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.
The possibility of SPM-based data storage is described regarding both its recording density and readout speed for ultrahigh density data storage. We consider their gap control to achieve high-speed readout. Suitable SPM-based storages are selected and their details are studied. As a result, scanning near-field optical microscope (SNOM)-and atomic force microscope (AFM)-based storages are expected to be candidates for future storage. SNOM-based storage is for 100 Gb in −2 . AFM-based storage is for 1 Tb in −2 . Using new force modulation AFM pit recording, an ultrahigh recording density of 1.2 Tb in −2 and a readout speed of 1.25 Mb s −1 are demonstrated.
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.
A new thermomagnetic recording method using tunneling current in a scanning tunneling microscope as a heating source is proposed. In the experiment, pulse voltage of from 2–8 V with a pulse width of 1 ms is applied to the sample, while the probe position is kept at a bias voltage of 0.2 V and a tunneling current of 0.3 nA. As a result, we have demonstrated that thermally recorded magnetic domains are formed in a Pt/Co multilayered film and minimum domains as small as 0.2 μm in diameter are observed using a polarized optical microscope.
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