Takayuki Shima

Rigid bubble pit formation and huge signal enhancement in super-resolution near-field structure disk with platinum-oxide layer

Huge signal enhancement was observed by a super-resolution near-field structure disk with a platinum-oxide layer. The carrier-to-noise ratio of 200-nm-mark trains reached 46.1 dB, and 42.3 dB was obtained even at 150-nm-mark trains. The sizes of the marks were one-fifth to one-seventh of the laser spot diameter of the readout system. The cross section of the mark trains was also observed by transmission electron microscopy. It was confirmed that 200-nm-size bubble pits were rigidly formed in good separation and ∼20-nm-platinum particles precipitated inside the bubble. The computer-simulation based on the model supported the huge signal enhancement.

Ferroelectric catastrophe: beyond nanometre-scale optical resolution

The optical diffraction limit is rigidly determined as a simple equation of wavelength ? and lens numerical aperture NA (): ?/2/NA. In this paper, we report that Ag5.8In4.4Sb61.0Te28.8 and Ge2Sb2Te5 chalcogenide thin films, which are typical of optical recording materials used in digital versatile discs (DVDs), enable a resolution of under ?/10 due to their ferroelectric properties. In the Ag5.8In4.4Sb61.0Te28.8 film it was found that this optical super-resolution can be observed between?350 and 400??C, resulting in a second phase transition from a hexagonal (A7 belonging to ) to a rhombohedral structure of R32 or R3m. In Ge2Sb2Te5, on the other hand, the temperature range is much wider, between?250 and 450??C, which is also due to a second phase transition from a NaCl-type fcc to a hexagonal structure.

Super-resolution by elliptical bubble formation with PtOx and AgInSbTe layers

The recording and retrieval of signals below 100 nm mark length were attempted with elliptical bubble-type super-resolution technology with platinum oxide (PtOx) and ductile AgInSbTe layers, using the same optical system as that of a digital versatile disk (a 635 nm wavelength red laser system). The carrier-to-noise ratio (CNR) of over 47 dB for 100 nm mark length signals (over 43 dB for 80 nm mark length signals) was obtained, which can be considered as a commercially acceptable level of CNR. The recording mechanism of the sample disk was shown through the transmission electron microscopy cross-section image observation to be by rigid elliptical bubble formation at the PtOx layer located between the AgInSbTe layers. The results of this report represent the potential for a much higher-density storage using the red laser system and a subterabyte optical storage using the blue laser system.

Role of Ge Switch in Phase Transition: Approach using Atomically Controlled GeTe/Sb2Te3 Superlattice

Germanium–antimony–tellurite (GST) is a very attractive material not only for rewritable optical media but also for realizing solid state devices. Recently, the study of the switching mechanism between the amorphous and crystal states has actively been carried out experimentally and theoretically. Now, the role of the flip-flop transition of a Ge atom in a distorted simple-cubic unit cell is the center of discussion. Turning our viewpoint towards a much wider region beyond a unit cell, we can understand that GeSbTe consists of two units: one is a Sb2Te3 layer and the other is a Ge2Te2 layer. On the based of this simple model, we fabricated the superlattice of GST alloys and estimated their thermal properties by differential scanning calorimetry (DSC). In this paper, we discuss the proof of the Ge switch on the basis of thermo-histories.

On a thermally induced readout mechanism in super-resolution optical disks

We have simultaneously measured the carrier-to-noise ratio (CNR) as well as the transmitted and reflected light intensities from platinum oxide based super-resolution near-field structure (PtOx super-RENS) disks. The the reflected and transmitted light intensities were found to decrease and increase, respectively, as the CNR value increased. The phase-change material AgInSbTe (AIST) used in PtOx super-RENS disks was found to exhibit a strong optical nonlinearity with respect to readout laser power. AIST becomes transparent at higher laser powers. To ascertain whether the presence of Pt nanoparticles is important to the readout mechanism, a super-RENS disk was fabricated in which the PtOx layer was replaced with a metal-free phthalocyanine (H2Pc) layer and the CNR of the H2Pc disk was measured. From the observation that the CNR value was equivalent to that of a disk made using PtOx, we conclude that the presence of nanoparticles does not play an important role in the super-RENS readout mechanism. Finally, ...

Observations of Immuno-Gold Conjugates on Influenza Viruses Using Waveguide-Mode Sensors

Gold nanoparticles were conjugated to an antibody (immuno-AuNP) against A/Udorn/307/1972 (H3N2) influenza virus to detect viruses on a sensing plate designed for an evanescent field-coupled waveguide-mode sensor. Experiments were conducted using human influenza A/H3N2 strains, and immuno-AuNP could detect 8×105 PFU/ml (40 pg/µl) intact A/Udorn/307/1972 and 120 pg/µl A/Brisbane/10/2007. Furthermore, increased signal magnitude was achieved in the presence of non-ionic detergent, as the virtual detection level was increased to 8×104 PFU/ml A/Udorn/307/1972. Immuno-AuNPs were then complexed with viruses to permit direct observation, and they formed a ring of confined nanodots on the membrane of both intact and detergent-treated viruses as directly visualized by scanning electron microscopy. With this complex the detection limit was improved further to 8×103 PFU/ml on anti-rabbit IgG immobilized sensing plate. These strategies introduce methods for observing trapped intact viruses on the sensing plates generated for optical systems.

Thermal Origin of Readout Mechanism of Light-Scattering Super-Resolution Near-Field Structure Disk

We have elucidated the readout mechanism of a platinum oxide super-resolution near-field structure (PtOx super-RENS) disk. It was found that threshold readout power (Pth) depends strongly on disk rotation speed. A rough estimate of the disk temperature during readout showed Pth to be approximately 340°C, irrespective of rotation speed. Additionally, it was revealed that the phase-change recording film (AgInSbTe) has optical nonlinearity with respect to incident laser power. The results indicate that thermal effects in the AgInSbTe (AIST) film play an important role in the super-RENS readout mechanism.

Optical and Structural Property Change by the Thermal Decomposition of Amorphous Platinum Oxide Film

Refractive indices of amorphous platinum oxide film (a-PtO1.1 and a-PtO1.6) at the wavelength of 400 nm and 630 nm are evaluated. A transmittance measurement obtained during heating the film demonstrated an optical property change at 550–600°C. X-ray diffraction and Raman scattering measurements confirmed that the change derives from the thermal decomposition of PtOx. Furthermore, Pt particles (diameter: 20–30 nm) are formed when thin PtOx film (thickness: about 4 nm) is thermally decomposed.

Thermal decomposition of a thin AgOx layer generating optical near-field

Thermal decomposition of AgOx thin layers generating optical near field have been studied by Ag LIII edge x-ray absorption near-edge structure. We found that, different from previous assumptions, the starting layer is a mixture of AgO (∼40%) and Ag2O (∼60%). We further observed that thermal decomposition starts at a temperature as low as 50 °C. The decomposition process exhibits three stages and the oxide layer at intermediate stages consists of a mixture of AgO, Ag2O, and metallic Ag with different fractions of each phase. Activation energies of the decomposition of the thin oxide layer have been determined for different decomposition stages, the obtained values being different from that for powder oxides.

Optical transmittance study of silver particles formed by AgOx thermal decomposition

Silver oxide (AgOx) thin films were found to exhibit localized surface plasmon resonance absorption when they were heated above the decomposition temperature. The resonance absorption for annealed AgO was obvious with the film thickness of 5 nm, and it became weak at 15 nm. Atomic force microscope images of a 15 nm film have shown that various-size particles (diameter in lateral direction: 100–600 nm) are dispersed after annealing at 600 °C. Similar optical and morphological properties were obtained with the oxygen composition ratio in the range of 33–48 at. % (i.e., Ag2O and AgO). AgOx film with about 15 nm thickness is mostly used in super-resolutional near-field structure (super-RENS) when combined with an optical disk for the readout of small marks beyond the diffraction limit. The results did not show, however, any evidence that the absorption properties and the readout process of super-RENS disk are well correlated.