The formation and observation, with reflected light, of 60-nm-diam phase-changed domains in a thin GeSbTe film using a scanning near-field optical microscope with a 785 nm wavelength laser diode is demonstrated. The dependence of the domain size on incident laser power was obtained, and the size changed from 150 to 60 nm in diameter with incident power of 8.4–7.3 mW in the probe. At the threshold power of 7.3 mW, the film temperature rose to around 180 °C to partially phase change the local area of the film from amorphous to crystalline. A detected reflectivity increase due to phase change in the formed domain was 8%–2%. The observing (reading) was performed with an incident laser power of 0.2 mW, which corresponds to 10−2–10−3 times less than in a magneto-optical recording. The incident laser power shows that the phase change reading using the reflection scanning near-field optical microscope has the potential to read the recorded bit at a speed over 10 MHz.
We present for the first time a nanometer-sized phase-change recording using a scanning near-field optical microscope (PC-SNOM recording). The recording experiments were performed with a SNOM using a 785-nm-wavelength semiconductor laser diode, shear force detection for gap control and reflected light detection for observing the domains (reading). The recording media of ZnS·SiO2(20 nm)/GeSbTe(30 nm)/ZnS·SiO2(150 nm)/polycarbonate substrate were used. The writings were done at laser powers of 8.4–7.3 mW in the probe for pulse widths of 5 or 0.5 ms. As a result, we obtained a minimum recorded domain size of 60 nm in diameter. This size shows a potential to achieve an ultrahigh density PC-SNOM recording with about 170 Gb/in2. A possibility of achieving high speed readout for the future data storage is also discussed.
Characteristics of a phase-change optical disk using a (Ge–Sb–Te)-(Cr–Te) recording film containing a high-melting-point component Cr–Te are studied. The high-melting-point component Cr–Te precipitates in the recording film, and prevents a material flow of the recording film during repeated rewrites in which the recording film is melted. There is no drawback such as noise increase by the addition of Cr–Te. Thus the phase-change optical disk using this recording film shows very small distortion in the reproduced signal wave form even after 2×104 rewrites of high-density recording signals that are liable to cause the material flow by forming long and short recording marks on the disk. With a phase-change optical disk, it is easy to overwrite (rewrite without prior erasure) information, which makes it highly suitable for digital recording of motion pictures and sound. They are expected to be used as rewritable compact disks, rewritable CD-ROM disks, rewritable video disks, and small recording media for personal computers.
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