating into TeSe networks in a hexagonal structure. Most of fluorine was unstable and evolved immediately during annealing even below 100 °C. But the residual a few at. % of fluorine was strongly in...

Mononuclear tetracarbonylrhodate Rh(CO)4–. A new aspect of syngas conversion into ethylene glycol

Syngas treatment of Rh4(CO)12 in 1-methylpyrrolidin-2-one gives a colourless solution of mononuclear tetracarbonylrhodate, Rh(CO)4–, which is closely related to the active catalytic species that produces ethylene glycol.

Adhesion between Te‐based alloy films and fluorocarbon sublayers during the ablative hole opening process

Adhesion between thin Te‐based alloy films and fluorocarbon polymer sublayers, prepared by sputtering or plasma polymerization, was investigated by observing the 1 μm‐sized ablative hole opening process with a focused laser beam. Interpretations of the mechanisms for the change in energy required for the hole opening and pit geometry were based on the framework of studies of the ablative hole opening process for optical recording. Observations suggest that the molten material flow during the hole opening includes a ductile fracture and a viscous flow of the molten sublayer material as well as of active layer material. Adhesion acts as an energy barrier against the above mentioned flow of molten material during the hole opening process. Since the fluorocarbon films used in the present work had highly cross‐linked structures, the adhesion was mainly dominated by the dynamic force of adhesion. Therefore, the hole opening process was mainly affected by the dynamic force of adhesion rather than the static forc...

Minimum magnetic domain width of TbFeCo by magnetic field modulation recording

Stability of magnetic domains is evaluated on TbFeCo by measuring the minimum magnetic domain width (Wmin). Domains are recorded by magnetic field modulation method. Smaller Wmin can be observed by the sample with lower Tb content and higher sputtering pressure of under-layer. This can be explained by the temperature dependency of magnetization (Ms) and coercivity (Hc) qualitatively. From these results, we conclude TbFeCo has capability to record 0.1 micrometers .

Characteristics of optical read-only media with PWM recording

Characteristics of optical read-only media (O-ROM) having both grooves for tracking and pits that represent data by length were studied. Servo signals were observed over a wide bandwidth up to the data clock frequency and, in addition, the surface structures of the disks were observed. These observations showed that servo signals depend not only on the depth of grooves but also on that of the embossed data pits. Optimizing the depths of pits and grooves based on the results of pit density dependency of servo signals is necessary to ensure good characteristics of pit and groove signals.