Toshimichi Shintani

Nanometer-sized Phase-Change Recording using a Scanning Near-Field Optical Microscope with a Laser Diode.

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 ZnSSiO2(20 nm)/GeSbTe(30 nm)/ZnSSiO2(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.

Phase change recording using a scanning near‐field optical microscope

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.

SPM-based data storage for ultrahigh density recording

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 . AFM-based storage is for . Using new force modulation AFM pit recording, an ultrahigh recording density of and a readout speed of are demonstrated.

Nanosize fabrication using etching of phase-change recording films

An etching technique called phase-change etching was developed. In this technique, only crystalline regions in a phase-change recording film are selectively etched by an alkaline solution, and amorphous regions remain on the sample surface, which means that a phase-change recording film can be used as a resist for pattern formation. By combination of this technique and phase-change recording, fabrication of the dot pattern with a size of about 1∕10 of the fabricating spot was demonstrated. This result indicates the possibility of nanosize fabrication using the phase-change etching technique.

Fabrication of nanostructures using scanning probe microscopes

We present nanostructure fabrication techniques using field evaporation and local heating in scanning probe microscopes, especially the scanning tunneling microscope (STM), atomic force microscope (AFM), and the scanning near‐field optical microscope (SNOM). The detachment of sulfur atoms from the surface of cleaved MoS2 and atomic scale fabrication were demonstrated with a field evaporation in STM. Field evaporation in AFM forms nanometer‐sized gold dots on a SiO2/Si substrate. Local heating with SNOM changes a phase of the GeSbTe recording film from amorphous to crystalline, and forms high reflectivity domains 60 nm in diameter. Moreover, we discuss these applications to a semiconductor process and data storage.

A New Super-Resolution Film Applicable to Read-Only and Rewritable Optical Disks

A new super-resolution material for optical disks is proposed which contains cobalt oxide as a main component and shows a refractive index change upon irradiation of a laser beam. This new material is different from the ones already proposed for super-resolution in that it is durable against high-power laser irradiation and thus is applicable to rewritable optical disks as well as read-only (ROM) disks. This paper reports fundamental properties of this material, C/N improvement of ROM and phase-change disks with this material, and its durability against continuous many-time readout. The potential of this technique is discussed.

Control of Aperture Size of Optical Probes for Scanning Near-Field Optical Microscopy Using Focused Ion Beam Technology

We propose a fabrication technique for apertures of optical probes for scanning near-field optical microscopy (SNOM) using a focused ion beam (FIB) process. We tried two FIB processes, FIB drilling and FIB slicing. The FIB slicing technique is very useful for fabrication of nm-sized SNOM apertures of less than 50 nm. The problem with the FIB drilling process is that it is difficult to identify the apex of the tip and to control the beam onto the apex. The FIB slicing technique can easily fabricate an aperture at an apex and control aperture size by cut-off-depth. It is easy for a sharp tip to obtain accurate size of aperture. It can be considered to obtain accurate size of aperture with fabricated error of 35 nm in a sharp tip with cone angle of 30 deg.

Scanning near-field optical microscope with a laser diode and nanometer-sized bit recording

We demonstrate 80 nm diameter bit recording for the first time using a phase change recording film and a reflection scanning near-field optical microscope with a 785 nm wavelength laser diode. The sample structure was a 20 nm thick ZnS-SiO 2 protection layer/30 nm thick Ge 2 Sb 2 Te 5 recording film/150 nm thick ZnS-SiO 2 protection layer/polycarbonate substrate. Writing was performed with pulsed laser light of 8.4 mW for 5 ms and 0.5 ms, and 8.0 mW for 5 ms. Written bits were observed in reflection by illuminating a small light of 0.2 mW. In this form of recording, a formation of phase change domains of about 50 nm in diameter is expected if the surface deformation is suppressed. Our results indicate the possibility to achieve an ultra-high recording density of more than 100 Gb in -2 .

Sub-Terabyte-Data-Capacity Optical Discs Realized by Three-Dimensional Pit Selection

To realize optical discs with the sub-terabyte data capacity, we propose the three-dimensional pit selection (3DPS) method where a single data pit to be read out in a multi-layer disc is selected three-dimensionally to obtain super-resolution in the disc plane and to reduce layer cross-talk. To examine the feasibility of this method, the phase-change pit capsule method was tested where the data pits consist of a phase-change material which melts during readout. The super-resolution effect was observed for both layers of a dual-layer disc. It was shown that a quadric-layer disc can be designed because of the high transmittance of each layer. Thus, 3DPS is considered to have the potential for a data capacity of hundreds of gigabytes with a conventional optical system.

Ultra-low switching power, crystallographic analysis, and switching mechanism for SnXTe100−X/Sb2Te3 diluted superlattice system

Ultra-low switching power (∼1/50th–1/2250th that of a Ge2Sb2Te5 device) was obtained in a SnXTe100−X/Sb2Te3 diluted superlattice (SL) device (X = 10, 20, and 35 at. %). XRD analysis showed that there was little coexistence of the SnTe/Sb2Te3 SL, Bi2Te3-type SnSbTe-alloy and Te phases. Detailed crystallographic analysis showed that there is a high probability that the SnSbTe-alloy phase independently changed into a SL structure. This self-assembled SL structure had a vacancy layer in a specific Te layer. Some phenomenon, such as Sn switching, in the self-assembled SL might lead to the ultra-low switching power.