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.

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.

The optical diffraction limit is rigidly determined as a simple equation of wavelength λ and lens numerical aperture NA (): λ/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 λ/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.

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 simplecubic 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 Sb 2 Te 3 layer and the other is a Ge 2 Te 2 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.

Activation energy is one of the basic parameters used to estimate the physical and chemical features of optical and electrical phase-change (PC) films. However, its origin has not been discussed well because of insufficient understanding of the amorphous structures. In this paper, we reveal the origin of the activation energy using a GeSbTe-superlattice model and ab-initio local density approximation (LDA) calculations. The simulated energy required for transition from amorphous to crystal formation in a 9-atomic system was 2.34 eV; This is in good agreement with experimentally reported values. #

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Effect of constituent phases of reactively sputtered Ag O x film on recording and readout mechanisms of superresolution near-field structure diskRecording and readout mechanisms of super-resolution near-field structure disk with a silver oxide mask layerWe have simultaneously measured the carrier-to-noise ratio ͑CNR͒ as well as the transmitted and reflected light intensities from platinum oxide based super-resolution near-field structure ͑PtO x super-RENS͒ 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 ͑AIST͒ used in PtO x 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 PtO x layer was replaced with a metal-free phthalocyanine ͑H 2 Pc͒ layer and the CNR of the H 2 Pc disk was measured. From the observation that the CNR value was equivalent to that of a disk made using PtO x , we conclude that the presence of nanoparticles does not play an important role in the super-RENS readout mechanism. Finally, we also investigated the use of Si and the alloy Ge 2 Sb 2 Te 5 in lieu of AIST in a super-RENS disk and simple three layer structure disks. The super-resolution effect was observed for all disk types. Based upon these observations, we discuss the possibility of a thermal origin for the super-resolution effect in all super-resolution disks.